Songhua River basin, encompassing numerous vital ecological protection areas and water conservation zones, is crucial in facilitating sustainable economic development in Northeast China. The basin exhibits a complex array of land use types, resulting in a diverse ecosystem. The dynamic monitoring of watershed-scale land use/land cover changes (LULCC) and carbon stocks estimation of the terrestrial ecosystem can provide suggestions for optimizing land utilization, enhancing terrestrial ecosystem carbon storage, and achieving the objective of "dual carbon". Based on the Landsat 5 TM and Landsat 8 OLI images from 1986 to 2022, this study employed random forest to obtain ten land use/land cover maps of the Songhua River Basin with high accuracy and conducted dy-namic monitoring of LULCC and its ecosystem carbon storage using an Integrated Valuation of Ecosystem Ser-vices and Trade-offs model, Mann-Kendall tests and Theil-Sen Median trend analysis. Results showed that farm-land has the largest area in the basin, followed by forest land, grasslands, unused lands, water, construction land, sparse forest land, and shrub land. Among them, farmland, forest, and grassland are the dominant land use types in the study area. During 1986-2022 period, the farmland expanded 11462.68 km2 while forest land decreased 18567.21 km2; the construction land experienced the largest change rate of 5.3% with an increased area of 3505.82 km2; the change rate of the sparse forest is 4.7%, ranking the second after construction land, but having minimal impact on the overall basin due to limited area changes. The change rate of unused land was 4.5%, with an increased area of 5385.43 km2. There was evident spatial heterogeneity in the distribution of the terrestrial ecosystem carbon stocks within the Songhua basin, with high carbon stocks predominantly found in the Dax-ingan and Xiaoxingan as well as the Changbai Mountains. The median carbon stock values were observed in Hinggan League, Songnen Plain, and Sanjiang Plain. In contrast, the areas with low carbon values were observed in Daqing and Baicheng. Over the 36 years, there was an overall decline in carbon storage within the basin, pri-marily concentrated in the regions initially characterized by high carbon stock values. However, the area with increased carbon stock is scatterly located in the basin. Notably, three recovery instances of ecosystem carbon stock occurred in 1994, 2002, and 2018 within the Songhua River Basin, all related to the changes in forest land. Based on ensuring no reduction of current forest land, it is recommended to expand forestland and continue im-plementing forestry projects to effectively prevent further depletion of terrestrial ecosystem carbon storage in the Songhua River basin.

Aims Carbon sequestration in terrestrial ecosystems is one of the important ways to slow down the rise of atmospheric CO₂ concentration. Therefore, understanding the natural vegetation ecosystems carbon storage (ECS) in response of future climate change is critical for making of regional land management policies.
Methods In this study, the sensitive parameters of LPJ-GUESS model are calibrated based on genetic algorithm. Using the downscale climate data-driven model, combined with Mann Kendall test, Sen’s slope estimation and partial correlation analysis, the temporal and spatial patterns, trend change characteristics and climate dominant factors of China’s ECS from 2001 to 2100 are analyzed.
Important findings The Nash-Sutcliffe efficiency coefficient and Pearson correlation coefficient of the calibrated LPJ-GUESS model in simulating ECS are 0.751 and 0.901, respectively, indicating that the LPJ-GUESS model can simulate China’s ECS well. During 2001-2020, China’s ECS decreased from southeast to northwest, with a total amount of 156.06 Pg. Vegetation, litter and soil carbon storage accounted for 34.2%, 1.9% and 63.8% of total ECS, respectively. The ECS in 2081-2100 shows similar spatial pattern with that in historical periods. The total amount of ECS at the end of this century are expected to increase by 0.51-11.16 Pg. The growth rates of China’s ECS was 8.5 g·m^-2·a^-1 and 3.7-21.0 g·m^-2·a^-1 during 2001-2020 and 2021-2100, respectively. During 2021-2100, significant increases of ECS are observed in southeast China, Nei Mongol Plateau, Qingzang Plateau (37-44 g·m^-2·a^-1), while obvious decreases (45-72 g·m^-2·a^-1, in the southern Yunnan-Guizhou Plateau, hilly areas in Guangxi and Guangdong. In northwest China, temperature is the dominant factor affecting ECS. The influences of precipitation on ECS are strengthened from the southeast to northwest. In high latitude and high-altitude areas, radiation is the dominant factor of ECS. CO₂ plays the most important role on ECS across about 47.9%-56.1% of China’s area.

Aims Due to complex root-soil interactions, the responses of carbon (C) dynamics in the rhizosphere soil to nitrogen (N) deposition may be different from those in bulk soil. However, the potentially different responses of C dynamics between the rhizosphere and bulk soil and their contributions to soil C sequestration under N deposition are still not elucidated.
Methods In this study, a typical subalpine coniferous plantation (Picea asperata) with chronic N addition treatments in southwestern China was selected as the research object. Based on the experimental plots of simulated N deposition (control: 0 kg·hm^-2·a^-1; N addition: 25 kg·hm^-2·a^-1), we measured the contents of soil organic carbon and its different physical and chemical fractions. Afterwards, by combining the rhizosphere spatial numerical model, we explored the differences in the C pool size of SOC and its fractions and their relative contribution to SOC pools between the rhizosphere and bulk soil, and further quantified the effects of N addition on soil C sequestration in rhizosphere soil.
Important findings The results showed that: 1) Although the addition of N increased the content of SOC and its physical and chemical components in the rhizosphere and non-rhizosphere at the same time, it only reached a significant level in the rhizosphere. Specifically, the rhizosphere SOC content increased by 23.64% under N addition, in which particulate organic carbon (POC), mineral-associated organic carbon (MAOC), labile carbon (LP-C) and recalcitrant carbon (RP-C) content increased by 19.63%, 18.01%, 30.48% and 15.01%, respectively. 2) The total SOC pool increment of spruce forest (0.88 kg·m^-2) was verified with the results of the rhizosphere space numerical model, and the effective rhizosphere extent of the southwest mountain coniferous forest was estimated to be 1.6 mm. Within this extent, N addition increased the SOC stocks of the rhizosphere and bulk soil by 33.37% and 7.38%, contributing to 45.45% and 54.55% of the total SOC pool increment, respectively. Among them, labile C components (POC and LP-C) are the major contributors to rhizosphere SOC accumulation under N addition. These results suggested that the rhizosphere and bulk soil of coniferous forest in southwestern mountainous area had great C sequestration potential under N deposition, and the C sink was more obvious in the rhizosphere soil. Our results highlight the importance of integrating rhizosphere processes into land surface models to accurately predict ecosystem functions in the context of increasing N deposition.

Aims Ecosystem services such as carbon sequestration and climate regulation of wetland ecosystems are very important. Accurately assessing the carbon storage of natural reserves in the Yellow River Basin is helpful for carbon neutrality research and regional ecological protection and high-quality development.

Methods Based on field sampling and laboratory analysis, combined with remote sensing data, this study assessed carbon storage in the aboveground plant biomass and the top 50 cm soils of typical natural vegetation in Shaanxi Yellow River Wetland Provincial Nature Reserve. The total target area for assessment is 13 086.52 hm², accounting for 23.87% of the nature reserve.

Important findings The results showed that the aboveground carbon storage of the tall-grass vegetation was significantly higher than that of the short-grass vegetation and shrubland, and their carbon densities were 496.73, 23.45 and 138.38 g·m^-2, respectively; the carbon density of the soil at 0-50 cm was 7.15-11.98 kg·m^-2, and the soil carbon storage in the tall-grass vegetation area (5.02 × 10⁵ t) was significantly higher than that of the beach without vegetation (2.09 × 10⁵ t), the short-grass vegetation area (3.40 × 10⁵ t) and short-shrubland area (1.45 × 10⁵ t); finally, combining the aboveground carbon storage in plant biomass and the soil carbon storage in the top 50 cm, the total carbon storage is estimated around 1.22 × 10⁶ t for the natural vegetation area of Shaanxi Yellow River Wetland Provincial Nature Reserve, of which proportions of carbon storage were 17.13%, 27.95%, 12.13% and 42.79% for beaches, short-grass vegetation area, short-shrubland, and tall-grass vegetation area. These results can provide basic data for the protection and restoration of natural wetlands and the improvement of carbon sink function in the middle reaches of the Yellow River.

Aims As one of the major terrestrial ecosystems of the world, a small fluctuation of grassland soil carbon (C) would affect the carbon cycle of the terrestrial ecosystem and ecosystem multifunctionlity (EMF). The carbon accumulation rate (CAR) of aboveground community well reflects the capacity and efficiency of carbon sequestration in a field from the start to the peak of a growing season. The changes in plant CAR could influence the ability of above- and below-ground community. Currently, the majority of studies have primarily focused on the relationship between community diversity and EMF, while the linkages of CAR with EMF were understudied. We aimed to explore the process and underlying mechanism of how CAR affecting EMF in alpine grassland community. Our results would improve the understanding of EMF maintenance mechanism and provide theoretical support for alpine ecosystem management.
Methods We conducted a field transect survey which consists of a total of 115 sample sites of alpine grasslands on the Qingzang Plateau from July to August 2015. The ecosystem multifunctionality index (M) was calculated from 13 key ecosystem parameters including soil organic carbon content, total nitrogen content, total phosphorus content above- and belowground biomass etc. The normalized difference vegetation index (NDVI, 1982-2013) was adopted to obtain the phenology in 2015. We calculated the CAR value. To explore the underlying mechanism of how CAR affecting EMF, the annual total precipitation and temperature were extracted by the method of thin disk smooth spline interpolation based on observations of meteorological stations from 2011-2015.
Important findings Belowground biomass, soil organic carbon content, total phosphorus content and microbial biomass carbon content had high weighting for CAR (0.58, 0.80, 0.83 and 0.79) and M (1.05, 0.98, 1.02 and 0.97). There was a significantly positive correlation between CAR and M (R² = 0.45, p < 0.01). Our findings suggested that the synergism of plant community and soil elements affected CAR and further regulated EMF under the influences of precipitation and temperature.

Aims The balance between soil organic carbon (SOC) input and output processes determines SOC content. However, it is not clear which of the two processes dominantly affect SOC content during the degradation of alpine meadows in Zoigê Wetland. In this study, the changes in SOC contents of alpine meadows and their causes at different degradation stages (alpine meadow (AM), slightly degraded alpine meadow (SD), and heavily degraded alpine meadow (HD)) in the Zoigê Wetland were investigated using the method of spatial sequence instead of temporal successional sequence.
Methods First, the changes in C input to soil and their causes along the degradation gradient were analyzed by investigating main soil physicochemical properties, microbial biomass, plant biomass and community composition of plant functional groups at different degradation stages. Secondly, the changes in the C output from soil were estimated based on lab incubation experiments of soil C mineralization and the temperature sensitivity of soil respiration (Q₁₀) and monthly average air temperature of the Zoigê Wetland. Finally, the main causes and processes leading to changes in SOC content along the degradation gradient were analyzed.
Important findings The results showed that soil water content (SWC), SOC content, total nitrogen (TN) content, microbial biomass C and N content decreased with the increase of degradation. Plant community composition gradually changed from sedges and grasses dominated community to forbs dominated community. Plant biomass and SOC mineralization rate decreased during the degradation of alpine meadows. The potential accumulation of organic C reduced during the degradation (compared with AM, the potential input, output and accumulation of organic C in SD and HD decreased by 16%, 18%, 15% and 59%, 63%, 41%, respectively). The decrease in SWC changed soil physical and chemical properties, including bulk density, SOC content, TN content, total phosphorus content, and C:N, which led to the shifts in the distribution pattern of plant functional groups and in soil microorganisms, consequently reducing the inputs and outputs of SOC. The decrease in potential plant-derived C input to soil caused by decreased SWC was the main reason for the decline in SOC content along the degradation gradient of alpine meadows in Zoigê Wetland.

Aims Regeneration of sub-alpine forests have an capacity to sequester carbon and nitrogen. Our objectives were to quantify variations of soil organic carbon and nitrogen content and enzyme activities at different successional stages of natural secondary forests, and to better understand the underlying mechanisms of carbon and nitrogen sequestration in these sub-alpine forests.
Methods We used the space-for-time substitution method and selected four sub-alpine forests in Miyaluo forest of Western Sichuan, China. The secondary forests were at different successional stages with natural regeneration on cutting-blanks in 1960s (60-NSF), 1970s (70-NSF) and 1980s (80-NSF), and the Abies faxoniana primary forest was used as control (CK). The soil samples were taken from 0 to 20 cm depths in each forest in late July, 2019, and were transferred to the laboratory. Soil organic carbon (SOC), soil total nitrogen (TN), dissolved organic carbon (DOC) and nitrogen (DON), light fraction organic carbon (LFOC) content and soil enzyme activities were measured. The activities of five soil extracellular enzymes related to soil carbon and nitrogen cycling were determined to explain their relationships with soil physico-chemical properties.
Important findings The contents of topsoil SOC, DOC, LFOC decreased with succession stage, whereas TN and DON were all in the order of 60-NSF < 80-NSF < 70-NSF, although 80-NSF and 70-NSF exhibited no significant difference. The topsoil organic carbon and nitrogen and their active fractions contents in natural secondary forests were lower than those in the primary forest, while no significant difference in DOC and DON contents was observed between 80-NSF and CK. The activities of soil β-4-glucosidase (βG), β-4-N-acetylglucosa- minidase (NAG) and polyphenol oxidase (PHO) in CK were significantly higher than those in natural secondary forests, whereas soil cellulose hydrolysis (CBH) and phenol oxidase (PEO) activities had no significant difference between secondary forests and CK. Activities of βG and CBH in 60-NSF were significantly lower than those in 70-NSF and 80-NSF, but activities of NAG in 80-NSF were significantly higher than those in 60-NSFand 70-NSF. There was no significant difference in PEO activities among different types of forest. Both Pearson correlation analysis and redundancy analysis showed that soil enzyme activities were significantly correlated with soil TN, LFOC and DOC contents. TN content explained 65.4% of the variations in enzyme activity, which implied that change in soil nitrogen content might affect C-related hydrolytic enzyme activities (e.g. βG, CBH and NAG). Meanwhile soil microorganisms prefer to use readily decomposable carbon and nitrogen. Therefore, activities of some soil enzymes such as βG, CBH and NAG in natural secondary forests decreased due to the declines in soil TN, LFOC and DOC contents. We conclude that soil enzyme activities could be more favorable to C and N cycling in the Abies faxoniana primary forest than in the secondary forest at the early-successional stages (<60 a) in high-altitude sub-alpine forest ecosystems in Western Sichuan, China.

Aims The objective of this study was to estimate the carbon storage and its allocation in the Betula platyphylla forests of three different ages (25, 40, 61-year-old) in the cold temperate zone, NE China. Methods Through analyzing the field data, we estimated the carbon storage and sequestration rates of tree, understory layer (shrub layer, herb layer, litter layer) and soil layer (0-100 cm) of the 25, 40 and 61-year-old Betula platyphylla ecosystems in the north section of the Da Hinggan Ling Mountains. Important findings The results showed that the carbon content of each organ in the tree layer of the forests ranged from 440.7 to 506.7 g·kg^-1, that decreased as the forest age increases. Carbon content in the shrub and herb layers decreased first and then increased as the forest aged, while that in the litter layer decreased with the increase of forest age. The carbon content in soil layer (0-100 cm) increased significantly with the forest age (p < 0.05), and decreased as soil drought intensified. The carbon storage of B. platyphylla ecosystem at all levels increased significantly with the increase of forest age. The carbon storage of tree layer in the forests of 25, 40 and 61-year-old were 11.9, 19.1 and 34.2 t·hm^-2, respectively. The carbon storage of the organs follow the order of: trunk > root > branch > leaf, and the allocation ratio of trunk carbon increased as the forest aged. The carbon storage in the Betula platyphylla forest ecosystems of 25, 40 and 61-year-old were 77.4, 180.9 and 271.4 t·hm ^-2, respectively. Soil layer, the main carbon pool of the ecosystems, accounted for 81.6%, 87.7% and 85.9% of the total carbon storage. The annual net productivity (2.0-4.4 t·hm ^-2·a ^-1) and annual net carbon sequestration (1.0-2.1 t·hm ^-2·a ^-1) of the forests increased with the age increase of the forest, and the old-growth B. platyphylla forests hold a strong carbon sequestration capacity.

Aims Our objective was to estimate the carbon storage in the forest tree layer in Qinghai Province, China.
Methods Based on forest resource inventory data and field investigation data, we estimated the carbon storage, sequestration rate and potentials in the forest tree layer in the Qinghai Province.
Important findings The carbon density and total carbon storage of forest tree layer in Qinghai Province was 76.54 Mg·hm ^-2 and 27.38 Tg, respectively, of which four forest types (Picea spp. forest, Cupressus funebris forest, Betula spp. forest and Populus spp. forest) accounted for 86.67% while their areas were 96.23% of total forest areas in Qinghai. The carbon density and carbon storage of Picea spp. forest was 106.93 Mg·hm ^-2 and 14.78 Tg, respectively, which was the largest among all forest types. The carbon storage of the forest tree layer at different stand ages followed the sequence of over-mature forest > middle-aged forest > mature forest > near-mature forest > young forest. In addition, the carbon storage of forest tree layer in the province increased from 23.30 Tg in 2003 to 27.38 Tg in 2011. The average annual growth of carbon and carbon sequestration rate were 0.51 Tg and 1.06 Mg·hm ^-2·a ^-1, respectively. The maximum and minimum of carbon sequestration rate were respectively found in Cupressus funebris forest (0.44 Mg·hm ^-2·a ^-1) and Betula spp. forest (-1.06 Mg·hm ^-2·a ^-1). The mean carbon sequestration potential reached 8.50 Tg in 2011, with the highest value found in Picea spp. forest (3.40 Tg). These findings suggested high carbon sequestration potential of forest tree layer in Qinghai Province. Therefore, the carbon storage in Qinghai Province could be increased through better forest management and utilization.

Aims Stand age plays a vital role in carbon (C) stock and its distribution (vegetation, woody debris, litter and soil) within forest ecosystems. Subtropical forests are pivotal in the C cycling of terrestrial ecosystems. In subtropical China, Fagus trees are widely distributed and of great importance. However, the analyses of C storage in chronosequent Fagus forests have not been well performed.

Methods Nine Fagus lucida forests at three succession stages (33, 82 and 208 year-old) were studied in Mt. Yueliang, Guizhou Province, and their C stocks and distributions within the forests were investigated and estimated.

Important findings Ecosystem C stock increased significantly with increasing stand age, which was (186.9 ± 46.0), (265.8 ± 82.3) and (515.1 ± 176.4) Mg·hm^-2 in the 33, 82 and 208 year-old forests, respectively. The increase in the C stock appeared mainly attributed from increase in vegetation C stocks that accounted for 32%-79% of the total C stock. The woody debris and litter carbon stocks also increased significantly with increasing stand age, but accounted for <1% of the total C stock. While soil C stock showed no significant change with increasing stand age, it decreased its contribution to the total C stock (from 67% to 20%). These results confirmed the importance of stand age on C storage and the dynamic reallocations in the subtropical forests. Results from this study also added additional evidences in understanding the significance of disturbance and land use in C accumulation.

Aims Vegetation restoration plays an important role in the accumulation and storage of soil organic carbon (SOC). Our objectives were to investigate the effects of vegetation restoration on SOC and to explain the underlying mechanisms of carbon sequestration during vegetation restoration in the mid-subtropical China.

Methods According to the disturbance intensity and the degree of restoration, we used the space-for-time substitution method by selecting four different types of vegetation communities, composed of Loropetalum chinense-Vaccinium bracteatum-Rhododendron simsii scrub-grass-land (LVR), Loropetalum chinense-Cunninghamia lanceolata-Quercus fabri shrubbery (LCQ), Pinus massoniana-Lithocarpus glaber-Loropetalum chinense coniferous-broad leaved mixed forest (PLL), and Lithocarpus glaber-Cleyera japonica-Cyclobalanopsis glauca evergreen broad-leaved forest (LAG) to represent the successional sequence in the secondary forests in Changsha County, Hunan Province, China. Permanent plots were established in each vegetation communities. Soil samples (0-40 cm) were collected and divided into four layers (0-10, 10-20, 20-30 and 30-40 cm). Soil organic carbon concentration (C_SOC) and soil organic carbon density (D_SOC) were measured. The main influencing factors on C_SOC and D_SOC were analyzed with Principal Component Analysis and Stepwise Regressions Analysis.

Important findings 1) Along vegetation restoration, C_SOC and D_SOC increased dramatically. The C_SOC was the highest in LAG, which was 12.5, 9.3 and 4.7 g·kg ^-1 higher than in LVR, LCQ and PLL in 0-40 cm soil depth, increasing by 248.5%, 113.1% and 58.5%, respectively. The increments of D_SOC in LAG at 0-40 cm soil depth were 67.1, 46.1 and 32.5 t C·hm ^-2, and increased by 182.0%, 79.7% and 45.6% compared to D_SOC in LVR, LCQ and PLL, respectively. 2) Correlation analysis showed that C_SOC and D_SOC were strongly and positively correlated with species diversity index, community total biomass, aboveground biomass, root biomass, existing biomass in litter layer, nitrogen (N), phosphorus (P) concentration in litter layer, soil total P, soil available P, soil C/N ratio (except C_SOC), soil C/P ratio, soil N/P ratio and percentage of soil clay (< 0.002 mm), but significantly and negatively correlated with C/N in litter layer (except D_SOC), C/P in litter layer, soil pH and soil bulk density, suggesting that the differences in C_SOC and D_SOC under different vegetation stages were related to both vegetation and soil properties. 3) The results of principal component analysis and stepwise regression analysis revealed that soil C/P, pH, concentration of soil clay (except C_SOC) and C/P in litter layer were the dominant factors affecting C_SOC and D_SOC during vegetation restoration. Among them, soil C/P ratio ranked first. These results indicated that the differences in soil C/P ratio, pH, soil clay concentration and C/P in litter layer were responsible for the changes in SOC during vegetation restoration.

Aims Forest conversion is an important factor affecting the ecosystem organic matter cycle, and has an impact on the productivity of forest ecosystems, carbon sequestration and nutrient conservation. This study aims to provide more scientific evidence for better understanding the mechanism of different forest types regulating forest soil carbon and nitrogen cycling in the context of forest conversion.

Methods The study site is located in Sanming City, Fujian Province, in subtropical China. Soil samples in the A horizon from an artificial-assisted natural regeneration forest of Castanopsis carlesii (AR), a natural secondary forest of C. carlesii (SF) and a plantation of Pinus massoniana (PM) sites were collected in November, 2016. We investigated the contents of soil organic carbon, soil organic nitrogen, soil dissolved organic matter (DOM), NH₄ ⁺-N and NO₃ ^--N. The spectroscopic characteristics of soil DOM were also measured by means of ultraviolet absorbance and fluorescence emission spectroscopic techniques. The activity of five kinds of enzymes related to carbon and nitrogen cycle were determined to decipher their relationships with soil properties.

Important findings The results showed that, due to different tree species and man-made disturbance, the contents of dissolved organic carbon (DOC), DON, humification index of fluorescence emission spectrum were all in the order SF > AR > PM, whereas the aromatization index was in the order PM > AR > SF. NH₄ ⁺-N were significantly richer for SF and AR than for PM, while NO₃ ^--N content was low and similar across the three stands. The β-glucosidase activity of PM was significantly lower than that of SF and AR. The activities of cellulolytic enzyme were in sequence of AR > SF > PM. The activities of polyphenol oxidase enzyme in PM was significantly higher than in SF and AR. There was no significant difference in the type of forest peroxidase. The activity of β-N-acetylglucosaminidase of AR was significantly higher than those of the other two kinds of stands. The redundancy analysis indicates that total nitrogen (TN) and DON are the major environmental factors driving soil enzyme activity. Soil total nitrogen content and NAG activity were positively correlated, and DON may be an important component of the N cycle. Soil microorganisms prefer to use readily decomposable carbon; and there is a certain coupling relationship between carbon and nitrogen cycles. Higher soil N contents would increase the C-related hydrolytic enzyme activity, thereby promoting carbon turnover.

Aims The complexity of environments and high spatial heterogeneity of desert ecosystems are important factors contributing to the uncertainty in the estimation of soil organic carbon storage.

Methods Ten types of desert grassland communities in the southeastern fringe of the Tengger Desert, China were investigated. The content and vertical distribution of soil organic carbon (SOC) content in seven soil depths (0-5, 5-10, 10-20, 20-30, 30-50, 50-70 and 70-100 cm) and the underlying drivers were examined. Soil organic carbon density (SOCD) of four soil profiles (0-5, 0-20, 0-50 and 0-100 cm) were quantified.

Important findings We found significant differences in SOC content among the 10 vegetation communities, and the shrub community type was an important factor affecting SOC content. Two types of trends in SOC content changes with soil depth were observed: 1) monotonic decrease, 2) increase followed by decrease. The SOC content was significantly positively correlated with clay content, total N, total P and conductivity, but negatively correlated with sand content. There were significant differences in SOCD for soil profiles of 0-5, 0-20, 0-50 and 0-100 cm among different communities, of which the mean values of SOCD were 0.118, 0.478, 1.159 and 1.936 kg·m^-2, respectively. Our results show that SOCD is far below the mean value of global or national grasslands. Using the average values of SOCD across either global or national grasslands (including the grassland in this study) to estimate the SOC storage of desert ecosystems may lead to the overestimation or underestimation. Using the SOCD of specific communities may greatly increase the accuracy of SOC storage estimation in desert grasslands.

Aims The bank of soil carbon of forests plays an important role in the global carbon cycle. Our aim is to understand the characteristics of soil carbon storage and its determinants in the forests in Shaanxi Province.Methods The data of forest inventory in 2009 and resampling in 2011 were used to analyze the characteristics of soil carbon storage and its determinants in the forest soil in Shaanxi Province.Important findings The soil carbon storage in the forests in Shaanxi Province was 579.68 Tg. Soil carbon storage of Softwood and Hardwood forests were the highest among all forest types, accounting for 36.35% of the whole province forest soil carbon storage. The forest soil carbon storage was 4.15 times greater in the natural forest (467.17 Tg) than that in the plantations. The young and middle-aged forests were the main contributors to the total carbon storage across all age groups, accounting for about 57.30% of the total forest soil carbon storage. The average soil carbon density of forests in Shaanxi Province was 90.68 t∙hm^-2, in which the soil carbon density of Betula forests was the highest (141.74 t∙hm^-2). Soil carbon density of different forest types were gradually decreased with soil depth. In addition, it was highest in middle-aged forest. Soil carbon density was higher in the natural forest ecosystems than that in the plantations within the each age group, indicating natural forest ecosystems have higher capacity of carbon sequestration. Differences in the spatial patterns between carbon storage and density indicated that carbon storage was related to forest coverage. The soil carbon density and storage of forests in Yulin were the lowest across the province. This suggests that, in order to enhance the regional carbon sequestration capacity in this region, we need to appropriately strengthen artificial afforestation activities and manage them scientifically and rationally. The soil carbon density of forests in Shaanxi Province decreased with the increase of longitude, latitude, and annual temperature, but increased with the increase of altitude and annual rainfall. This study provides data basis for provincial estimation of forest soil carbon bank in China.

Aims Pinus sylvestris var. mongolica is one of the main afforestation tree species in North China. It is important to study the characters of growth and carbon (C) sequestration, which can provide scientific basis for the sustainable management. Therefore, our study aims at quantifying the growth characters and C sequestration in these middle-aged plantations, and to investigate the effect of diameter at breast height (DBH) on those dynamics. Methods We selected a middle-aged P. sylvestris var. mongolica plantation as our permanent experimental plot, which is located in Saihanba, Hebei Province, China. DBH and height of all stands in this plot were measured in 2006 and 2016. Based on the anatomical trees and allometric equation, we calculated C density and sequestration from 2006 to 2016. We also analyzed C sequestration in different DBH groups in the study area. Important findings Our results showed that the carbon sink of those middle-age (age between 28 and 38 years old) plantation would be enhanced in future, and there were differences in characters of growth and C sequestration among DBH groups. The decadal increment rate of DBH and height were 4.19% and 1.97%, and the increment rate was the lowest in the 0-10 cm DBH class. The mortality rate of the plantation was 8.39%, with 7.82% mortality occurred in 0-10 cm tree size class. The forest stands biomass carbon stocks in 2006 and 2016 were 59.04 and 109.64 t?hm^-2, respectively, and almost 87.1% of the carbon stocks were in the middle DBH-class, even though the number of trees only accounted for nearly 59.2%. The small class’s number of trees accounted for 39.1%, while the carbon stocks accounted for 8.3%. Our results also demonstrate that forests in Saihanba would continue to act as a carbon sink in the coming years. The variations among DBH groups highlights that the diameter class should be taken into consideration while assess the ecological efficiency and carbon sequestration capacity in a certain area.

Aims Studying storage of carbon (C), nitrogen (N) and phosphorus (P) in ecosystems is of significance in understanding carbon and nutrient cycling. Previous researches in ecosystem C, N and P storage have biased towards forests and grasslands. Shrubland ecosystems encompass a wide gradient in precipitation and soil conditions, providing a unique opportunity to explore the patterns of ecosystem C, N and P storage in relation to climate and soil properties.
Methods We estimated densities and storage of organic C, N and P of shrubland ecosystems in Northern China based on data from 433 shrubland sites.
Important findings The main results are summarized as follows: the average organic C, N and P densities in temperate shrubland ecosystems across Northern China were 69.8 Mg·hm^-2, 7.3 Mg·hm^-2 and 4.2 Mg·hm^-2, respectively. The average plant C, N and P densities were 5.1 Mg·hm^-2, 11.5 × 10^-2 Mg·hm^-2 and 8.6 × 10^-3 Mg·hm^-2, respectively, and were significantly correlated with precipitation and soil nutrient concentrations. The average litter C, N and P densities were 1.4 Mg·hm^-2, 3.8 ×10^-2 Mg·hm^-2, 2.5 ×10^-3 Mg·hm^-2 and were significantly correlated with temperature and precipitation. The average soil organic C, N and P densities in the top 1 m were 64.0 Mg·hm^-2, 7.1 Mg·hm^-2 and 4.2 Mg·hm^-2, respectively and the former two were significantly correlated with temperature and precipitation. The total organic C, N and P storage of shrublands in Northern China were 1.7 Pg, 164.9 Tg and 124.8 Tg, respectively. The plant C, N and P storage were 128.4 Tg, 3.1 Tg and 0.2 Tg, respectively. The litter C, N and P storage were 8.4 Tg, 0.45 Tg, 0.027 Tg, respectively. Soil is the largest C, N and P pool in the studied area. The soil organic C, N and P storage in the top 1 meter were 1.6 Pg, 161.3 Tg and 124.6 Tg, respectively.

Aims
This study was conducted to investigate carbon stocks in forest ecosystems of different stand ages in Anhui Province, and to identify the carbon sequestration potential of climax forests controlled by the natural environment conditions.
Methods
Data were collected based on field investigations and simulations were made with the BIOME4 carbon cycle model.
Important findings
Currently, the total forest carbon stocks in Anhui Province amounts to 714.5 Tg C: 402.1 Tg C in vegetation and 312.4 Tg C in soil. Generally, both the total and vegetation carbon density exhibit an increasing trend with the natural growth of forest stands. Soil carbon density increases from young to near mature forests, and then gradually decreases thereafter. Young and middle-aged forests account for 75% of the total forest area in Anhui Province, with potentially an additional 125.4 Tg C to be gained after the young and middle-aged forests reach near mature stage. Results of BIOME4 simulations show that potentially an additional 245.7 Tg C, including 153.7 Tg C in vegetation and 92 Tg C in soil, could be gained if the current forests are transformed into climax forest ecosystems in Anhui Province.

Aims
This study aims to evaluate the impacts of future climate change on vegetation and soil carbon accumulation rate in China’s forests.
Methods
The vegetation and soil carbon storage were predicted by the atmosphere-vegetation interaction model (AVIM2) based on B2 climate change scenario during the period of 1981-2040. This study focused on mature forests in China and the forested area maintained constant over the study period. The carbon accumulation rate in year t is defined as the carbon storage of year t minus that of year t-1.
Important findings
Under B2 climate change scenario, mean air temperature in China’s forested area was projected to rise from 7.8 °C in 1981 to 9.0 °C in 2040. The total vegetation carbon storage was then estimated to increase from 8.56 Pg C in 1981 to 9.79 Pg C in 2040, meanwhile total vegetation carbon accumulation rate was estimated to fluctuate between -0.054-0.076 Pg C·a^-1, with the average of 0.022 Pg C·a^-1. The total soil carbon storage was estimated to increase from 30.2 Pg C in 1981 to 30.72 Pg C in 2040, and total soil carbon accumulation rate was estimated to vary in the range of -0.035-0.072 Pg C·a^-1, with the mean of 0.010 Pg C·a^-1. The response of vegetation and soil carbon accumulation rate to climate change had significant spatial difference in China although the two time series did not show significant trend over the study period. Our results also showed warming was not in favor of forest carbon accumulation, so in the northeastern and southeastern forested area, especially in the Changbai Mountain, with highest temperature increase in the future, the vegetation and soil carbon accumulation rate were estimated to decrease greatly. However, in the southern of southwestern forested area and other forested area, with relatively less temperature increase, the vegetation and soil carbon accumulation rate was estimated to increase in the future.

Aims
The concentration of CO₂ and other greenhouse gases in the atmosphere has considerably increased over last century and is set to rise further. Forest ecosystems play a key role in reducing CO₂ concentration in the atmosphere and mitigating global climate change. Our objective is to understand carbon storage and its distribution in forest ecosystems in Zhejiang Province, China.
Methods
By using the 8th forest resource inventory data and 2011-2012 field investigation data, we estimated carbon storage, density and its distribution in forest ecosystems of Zhejiang Province.
Important findings
The carbon storage of forest ecosystems in Zhejiang Province was 602.73 Tg, of which 122.88 Tg in tree layer, 16.73 Tg in shrub-herb layer, 11.36 Tg in litter layer and 451.76 Tg in soil layer accounting for 20.39%, 2.78%, 1.88% and 74.95% of the total carbon storage, respectively. The carbon storage of mixed broadleaved forests was 138.03 Tg which ranked the largest (22.90%) among all forest types. The young and middle aged forests which accounted for 70.66% of the total carbon storage were the main body of carbon storage in Zhejiang Province. The carbon density of forest ecosystems in Zhejiang Province was 120.80 t·hm^-2 and that in tree layer, shrub-herb layer, litter layer and soil layer were 24.65 t·hm^-2, 3.36 t·hm^-2, 2.28 t·hm^-2 and 90.51 t·hm^-2, respectively. The significant relationship between soil organic carbon storage and forest ecosystem carbon storage indicated that soil carbon played an important role in shaping forest ecosystem carbon density. Carbon density of tree layer increased with age in natural forests, but decreased in the order over-mature > near-mature > mature > middle-aged > young forest in plantations. The proportions of young and middle aged forests were larger than any other age classes. Thereby, the carbon storage of forest ecosystems in Zhejiang Province could be increased through a proper forest management.

Aims
Accurate estimation of carbon density and storage is among the key challenges in evaluating ecosystem carbon sink potentials for reducing atmospheric CO₂ concentration. It is also important for developing future conservation strategies and sustainable practices. Our objectives were to estimate the ecosystem carbon density and storage of Picea schrenkiana forests in Tianshan region of Xinjiang, and to analyze the spatial distribution and influencing factors.
Methods
Based on field measurements, the forest resource inventories, and laboratory analyses, we studied the carbon storage, its spatial distribution, and the potential influencing factors in Picea schrenkiana forest of Tianshan. Field surveys of 70 sites, with 800 m² (28.3 m × 28.3 m) for plot size, was conducted in 2011 for quantifying arbor biomass (leaf, branch, trunk and root), grass and litterfall biomass, soil bulk density, and other laboratory analyses of vegetation carbon content, soil organic carbon content, etc.
Important findings
The carbon content of the leaf, branch, trunk and root of Picea schrenkiana is varied from 46.56% to 52.22%. The vegetation carbon content of arbor and the herbatious/litterfall layer was 49% and 42%, respectively. The forest biomass of Picea schrenkiana was 187.98 Mg·hm^-2, with 98.93% found in the arbor layer. The biomass in all layers was in the order of trunk (109.81 Mg·hm^-2) > root (39.79 Mg·hm^-2) > branch (23.62 Mg·hm^-2) > leaf (12.76 Mg·hm^-2). From the age-group point of view, the highest and the lowest biomass was found at the mature forest (228.74 Mg·hm^-2) and young forest (146.77 Mg·hm^-2), respectively. The carbon density and storage were 544.57 Mg·hm^-2 and 290.84 Tg C, with vegetation portion of 92.57 Mg·hm^-2 and 53.14 Tg C, and soil portion of 452.00 Mg·hm^-2 and 237.70 Tg C, respectively. The spatial distribution of carbon density and storage appeared higher in the western areas than those in the eastern regions. In the western Tianshan Mountains (e.g., Ili district), carbon density was the highest, whereas the central Tianshan Mountains (e.g., Manas County, Fukang City, Qitai County) also had high carbon density. In the eastern Tianshan Mountains (e.g., Hami City), it was low. This distribution seemed consistent with the changes in environmental conditions. The primary causes of carbon density difference might be a combined effects of multiple environmental factors such as terrain, precipitation, temperature, and soil.

Aims
Forest carbon storage in Nei Mongol plays a significant role in national terrestrial carbon budget due to its large area in China. Our objectives were to estimate the carbon storage in the forest ecosystems in Nei Mongol and to quantify its spatial pattern.
Methods
Field survey and sampling were conducted at 137 sites that distributed evenly across the forest types in the study region. At each site, the ecosystem carbon density was estimated thorough sampling and measuring different pools of soil (0-100 cm) and vegetation, including biomass of tree, grass, shrub, and litter. Regional carbon storage was calculated with the estimated carbon density for each forest type.
Important findings
Carbon storage of vegetation layer in forests in Nei Mongol was 787.8 Tg C, with the biomass of tree, litter, herbaceous and shrub accounting for 93.5%, 3.0%, 2.7% and 0.8%, respectively. Carbon density of vegetation layer was 40.4 t·hm^-2, with 35.6 t·hm^-2 in trees, 2.9 t·hm^-2 in litter, 1.2 t·hm^-2 in herbaceous and 0.6 t·hm^-2 in shrubs. In comparison, carbon storage of soil layer in forests in Nei Mongol was 2449.6 Tg C, with 79.8% distributed in the first 30 cm. Carbon density of soil layer was 144.4 t·hm^-2. Carbon storage of forest ecosystem in Nei Mongol was 3237.4 Tg C, with vegetation and soil accounting for 24.3% and 75.7%, respectively. Carbon density of forest ecosystems in Nei Mongol was 184.5 t·hm^-2. Carbon density of soil layer was positively correlated with that of vegetation layer. Spatially, both carbon storage and carbon density were higher in the eastern area, where the climate is more humid. Forest reserves and artificial afforestations can significantly improve the capacity of regional carbon sink.

Aims
Carbon sequestration is the basic function and most primary service of forest ecosystems, and plays a vital role in mitigating the global climate change. However, carbon storage and allocation in forest ecosystems have been less studied at regional scales than at forest stand levels, and the results are subject to uncertainty due to inconsistent methodologies. In this study we aim to obtain relatively accurate estimates of forest carbon stocks and sequestration rate at a provincial scale (regional) based on plot surveys of plants and soils.
Methods
In consideration of the areas and distributions of major forest types, 212 sampling plots, covering different age classes and origins (natural forests vs. planted forests), were surveyed in Gansu Province in northern China. Field investigations were conducted for vegetation layers (trees, shrubs, herbs and litter), soil profiles, and sampling of both plant materials and soils for laboratory analyses. Regional carbon stocks were calculated by up-scaling the carbon densities of all forest types with their corresponding areas. Carbon sequestration rate was estimated by referencing the reports of national forest inventory data for different periods.
Important findings Forest carbon stocks at the provincial scale were estimated at 612.43 Tg C, including 179.04 Tg C in biomass and 433.39 Tg C in soil organic materials. Specifically, natural forests stored 501.42 Tg C, approximately 4.52 times than that of the plantations. Biomass carbon density in both natural forests and plantations showed an increasing trend with stand age classes, and was greater in natural forests than in plantations within the same age classes. Soil carbon density also increased with stand age classes in natural forests, but the highest value occurred at the pre-mature stage in plantations. The weighted average of regional biomass carbon density was at 72.43 Mg C·hm^-2, with the average value of 90.52 Mg C·hm^-2 in natural forests and 33.79 Mg C·hm^-2 in plantations, respectively. In 1996, vegetation stored 132.47 Tg C in natural forests and 12.81 Tg C in plantations, respectively, and the values increased to 152.41 and 26.63 Tg C in 2011, with the mean carbon sequestration rates of 1.33 and 0.92 Tg C·a^-1. Given that young and middle-aged forests account for a large proportion (62.28%) of the total forest areas, the region is expected to have substantial potential of carbon sequestration.

Aims
Our objective was to explore the vegetation carbon storages and their variations in the broad-leaved forests in the alpine region of the Qinghai-Xizang Plateau that includes Qinghai Province and Xizang Autonomous Region.
Methods
Based on forest resource inventory data and field sampling, this paper studied the carbon storage, its sequestration rate, and the potentials in the broad-leaved forests in the alpine region of the Qinghai-Xizang Plateau.
Important findings
The vegetation carbon storage in the broad-leaved forest accounted for 310.70 Tg in 2011, with the highest value in the broad-leaved mixed forest and the lowest in Populus forest among the six broad-leaved forests that include Quercus, Betula, Populus, other hard broad-leaved species, other soft broad-leaved species, and the broadleaved mixed forest. The carbon density of the broad-leaved forest was 89.04 Mg·hm^-2, with the highest value in other hard broad-leaved species forest and the lowest in other soft broad-leaved species forest. The carbon storage and carbon density in different layers of the forests followed a sequence of overstory layer > understory layer > litter layer > grass layer > dead wood layer, which all increased with forest age. In addition, the carbon storage of broad-leaved forest increased from 304.26 Tg in 2001 to 310.70 Tg in 2011. The mean annual carbon sequestration and its rate were 0.64 Tg·a^-1 and 0.19 Mg·hm^-2·a^-1, respectively. The maximum and minimum of the carbon sequestration rate were respectively found in other soft broad-leaved species forest and other hard broad-leaved species forest, with the highest value in the mature forest and the lowest in the young forest. Moreover, the carbon sequestration potential in the tree layer of broad-leaved forest reached 19.09 Mg·hm^-2 in 2011, with the highest value found in Quercus forest and the lowest in Betula forest. The carbon storage increased gradually during three inventory periods, indicating that the broad-leaved forest was well protected to maintain a healthy growth by the forest protection project of Qinghai Province and Xizang Autonomous Region.

Aims
Forests represent the most important component of the terrestrial biological carbon pool and play an important role in the global carbon cycle. The regional scale estimation of carbon budgets of forest ecosystems, however, have high uncertainties because of the different data sources, estimation methods and so on. Our objective was to accurately estimate the carbon storage, density and sequestration rate in forest vegetation in Jilin Province of China, in order to understand the role of the carbon sink and to better manage forest ecosystems.
Methods
Vegetation survey data were used to determine forest distribution, size of area and vegetation types regionally. In our study, 561 plots were investigated to build volume-biomass models; 288 plots of shrubs and herbs were harvested to calculate the biomass of understory vegetation, and samples of trees, shrubs and herbs were collected to analyze carbon content. Carbon storage, density and sequestration rate were estimated by two forest inventory data (2009 and 2014), combined with volume-biomass models, the average biomass of understory vegetation and carbon content of vegetation. Finally, the distribution patterns of carbon pools were presented using ArcGIS soft ware.
Important findings
Understory vegetation biomass overall was less than 3% of the tree layer biomass, varying greatly among different forest types and even among the similar types. The carbon content of trees was between 45.80%-52.97%, and that of the coniferous forests was higher than that of the broadleaf forests. The carbon content of shrub and herb layers was about 39.79%-47.25% and 40%, respectively. Therefore, the vegetation carbon conversion coefficient was 0.47 or 0.48 in Jilin Province, and the conventional use of 0.50 or 0.45 would cause deviation of ±5.26%. The vegetation carbon pool of Jilin Province was at the upper range of regional carbon pool and had higher capacity of carbon sequestration. The value in 2009 and 2014 was 471.29 Tg C and 505.76 Tg C, respectively, and the total increase was 34.47 Tg C with average annual growth of 6.89 Tg C·a^-1. The corresponding carbon sequestration rate was 0.92 t·hm^-2·a^-1. The carbon density rose from 64.58 t·hm^-2 in 2009 to 66.68 t·hm^-2 in 2014, with an average increase of 2.10 t·hm^-2. In addition, the carbon storage of the Quercus mongolica forests and broadleaved mixed forests, accounted for 90.34% of that of all forests. The carbon increment followed the order of young > over-mature > near mature > middle-aged > mature forests. The carbon sequestration rate of followed the order of over-mature > young > near mature > middle-aged > mature forests. Both the carbon increment and the carbon sequestration rate of mature forests were negative. Furthermore, spatially the carbon storage and density were higher in the east than in the west of Jilin province, while the carbon increment was higher in northeast and middle east than in the west. The carbon sequestration rate was higher in Tonghua and Baishan in the south, followed by Jinlin in the middle and Yanbian in the east, while Baicheng and Songyuan, etc. in west showed negative values.

The objective of this study was to understand the distribution patterns of carbon stock in forest ecosystems in Shaanxi Province following the implementation of the ecological restoration project―the Grain for Green―in the 90’s of 20th century for combating the severe soil erosion and other environment problems.

Based on forest resources inventory data and field measurements, we estimated carbon storage of tree, shrub, herb, litter, and soil layer within each forest ecosystem of Shaanxi Province.

Forest ecosystems in Shaanxi Province stored a total of 790.75 Tg C, and the proportion occupied by soil, vegetation and litter carbon were 72.14%, 26.52% and 1.34%, respectively. Carbon storage within Quercus spp. was the highest (44.17%) among all forest types. Given the large proportion of the areas occupied, the young and middle-aged forests accounted for almost half of the total carbon stores in forest ecosystems. The average carbon density of forest ecosystem was 123.70 t·hm^-2. Similar to the patterns among carbon pools, carbon density was also highest in soil, lowest in litter, and medium in vegetation for each forest type. Carbon density increased with stand age for natural and planted forest ecosystems, and was higher in the natural forest ecosystems than in the planted forests within the same stand ages. Differences in the spatial patterns between carbon stores and density indicate that carbon storage is related not only to forest quality, but also to forest areas. Therefore we could select tree species with high carbon concentration for reforestation and afforestation, and improve forest management practices to increase carbon sequestration potential, which would be beneficial to mitigation of global climate change.

Forests are the world’s largest carbon (C) pool and sink among the terrestrial ecosystems. The amount of C in vegetation plays an important role in the global C cycle and balance. Our objectives were to assess C density and sequestration capacity in seven typical forest types of the Xiaoxing’an Mountains, Heilongjiang Province, China and to understand the implication of the C sink to the regional C budget and future forest C management.

Field surveys were combined with laboratory analysis and allometric equations for obtaining data for a variety of variables. Seven typical forest types in the Xiaoxing’an Mountains were studied based on age groups and plant functional groups (trees, shrubs, herbaceous and litter), including Pinus koraiensis, Larix gmelinii, Pinus sylvestris var. mongolica, Picea-Abies, Betula platyphylla, Quercus mongolica, and Populus davidiana forests. Surveys were made on C density and annual carbon gains in trees, understory shrubs, herbaceous plants and litter for each forest type. The forest stands were classified into age groups for estimating the biomass and C density of the study area.

The C density of the seven forest types in different age groups varied widely. The C density per unit area for young, middle-aged, near mature and mature forests of each forest type were as follows: 31.4, 74.7, 118.4 and 130.2 t·hm^-2 in Pinus koraiensis; 28.9, 44.3, 74.2 and 113.3 t·hm^-2 in L. gmelinii; 22.8, 52.0, 71.1 and 92.6 t·hm^-2 in Pinus sylvestris var. mongolica; 23.1, 44.1, 77.6 and 130.3 t·hm^-2 in Picea-Abies; 18.8, 35.3, 66.6 and 88.5 t·hm^-2 in B. platyphylla; 25.0, 20.0, 47.4 and 68.9 t·hm^-2 in Q. mongolica; and 19.8, 28.7, 43.7 and 76.6 t·hm^-2 in Populus davidiana forests, respectively. These results show that biomass C stocks in the Xiao- xing’an Mountains play an important role in the C cycle and regional C balance. Different forest types and stands of different age groups varied greatly in C stocks. Because most growth in the seven forest types occurs in the young and middle-aged forest stands, these age groups are considered to have a great potential to increase the biomass C density. This significant C sink will be further enhanced in the Xiaoxing’an Mountains with the development and restoration designed to provide specific ecological services including C sequestration.

Aims Land-use change is one of the key factors affecting global carbon cycle, and plant functional traits have been widely used to study the linkage between environmental factors and ecosystem functioning. With the help of plant functional traits, we can better understand how plants respond to land-use changes. This study aims to 1) determine how plant traits related to carbon sequestration differ among different functional groups, organs and species of common plants in a Stipa grandis steppe in Nei Mongol; 2) explore the underlying impacts of four different land-use types on traits related to carbon sequestration of the studied plants.
Methods The study was conducted in Maodeng pastureland, Xilinhot, Nei Mongol. Samples of common plant species were collected in four plots, including a long-term reserved plot, a long-term free grazing plot, a 4-year enclosed plot and a 4-year enclosed plot with hay harvesting. We separated the plants into organs and determined the contents of carbon, total nitrogen, cellulose, lignin and acid detergent fiber, and then calculated the ratio of carbon to nitrogen. All data were analyzed in IBM SPSS Statistics for Windows 19.0.
Important findings There were marked differences in the traits related to carbon sequestration among different plant functional groups, species and organs. Land-uses significantly affected these traits at the three organizational levels. Four-year enclosure with hay harvesting resulted in a decrease in nitrogen content of the plants compared with other three land-use types. Both Cleistogenes squarrosa and Salsola collina were susceptible in the traits related to carbon sequestration to long-term free grazing, but their patterns of responses were reversed.

Aims Our objectives were to: 1) examine fine root biomass, morphological characteristics and content of C and N of Alnus formosana in an A. formosana-Hemarthria compressa composite model in Danling, Sichuan Province, China, 2) examine the effects of fertilization on each order of fine roots, and 3) analyze the relationship between soil nutrients and fine root biomass, architecture and content of C and N.
Methods In September 2010, we established two subdistricts, eradicated weeds and planted H. compressa. We fertilized one subdistrict with N-P-K fertilizer in April, June, August and October and did not fertilize the other subdistrict. We excavated soil blocks of 20 cm × 20 cm × 10 cm (height) to sample intact fine root branches of at least the first branch orders. We dissected the intact root branches by orders and measured the diameter, specific root length, biomass, and C and N content of each order.
Important findings Fertilization reduced fine-root average diameter in soil surface and increased that in soil subsurface. In fine-root orders 1-5, specific root length increased as root order decreased. Fertilization significantly increased specific root length in fine-root orders 1-3 in soil surface and subsurface (p < 0.01). Fertilization reduced fine-root biomass in all soil layers and significantly reduced the ratio of fine-root biomass to total root biomass in orders 1-3 (p < 0.05), while fine root biomass increased in orders 4 and 5. The effect of fertilization on fine-root C content was not significant in all orders (p > 0.05). Soil surface total N content of fine roots of 1-5 orders was higher than that in subsurface. Fertilization significantly (p < 0.01) increased fine-root N content of order 1 fine roots in soil surface and orders 1 and 2 in the subsurface, but had no significant effects on orders 3-5 (p > 0.05).

Aims Our objective was to document the effects of different forest management strategies on carbon storage in both vegetation and soil in a Cinnamomum camphora plantation.
Methods We investigated the biomass of trees, shrubs, herb and the litter layer to calculate the carbon storage of vegetation and collected soil samples of 0-60 cm depth to analyze the soil carbon storage in a C. camphora plantation.
Important findings The carbon storage of vegetation was higher in understory removal stands than that of non-removal stands, with an increase of 48.87% and an increment of 0.62 t·hm^-2·a^-1. The soil carbon content was lower when the understory vegetation was removed, with a significant decrease ranging from 4.79% to 34.13%, and a significant decline of 10.16 g·kg^-1and 8.58 g·kg^-1in the 0-10 and 10-20 cm layers, respectively (p < 0.05). Carbon storage in soil was reduced by understory removal treatment in each interval of 0-60 cm depth with a decrease ranging from 1.98% to 43.45% and an especially sharp decline of 15.39 t·hm^-2 and 11.58 t·hm^-2in 0-10 cm (p < 0.01) and 10-20 cm (p < 0.01) layers, respectively. However, the total forest carbon storage in the C. camphora plantation was not significantly reduced by understory removal treatment. Therefore, understory removal contributed to the accumulation of carbon storage in vegetation, but lowered the soil carbon content and storage.

Agroforestry is regarded as a sustainable land-use management due to its potential for solving the problem of resource deficiency, improving the livelihood of rural areas and reducing environmental degradation. Agroforestry has attracted considerable scientific attention since the Kyoto Protocol because it has relatively high potential for carbon sequestration. Comprehensively understanding the process of carbon sequestration in agroforestry and its response to climate change, environmental variation and management practices is essential for predicting the carbon sequestration potential of agroforestry under varying climate and land-use patterns. This paper first reviews the concept and classification of agroforestry and then proposes the mechanism of higher carbon sequestration in agroforestry systems compared with monocropping or monoculture pasture systems. Furthermore, the methods used for quantifying the carbon sequestration potential of agroforestry and the present challenges are discussed. Based on the systematic review of previous studies, the effects of climatic factors, environmental conditions and management practices on carbon sequestration potential of agroforestry are illustrated. The carbon sequestration potential of agroforestry is relatively low in China compared with other regions around the world. In order to improve the carbon sequestration potential of agroforestry, future studies should focus on enlarging the area of agroforestry, developing appropriate designs and management of agroforestry, selecting appropriate species composition and optimizing the multi-layer structure of agroforestry.

Aims Fine root carbon storage is an important part of forest ecosystem carbon pools. Our objective was to determine the effects of thinning on fine root biomass and carbon storage in a Picea asperata plantation in Western Sichuan Province, China.

Methods We sampled fine roots of a 50 year-old P. asperata plantation thinned by different treatments in August 2010. We excavated soil blocks of 20 cm × 20 cm × 20 cm to sample intact fine root branches of at least the first five branch orders, dissected the intact root branches by order and measured the biomass and carbon storage of each order.

Important findings Fine root biomass and carbon storage significantly increased with root order (p < 0.05). The first order roots had the smallest biomass and carbon storage, and the fifth order roots had the largest. Compared with the control, thinning the plantation had significant effects on fine roots biomass and carbon storage (p < 0.05), while the effects of fine roots biomass per plant varied. Thinning treatments of 10% and 20% were not significantly different from the control (p > 0.05). Thinning significantly affected the distribution of fine root biomass in the five root orders. As the thinning intensity increased, the ratio of biomass distribution in the first and second fine order increased. The first order had the largest increase. The ratio of biomass distribution in orders 3 to 5 decreased, and order 5 had the largest decrease. The 50% thinning significantly reduced the fine root biomass ratio in the lower soil layer (20-40 cm), but there was no significant difference compared with 20% and 30% (p > 0.05).

Aims Knowledge of fine root morphology, anatomy and tissue chemistry is critical to understanding root functions (e.g., longevity), but little is known about these root traits and their relationships in woody plants. We investigated root morphology, anatomy and tissue chemistry of the first five orders in four tropical tree species (Altingia obovata, Cryptocarya chinensis, Elaeocarpus sylvestris and Endospermum chinense) in Jianfengling of Hainan Island, China. Our objectives were to: 1) examine how root morphology (diameter, length, specific root length (SRL) and tissue density), anatomy (cortex thickness and stele to root diameter ratio (V/R)) and tissue chemistry (N and C content) changes with root branch orders and 2) reveal the relationships between anatomical structures and root diameter or tissue N or C concentrations in the four tree species.
Methods Tree roots of the four species were sampled in August 2009, and root samples were sorted into different orders. Root morphology of the first five orders was analyzed by the Win-RHIZO system. Root tissue C and N concentrations in roots of each order were analyzed by the Vario MACRO Element Analyzer. Individual roots in each order were made into paraffin slices stained by safranin and fast green to observe root anatomical structures and to calculate cortical thickness, stele diameter and V/R.
Important findings From the first to fifth order, root diameter, length and tissue density as well as stele diameter and V/R increased, and SRL and cortex thickness decreased in all species. The first two or three orders exhibited primary development with an intact cortex and lower V/R ratio, whereas higher order roots showed secondary development with no cortex and higher V/R ratio. Correlation analysis indicated that cortex thickness can explain 97% of the variations of root diameter and 70% of stele diameter. In all species, tissue N concentration decreased and tissue C concentrations increased with ascending root order. Moreover, C/N ratio in roots was mainly affected by tissue N rather than tissue C concentrations. These results suggest that there are systematic differences in root morphology, anatomy and tissue chemistry among different orders, and root morphology and tissue chemistry are closely linked to root anatomical traits such as cortex thickness in these tropical tree species.

Aims Improved rangeland management activities, such as prohibiting grazing, contribute significantly to increased carbon storage in grassland at low cost. Estimating carbon sequestration is important to evaluating cost and potential of carbon sequestration in grassland. We described and compared two methods for estimating carbon sequestration, stock-difference and gain-loss, in order to assess their suitability and accuracy for estimating cost of carbon sequestration in grassland.

Methods Using the grassland in Xilin River Basin of Inner Mongolia as a case study, we estimated the amount and cost of carbon sequestration by the stock-difference and gain-loss methods and compared results through sensitivity analysis.

Important findings There are significant differences in the amount and cost of carbon sequestration between the two methods, because of different grazing intensities. The cost of carbon sequestration is a function of grazing intensity and size of study area, with a linear relationship between cost and grazing intensity and a nonlinear relationship between cost and size of study area. The gain-loss method is more sensitive to grazing intensity and size of study area. The stock-difference method is more accurate and suitable for estimating cost of grassland carbon sequestration. However, the main reason for the difference between the two methods is different conditions of study areas. The two methods are essentially the same with regard to grassland succession. With sufficient data, both methods to estimate the amount and cost of carbon sequestration in grassland will give similar results.

Aims In this study, variations of soil particle size distribution and correlations with soil C and N were studied on sites representing six different land-use types in the steppe grasslands of Inner Mongolia, Northern China. The six land-use types are grazing exclusion by fencing (GE), mowing (MW), free grazing (FG), fallow (FL), alfalfa pasture (AP), and corn plantation (CP). Our objectives were to: (a) assess variability of soil particle size distribution across different land-use types in the steppe grasslands of northern China and (b) examine correlations of soil particle size distribution with soil C and N as affected by land-uses.

Methods Twenty-four sampling plots, each 30 m×30 m, were established on sites representing the six land-use types. Measurements were made on soil particle size distribution, aboveground biomass, root biomass, litter, soil organic carbon (SOC) and soil total nitrogen (TN) in the 0-10, 10-20 and 20-30 cm soil layers. Data were evaluated by one-way analysis of variance and correlation analysis using SPSS. Fractal dimension of soil particle size distribution was calculated using the method of Yang et al. (1993).

Important findings Fractal dimension of soil particle size distribution was lowest in the FG among the six land-use types. Soil clay (<0.005 mm) and silt (0.005-0.05 mm) content of the FL and AP were consistently higher than the other four land-use types; whereas those of the FG were consistently lower. Clay and silt content decreased with soil depth except for the AP and FG. Soil sand content was significantly negatively correlated withSOC and TN for all land-use types, while soil clay content was significantly positively correlated with SOC and TN except for FG and AP. Regardless of the land-use types, root biomass was found to be significantly positively correlated with SOC, TN and soil clay and silt content. Aboveground biomass and litter were significantly positively correlated with only clay content. Root biomass and clay content together explained 70% of the variance in SOC and soil TN, and separately only 20% of the variance each. The relationships were best described as: SOC = 1.08 × clay% + 0.01 × biomass _roots-19.45,TN=0.079×clay%+0.001×biomass_roots-1.143. Findings indicate that land-use types can have significant effects on soil physical properties as well as SOC and soil TN and consequently alter the relationships of soil particle size distribution with SOC and soil TN.

Aims Our objectives were to measure the soil microbial biomass carbon (SMB C), soil microbial biomass nitrogen (SMB N) content and soil microbial activity, and determine the relationship between these parameters and other soil properties (including organic carbon, total nitrogen content and water content) in montane forest (dominated by Picea crassifolia), steppe and alpine meadow ecosystems in Qi Lian Mountains, China.
Methods We measured SMB C and SMB N content using fumigation-incubation method and soil microbial activity using substrate-induced respiration.
Important findings The SMB C content under forest was 60% and 120% higher than under steppe and alpine meadow, respectively, and it was 40% higher under steppe than alpine meadow. The SMB N content was 64% and 111% higher in 0-5 cm soil depth under forest than alpine meadow and steppe, respectively, and it was 29% higher under alpine meadow than steppe. Also, it was 7% and 191% higher in 5-15 cm soil depth under forest than steppe and alpine meadow, respectively, and it was 171% higher under steppe than alpine meadow (p<0.05). The ratio SMB C (SMB C-to-SOC (Soil organic carbon), 0.4%-2.8%) was 32% higher under forest and steppe than alpine meadow, and the ratio of SMB N (SMB N-to-total soil N, 0.5%-2.8%) in 0-5 and 5-15 cm soil depths was 150% higher under forest and steppe than alpine meadow (p<0.05). Soil microbial activity in 0-5 or 5-15 cm soil depth was 26% higher under forest or alpine meadow than steppe, and in 15-35 cm soil depth it was 28% higher under forest than steppe and alpine meadow (p<0.05). The SMB C and SMB N content was positively correlated with SOC content, and the SMB N content or its ratio was also positively correlated with the SMB C content and its ratio (r²>0.30, p<0.000 1). The SMB N content, SMB C ratio, SMB N ratio and microbial activity were significantly negatively correlated with soil pH. The SMB C content, SMB N content and their ratio and microbial activity were positively correlated with soil water content.

Background and Aims Accurate estimates on the size of terrestrial organic carbon stocks are necessary for understanding their importance in regulating atmospheric CO₂ concentrations. In this paper, biomass and SOC contents in alpine grasslands (alpine steppe and alpine meadow) in Bayinbulak were estimated. In addition, the vertical distribution of belowground carbon was discussed. Our objectives were to (a) estimate biomass and SOC contents of two different alpine grasslands, (b) investigate the root distribution of two alpine grasslands, and (c) explore the vertical distribution of SOC of two alpine grasslands.
Methods SOC content was estimated by an improved method (integral arithmetic method). Based on continuous decrease of SOC density with soil depth, integral arithmetic method could estimate SOC content to a given soil depth.
Key Results There were significant differences in the biomass between the alpine steppe and alpine meadow; aboveground biomass of the alpine steppe was 71.4 g C·m^-2, whereas aboveground biomass of the alpine meadow was 94.9 g C·m^-2; belowground biomass of the two alpine grasslands was 1 033.5 and 1 285.2 g C·m^-2, respectively. No significant differences were found between integral arithmetic and traditional methods of estimating SOC contents. SOC contents of the alpine meadow was higher than in the alpine steppe; SOC contents in the two alpine grasslands was 25.7 and 38.8 kg·m^-2, respectively. Most of the root biomass of the two alpine grasslands was in the upper 40 cm of the soil profile, while SOC was concentrated in the top 60 cm. The two alpine grasslands had different root distributions; the percentage of root biomass in the top 20 cm averaged 76%-80% for the alpine steppe and alpine meadow. Alpine meadows had a deeper root profile with only 49% of the SOC in the upper 20 cm, whereas the alpine steppe had 55% of the total SOC in the top 20 cm.
Conclusions This study suggests that vegetation determines the vertical distribution of SOC through root: shoot ratio and its vertical root distribution.

Background and Aims Shrublands is one of the major types of terrestrial ecosystems, which widely distributes from tropical to polar regions. Due to their largely distributional area in China, it is very important for us to exactly estimate their carbon storages and spatial distributions. Answers to the following questions were sought: (a) How much is the vegetation carbon storage of major shrublands in China? (b) How are their spatial distributions in China?
Methods Based on published biomass data in shrublands and 1∶4 000 000 digital vegetation map of China, carbon storage of major shrublands in China was estimated using the method of mean biomass carbon density for different shrublands types.
Key Results The carbon storage of six shrublands in China is 1.68±0.12 Pg C (1 Pg = 10¹⁵ g) with an total area of 15 462.64×10⁴ hm². The average vegetation carbon density is 10.88±0.77 Mg C·hm^-2, varying from 5.92 to 17.00 Mg C·hm^-2 for different shrubland types. The distribution of shrublands is spatially heterogeneous in the country. Shrublands in three provinces (Yunnan, Guizhou and Sichuan) in Southwest China occupies 23.5% of the total area and contributes to approximately one-third (32.6%) of the total carbon storage of six shrubland types in China due to favorable climeste and soil conditions. The area of six shrubland types in Inner Mongolia is the second largest among all the provinces. However, the vegetation carbon storage in Inner Mongolia shrublands is only 84.81 Tg C (1 Tg = 10¹² g), following that of Yunnan, Guizhou, Sichuan, Jiangxi, and Hunan. The probable reason is ascribed to its arid or semiarid climatic conditions. Although shrublands hold about 1.5 times the area of forests in China, the carbon storage of shrublands corresponds 27%-40% of forests because carbon density of shrublands accounts for only one-fifth of forests. Similarly, the proportion of vegetation carbon storage of shrublands to that of grasslands in China varies from 36% to 55% due to the different areas of grasslands used in previous studies.
Conclusions This study draw the following conclusions: (a) As important ecosystem types in China, shrublands hold large vegetation carbon storage, which is main component of China's vegetation carbon storage. (b) Because of different climatic and soil conditions, their distributions are spatially heterogeneous in China and The average vegetation carbon density varies greatly for different shrubland types.