Estimating forest biomass at regional scale with high accuracy is among the pressing challenges in evaluating ecosystem functions and characteristics (e.g., carbon storage).

This study is based on airborne small-footprint discrete-return LiDAR data, Landsat 8 OLI multispectral data, and in situ measurements from 55 forest plots in Yushan, Changshu, Jiangsu Province. A total of 87 independent variables (53 from OLI metrics and 34 from LiDAR metrics) were used in the Pearson correlation analysis for estimating aboveground (W_A) and belowground (W_B) biomass by identifying the significant independent variables. Three independent models by using OLI, LiDAR and their combinations (i.e., the combo model) were established through stepwise regression analysis.

The correlation coefficients of determination (R²) for W_A and W_B models are greater than 0.4. The R² seemed much higher when the estimations were type-specific (e.g., coniferous, broad-leaf and mixed forest), with R² of >0.67. The Combo model by forest type yielded an R² of 0.88 for W_A and 0.92 for W_B, while the OLI-based model had R² of 0.73 and 0.81 for W_A and W_B, respectively. The LiDAR-based model has R² of 0.86 and 0.83 for W_A and W_B, respectively.

Forest net primary production (NPP) is an important parameter on measuring the terrestrial carbon source/sink. More accurately estimating NPP of forest ecosystems is the focus of carbon cycle. Our objective was to explore how to use remote sensing process model to simulate NPP of the northeast forest more accurately, and what impacts of forest fire disturbance have on NPP.

In this study, based on remote sensing data and meteorological data, Boreal Ecosystem Productivity Simulator (BEPS) model was used to simulate NPP of the northeast forest in 2003; The result of BEPS model acted as the reference year data of Integrated Terrestrial Ecosystem C-budget (InTEC) model to simulate NPP from 1901 to 2008 of the northeast forest. Then forest fire disturbance data was incorporated in the InTEC model to simulate NPP from 1966 to 2008 of Daxing’an Mountain.

The average value of NPP of the northeast forest was only 278.8 g C·m^-2·a^-1 in 1901. In 1950, average NPP had reached to 338.5 g C·m^-2·a^-1. The average NPP of the northeast forest in 2008 was 378.4 g C·m^-2·a^-1; Substantial increase was evidenced for Daxing’an Mountain, Xiaoxing’an Mountain and Changbai Mountain with 200 g C·m^-2·a^-1 to 300 g C·m^-2·a^-1 increase for Changbai Mountain. The average and total value of NPP of Liaoning in 2008 was relatively low, but was still 70 percent higher than that in 1901. Moderate and large fires did not drastically reduce NPP, with less than 10 percent reduction during the year of fire occurrence. In the following years, NPP recovered quickly and maintained at a high level. NPP reduced substantially in each of the four years with burned area exceeding 100000 hm² in Daxing’an Mountain.

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.

A plant’s photosynthetic characteristics reflect its adaptive strategies to a given environment. Using pasture plants within enclosures representing communities at different stages of habitat restoration, our objective was to determine how photosynthetic characteristics vary between these different communities and what causes these differences in order to find the theoretical basis to foster rehabilitation of degraded grassland in sub-alpine meadows.

We predicated a succession sequence according to the species richness and the Shannon-Wiener diversity indices, the important values of the main species, and the biotype of five different communities. We measured several photosynthetic parameters including area-based leaf CO₂ assimilation rate (A_area), special leaf area (SLA), foliar nitrogen content based on mass (N_mass), photosynthetic nitrogen-use efficiency (PNUE), water-use efficiency (WUE) and chlorophyll content (SPAD) of dominant species and three common species in each succession stage. Soil water content and total nitrogen of surface soil (0-20 cm) for each community were measured as well. One-way ANOVA was used to find the differences between dominant species, while principal components analysis (PCA) was used to reveal the variation in different communities for each measured parameter.

Photosynthetic traits were different among dominant species and different succession communities. The A_area, WUE and SPAD of the dominant species decreased as succession progressed, but the N_mass, PNUE and SLA showed no consistent patterns related to succession; they varied between different functional groups. For each of the non-dominant species, the A_area and SPAD gradually decreased as succession proceeded from initial stage to climax stage. With succession, WUE and PNUE of the non-leguminous plants (Elymus dahuricus and Geranium wilfordii) decreased while SLA and N_mass increased. However, there were no obvious changes in these parameters for the leguminous plant (Medicago sativa). Soil water content and total nitrogen increased with succession, suggesting that water content and nitrogen are two important factors affecting variation of community photosynthetic characteristics in different stages of restoration succession.

Investigating tree water use efficiency (WUE) is important for understanding the coupling of carbon and water cycles in terrestrial ecosystems and its responses and adaptation to climatic change. Dahurian larch (Larix gmelinii), the dominant tree species in the Chinese boreal forest, plays an important role in the regional carbon budget. In this study, we measured the foliar WUE and associated physiological parameters of 30-year-old Dahurian larch trees from 17 provenances with divergent climatic conditions in a common garden. Our specific aims were to compare differences in WUE among the provenances and explore whether the observed differences are attributed to potential adaptation or acclimation to local habitats.

We have measured net photosynthetic rate (P_n), transpiration rate (T_r), stomatal conductance (G_s), and leaf nitrogen concentration (N_L) of three replicate trees per provenance from mid June to mid September of 2010. WUE was calculated as the ratio of P_n to T_r. Specific leaf area (SLA) was calculated as one-side projected leaf area divided by the leaf dry mass. The aridity index (AI) of each provenance was calculated as the ratio of mean annual evaporation to mean annual precipitation.

WUE, P_n, G_s, T_r, SLA and N_L all differed significantly among the provenances. WUE showed a significant exponential relationship with G_s. WUE increased significantly with the increase of G_s when the G_s was less than 0.2, and was relatively stable when the G_s was greater than 0.2. WUE was significantly and positively correlated with N_L, but negatively with SLA. The degree of these correlations increased with increasing AI values of the tree origins. WUE was negatively correlated with the mean annual temperature and mean annual precipitation of the tree origins, but positively correlated with the AI of the tree origins. T_r and P_n were positively correlated with both mean annual temperature and AI of the tree origins, these results suggest that the trees may adapt to the local climatic conditions of their origins, which results in the significant difference in the needle morphological and physiological properties, and thus WUE among the provenances of Dahurian larch trees.

The growth relationship between twigs and leaves is a strategy that plants enhance the ability to use space resources under environmental stresses, and elucidation of this characteristics is important for understanding the phenotypic plasticity of plants in coping with environmental heterogeneity. Our objective was to examine how Robinia pseudoacacia would vary in twig and leaf configuration in response to changes in slope aspect.

In the northern mountains of Lanzhou in Gansu Province, China, 20 transects were laid out horizontally along the contour at intervals of 50 m from an elevation of 1550 m upward in four different slope aspects, and 12 plots were set up along each transect at intervals of 5 m. A handheld GPS was used to measure latitude, longitude and altitude of each plot. Community traits were investigated and all individuals of R. pseudoacacia were used for measurements of the cross-sectional area of twigs, total leaf area, leafing intensity, and average area of a single leaf on each twig. ArcGIS was used to construct the digital elevation model (DEM). The 240 plots were categorized into groups of northern, eastern, western and southern aspects, and the standardized major axis (SMA) estimation method was then used to examine the allometric relationship between the cross-sectional area of twigs, total leaf area, leafing intensity and average area of a single leaf.

With changes in the slope aspect from north to east, south and west, the crown density, average tree height and soil moisture of the plant community displayed a pattern of decrease—increase, and the cross-sectional area of twigs, total leaf area and average area of a single leaf of R. pseudoacacia displayed a pattern of decrease—increase and the leafing intensity displayed a pattern of increase—decrease. Significant positive relationships between the cross-sectional area of twigs and total leaf area were found in R. pseudoacacia in all slope aspects (p < 0.05), and the common slope of the regressions was significantly greater than 1; significant negative relationships between leafing intensity and average area of a single leaf were found in all slope aspects (p < 0.05), and the common slope of the regressions was significantly close to -1. In addition, when the slope aspect changed from north to east, south and west, the y-intercepts in the scaling relationships of the cross-sectional area of twigs vs. total leaf area and the leafing intensity vs. individual leaf area both displayed a pattern of decrease—increase. The allometric relationship between twig and leaf with changes in slope aspect of the habitat reflected the response and adaption of plant functional traits to their biotic and abiotic environments and the investment balance mechanism of plant architecture construction.

Phyllostachys heterocycla ‘Pubescens’, through its unique growth feature, is easy to encroach on, and replace surrounding evergreen broad-leaved forests or coniferous and broad-leaved mixed forests rapidly. The expansion leads to coniferous and broadleaved tree species withering and dying gradually, and inhibits the forest regeneration. Mycorrhizal weakening hypothesis suggests that expansion of P. heterocycla ‘Pubescens’ would interrupt the original mycorrhizal associations and causes the subsequence dieback of the forests. This study was to investigate the changes of mycorrhiza along a bamboo forest, bamboo-forest transition, mixed forest transect to examine the hypothesis.

A transect, perpendicular to the bamboo expansion direction, went through P. heterocycla ‘Pubescens’ forest (PPF), bamboo-forest transition (BFT), coniferous and broad-leaved mixed forest (CBF), and were sampled in the Tianmu Mountain National Reserve, Zhejiang Province. Six dominant tree and shrub species (Cunninghamia lanceolata, Liquidambar formosana, Cyclobalanopsis glauca, Cryptomeria fortune, Lindera chienii, Camellia fraterna) existing in both CBF and BFT, were chosen for collecting their root tips for measuring the frequency and intensity of arbuscular mycorrizal (AM) colonization for AM species, and frequency of ectomycorrhizal (EM) colonization for EM species. The AM colonization frequency and intensity of P. heterocycla ‘Pubescens’ in PPF and BFT were also measured and compared.

1) Before and during the encroachment of P. heterocycla ‘Pubescens’, frequency of the mycorrhizal fungi root colonization of the six tree species were very high (>95%), and there was no significant difference between CBF and BFT (p > 0.1); 2) In BFT, intensity of the AM fungi root colonization of Cunninghamia lanceolata and Liquidambar formosana increased significantly than those in CBF (p < 0.1); 3) The frequency and intensity of the AM fungi root colonization of P. heterocycla ‘Pubescens’ were much lower than any other tree species, with no significant change during the expansion. The findings reject the mycorrhizal weakening hypothesis i.e., P. heterocycla ‘Pubescens’ realizing its population expansion and replacing surrounding forests IS NOT caused by destructing mycorrhizal associations of adjacent forests.

The objective of this study was to understand how arbuscular mycorrhizal (AM) fungal community would vary with plant evolution.

Data-mining was carried out against MaarjAM database with ribosomal small subunit (SSU) gene. We predicted that the richness of root-associated AM fungal species increases from lower to higher modern land plants. Totally, 188 host plant species were selected in this analysis.

The AM fungal species richness increased with the divergence of host plant species, and significantly differed among plant phylogenetic groups. The more recently diverged host plants (i.e. gymnosperms and angiosperms) harbored higher AM fungal species richness, whereas the earlier-originated plants (liverworts, hornworts and ferns) possessed lower AM fungal species richness. The myco-heterotrophytes in angiosperms showed similarly low richness of AM fungal species to the lower plants. In addition, the AM fungal community composition significantly differed among different plant phylogenetic groups. Findings in this study provided some indirect evidence that AM fungal communities varied with plant evolution. It is suggested that plants might maintain the most effective AM fungi but discard those inefficient ones during evolution.

Determination of carbon cycling model parameters is critical to simulate the net ecosystem CO₂ exchange (NEE). The objectives of this study were to determine the parameters of vegetation photosynthesis and respiration model (VPRM) and improve the calculation of NEE to benefit regional modeling of CO₂.

Two schemes are examined in optimization of the parameters in VPRM. Two years CO₂ flux and meteorological observational data in 2010-2011 at the Qianyanzhou (QYZ) eddy tower site are used to determine the parameters in VPRM and another full year flux observational data in 2012 are used to evaluate the model performance. Several statistics metrics are calculated to evaluate the model performance on NEE simulations.

The results indicate, traditional method with Michaelis-Menten equation is not suitable to determine the parameters of VPRM, whereas the method with parameters retrieved from the VPRM calculation equation provides much more reasonable results. The parameter of maximum light use efficiency (λ) is critical for the VPRM calculation of NEE. Our result is larger than the typical value of C₃ plant (1/6), but consistent with the other studies. Using the optimized parameters, VPRM is able to capture NEE variations for different seasons. The statistics calculation with one-year NEE simulation shows that, the mean bias is -0.86 μmol·m^-2·s^-1 and correlation coefficient is 0.72. Overall, the VPRM performs much better in growing season than the non-growing season when the peak value of NEE is underestimated by 52%. The VPRM simulated NEE shows better agreement with observations on sunny days than rainy or cloudy days.

Spring drought greatly limits the sugarcane (Saccharum officinarum) seedling growth in the southwest China. A major objective of this study is to investigate the change of the energy allocation in photosystem II (PSII) resulted from the stomatal and non-stomatal limit of photosynthesis under the drought stress condition. The study results can be used for drought resistant breeding and rapid drought stress diagnosis.

Four levels (40%, 25%, 10% and 8%) of soil volumetric water content (VWC) have been chosen from natural drought treatments. The chlorophyll fluorescence parameters based on Lake-model were measured and analyzed with various levels of photosynthetically active radiation (PAR).

Results of the study in the enhanced drought stress for two tested cultivars (‘ROC22’ and ‘ROC16’) showed 1) decreased numbers in the maximum quantum use efficiency (F_v/F_m), the relative electron transport rate (rETR), the quantum efficiency of PSII (Φ_II) and the photochemical quenching (q_L) and 2) increased numbers in the down-regulated energy dissipation (Φ_NPQ) and the non-light induced energy dissipation (Φ_NO). There was no significant difference between the parameter q_L of ‘ROC16’ and ‘ROC22’, except for the 8% level where the q_L showed a sharp decline. The results indicated that the PSII of ‘ROC16’ remained a relatively high open fraction during the mild drought stress, but suffered severe damage in serious drought stress. The rising range of Φ_NPQ for ‘ROC22’ were higher and more sensitive to drought stress than that of ‘ROC16’, which revealed a strong drought resistance resulted from strong photo-protective mechanism in‘ROC22’. The Φ_NO was more sensitive to drought stress than F_v/F_m especially for non drought resistant variety, and remained high stability under different PAR. Therefore, Φ_NO could be properly used as an indicator in drought stress diagnosis and resistance evaluation. Photo inhibition could be the initial factor leading to PSII damage and its signal had been amplified under high PAR related to photo inhibition since the appeared peak or decline of rETR related to increased PAR and its no significance at each water level and low PAR during drought stress.

In recent years, international studies have found that poplar species could accumulate high boron with hypertolerance ability. Our objective was to investigate the effect of growth and physiological indicators of Populus russkii and P. bolleca under different boron concentrations, and determine the interspecific difference on boron tolerance, to help explaining and providing certain theoretical basis of phytoremediation technology for boron pollution treatment.

Poplar cuttings were grown in potting soil and added boron after three months. Physiological properties tested included plant height, fresh biomass, chlorophyll fluorescence parameters, chlorophyll content, activities of catalase (CAT) and guaiacol peroxidase (Gu-POD), soluble protein (SP) content and soluble carbohydrate (SC) content.

Boron stress seriously inhibited the growth and affected the chlorophyll fluorescence parameters of the two poplar species. Populus russkii was more sensitive than P. bolleca to boron stress, and P. bolleca could stand higher boron level than P. russkii. The boron damage threshold (10%) of P. russkii and P. bolleca were 19 and 35 mg·kg^-1, respectively. The plant height, fresh mass and chlorophyll decreased linearly with the increase of soil boron concentrations. For antioxidant parameters analysis, the activities of CAT and Gu-POD increased at first, and then decreased with increasing concentration of applied boron. Populus bolleca kept higher chlorophyll a/b and non-photochemical quenching than P. russkii under boron stress. Soluble protein and soluble carbohydrate increased with the increasing concentration of applied boron. These results demonstrated that the two poplar species eased the boron toxicity by strengthen the metabolism of protein synthesis but the capacity of clearing up the harmful peroxide was limited, and the CAT and Gu-POD activities were inhibited under high boron concentrations.