Aims Shrubland is one of the most important vegetation types in subtropical region, but studies on its life-form composition and geographic patterns are scarce. In this paper, we addressed the following questions: what are the characteristics of the composition of plant life forms of subtropical shrublands in China? And what are the relation-ships between the life form compositions, geographic patterns of subtropical shrublands and hydrothermal factors?Methods A total of 688 plots, designed with the stratified random sampling method, were systematically set and investigated in subtropical shrublands in China. Life forms were identified based on Raunkiaer’s (1934) life form systems. Life form spectrums were compiled at each sampling site and within the whole shrubland, respectively. Partial correlation analysis was applied to reveal the latitudinal, longitudinal and altitudinal patterns of each life form. Pearson’s correlation analysis was adopted to evaluate the relationships between each life form and hydrothermal factors. Further, redundancy analysis (RDA) was used to distinguish the effect of temperature and precipitation on geographical variations of life forms.Important findings (1) In subtropical shrublands in China, 56.37% of the total species were woody species, among which 33.88% were deciduous species and 22.49% were evergreen species. The remaining 43.63% of the total species were herbaceous species, dominated by 35.15% perennials. Generally, phaenerophytes (Ph) was the most dominant component, while the second dominant one was hemicryptophytes (H). The life form spectrum showed a pattern of Ph (55.74%) > H (31.03%) > T (therophytes 8.80%) > Cr (cryptophytes 4.08%) > Ch (chamaephytes 1.34%). (2) Plant life forms mainly exhibited longitudinal and altitudinal patterns. With the increase of longitude, the percentage of Ph tended to increase while H, Cr and T tended to decrease. Furthermore, an increase in altitude would lead to an increase in H and Cr but a decrease in Ph, Ch and T. (3) Among all the investigated climatic factors, the mean temperature of the warmest month (MWT) and the mean precipitation of the coldest month (MCP) had the greatest impact on Ph, H, Cr and T. With an increase of MWT and MCP, Ph would increase while H, Cr and T would decrease. Taken together, MWT and MCP could explain 41.97% of the variation of life form spectrum, among which 28.35% was attributed to their joint-effect. The results suggested that Ph and H were mainly influenced by both temperature and precipitation, and that Cr was more sensitive to temperature gradients. Besides, T was more sensitive to precipitation, and Ch showed little fluctuation along hydrothermal gradients. In conclusion, MWT and MCP are the most important hydrothermic factors that determine the geographic patterns of life forms in subtropical shrublands in China.
Aims Carbon (C), nitrogen (N) and phosphorus (P) play important roles in plant growth and physiological functions. We aimed at exploring the intrinsic relationships of C, N and P in Myrica nana—a common shrub in Yunnan Province—as well as their relationships with pant biomass and soil nutrients.Methods We measured the concentration of C, N and P of M. nana from 29 sites for their magnitudes and correlations with soil nutrients. Important findings 1) The arithmetic mean value of C, N and P concentration in the roots, stems and leaves of M. nana was 45.94%, 0.54%, 0.03%, and 46.32%, 0.58%, 0.03%, and 49.05%, 1.70%, 0.06%, respectively. C, N and P concentrations in the leaves were significantly higher than those in the roots and the stems. The C:N:P in roots, stems and leaves was 1531:18:1, 1544:19:1, and 818:10:1, respectively. 2) The C concentration and N:P in leaves of M. nana decreased with the increase of biomass of M. nana; the leaf C concentration was significantly correlated with biomass (p < 0.01), while the correlation between N:P and biomass was not significant (p > 0.05). The leaf N increased with the increase of plant biomass, the P was significantly correlated with biomass (p < 0.05), but the correlation between N concentration and biomass was not significant (p > 0.05). N:P in leaves was 34.2, suggesting that plant growth was limited by P. 3) C, N and P concentration in the roots were significantly correlated with soil P (p < 0.05), with N, P concentrations correlated with soil P positively (p < 0.01) and C negatively (p < 0.05). C concentration in the stems was significantly and negatively correlated with soil C, N, with significant correlation with C, N, and P concentration (p < 0.01). P concentration in the stems was significantly and positively correlated with soil P concentration (p < 0.01), while leaf P significantly and positively correlated with soil C, N and P (p < 0.01); leaf C concentration was significantly and negatively correlated with soil P (p < 0.01).
Aims Little is known about the stoichiometric characteristics of carbon (C), nitrogen (N) and phosphorus (P) in plateau shrubs across China. Sibiraea angustata is a typical and representative shrub species on the eastern Qinghai- Xizang Plateau, and exploring its C, N and P distribution patterns and stoichiometric properties in different organs (including root, shoot, leaf, twig and fruit) would help us better understand the mechanisms of C, N and P cycling and balance in the S. angustata dominated shrub ecosystem.Methods Sixteen sampling sites were selected on the eastern Qinghai-Xizang Plateau by the stratified sampling method. The height and coverage of the dominant shrubs, latitude, longitude and altitude of the sites were recorded. Three 5 m × 5 m plots were selected at each site. At least 128 biological samples of plant organs of S. angustata were collected and measured, respectively. The C and N concentrations of plant samples were analyzed using an elemental analyzer (2400 II CHNS). The P concentration was analyzed using the molydate/ascorbic acid method after H2SO4-H2O2 digestion.Important findings The C, N and P concentrations of different organs followed the order of: shoot (495.07 g·kg-1) > twig (483.37 g·kg-1) > fruit (480.35 g·kg-1) > root (468.47 g·kg-1) > leaf (466.33 g·kg-1); leaf (22.27 g·kg-1) > fruit (19.74 g·kg-1) > twig (7.98 g·kg-1) > shoot (4.54 g·kg-1) > root (4.00 g·kg-1) and fruit (2.85 g·kg-1) > leaf (1.92 g·kg-1) > twig (0.96 g·kg-1) > root (0.52 g·kg-1) > shoot (0.45 g·kg-1), respectively. The ranges of the coefficient of variation (CV) for C, N and P concentrations were 1.71%-4.44%, 14.49%-25.50% and 11.46%-46.15%, respectively. Specifically, the C concentration was relatively high and stable, and the maximum CV values for N and P were found in roots. The N:P value of different organs varied from 7.12-12.41 and the minimum CV for N:P was found in twig, which indicated that N:P in twig had higher internal stability. In addition, correlation analysis indicated that the C concentration was significantly negatively correlated with N and P concentrations and correlation coefficients were -0.407 and -0.342, respectively. However, N concentration had dramatically positive correlation with P concentration and the correlation coefficient was 0.814. These results also could indicate that the C, N and P stoichiometric characteristics in the S. angustata shrub accorded with the homeostatic mechanism and growth rate hypothesis to some extent, the distributions of C, N and P concentrations were closely related to the function of the organs and it should be prudent to use ecological stoichiometric ratios to judge the condition of nutrient limitation at the species level.
Aims Shrub species have evolved specific strategies to regulate biomass allocation among various organs or between above- and belowground biomass and shrub biomass model is an important approach to estimate biomass allocation among different shrub species. This study was designed to establish the optimal estimation models for each organ (leaf, stem, and root), aboveground and total biomass of 14 common shrub species in Mountain Luya, Shanxi Province, China. Furthermore, we explored biomass allocation characteristics of these shrub species by using the index of leaf biomass fraction (leaf to total biomass), stem biomass fraction (stem to total biomass), root biomass fraction (root to total biomass), and root to shoot mass ratio (R/S) (belowground to aboveground biomass).Methods We used plant height, basal diameter, canopy diameter and their combination as variables to establish the optimal biomass estimation models for each shrub species. In addition, we used the ratios of leaf, stem, root to total biomass, and belowground to aboveground biomass to explore the difference of biomass allocation patterns of 14 shrub species. Important findings Most of biomass estimation models could be well expressed by the exponential and linear functions. Biomass for shorter shrub species with more stems could be better estimated by canopy area; biomass for taller shrub species with less stems could be better estimated by the sum of the square of total base diameter multiply stem height; and biomass for the rest shrub species could be better estimated by canopy volume. The averaged value for these shrub species was 0.61, 0.17, 0.48, and 0.35 for R/S, leaf biomass fraction, stem biomass fraction, and root biomass fraction, respectively. Except for leaf biomass fraction, R/S, stem biomass fraction, and root biomass fraction for shrubs with thorn was significantly greater than that for shrubs without thorn.
Aims Biomass is the most fundamental quantitative character of an ecosystem. Biomass allocation patterns reflect the strategies of plants to adapt various habitat conditions and play a vital role in evolution, biodiversity conservation and global carbon cycle. Loropetalum chinense shrub is one of the most dominant shrub types in subtropical China. The objectives of this study were to quantify the allometric relationships and the biomass allocation pattern among organs, and to investigate the effects of body size, shrub regeneration origin and site factors on allometry and biomass allocation.Methods Individual samples of L. chinense were harvested from shrublands in subtropical China and were further divided into leaves, stems and roots. The allometric relationships between different organs were modeled with standard major axis (SMA) regression and the biomass allocation to different organs was quantified. The effects of body size, shrub regeneration origin and other habitat factors on allometry and allocation were examined using Pearson’s correlation analysis and multiple linear regressions.Important findings The isometric scaling relationships between shoot and root changed to allometric relationships with increasing basal diameter. The scaling relationships between leaf and stem and between leaf and root were isometric for smaller diameter classes, while for larger diameter classes they were allometric. These relationships were significantly different among shrub regeneration origin types. The scaling relationships between different organs were not affected by habitat factors; while the coverage of shrub layer and slope affected biomass allocation due to their influences on the allometric relationships between different organs at the initial stage of growth. The mean dry mass ratios of leaf, stem, root and the mean root to shoot ratio were 0.11, 0.55, 0.34 and 0.65, respectively. With the increase of basal diameter class, stem mass ratio (0.50-0.64) increased, while leaf mass ratio (0.12-0.08) and root mass ratio (0.38-0.28) decreased, and consequently root to shoot ratio (0.91-0.43) also decreased. In secondary shrublands, the leaf mass ratio was 0.12 and the root mass ratio was 0.33, while these values were 0.07 and 0.36 respectively in natural shrublands. The ratio of aboveground allocation was significantly correlated to shrub layer coverage (r = 0.44, p < 0.05). Leaf mass ratio was significantly correlated to slope (r = -0.36, p < 0.05) and root mass ratio was significantly correlated to mean annual temperature (r = 0.34, p < 0.05). Results showed that with the increase of body size, the scaling relationships between different organs of L. chinense changed from isometric to allometric, and more biomass was allocated to aboveground part, and concretely, to stems. Human disturbance affected biomass allocation by its influences on the allometric relationships between different organs, and by increasing biomass allocation to leaves and decreasing allocation to roots. Reduced light resource promoted the biomass allocation to aboveground part, and higher slope resulted in decreased biomass allocation to leaves, while higher mean annual temperature promoted biomass allocation to roots. The variation in annual precipitation had no significant influences on biomass allocation. The biomass allocation strategies of L. chinense partially support the optimal partitioning theory.
Aims As the second largest C flux between the atmosphere and terrestrial ecosystems, soil respiration plays a vital role in regulating atmosphere CO2 concentration. Therefore, understanding the response of soil respiration to the increasing nitrogen deposition is urgently needed for prediction of future climate change. However, it is still unclear how nitrogen deposition influences soil respiration of shrubland in subtropical China. Our objectives were to explore the effects of different levels of nitrogen fertilization on soil respiration, root biomass increment, and litter biomass, and to analyze the relationships between soil respiration and soil temperature and moisture. Methods From January 2013 to September 2014, we conducted a short-term simulated nitrogen deposition experiment in the Rhododendron simsii shrubland of Dawei Mountain, located in Hunan Province, southern China. Four levels of nitrogen addition treatments (each level with three replicates) were established: control (CK, no nitrogen addition), low nitrogen addition (LN, 2 g·m-2·a-1), medium nitrogen addition (MN, 5 g·m-2·a-1) and high nitrogen addition (HN, 10 g·m-2·a-1). Soil respiration was measured by LI-8100 soil CO2 efflux system. At the same time, we measured root biomass increment and litter biomass in each plot.Important findings Soil respiration exhibited a strong seasonal pattern, with the highest rates found in summer and the lowest rates in winter. Annual accumulative soil respiration rate in the CK, LN, MN and HN was (2.37 ± 0.39), (2.79 ± 0.42), (2.26 ± 0.38) and (2.30 ± 0.36) kg CO2·m-2, respectively. Annual mean soil respiration rate in the CK, LN, MN and HN was (1.71 ± 0.28), (2.01 ± 0.30), (1.63 ± 0.27) and (1.66 ± 0.26) μmol CO2·m-2·s-1, respectively, and it was 17.25% higher in the LN treatment compared with CK (p = 0.06). The root biomass increment was increased by LN, MN, and HN treatments by 18.36%, 36.49% and 61.63%, respectively, compared to CK. The litter biomass was increased by LN, MN, and HN treatments by 35.87%, 22.17% and 15.35%, respectively, compared with CK. Soil respiration exhibited a significant exponential relationship with soil temperature (p < 0.01, R2 is 0.77 to 0.82) and a significant linear relationship with soil moisture at the depth of 5 cm (p < 0.05, R2 is 0.10 to 0.15). The temperature sensitivity (Q10) value of CK, LN, MN and HN plots was 3.96, 3.60, 3.71 and 3.51, respectively. These results suggested that nitrogen addition promoted plant growth and decreased the temperature sensitivity of soil respiration. The increase of root biomass under N addition may be an important reason for the change of soil respiration in the study area.
Aims Soil respiration from terrestrial ecosystems is an important component of terrestrial carbon budgets. Compared to forests, natural or semi-natural shrublands are mostly distributed in nutrient-poor sites, and usually considered to be relatively vulnerable to environmental changes. Increased nitrogen (N) input to ecosystems may remarkably influence soil respiration in shrublands. So far the effects of N deposition on shrubland soil respiration are poorly understood. The aim of this study is to investigate the soil respiration of Vitex negundo var. heterophylla and Spiraea salicifolia shrublands and their response to N deposition. Methods We carried out a N enrichment experiment in V. negundo var. heterophylla and S. salicifolia shrublands in Mt. Dongling, Beijing, with four N addition levels (N0, control, 0; N1, low N, 20 kg N·hm-2·a-1; N2, medium N, 50 kg N·hm-2·a-1 and N3, high N, 100 kg N·hm-2·a-1). Respiration was measured from 2012-2013 within all treatments.Important findings Under natural conditions, annual total and heterotrophic respiration were 5.91 and 4.23, 5.76 and 3.53 t C·hm-2·a-1 for the V. negundo var. heterophylla and S. salicifolia shrublands, respectively and both were not affected by short-term N addition. In both shrubland types, soil respiration rate exhibited significant exponential relationships with soil temperature. Temperature sensitivity (Q10) of total soil respiration in V. negundo var. heterophylla and S. salicifolia shrublands ranged from 1.44 to 1.58 and 1.43 to 1.98, and Q10 of heterotrophic soil respiration ranged from 1.38 to 2.11 and 1.49 to 1.88, respectively. Short-term N addition decreased only autotrophic respiration rate during the growing season, but had no significant effects on total and heterotrophic soil respiration in V. negundo var. heterophylla shrubland. In contrast, N addition enhanced the heterotrophic soil respiration rate and did not influence autotrophic and total soil respiration in S. salicifolia shrubland.
Aims The shrublands of northern China have poor soil and nitrogen (N) deposition has greatly increased the local soil available N for decades. Shrub growth is one of important components of C sequestration in shrublands and litterfall acts as a vital link between plants and soil. Both are key factors in nutrient and energy cycling of terrestrial ecosystems, which greatly affected by nitrogen (N) addition (adding N fertilizer to the surface soil directly). However, the effects and significance of N addition on C sequestration and litterfall in shrublands remain unclear. Thus, a study was designed to investigate how N deposition and related treatments affected shrublands growth related to C sequestration and litterfall production of Vitex negundo var. heterophylla and Spiraea salicifolia in Mt. Dongling region of China. Methods A N enrichment experiment has been conducted for V. negundo var. heterophylla and S. salicifolia shrublands in Mt. Dongling, Beijing, including four N addition treatment levels (control (N0, 0 kg N·hm-2·a-1), low N (N1, 20 kg N·hm-2·a-1), medium N (N2, 50 kg N·hm-2·a-1) and high N (N3, 100 kg N·hm-2·a-1)). Basal diameter and plant height of shrub were measured from 2012-2013 within all treatments, and allometric models for different species of shrub’s live branch, leaf and root biomass were developed based on independent variables of basal diameter and plant height, which will be used to calculate biomass increment of shrub layer. Litterfall (litterfall sometimes is named litter, referring to the collective name for all organic matter produced by the aboveground part of plants and returned to the surface, and mainly includes leaves, bark, dead twigs, flowers and fruits.) also was investigated from 2012-2013 within all treatments.Important findings The results showed 1) mean basal diameter of shrubs in the V. negundo var. heterophylla and S. salicifolia shrublands were increased by 1.69%, 2.78%, 2.51%, 1.80% and 1.38%, 1.37%, 1.59%, 2.05% every year; 2) The height growth rate (the shrub height relative growth rate is defined with the percentage increase of plant height) of shrubs in the V. negundo var. heterophylla and S. salicifolia shrublands were 8.36%, 8.48%, 9.49%, 9.83% and 2.12%, 2.86%, 2.36%, 2.52% every year, respectively. Thee results indicated that N deposition stimulated growth of shrub layer both in V. negundo var. heterophylla and S. salicifolia shrublands, but did not reach statistical significance among all nitrogen treatments. The above-ground biomass increment of shrub layer in the V. negundo var. heterophylla and S. salicifolia shrublands were 0.19, 0.23, 0.14, 0.15 and 0.027, 0.025, 0.032, 0.041 t C·hm-2·a-1 respectively, which demonstrated that short-term N addition had no significant effects on the accumulation of C storage of the two shrublands. The litter production of the V. negundo var. heterophylla and S. salicifolia communities in 2013 were 135.7 and 129.6 g·m-2 under natural conditions, respectively. Nitrogen addition promoted annual production of total litterfall and different components of litterfall to a certain extent, but did not reach statistical significance among all nitrogen treatments. Above results indicated that short-term fertilization, together with extremely low soil moisture content and other related factors, lead to inefficient use of soil available nitrogen and slow response of shrublands to N addition treatments.
Aims Shrub recovery is recognized as an important cause of the increase of carbon stocks in China, and yet there are great uncertainties in the carbon sink capacities of shrubs. Our objectives were to estimate carbon density and its spatial distribution in alpine shrubs.Methods Eight sites in Potentilla fruticosa dominated shrublands across Qinghai, China were investigated. Plant biomass and carbon content in leaves, branches and stems, and roots were measured to analyze the biomass allocation and carbon density.Important findings Mean carbon densities in biological carbon, litter, soil and whole ecosystem of P. fruticosa shrublands were 5088.54, 542.1, 35903.76 and 41534.4 kg·hm-2, respectively. Carbon density in the shrub layer was more than 68% of the biological carbon density of the whole ecosystem and was mainly distributed in roots (49.5%-56.1%). Carbon density of the herbaceous layer was 22.5% of the biological carbon density of the whole ecosystem and was also mainly distributed in roots (59.6%-75.1%). The biological carbon density of P. fruticosa shrublands (5.08 t·hm-2) was lower than the average carbon density of shrub communities in China (10. 88 t·hm-2). Soil carbon density contributed the largest proportion (85.8%) of total carbon density in P. fruticosa shrublands.
Aims The expansion of shrublands is considered as one of the key reasons leading to the increase of carbon density in terrestrial ecosystems in China. In the present study, our aims were to explore the biomass allocation and carbon density of Sophora moorcroftiana shrublands in Xizang. Methods We sampled the biomass of S. moorcroftiana shrubs from 18 sites in the middle reaches of Yarlung Zangbo River, Xizang. Using concentrations of different organs, we estimated the carbon density of different layers in S. moorcroftiana shrublands. Important findings The plant cover rather than biomass volume (the product of cover and height) provided the best fit for aboveground biomass. The average of the total biomass was 5.71 Mg·hm-2, ranging from 2.32 to 8.96 Mg·hm-2. The average biomass of shrub layer, the main component of shrub ecosystem, was 4.08 Mg·hm-2, accounting for 71% of the total biomass. The belowground biomass of shrub and herb layers was 2.08 and 0.86 Mg·hm-2, respectively, which was higher than the corresponding aboveground biomass. The average biomass carbon density was 2.48 Mg·hm-2. Shrub vegetation in the eastern part of the middle reaches has lower carbon density than that in the western part. The relatively high biomass allocation to roots to increase water and nutrient undertake as well as physical support for plants is an important strategy of S. moorcroftiana to cope with the arid environment on the Qinghai-Xizang Plateau. Moreover, the lower carbon density in the eastern part of the middle reaches might be due to the dry environment resulted from high temperature and evapotranspiration and enhanced human activities at low altitudes. The continuous decrease of evapotranspiration under scenarios of future climate change may lead to increase in carbon density in S. moorcroftiana shrublands.
Aims As an important potential carbon sink, shrubland ecosystem plays a vital role in global carbon balance and climate regulation. Our objectives were to derive appropriate regression models for shrub biomass estimation, and to reveal the biomass allocation pattern and carbon density in Rhododendron simsii shrubland.Methods We conducted investigations in 27 plots, and developed biomass regression models for shrub species to estimate shrub biomass. The biomass of herb and litterfall were obtained through harvesting. Plant samples were collected from each plot to measure carbon content in different organs.Important findings The results showed that the power and linear models were the most appropriate equation forms. The D and D2H (where D was the basal diameter (cm) and H was the shrub height (m)) were good predictors for organ biomass and total biomass of shrubs. All of the biomass models reached extremely significant level, and could be used to estimate shrub biomass with high accuracy. It was more difficult to predict leaf and annual branch biomass than stem biomass, because leaf and annual branch were susceptible to herbivores and inter-plant competition. The mean biomass of the shrub layer was 20.78 Mg·hm-2, in which Rhododendron simsii and Symplocos paniculata biomass accounted for 93.63%. Influenced by both environment and species characteristics, the biomass of the shrub layer organs was in the order of stem > root > leaf > annual branch. The root:shoot ratio of the shrub layer was 0.32, which was less than other shrubs in subtropical regions. The relative higher aboveground biomass allocation reflected the adaptation of plants to the warm and humid environment for more photosynthesis. The mean total community biomass was 26.26 Mg·hm-2, in which shrub layer, herb layer and litter layer accounted for 79.14%, 7.62% and 13.25%, respectively. Litter biomass was relatively high, which suggested that this community had high nutrient return. There were significant correlations among aboveground biomass, belowground biomass and total biomass of shrub layer and herb layer. The mean biomass carbon density of the community was 11.70 Mg·hm-2 and the carbon content ratio was 44.55%. The carbon density was usually obtained using the conversion coefficient of 0.5 in previous studies, which could overestimate carbon density by 12.22%.
Aims Understanding the changes in N and P concentration in plant organs along the environmental gradients can provide meaningful information to reveal the underline mechanisms for the geochemical cycles and adaptation strategies of plants to the changing environment. In this paper, we aimed to answer: (1) How did the N and P concentration in leaves of evergreen and deciduous woody plants change along the environmental gradients? (2) What were the main factors regulating the N and P concentration in leaves of woody plants in the shrublands across southern China? Methods Using a stratified random sampling method, we sampled 193 dominant woody plants in 462 sites of 12 provinces in southern China. Leaf samples of dominant woody plants, including 91 evergreen and 102 deciduous shrubs, and soil samples at each site were collected. N and P concentration of the leaves and soils were measured after lapping and sieving. Kruskal-Wallis and Nemenyi tests were applied to quantify the difference among the organs and life-forms. For each life-form, the binary linear regression was used to estimate the relationships between leaf log [N] and log [P] concentration and mean annual air temperature (MAT), mean annual precipitation (MAP) and log soil total [N], [P]. The effects of climate, soil and plant life-form on leaf chemical traits were modeled through the general linear models (GLMs) and F-tests.Important findings 1) The geometric means of leaf N and P concentrations of the dominant woody plants were 16.57 mg·g-1 and 1.02 mg·g-1, respectively. The N and P concentration in leaves (17.91 mg·g-1, 1.14 mg·g-1) of deciduous woody plants was higher than those of evergreen woody plants (15.19 mg·g-1, 0.89 mg·g-1). The dependent of leaf P concentration on environmental (climate and soil) appeared more variable than N concentration. 2) Leaf N and P in evergreen woody plants decreased with MAT and but increased with MAP, whereas those in deciduous woody plants showed opposite trends. With increase in MAP, leaf P concentration decreased for both evergreen and deciduous woody plants. 3) Soil N concentration had no significant effect on both evergreen and deciduous woody plants. However, leaf P concentration of the tow increased significantly with soil P concentration. (4) GLMs showed that plant growth form explained 7.6% and 14.4% of variation in leaf N and P, respectively. MAP and soil P concentration contributed 0.8% and 16.4% of the variation in leaf P, respectively. These results suggested that leaf N was mainly influenced by plant growth form, while leaf P concentration was driven by soil, plant life-form, and climate at our study sites.
Aims Shrubland is one of the most widely distributed vegetation types in northern China. Previous studies on pattern and dynamics of plant biomass have been focused on forest and grassland ecosystems, while relevant knowledge on shrubland ecosystems is lacking. It is important to include shrublands in northern China to improve the accuracy in estimating the terrestrial ecosystem biomass in China. Methods Based on investigations and samplings from 433 shrubland sites, we explored the distribution and allocation patterns of biomass in relation to climatic and soil nutrient factors of shrublands of temperate China. Important findings The average shrubland biomass density in northern China is 12.5 t·hm-2. It decreases significantly from temperate deciduous shrubland in northeast to desert shrubland in northwest. The average biomass density of temperate deciduous shrubland, alpine shrubland, and desert shrubland is 14.4, 28.8, and 5.0 t·hm-2, respectively. Within temperate deciduous shrublands, plant biomass is lower in North China than in Northeast China. The average aboveground and belowground biomass density of shrub layer is 4.5 and 5.4 t·hm-2, respectively; while that of grass layer is 0.8 and 1.8 t·hm-2, respectively. Environmental factors affect biomass allocation across different plant organs. The belowground-aboveground biomass ratio of shrub exhibits no significant changes with environmental variables. The leaf-stem ratio increases with annual precipitation, and leaf biomass is low in arid region.
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 Litter is an important component of terrestrial ecosystems, which plays significant roles in carbon and nutrient cycles. Quantifying regional-scale pattern of litter standing crop would improve our understanding in the mechanism of the terrestrial ecosystem carbon cycle, also with help in predicting the responses of carbon cycle of terrestrial ecosystems to future climate change. Our objective was to examine variation in litter standing crop of shrublands along the environmental gradients in southern China.Methods During 2011-2014, we investigated the litter standing crop at 453 shrublands sites by the stratified random sampling, reflecting climatic and soil attributes across southern China.Important findings We found that the mean value of litter standing crop in these shrubland ecosystems across southern China was 0.32 kg·m-2. It was 68% of forest litter standing crop (0.47 kg·m-2) and was five times higher than that in grasslands (0.06 kg·m-2) in China. Litter standing crop increased with latitude. Our results showed that litter standing crop was negatively correlated with mean annual temperature, soil total P and soil pH, but not significantly correlated with other environmental variables, including mean annual precipitation, soil carbon, nitrogen and soil organic matter. The conversion coefficient of carbon in litter standing crop was 0.41, which is significantly lower than that of vegetation in shrublands (0.50), resulting in an overestimate in carbon storage of litter standing crop in shrubland up to 22% by applying wrong conversion coefficient. We concluded that litter standing crop of shrublands is an important component in terrestrial ecosystems. Mean annual temperature was the most important environmental variable, accounting for the variation in litter standing crop of shrublands in southern China. To our best of knowledge, this is the first study to quantify variation in litter standing crop of shrublands at the regional scale. Therefore, our study will have important implications for assessing the carbon budget of terrestrial ecosystems in China.
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