Ammonia emissions from soil under sheep grazing in Inner Mongolian grasslands of China

Ammonia （NH3） emission and redeposition play a major role in terrestrial nitrogen （N） cycles and can also cause environmental problems, such as changes in biodiversity, soil acidity, and eutrophication. Previous field grazing experiments showed inconsistent （positive, neutral, and negative） NH3 volatilization from soils in response to varying grazing intensities. However, it remains unclear whether, or to what extent, NH3 emissions from soil are affected by increasing grazing intensities in Inner Mongolian grasslands. Using a 5-year grazing experiment, we investigated the relationship between NH3 volatilization from soil and grazing pressure （0.0, 3.0, 6.0, and 9.0 sheep/hm2） from June to September of 2009 and 2010 via the vented-chamber method. The results show that soil NH3 volatilization was not significantly different at different grazing intensities in 2009, although it was higher at the highest stocking rate during 2010. There was no significant linear relationship between soil NH3 volatilization rates and soil NH4^-N, but soil NH3 volatilization rates were significantly related to soil water content and air temperature. Grazing intensities had no significant influence on soil NH3 volatilization. Soil NH3 emissions from June to Sep- tember （grazing period）, averaged over all grazing intensities, were 9.6±0.2 and 19.0±0.2 kg N/hm2 in 2009 and 2010, respectively. Moreover, linear equations describing monthly air temperature and precipitation showed a good fit to changes in soil NH3 emissions （r=0.506, P=0.014）. Overall, grazing intensities had less influence than that of climatic factors on soil NH3 emissions. Our findings provide new insights into the effects of grazing on NH3 volatili- zation from soil in Inner Mongolian grasslands, and have important implications for understanding N cycles in grassland ecosystems and for estimating soil NH3 emissions on a regional scale.

Implication of community-level ecophysiological parameterization to modelling ecosystem productivity:a case study across nine contrasting forest sites in eastern China

Parameterization is a critical step in modelling ecosystem dynamics.However,assigning parameter values can be a technical challenge for structurally complex natural plant communities;uncertainties in model simulations often arise from inappropriate model parameterization.Here we compared five methods for defining community-level specific leaf area(SLA)and leaf C:N across nine contrasting forest sites along the North-South Transect of Eastern China,including biomass-weighted average for the entire plant community(AP_BW)and four simplified selective sampling(biomass-weighted average over five dominant tree species[5DT_BW],basal area weighted average over five dominant tree species[5DT_AW],biomass-weighted average over all tree species[AT_BW]and basal area weighted average over all tree species[AT_AW]).We found that the default values for SLA and leaf C:N embedded in the Biome-BGC v4.2 were higher than the five computational methods produced across the nine sites,with deviations ranging from 28.0 to 73.3%.In addition,there were only slight deviations(<10%)between the whole plant community sampling(AP_BW)predicted NPP and the four simplified selective sampling methods,and no significant difference between the predictions of AT_BW and AP_BW except the Shennongjia site.The findings in this study highlights the critical importance of computational strategies for community-level parameterization in ecosystem process modelling,and will support the choice of parameterization methods.

Changes in leaf stomatal traits of different aged temperate forest stands

Stomata control carbon and water vapor exchange between the leaves and the atmosphere,thus infl uencing photosynthesis and transpiration.Combinations of forest patches with different stand ages are common in nature,however,information of which stomatal traits vary among these stands and how,remains limited.Here,seven different aged forest stands(6,14,25,36,45,55,and 100 years)were selected in typical temperate,mixed broadleaf-conifer forests of northeast China.Stomatal density,size and relative area of 624 species,including the same species in stands of different ages were selected.Stomatal density,size and relative area were distributed log-normally,differing across all species and plant functional groups.Stomatal density ranged from 4.2 to 1276.7 stomata mm^(–2),stomatal size ranged from 66.6 to 8315.7μm^(2),and stomatal relative area 0.1–93.3%.There was a significant negative relationship between density and size at the species and functional group levels,while the relative stomatal area was positively correlated with density and size.Stomatal traits of dominant species were relatively stable across different stand ages but were significantly different for herbs.The results suggest that stomatal traits remain relatively stable for dominant species in natural forests and therefore,spatial variation in stomatal traits across forest patches does not need to be incorporated in future ecological models.

Selective harvesting at rational intervals promotes carbon sequestration in temperate coniferous and broad-leaved mixed forests in China

Evidence-based selective cutting at prescribed intervals as part of good forest management can enhance the carbon sequestration capacity of the forest.The effect of forest management on carbon sequestration has,however,not been quantified.Thus,carbon content of various organs was measured for 323 tree species,247 shrub species,and233 herb species in seven temperate coniferous and broadleaved mixed forests that were subjected to selective cutting with restoration durations of 100,55,45,36,25,14,and6 years to explore dynamic changes in carbon storage.The results showed that biomass carbon allocation in different organs followed a pattern:trunk>root>branch>leaf for all forests.With longer restoration durations,more carbon accumulated in different organs and in soils.Interestingly,when the restoration duration exceeded 50 years,carbon storage in ecosystem was larger than that in primary forests with 100-year cutting intervals,suggesting that a reasonable selective cutting interval can increase forest carbon sequestration.Mean diameter at breast height(DBH)and forest carbon storage were significantly positively correlated,and carbon storage of selectively cut forests exceeded that of primary forests when the stand mean DBH exceeded 15.66 cm.Therefore,mean DBH of forests can be an indicator for combining sustainable forest management and forest carbon sequestration.Additionally,the classic coefficients of 0.45 and 0.50 used to estimate carbon sequestration underestimated values by 2.65%and overestimated by 8.16%,respectively,in comparison with the measured carbon content from different plant organs.

Soil acidification in China’s forests due to atmospheric acid deposition from 1980 to 2050

A stable soil pH is essential for maintaining the structure and functions of ecosystems[1].In previous decades,the development model of high energy consumption has rapidly increased the emission of acid precursors.This has not only resulted in the direct input of acidity into the soil but also in the production of acidity through elements cycling,both of which produce protons(Fig.S1 online)[2].Recent studies have shown that atmospheric acid deposition has decreased by more than half compared with that during the 1990s.The decrease in acid deposition in Europe and North-America has resulted in recovery of soil acidification[3].

China's current forest age structure will lead to weakened carbon sinks in the near future

Forests are chiefly responsible for the terrestrial carbon sink that greatly re duces the buildup of CO_(2)concentrations in the atmosphere and alleviates climate change.Current predictions of terrestrial carbon sinks in the future have so far ignored the variation of forest carbon uptake with forest age.Here,we predict the role of China's current forest age in future carbon sink capacity by generating a high-resolution(30 m)forest age map in 2019 over China's landmass using satellite and forest inventory data and deriving forest growth curves using measurements of forest biomass and age in 3,121 plots.As China's forests currently have large proportions of young and middle-age stands,we project that China's forests will maintain high growth rates for about 15 years.However,as the forests grow older,their net primary productivity will decline by 5.0%±1.4%in 2050,8.4%±1.6%in 2060,and 16.6%±2.8%in 2100,indicating weakened carbon sinks in the near future.The weakening of forest carbon sinks can be potentially mitigated by optimizing forest age structure through selective logging and implementing new or improved afforestation.This finding is important not only for the global carbon cycle and climate projections but also for developing forest management strategies to enhance land sinks by alleviating the age effect.

Effects of the frequency and the rate of N enrichment on community structure in a temperate grassland

Aims Nitrogen(N)enrichment caused by human activities threatens bio-diversity and alters plant community composition and structure.It has been found that heavy and infrequent N inputs may over-estimate species extinction,but it remains unclear whether plant community structure will equally respond to frequent reactive N enriched conditions.Methods We independently manipulated the rates and the frequencies of N addition in a temperate steppe,northern China,between 2008 and 2013.Important Findings We found that plant community structure changes,measured by‘Euclidean distance’involving species richness,composition and productivity,were significantly positively related to increasing N enrichment rates rather than frequencies.Changes in aboveground net primary productivity(ANPP),plant species richness and shifts in dominant species were observed.Community ANPP increased with N enrichment,whereas species richness reduced.The frequency of N enrichment increased species richness but had no impacts on community ANPP and the relative ANPP of the two dominant spe-cies,C3 perennial bunchgrass Stipa grandis and C3 perennial rhi-zome grass Leymus chinensis.The ANPP and relative ANPP of the two dominant species were significantly negatively correlated with each other.Moreover,changes in the relative ANPP of S.grandis was negatively associated with the changes in community structure.After 5 years’treatment,direct influence of the frequency of N en-richment on plant community structure was not observed,but the effects of the rate of N enrichment were apparent.Our results sug-gested that further study in various ecosystems and with long-term and well-controlled comparisons the frequency vs.the rate of N enrichment may still be needed.

青藏高原北部戈壁植物群落物种、功能与系统发育β多样性分布格局及其影响因素

戈壁荒漠广泛分布于全球干旱和极旱区域,是我国陆地生态系统的重要组成部分。由于自然环境恶劣和交通条件限制,目前有关戈壁植物群落物种、功能和系统发育等多维度β多样性形成机制的系统研究还很缺乏,严重制约着对戈壁植物多样性维持机制的认知。本文以青藏高原北部61个典型戈壁生境植物群落为研究对象,通过构建系统发育树和测量8个关键功能性状,获取戈壁生境的物种、功能和系统发育β多样性,比较3个维度β多样性格局与零模型的差异,同时量化环境距离和地理距离对其的相对影响,以探讨戈壁植物多样性的形成机制。结果显示:(1)戈壁植物的物种、功能和系统发育β多样性均表现出显著的距离衰减效应;(2)戈壁植物的物种、功能和系统发育β多样性均表现为非随机的格局;(3)由于功能性状趋同进化,植物功能和系统发育β多样性变化趋势并不一致;(4)环境差异对植物3个维度β多样性均有着比空间距离更为重要的影响,且土壤含水量、地表砾石盖度等局域生境因素的影响比气候更为强烈。以上结果表明,戈壁植物的β多样性可能主要由局域生境过滤作用控制,且不同维度的β多样性分布格局并不一致。

中国温带荒漠植物群落生态特异性格局及其影响因素

局域取样单元对beta多样性的贡献可用于测度每个局域群落物种组成的生态特异性(ecological uniqueness)。温带荒漠生态系统广泛分布于全球干旱和极端干旱区域,极易受到气候变化和人类活动的影响。然而目前温带荒漠植物群落生态特异性大尺度地理分布格局及其形成机制的系统研究还很缺乏,制约着我们对荒漠植物群落多样性维持机制的认知。本文在温带灌木、矮半乔木及草原化灌木荒漠等6个中国温带荒漠区的主要地带性植被类型中设置了948个样方,通过开展系统的野外调查采样和室内分析,以及量化每个取样单元对beta多样性的贡献,并结合土壤和气候变量等环境数据,探讨了中国荒漠植物群落生态特异性大尺度地理分布格局及其影响因素。结果表明:(1)温带荒漠植物群落生态特异性存在显著的经度、纬度和海拔分布格局,随着经度增加显著降低,但随着纬度或海拔的升高呈现出先下降后增加的变化趋势;(2)土壤、气候、群落特征(植物物种丰富度和群落盖度)对植物群落生态特异性都有着显著的单独影响,植物群落生态特异性随着物种丰富度增加呈先下降后上升的变化趋势;经度、土壤、气候和植物群落特征共同解释了温带荒漠植物群落生态特异性33.5%的空间变异,其中气候因子有着更强的单独解释率。上述结果说明环境过滤和中性过程以及其他未知过程共同调控了温带荒漠植物群落的生态特异性大尺度分布格局的形成,且气候和土壤因素的过滤作用有着重要影响。

Carbon sequestration of Chinese forests from 2010 to 2060:spatiotemporal dynamics and its regulatory strategies

Forestation is important for sequestering atmospheric carbon,and it is a cost-effective and nature-based solution(NBS)for mitigating global climate change.Here,under the assumption of forestation in the potential plantable lands,we used the forest carbon sequestration(FCS)model and field survey involving 3365 forest plots to assess the carbon sequestration rate(CSR)of Chinese existing and new forestation forests from 2010 to 2060 under three forestation and three climate scenarios.Without considering the influence of extreme events and human disturbance,the estimated average CSR in Chinese forests was 0.358±0.016 Pg C a^(-1),with partitioning to biomass(0.211±0.016 Pg C a^(-1))and soil(0.147±0.005 Pg C a^(-1)),respectively.The existing forests account for approximately 93.5%of the CSR,which will peak near 2035,and decreasing trend was present overall after 2035.After 2035,effective tending management is required to maintain the high CSR level,such as selective cutting,thinning,and approximate disturbance.However,new forestation from 2015 in the potential plantable lands would play a minimal role in additional CSR increases.In China,the CSR is generally higher in the Northeast,Southwest,and Central-South,and lower in the Northwest.Considering the potential losses through deforestation and logging,it is realistically estimated that CSR in Chinese forests would remain in the range of 0.161–0.358 Pg C a^(-1) from 2010 to 2060.Overall,forests have the potential to offset 14.1%of the national anthropogenic carbon emissions in China over the period of 2010–2060,significantly contributing to the carbon neutrality target of 2060 with the implementation of effective management strategies for existing forests and expansion of forestation.

Variation and adaptation in leaf sulfur content across China

Sulfur is an essential functional element in leaves,and it plays important roles in regulating plant growth,development and abiotic stress resistance in natural communities.However,there has been limited information on the spatial variation in leaf sulfur content(LSC)and adaptive characters on a large community scale.Sulfur in leaves of 2207 plant species from 80 widespread ecosystems(31 forests,38 grasslands and 11 deserts)in China was measured.One-way analysis of variance with Duncan’s multiple-range tests were used to evaluate the differences in LSC among different plant growth forms and ecosystems.We fitted the relationships of LSC to spatial and climate factors using regression.Structural equation modeling analysis and phylogenetic analysis helped us further explore the main factors of LSC variation.LSC ranged from 0.15 to 48.64 g·kg^(-1),with an average of 2.13±0.04 g·kg^(-1) at the community scale in China.We observed significant spatial variation in LSC among different ecosystems and taxa.Overall,LSC was higher in arid areas and herbs.Furthermore,higher LSC was observed under environments of drought,low temperatures and intense ultraviolet radiation.Temperature,precipitation,radiation,soil sulfur content and aridity jointly regulated LSC,explaining 79%of the spatial variation.However,LSC was not significantly related to phylogeny.Our results demonstrate that LSC plays an important role in plant adaptations to extreme environments and further extend our understanding of the biological function of sulfur from the organ to the community level.These findings highlight the importance of sulfur metabolism for our understanding of the impact of global climate change on plants.

Effects of pulse precipitation on soil organic matter mineralization in forests:spatial variation and controlling factors

Aims Pulse effects of precipitation cause soil organic matter to rapidly decompose and release CO2 in a short period.The pulse effects of precipitation are important for ecosystem C cycling and soil C balance,although their spatial variation in forest soils and the underlying mechanisms remain unclear.Methods Soil samples(0–10 cm)from 22 typical forest ecosystems in eastern China were used,to investigate the effects of simulated pulse precipitation on soil microbial respiration rates(Rs).We simulated pulsed precipitation to reach 65%water-holding capacity,the Rs was measured on a minute scale for 48 h.Important Findings Precipitation pulses can cause a rapid 1.70–38.12-fold increase in the rate of mineralized decomposing organic matter.Maximum Rs(_(Rs-soil-max)),cumulative Rs(A_(Rs-soil))and the time taken to arrive at the maximal Rs(T_(Rs-soil-max))were significant differences among different soil samples.Furthermore,the pulse effects in different climate zones were significantly different.R_(s-soil-max)(11.701μg C g^(-1)soil h^(-1))and A_(Rs-soil)(300.712μg C g^(-1) soil)were the highest in the mid-temperate zone.Soil chemical properties(total C and,N,pH and oxidation–reduction potential)and soil fractions were strongly correlated with the pulse effects in forest soils,but soil microbes contributed less.Our findings demonstrated that the pulse effects increase forest soil carbon emissions in the short term at a regional scale,and identified the factors with the greatest influence on this change.These findings help guide future studies on the C cycles of forest ecosystems and regulating ecosystem C cycles.

Nitrogen storage and allocation in China’s forest ecosystems

Forests are important parts of terrestrial ecosystems and play a leading role in regional and global nitrogen(N)cycles.Detailed assessment of N storage and allocation in China’s forests is critical to improve the accuracy of regional or global N estimates and to guide policy-makers in the formulation of scientific and effective N management measures.However,the fore stN storage at national scale remains unclear.Based on 4420 forest field-investigated data,we investigated the N storage allocation in China’s forests,explored the spatial patterns and influence factors.The data included vegetation information on various organs(i.e.,leaf,branch,stem,and root)and soil information at different depths(0-30 cm and 0-100 cm).The total N storage in China’s forest ecosystems was 14.45±8.42 tN hm^–2;0.86±0.51 tN hm^–2(5.95%)in vegetation and 13.59±8.40 tN hm^–2(94.05%)in soil(0–100 cm).The storage and allocation of N varied significantly across various regions and forest types.For different ecological regions,N storage varied from 10.34 to 23.11 tN hm^–2,and the allocation ratio of N storage between vegetation and soil(0–100 cm)varied from 0.03 to 0.16.For different forest types,the N storage varied from 12.87 to 18.32 tN hm^–2,and the allocation ratio of N storage between vegetation and soil(0–100 cm)varied from 0.03 to 0.09.The spatial patterns relative to N storage and allocation in forests were different.Climate was the primary factor influencing the spatial variation in forestN storage,while soil texture was the main factor influencing the spatial variation in N allocation.These first estimates of N storage and allocation ratio in China’s forests are keys for improving the fitting accuracy of regional N cycle models and provide a reference for regional management of forestN.

中国典型草原植被高度组合的普适性规律与区域差异

详细测定每株植物高度是精细评估草地生态系统中植物群落高度结构的重要方法,并经常用来分析草地植被生长与环境因子关系的普适性和区域差异。本研究在我国青藏高原、内蒙古高原和黄土高原,分别沿降水梯度布设了3条从草甸-草原-荒漠的典型草地生态系统样带。研究结果发现,我国3大高原的草地生态系统植被平均高度为30.38±22.44 cm,其中黄土高原最高,内蒙古高原次之,青藏高原最低。这3个高原草地生态系统的植被聚合高度分布都呈现偏正态分布(0.91,3.60),而且从青藏、内蒙古到黄土高原,该分布逐渐趋于正态(0,3)。然而,在青藏高原的草甸和荒漠生态系统中分别呈现出指数分布和均匀分布。在3大高原中,气候和土壤营养对植被平均高度解释率超过70%,然而对植被聚合高度的解释率最高仅为29%(青藏高原)。从青藏高原、内蒙古高原至黄土高原,植被平均高度对环境综合响应强度逐渐增强,具体表现为气温、降水的影响逐渐增强,而辐射、风速和营养物浓度影响逐渐减弱。我们的研究表明,正态分布是草地植被高度构建的普适性原则,而环境因素的协同作用在不同区域存在差异。