Inter‐annual variation in primary production of a semi‐arid grassland related to previous‐year production

Mean annual precipitation accounts for a large proportion of the variation in mean above‐ground net primary production (ANPP) of grasslands worldwide. However, the inter‐annual variation in production in any grassland site is only loosely correlated with precipitation. The longest record of variation in production and precipitation for a site corresponds to a shortgrass steppe in Colorado, USA. A previous study of this record showed that current‐year precipitation accounted for 39% of the inter‐annual variation in ANPP. In this note, we show that ca. one third of the unexplained variation is related to previous‐year ANPP: ANPP per mm of precipitation was higher in years preceded by wet, more productive years than in years preceded by average years; similarly, ANPP per mm of precipitation was lower in years preceded by dry, less productive years than in years preceded by average years. Since previous‐year ANPP was, in turn, associated with precipitation of a year before, current‐year ANPP was also explained by precipitation of two previous years. Our finding not only increases our predictive ability, but it also changes our understanding of how ANPP responds to fluctuations in precipitation. If ANPP is thought to vary according to current‐year precipitation only, it will simply track annual precipitation in time. According to this new result, however, ANPP fluctuations are buffered if wet, more productive years alternate with dry, less productive years, and they are amplified if wet or dry sequences of several years take place.     

1982-2010年中国草地净初级生产力时空动态及其与气候因子的关系

植被净初级生产力（NPP）及其与气候变化的响应研究是全球变化的核心内容之一。论文基于长时间序列遥感数据和气象数据,通过光能利用率模型（Carnegie-Ames-Stanford approach, CASA模型）模拟了1982-2010 年中国草地NPP,进而分析其时空变化特征及其与气候水热因子的相关性。结果表明：（1）1982-2010年中国草地年平均NPP为282.0 gC m^-2a^-1,年总NPP的多年平均值为988.3 TgC;空间分布上呈现东南部高西北部低的特征。（2）近30年中国草地NPP增加速率为0.6 gC m^-2a^-1,呈增加趋势的面积占中国草地总面积的67.2%;总体上,中国草地NPP呈极显著和显著增加的比例（35.8%、8.0%）大于呈极显著和显著减少的比例（5.8%、4.8%）;NPP明显增加的区域主要包括青藏高原西部、阿拉善高原、新疆西部;明显降低的区域主要分布在内蒙古地区;不同年代际和不同草地类型的NPP变化趋势差异明显。（3）草地NPP与降水量的相关性高于与温度的相关性。不同草地类型NPP对气温、降水量的响应程度不同,其中温性荒漠草原 、温性草原、温性草甸草原的NPP与降水量均达到显著正相关（P<0.05）。     

基于碳-水-氮耦合过程改进模型的温带草地生态系统生产力模拟研究

基于碳-水-氮耦合过程改进模型的温带草地生态系统生产力模拟研究 预测气候变化背景下生态系统总初级生产力的响应是全球变化生态学研究领域的一项核心任务。然而,对模型研究领域来说,准确模拟干旱生态系统总初级生产力的年际变异仍然是一个巨大的挑战。土壤含水量和总初级生产力对土壤水敏感性的精确模拟,是预测干旱生态系统中总初级生产力年际变异的两个关键方面。为此,本研究以一个广泛应用的生态系统模型(Biome-BGC模型)为例,旨在改进温带草地生态系统的模型模拟效果。一方面,通过对蒸散模块、土壤水沿剖面的垂直分布和田间持水量计算的改进和调整,模型实现了对土壤水模拟的更新。另一方面,我们改进了影响水-氮关系的函数,从而调节了总初级生产力对土壤水的敏感性。研究结果表明,原有模型高估了土壤含水量,低估了总初级生产力敏感性的年际变异,从而导致模拟总初级生产力的年际变异低于观测值。例如,原模型严重低估了总初级生产力在干旱年份的减少。相比之下,改进后的模型准确地模拟了观测土壤水的季节和年际变化,特别是表层土壤水。通过优化影响氮矿化的参数,改进后的模型改善了总初级生产力对土壤水敏感性的模拟,使其更接近观测值。因此,改进后模型对总初级生产力年际变异的模拟得到了很大程度的提高。我们的结果表明,在对干旱生态系统总初级生产力年际变异进行模拟时,应优先考虑表层土壤水及其对氮有效性的影响。     

Spatial variations in aboveground net primary productivity along a climate gradient in Eurasian temperate grassland: effects of mean annual precipitation and its seasonal distribution

Concomitant changes of annual precipitation and its seasonal distribution within the context of global climate change have dramatic impacts on aboveground net primary productivity (ANPP) of grassland ecosystems. In this study, combining remote sensing products with in situ measurements of ANPP, we quantified the effects of mean annual precipitation (MAP) and precipitation seasonal distribution (PSD) on the spatial variations in ANPP along a climate gradient in Eurasian temperate grassland. Our results indicated that ANPP increased exponentially with MAP for the entire temperate grassland, but linearly for a specific grassland type, i.e. the desert steppe, typical steppe, and meadow steppe from arid to humid regions. The slope of the linear relationship appeared to be steeper in the more humid meadow steppe than that in the drier typical and desert steppes. PSD also had significant effect on the spatial variations in ANPP. It explained 39.4% of the spatial ANPP for the entire grassland investigated, being comparable with the explanatory power of MAP (40.0%). On the other hand, the relative contribution of PSD and MAP is grassland type specific. MAP exhibited a much stronger explanatory power than PSD for the desert steppe and the meadow steppe at the dry and wet end, respectively. However, PSD was the dominant factor affecting the spatial variation in ANPP for the median typical steppe. Our results imply that altered pattern of PSD due to climate change may be as important as the total amount in terms of effects on ANPP in Eurasian temperate grassland.     

高寒草地植物群落地上-地下净初级生产力权衡

植物生产力分配和权衡是植物生态学研究中的热点,反映植物对环境的适应性,是了解植物响应全球气候变化的关键。青藏高原作为气候变化敏感区,研究其植物地上与地下部分权衡对了解高寒草地植被生存策略和生态系统可持续发展具有重要意义。目前,生物量分配调控机制已被广泛研究,但主要使用植物根冠比和地上-地下生物量比等方法来表征植物分配模式,缺乏考虑因植物生长周期导致的差异。使用青藏高原高寒草地103个样点的地上和地下净初级生产力数据,分析高寒草甸和高寒草原两种主要草地类型的地上-地下净初级生产力权衡关系。利用气候因素和土壤因素等相关数据,结合方差分析、相关分析、相对重要性分析和结构方程模型的方法,探究环境因素对两种草地类型地上-地下净初级生产力权衡的影响机制。研究发现：（1）高寒草甸的地上净初级生产力、地下净初级生产力和土壤养分含量显著高于高寒草原（P<0.05）;（2）高寒草地植被生产力均向地下权衡（0.0199）,且高寒草原（0.0354）的权衡值高于高寒草甸（0.0173）;（3）结构方程模型发现,年平均降水量、土壤容重和土壤速效氮含量是影响高寒草甸生产力权衡的主导因子,而年平均温度和年平均降水量是影响高寒草原生产力权衡的主导因子。研究表明高寒草甸的生产力权衡主要受气候和土壤因素共同影响,而高寒草原主要受气候因素调节。研究为理解植物地上-地下生物量分配调控机制提供了新的视角和方法,对系统了解高寒草地生物量分配模式和准确预测高寒草地植被动态过程具有指导意义。     

中国温带草地物候对气候变化的响应及其对总初级生产力的贡献

气候变暖引起的植物物候变化影响了陆地生态系统功能和碳循环。目前研究着重关注温带和热带森林物候变化趋势、驱动因素,关于干旱半干旱地区草地物候变化及其对生态系统总初级生产力（gross primary productivity, GPP）影响仍知之甚少。因此,开展草地植物物候与生产力之间的关系研究对预测草地生态系统响应未来气候变化和区域碳循环至关重要。基于1982-2015年气象资料和GIMMS NDVI3g数据,分析了中国温带草原植被返青期（start of the growing season, SGS）和枯黄期（end of the growing season, EGS）变化及其对气候的响应,并借助一阶差分法量化物候对GPP动态变化的贡献。结果表明：（1）季前1-2个月的夜间温度增温会显著提前SGS, 而当月至季前2个月的白天温度对SGS有着微弱的促进作用;季前3个月的累积降水对SGS提前作用最为强烈,累积太阳辐射在各个时期对SGS影响相对较弱。（2）不同季前时间尺度昼夜温度对草地EGS均表现出相反的作用,短期累积降水对EGS起到显著延迟的区域范围最大,太阳辐射随着季前时间的增加对草地枯黄期的延迟作用逐渐转变为提前作用。（3）EGS对草地GPP年际变化趋势的相对贡献率强于返青期。研究结果有助于深化陆地生态系统与气候变化、碳循环之间相互作用的认识,为草地适应未来气候变化和生态建设提供科学依据。     

Phytoplankton and zooplankton population dynamics and production of a recently formed African reservoir

The study provides a 2.5 year record of Rhenosterkop Dam (KwaNdebele, South Africa) plankton population dynamics and production in relation to physical and chemical changes which occurred during the trophic depression and stabilization phases of the reservoir. The mean volume of the reservoir was 4% of full storage capacity. Water temperatures ranged from 14 °C to 27 °C. Due to inorganic suspensoids, the euphotic zone averaged 2.6 m. An anaerobic zone developed each summer. The nitrogen, soluble reactive phosphorus (SRP) and silica concentrations did not displaya seasonal pattern, but the latter two nutrients declined over the study. The dominant phytoplankton group was the cryptophytes while the zooplankton population was dominated by crustaceans. Chlorophyll a concentrations ranged from 1.1 to 27 mg m^–3 and were positively correlated to silica and SRP concentrations and inversely with NH₄-N concentrations. Primary production ranged from 22.6 to 375 mgC m^–2 h^–1; changes in A_max were positively correlated to silica and SRP concentrations. Total zooplankton dry weight biomass varied from <0.5 to >4 mg l^–1. Annual zooplankton (secondary) production was 8 to 15 gC m^–3 a^–1; both primary and secondary production were greatest in the first 12 months of study and remained at low levels for the remainder, similar to the trends for silica and SRP. The data indicate that the reservoir shifted from eutrophic to mesotrophic during the study, typical of events in new reservoirs, and that changes in the plankton populations were largely the result of changing nutrient concentrations.     

凋落物输入变化和氮添加对半干旱草原群落生产力及功能群组成的影响

不同的草原利用方式(围封、放牧和割草等)随着大气氮沉降的不断加剧, 改变了凋落物输入量。凋落物作为连接地上-地下碳循环过程的关键环节, 对草原生态系统生产力和碳循环过程影响显著。氮是草原生产力的主要限制因子, 凋落物输入量的变化对草原生态系统结构和功能的影响仍缺乏长期实验证据支持。该研究在内蒙古半干旱典型草原建立一个凋落物输入变化和氮添加控制实验平台, 通过连续6年对群落生产力和功能群组成的监测, 研究了凋落物添加与去除和氮添加对半干旱草原群落生产力和功能群组成的影响。研究发现: 1)凋落物输入量增加和氮添加均显著提高了群落生产力, 在对照和氮添加处理下, 凋落物去除处理导致生产力分别降低了8.4%和7.6%, 而凋落物添加处理使生产力分别提高了10.7%和6.3%; 2)不同植物功能群对凋落物输入变化和氮添加的响应存在差异, 导致群落功能群结构发生变化。随着凋落物输入量增加和氮添加, 群落优势功能群多年生禾草(包括多年生丛生禾草和多年生根茎禾草)的生物量显著提高, 对群落生产力的贡献增加, 在群落中的优势地位增强; 而另一优势功能群多年生杂类草生物量对凋落物和氮添加处理均无显著响应, 进而导致在氮添加处理下其对群落生物量的贡献比例显著降低; 3)凋落物输入主要改善土壤水分状况, 而氮添加则主要通过提高土壤养分含量, 促进群落生产力, 并通过影响主要功能群生物量, 导致群落结构发生变化。以上结果表明, 适当的草原管理方式如围封禁牧和降低放牧强度等都能通过增加凋落物的输入来提高草原生产力, 维持生态系统稳定性。而适量的氮等养分添加管理也有助于提高草原生产力, 促进其恢复。     

Asymmetry in above‐ and belowground productivity responses to N addition in a semi‐arid temperate steppe

Nitrogen (N) enrichment often increases aboveground net primary productivity (ANPP) of the ecosystem, but it is unclear if belowground net primary productivity (BNPP) track responses of ANPP. Moreover, the frequency of N inputs may affect primary productivity but is rarely studied. To assess the response patterns of above‐ and belowground productivity to rates of N addition under different addition frequencies, we manipulated the rate (0–50 g N m^?2 year^?1) and frequency (twice vs. monthly additions per year) of NH₄NO₃ inputs for six consecutive years in a temperate grassland in northern China and measured ANPP and BNPP from 2012 to 2014. In the low range of N addition rates, BNPP showed the greatest negative response and ANPP showed the greatest positive responses with increases in N addition (<10 g N m^?2 year^?1). As N addition increased beyond 10 g N m^?2 year^?1, increases in ANPP dampened and decreases in BNPP ceased altogether. The response pattern of net primary productivity (combined above‐ and belowground; NPP) corresponded more closely to ANPP than to BNPP. The N effects on BNPP and BNPP/NPP (f_BNPP) were not dependent on N addition frequency in the range of N additions typically associated with N deposition. BNPP was more sensitive to N addition frequency than ANPP, especially at low rates of N addition. Our findings provide new insights into how plants regulate carbon allocation to different organs with increasing N rates and changing addition frequencies. These root response patterns, if incorporated into Earth system models, may improve the predictive power of C dynamics in dryland ecosystems in the face of global atmospheric N deposition.     

Root production is determined by radiation flux in a temperate grassland community

Accurate knowledge of the response of root turnover to a changing climate is needed to predict growth and produce carbon cycle models. A soil warming system and shading were used to vary soil temperature and received radiation independently in a temperate grassland dominated by Holcus lanatus L. Minirhizotrons allowed root growth and turnover to be examined non‐destructively. In two short‐term (8 week) experiments, root responses to temperature were seasonally distinct. Root number increased when heating was applied during spring, but root death increased during autumnal heating. An experiment lasting 12 months demonstrated that any positive response to temperature was short‐lived and that over a full growing season, soil warming led to a reduction in root number and mass due to increased root death during autumn and winter. Root respiration was also insensitive to soil temperature over much of the year. In contrast, root growth was strongly affected by incident radiation. Root biomass, length, birth rate, number and turnover were all reduced by shading. Photosynthesis in H. lanatus exhibited some acclimation to shading, but assimilation rates at growth irradiance were still lower in shaded plants. The negative effects of shading and soil warming on roots were additive. Comparison of root data with environmental measurements demonstrated a number of positive relationships with photosynthetically active radiation, but not with soil temperature. This was true both across the entire data set and within a shade treatment. These results demonstrate that root growth is unlikely to be directly affected by increased soil temperatures as a result of global warming, at least in temperate areas, and that predictions of net primary productivity should not be based on a positive root growth response to temperature.     

Joint structural and physiological control on the interannual variation in productivity in a temperate grassland: A data‐model comparison

Given the important contributions of semiarid region to global land carbon cycle, accurate modeling of the interannual variability (IAV) of terrestrial gross primary productivity (GPP) is important but remains challenging. By decomposing GPP into leaf area index (LAI) and photosynthesis per leaf area (i.e., GPP_leaf), we investigated the IAV of GPP and the mechanisms responsible in a temperate grassland of northwestern China. We further assessed six ecosystem models for their capabilities in reproducing the observed IAV of GPP in a temperate grassland from 2004 to 2011 in China. We observed that the responses to LAI and GPP_leaf to soil water significantly contributed to IAV of GPP at the grassland ecosystem. Two of six models with prescribed LAI simulated of the observed IAV of GPP quite well, but still underestimated the variance of GPP_leaf, therefore the variance of GPP. In comparison, simulated pattern by the other four models with prognostic LAI differed significantly from the observed IAV of GPP. Only some models with prognostic LAI can capture the observed sharp decline of GPP in drought years. Further analysis indicated that accurately representing the responses of GPP_leaf and leaf stomatal conductance to soil moisture are critical for the models to reproduce the observed IAV of GPP_leaf. Our framework also identified that the contributions of LAI and GPP_leaf to the observed IAV of GPP were relatively independent. We conclude that our framework of decomposing GPP into LAI and GPP_leaf has a significant potential for facilitating future model intercomparison, benchmarking and optimization should be adopted for future data‐model comparisons.     

Effect of altered litter input and nitrogen addition on ecosystem aboveground primary productivity and plant functional group composition in a semiarid grassland

不同的草原利用方式(围封、放牧和割草等)随着大气氮沉降的不断加剧, 改变了凋落物输入量。凋落物作为连接地上-地下碳循环过程的关键环节, 对草原生态系统生产力和碳循环过程影响显著。氮是草原生产力的主要限制因子, 凋落物输入量的变化对草原生态系统结构和功能的影响仍缺乏长期实验证据支持。该研究在内蒙古半干旱典型草原建立一个凋落物输入变化和氮添加控制实验平台, 通过连续6年对群落生产力和功能群组成的监测, 研究了凋落物添加与去除和氮添加对半干旱草原群落生产力和功能群组成的影响。研究发现: 1)凋落物输入量增加和氮添加均显著提高了群落生产力, 在对照和氮添加处理下, 凋落物去除处理导致生产力分别降低了8.4%和7.6%, 而凋落物添加处理使生产力分别提高了10.7%和6.3%; 2)不同植物功能群对凋落物输入变化和氮添加的响应存在差异, 导致群落功能群结构发生变化。随着凋落物输入量增加和氮添加, 群落优势功能群多年生禾草(包括多年生丛生禾草和多年生根茎禾草)的生物量显著提高, 对群落生产力的贡献增加, 在群落中的优势地位增强; 而另一优势功能群多年生杂类草生物量对凋落物和氮添加处理均无显著响应, 进而导致在氮添加处理下其对群落生物量的贡献比例显著降低; 3)凋落物输入主要改善土壤水分状况, 而氮添加则主要通过提高土壤养分含量, 促进群落生产力, 并通过影响主要功能群生物量, 导致群落结构发生变化。以上结果表明, 适当的草原管理方式如围封禁牧和降低放牧强度等都能通过增加凋落物的输入来提高草原生产力, 维持生态系统稳定性。而适量的氮等养分添加管理也有助于提高草原生产力, 促进其恢复。     

中国森林生态系统氮循环特征与生产力间的相互关系

为了更好地了解森林生态系统净初级生产力(NPP)与氮循环之间的关系,本文对中国主要森林生态系统类型中净初级生产力(NPP)、枯落物氮、植被年氮积累量和土壤氮矿化速率之间的关系进行了研究分析.结果表明,我国森林生态系统净初级生产力与枯落物氮、植被年氮积累量和土壤氮矿化速率之间均存在比较显著的相关关系.其中相关性最显著的是净初级生产力与氮矿化速率之间的相关关系(R₂=0.7,n=37),其次是净初级生产力与植被年氮积累量之间的相关关系(R₂=0.60,n=37).     

21世纪上半叶内蒙古草地植被净初级生产力变化趋势

基于中国气象局国家气候中心新发布的中短期适应气候变化的新情景(RCP4.5)和极端情景(RCP8.5)下的气候预估数据,采用空间化后的CENTURY模型模拟探讨2011－2050年内蒙古草地植被净初级生产力(NPP)的时空变化特征.结果表明: 区域尺度上,未来气候变化情景下内蒙古草地NPP年下降速率分别为0.57 g C·m^-2·a^-1(RCP4.5)、0.89 g C·m^-2·a^-1(RCP8.5);相对于基准时段,RCP4.5情景下内蒙古草地NPP在2020s、2030s、2040s分别下降11.6%、12.0%、18.0%,而RCP8.5情景下降幅分别为23.8%、21.2%、30.1%.不同气候情景下内蒙古草地NPP时空变化特征差异较大,但即使在RCP4.5下未来40年绝大部分草地NPP也将呈现下降趋势,15.6%的草地减产超过20%.这表明未来气候变化情景下内蒙古草地降水略增的态势不足以补偿因温度升高对草地植被初级生产力所产生的负面作用,草地资源的可持续发展将面临更大挑战.     

Ecosystem allometry: the scaling of nutrient stocks and primary productivity across plant communities

A principal challenge in ecology is to integrate physiological function (e.g. photosynthesis) across a collection of individuals (e.g. plants of different species) to understand the functioning of the entire ensemble (e.g. primary productivity). The control that organism size exerts over physiological and ecological function suggests that allometry could be a powerful tool for scaling ecological processes across levels of organization. Here we use individual plant allometries to predict how nutrient content and productivity scale with total plant biomass (phytomass) in whole plant communities. As predicted by our model, net primary productivity as well as whole community nitrogen and phosphorus content all scale allometrically with phytomass across diverse plant communities, from tropical forest to arctic tundra. Importantly, productivity data deviate quantitatively from the theoretically derived prediction, and nutrient productivity (production per unit nutrient) of terrestrial plant communities decreases systematically with increasing total phytomass. These results are consistent with the existence of pronounced competitive size hierarchies. The previously undocumented generality of these 'ecosystem allometries' and their basis in the structure and function of individual plants will likely provide a useful quantitative framework for research linking plant traits to ecosystem processes.     

基于净初级生产力的中国生态足迹产量因子测算

生态足迹作为一种非货币化的生态系统评估工具,是近年来国际上一种重要的判别可持续发展程度的生物物理量方法。产量因子是生态足迹计算中的一个重要参数,其准确与否直接影响到计算结果的可靠性与可比性。随着生态足迹方法的广泛应用,其标准化和本地化成为迫切需要。为了便于区域水平上的生态足迹空间分析,本文采用中国2001年1kmMODIS数据,根据植被的净初级生产力,计算出全国和不同省份各种土地类型的产量因子。结果表明:就中国产量因子而言,由于中国农地生产力水平高于全球平均水平,其产量因子为1.74,而其余几种类型土地的产量因子均<1,分别为林地0.86,畜牧地0.51,渔场0.74;就不同省份而言,由于区域内不同土地利用类型的相对生产能力不同,产量因子各不相同。     

天山北坡不同海拔梯度山地草原生态系统地上净初级生产力对气候变化及放牧的响应

以天山北坡三工河流域为例,利用改进后的Biome-BGC模型分别模拟了仅气候变化（Clm）、气候变化与放牧联合作用（ClmGra）下研究区不同海拔梯度3种山地草原生态系统（低山干旱草原,LAG;森林草甸草原,FMG;高寒草甸草原,AMG）1959—2009年地上净初级生产力（Aboveground Net Primary Production,ANPP）的动态,并通过假设27种放牧强度情景（0—8 羊/ha）模拟了其ANPP随放牧强度增加的变化趋势。近50年气候变化致使研究区各海拔梯度草原生态系统ANPP整体均呈上升趋势,但在放牧联合作用下,不同草原类型ANPP变化趋势差异显著;放牧导致FMG和AMG的ANPP呈下降态势,分别减少30.0%和33.2%,对比之下,由于1980前较低放牧强度促进了LAG的ANPP,放牧导致其ANPP整体增加1.3%。随着放牧强度增加,LAG的ANPP呈先增后减趋势,且在干旱年份最为显著;而FMG和AMG的ANPP呈显著非线性递减趋势。这些结果表明,近50年气候波动可能有利于中亚干旱区山地草原生态系统生产力的提高,但日益增强的放牧活动导致其净初级生产力显著降低;放牧对FMG与AMG生产力的负面效应随放牧强度增加而增强,但适度放牧可能促进LAG净初级生产力,尤其在干旱年份。     

A test of two mechanisms proposed to optimize grassland aboveground primary productivity in response to grazing

Aims Mesic grasslands have a long evolutionary history of grazing by large herbivores and as a consequence, grassland species have numerous adaptations allowing them to respond favourably to grazing. Although empirical evidence has been equivocal, theory predicts that such adaptations combined with alterations in resources can lead to grazing-induced overcompensation in aboveground net primary production (ANPP; grazed ANPP> ungrazed ANPP) under certain conditions. We tested two specific predictions from theory. First, overcompensation is more likely to occur in annually burned grasslands because limiting nutrients that would be lost with frequent fires are recycled through grazers and stimulate ANPP. Second, overcompensation of biomass lost to grazers is more likely to occur in unburned sites where grazing has the greatest effect on increasing light availability through alterations in canopy structure.Methods We tested these nutrient versus light-based predictions in grazed grasslands that had been annually burned or protected from fire for>20 years. We assessed responses in ANPP to grazing by large ungulates using both permanent and moveable grazing exclosures (252 exclosures from which biomass was harvested from 3192 quadrats) in a 2-year study. Study sites were located at the Konza Prairie Biological Station (KPBS) in North America and at Kruger National Park (KNP) in South Africa. At KPBS, sites were grazed by North American bison whereas in KNP sites were grazed either by a diverse suite of herbivores (e.g. blue wildebeest, Burchell's zebra, African buffalo) or by a single large ungulate (African buffalo).Important findings We found no evidence for overcompensation in either burned or unburned sites, regardless of grazer type. Thus, there was no support for either mechanism leading to overcompensation. Instead, complete compensation of total biomass lost to grazers was the most common response characterizing grazing–ANPP relationships with, in some cases, undercompensation of grass ANPP being offset by increased ANPP of forbs likely due to competitive release. The capability of these very different grass-dominated systems to maintain ANPP while being grazed has important implications for energy flow, ecosystem function and the trophic dynamics of grasslands.     

羌塘高原高寒草地生态系统生产力动态

基于实测气象数据和遥感数据,分析了藏北地区气候变化趋势,并采用植被 气候综合模型和CASA模型模拟分析了藏北草地潜在和现实净第一性生产力(NPP)的动态变化和空间格局.结果表明：1955—2004年间,羌塘高原年平均气温上升了1.37 ℃,降水量增加了63 mm,中、东部区域的气候趋于暖湿化,西部区域趋于暖干化,目前气候变化尚未引起草地退化.草地潜在NPP平均值为东部 > 中部 > 西部.1982—2004年,由于水热条件的变化,中部区域的潜在NPP增加值最高,达0.55 t·hm^-2·a¹,东部和西部分别为0.51和0.21 t·hm^-2·a^-1;东、中、西部现实NPP增量分别为-0.19、-0.03 和0.20 t·hm^-2·a^-1.超载过牧是东、中部草地退化的主要原因,中部是草地保护恢复工程的最佳实施区域.     

黄土高原草地净初级生产力时空趋势及其驱动因素

草地净初级生产力是生态系统碳循环的关键环节和重要组成部分.本研究使用分段线性回归分析和Pearson相关分析,分析了黄土高原2000-2015年间土地利用类型未改变的草地净初级生产力(NPP)的变化趋势及气候核心因子(年降水量、年强降水量、年有效降水日数、年平均温度、年最高温度、年最低温度)对NPP变化的影响,并借助增...