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。     

不同利用方式和载畜率对内蒙古典型草原群落初级生产力和植物补偿性生长的影响

基于2005年6月开始的放牧控制实验, 研究了不同草地利用方式和放牧强度对内蒙古典型羊草(Leymus chinensis)草原群落初级生产力和补偿性生长的影响。草地利用方式包括: 传统放牧、传统割草和放牧与割草轮换利用(混合利用)。结果表明: 传统放牧和混合利用方式下, 羊草群落地上生物量均随放牧强度增加逐渐降低。高载畜率下, 羊草群落地上净初级生产力表现为: 混合利用>传统割草>传统放牧, 说明混合利用方式优于传统放牧和传统割草利用方式; 而低载畜率则有利于草原的可持续利用和植物的补偿性生长。这一实验结果在一定程度上验证了放牧优化假说。在不同利用方式、地形因素的影响和采用不同的群落净生长量计算方法时, 随着放牧强度的变化, 等补偿、超补偿和欠补偿效应都可能出现。在低载畜率下, 群落大多表现出等补偿生长, 在高载畜率下, 群落大多表现出欠补偿生长。植物群落的补偿性生长与载畜率的关系可以用开口向下的二次函数或者斜率为负的线性函数模拟。说明随着载畜率的增加, 一些系统表现为欠补偿生长, 而另一些系统则表现为超补偿生长, 这可能与植物群落组成、地形部位(平地、坡地)和载畜率以及净生长量的计算方法有关。     

内蒙古羊草草原植物群落地上初级生产力时间动态对降水变化的响应

植被生产力对水热因子的反应是气候 -植被关系研究的焦点之一。利用 1981～ 1994年的固定围栏样地植物群落调查数据及同期降水资料 ,分析了羊草草原群落地上初级生产力和降水的年际变化特征及植物群落地上初级生产力的时间动态与降水年际变化的相互关系。结果表明 ,羊草草原年降水以及月降水的年际波动明显 ;年内降水分配不均匀 ,降水集中分布于 6～ 8月份。月均降水以 7月份最高 ,基本呈对称分布。群落地上初级生产力年际间变化介于年降水与月降水的年际变化之间。影响群落地上初级生产力时间动态最显著的因子是植物生长周期内前一年 10月至当年 8月的累积降水 ,而与年降水和月降水无显著相关。群落地上初级生产力时间动态对累积降水波动的反应呈显著的二次曲线关系 ,与空间尺度上地上初级生产力与年降水呈线性相关关系不同。因此 ,降水波动对羊草草原地上初级生产力的影响是一个累积效应 ,确定对植物生长产生影响的有效降水时间对建立羊草草原生产力模型关系具有十分重要的意义。     

降水时间对内蒙古温带草原地上净初级生产力的影响

全球气候变化下降水时间的改变将深刻影响草原生态系统地上净初级生产力(ANPP),而草原生态系统ANPP是区域碳循环的重要过程.利用1998-2007年的SPOT-VEG NDVI数据并结合111个样点的ANPP地面样方调查数据,获得了内蒙古温带草原1998-2007年的ANPP区域数据,依此分析了中国内蒙古温带草原以及区域内的3种植被类型(荒漠草原、典型草原、草甸草原)降水时间对ANPP的影响.研究结果表明,对于整个内蒙古温带草原来说,一个水分年内(从上一年9月份到当年地上生物量达最大值时的8月份)影响ANPP较为重要的降水月份为2-7月份,其中,5-7月份降水尤为重要.具体到每个月降水的影响,研究发现,7月份降水最重要,而仍处于生长季的8月份降水相对于其他生长季降水作用最小;影响不同草地类型最重要的降水时期存在一定差异,对荒漠草原和典型草原地区来说,ANPP达最大值前3个月(5-7月份)的生长季降水最重要,而8月份降水影响较小,而草甸草原地区8月份和非生长季的3、4月份降水最重要,但各个降水时期降水对ANPP的影响都较荒漠草原和典型草原小,大部分地区降水对ANPP的影响不显著.     

Estimating net primary productivity from grassland biomass dynamics measurements

To address the need for a high quality data set based upon field observations suitable for parameterization, calibration, and validation of terrestrial biosphere models, we have developed a comprehensive global database on net primary productivity (NPP). We have compiled field measurements of biomass and associated environmental data for multiple study sites in major grassland types worldwide. Where sufficient data were available, we compared aboveground and total NPP estimated by six computational methods (algorithms) for 31 grassland sites. As has been found previously, NPP estimates were 2–5 times higher using methods which accounted for the dynamics of dead matter, compared with what is still the most commonly applied estimate of NPP (maximum peak live biomass). It is suggested that assumptions such as the use of peak biomass as an indicator of NPP in grasslands may apply only within certain subbiomes, e.g. temperate steppe grasslands. Additional data on belowground dynamics, or other reliable estimates of belowground productivity, are required if grasslands are to be fully appreciated for their role in the global carbon cycle.     

Asymmetric responses of primary productivity to precipitation extremes: A synthesis of grassland precipitation manipulation experiments

Climatic changes are altering Earth's hydrological cycle, resulting in altered precipitation amounts, increased interannual variability of precipitation, and more frequent extreme precipitation events. These trends will likely continue into the future, having substantial impacts on net primary productivity (NPP) and associated ecosystem services such as food production and carbon sequestration. Frequently, experimental manipulations of precipitation have linked altered precipitation regimes to changes in NPP. Yet, findings have been diverse and substantial uncertainty still surrounds generalities describing patterns of ecosystem sensitivity to altered precipitation. Additionally, we do not know whether previously observed correlations between NPP and precipitation remain accurate when precipitation changes become extreme. We synthesized results from 83 case studies of experimental precipitation manipulations in grasslands worldwide. We used meta‐analytical techniques to search for generalities and asymmetries of aboveground NPP (ANPP) and belowground NPP (BNPP) responses to both the direction and magnitude of precipitation change. Sensitivity (i.e., productivity response standardized by the amount of precipitation change) of BNPP was similar under precipitation additions and reductions, but ANPP was more sensitive to precipitation additions than reductions; this was especially evident in drier ecosystems. Additionally, overall relationships between the magnitude of productivity responses and the magnitude of precipitation change were saturating in form. The saturating form of this relationship was likely driven by ANPP responses to very extreme precipitation increases, although there were limited studies imposing extreme precipitation change, and there was considerable variation among experiments. This highlights the importance of incorporating gradients of manipulations, ranging from extreme drought to extreme precipitation increases into future climate change experiments. Additionally, policy and land management decisions related to global change scenarios should consider how ANPP and BNPP responses may differ, and that ecosystem responses to extreme events might not be predicted from relationships found under moderate environmental changes.     

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。     

刈割和施肥对高寒草甸功能多样性与地上净初级生产力关系的影响

功能多样性(FD)对群落地上净初级生产力(ANPP, g·m^-2·a^-1)有直接的影响, 但不同扰动因素对FD-ANPP关系将产生何种影响尚不明确。通过在青藏高原高寒矮生嵩草(Kobresia humilis)草甸连续7年(2007-2013)的刈割(3水平: 不刈割、留茬3 cm的中度刈割和留茬1 cm的重度刈割)和施肥(2水平: 施用12.75 g·m^-2·a^-1尿素+ 3.06 g·m^-2·a^-1 (NH₄)₂HPO₄、不施肥)控制实验, 研究了刈割、施肥、年份及其交互作用对ANPP和FD的影响以及FD-ANPP关系的变化。研究结果显示: (1)增加刈割强度和土壤养分均显著提高了ANPP, 但其效应随着年份的不同而有差异, ANPP随着时间呈波动下降趋势, 而FD则随年度增大; (2)施肥显著增加了FD, 而刈割对FD无显著影响(p > 0.05); (3)在6种刈割和施肥处理组合下, FD-ANPP关系随时间的变化主要受刈割扰动影响呈现正线性相关和无相关两种模式。无论施肥与否, 不刈割(C0)群落中FD和ANPP之间无相关(n = 90, p > 0.05); 而刈割群落中FD和ANPP之间为正相关(n = 90, p < 0.05)。由于刈割同时提高了FD和ANPP, 促使二者在刈割群落中呈现正线性相关。(4)尽管施肥不影响FD和ANPP的关系模式, 但与刈割共同作用, 影响FD-ANPP关系的截距或斜率。上述结果说明, 刈割扰动和土壤营养资源共同影响着FD-ANPP关系, 而刈割在改变其关系模式方面起主导作用。     

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。     

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.     

日尺度下水热因子变化对青藏高原高寒草原生产力的影响特征

温度和降水变化显著影响高寒生态系统植被生长和系统功能。草地生产力作为草地系统功能强弱的重要体现,对气候变化,特别是温度和降水变化十分敏感。探究高寒草原生产力如何响应气候变化,对预测未来气候变化情景下高寒草地系统功能变化意义重大。前期研究大都从年或季节尺度探究气候变化对草地生产力的影响特征,缺乏更精细时间尺度的关联分析。本研究基于1997—2020年青藏高原高寒草原长期植被观测数据及相应气候资料,应用简单线性回归及偏最小二乘回归法(Partial Least Squares regression, PLS)探究了研究区草地地上净初级生产力对日尺度温度和降水变化响应特征。结果表明：(1)近24 a来研究区年平均气温和降水量分别以0.03℃/a和4.36 mm/a的速率显著升高;(2)近24 a来研究区草地生产力显著升高(增幅为5.24 g m^-2 a^-1),且与年平均温度和降水量呈显著正相关关系;(3)日尺度分析表明,不同阶段温度和降水变化对草地生产力的影响不同,其中5—8月和9—10月的温度及5—7月和9—11月的降水是影响研究区草地生产力的气...     

Analysis of spatial and temporal patterns of aboveground net primary productivity in the Eurasian steppe region from 1982 to 2013

To explore the importance of the Eurasian steppe region (EASR) in global carbon cycling, we analyzed the spatiotemporal dynamics of the aboveground net primary productivity (ANPP) of the entire EASR from 1982 to 2013. The ANPP in the EASR was estimated from the Integrated ANPP_NDVI model, which is an empirical model developed based on field‐observed ANPP and long‐term normalized difference vegetation index (NDVI) data. The optimal composite period of NDVI data was identified by considering spatial heterogeneities across the study area in the Integrated ANPP_NDVI model. EASR's ANPP had apparent zonal patterns along hydrothermal gradients, and the mean annual value was 43.78 g C m^?2 yr^?1, which was lower than the global grasslands average. Compared to other important natural grasslands, EASR's ANPP was lower than the North American, South American, and African grasslands. The total aboveground net primary productivity (TANPP) was found to be 378.97 Tg C yr^?1, which accounted for 8.18%–36.03% of the TANPP for all grasslands. In addition, EASR's TANPP was higher than that of the grasslands in North America, South America, and Africa. The EASR's TANPP increased in a fluctuating manner throughout the entire period of 1982–2013. The increasing trend was greater than that for North American and South American and was lower than that for African grasslands over the same period. The years 1995 and 2007 were two turning points at which trends in EASR's TANPP significantly changed. Our analysis demonstrated that the EASR has been playing a substantial and progressively more important role in global carbon sequestration. In addition, in the development of empirical NDVI‐based ANPP models, the early–middle growing season averaged NDVI, the middle–late growing season averaged NDVI and the annual maximum NDVI are recommended for use for semi‐humid regions, semi‐arid regions, and desert vegetation in semi‐arid regions, respectively.     

Net primary production in three bioenergy crop systems following land conversion

Aims Identifying the amount of production and the partitioning to above- and belowground biomass is generally the first step toward selecting bioenergy systems. There are very few existing studies on the dynamics of production following land conversion. The objectives of this study were to (i) determine the differences in aboveground net primary production (ANPP), belowground net primary production (BNPP), shoot-to-root ratio (S:R) and leaf area index in three bioenergy crop systems and (ii) evaluate the production of these three systems in two different land use conversions.Methods This investigation included biometric analysis of NPP on three agricultural sites converted from conservation reserve program (CRP) management to bioenergy crop production (corn, switchgrass and prairie mix) and three sites converted from traditional agriculture production to bioenergy crop production.Important findings The site converted from conventional agriculture produced smaller ANPP in corn (19.03±1.90 standard error [SE] Mg ha^-1 year^-1) than the site converted from CRP to corn (24.54±1.43 SE Mg ha^-1 year^-1). The two land conversions were similar in terms of ANPP for switchgrass (4.88±0.43 SE for CRP and 2.04±0.23 SE Mg ha^-1 year^-1 for agriculture) and ANPP for prairie mix (4.70±0.50 SE for CRP and 3.38±0.33 SE Mg ha^-1 year^-1 for agriculture). The BNPP at the end of the growing season in all the bioenergy crop systems was not significantly different (P = 0.75, N = 8).     

Sensitivity of mean annual primary production to precipitation

In many terrestrial ecosystems, variation in aboveground net primary production (ANPP) is positively correlated with variation in interannual precipitation. Global climate change will alter both the mean and the variance of annual precipitation, but the relative impact of these changes in precipitation on mean ANPP remains uncertain. At any given site, the slope of the precipitation‐ANPP relationship determines the sensitivity of mean ANPP to changes in mean precipitation, whereas the curvature of the precipitation‐ANPP relationship determines the sensitivity of ANPP to changes in precipitation variability. We used 58 existing long‐term data sets to characterize precipitation‐ANPP relationships in terrestrial ecosystems and to quantify the sensitivity of mean ANPP to the mean and variance of annual precipitation. We found that most study sites have a nonlinear, saturating relationship between precipitation and ANPP, but these nonlinearities were not strong. As a result of these weak nonlinearities, ANPP was nearly 40 times more sensitive to precipitation mean than variance. A 1% increase in mean precipitation caused a ?0.2% to 1.8% change in mean ANPP, with a 0.64% increase on average. Sensitivities to precipitation mean peaked at sites with a mean annual precipitation near 500 mm. Changes in species composition and increased intra‐annual precipitation variability could lead to larger ANPP responses to altered precipitation regimes than predicted by our analysis.     

黄河流域草地净初级生产力时空动态及其驱动机制

黄河流域是生态系统的敏感区,流域草地生态系统在气候变化和人类活动驱动下发生了显著变化。基于多源遥感影像和气象站点资料等,采用改进后的CASA模型估算2001—2018年黄河流域草地净初级生产力(NPP),评估定量反演结果精度,分析研究时段内流域草地净初级生产力时空动态,探讨气候要素和人类活动对流域草地净初级生产力的影响。结果表明：1)基于改进的CASA模型能够高精度模拟黄河流域草地NPP。2)2001—2018年黄河流域草地NPP呈增加趋势,且在2013年发生突变。2001—2013年气候和人类活动均促进流域草地NPP增加,而2013年后人类活动抑制流域草地NPP增加的作用明显增强,抑制区域面积较前一阶段增加34.89%。整体上,人类活动对草地NPP的影响强度低于气候要素影响强度。3)耕地和建设用地面积的变化,是驱动实际净初级生产力动态的重要人类活动要素。耕地和建设用地面积的增加与草地面积减少、实际净初级生产力增加速率的降低紧密相关。伴随经济发展,应坚持实施退耕还林还草政策,并加强对草地生态保护的监督。     

Simulating root responses to grazing of a Mongolian grassland ecosystem

A new Sim-CYCLE grazing model has been obtained by combining a grazing model (Seligman et al. 1992, Ecol. Model. 60: 45–61) with the Sim-CYCLE model (Ito and Oikawa 2002, Ecol. Model. 151: 143–176). The new model has been validated against a set of field data obtained at Kherlen Bayaan-Ulaan (KBU) grassland. On the basis of the model, the root responses to grazing of KBU grassland have been studied under different conditions of stocking rates and precipitation. Model results indicate that both below-ground biomass (BB) and below-ground net primary production (BNPP) generally decrease with increasing stocking rate. However, if stocking rate is not higher than 0.7 sheep ha⁻¹, a sustainable state of the grassland ecosystem can be achieved after about 100 years, which suggests that the maximum sustainable stocking rate at KBU should be 0.7 sheep ha⁻¹. At the sustainable state, the maximum BB in a year is about 11 Mg DM ha⁻¹ under non-grazing condition, 5 Mg DM ha⁻¹ under 0.4 sheep ha⁻¹ stocking rate, and 4 Mg DM ha⁻¹ under 0.7 sheep ha⁻¹ stocking rate; the BNPP is 1.3 Mg DM ha⁻¹ year⁻¹ under non-grazing condition, and 0.6 Mg DM ha⁻¹ year⁻¹ under 0.4 sheep ha⁻¹ stocking rate, and 0.4 Mg DM ha⁻¹ year⁻¹ under 0.7 sheep ha⁻¹ stocking rate. Ratio of non-assimilation organ to assimilation organ (C/F) increases with increasing stocking rate. The C/F ratio is 10.99 under non-grazing conditions, and 12.11 under 0.7 sheep ha⁻¹ stocking rate. Root turnover rate decreases with increasing stocking rate. The rate is 12% each year under non-grazing conditions, and 11% each year under 0.7 sheep ha⁻¹ stocking rate. In addition, the effect of grazing on the grassland ecosystem under different scenarios of precipitation is also analyzed. Both BB and BNPP increase with increased precipitation, and vice versa. When precipitation is set to be 10% higher than the averaged from 1993 to 2002, the maximum sustainable stocking rate is 0.8 sheep ha⁻¹, and when the precipitation is set to be 15% lower than the averaged, the maximum sustainable stocking rate is 0.6 sheep ha⁻¹.     

Controls of primary productivity and nutrient cycling in a temperate grassland with year‐round production

Abstract Net primary production (NPP) and nutrient dynamics of grasslands are regulated by different biotic and abiotic factors, which may differentially affect functional plant groups. Most studies have dealt with grasslands that have extremely low or zero production over a significant period of the year. Here we explore the relative importance of a few environmental factors as controls of aerial and below‐ground plant biomass production and nutrient dynamics in a grassland that is active throughout the year. We investigate their effect on the response of three main plant functional groups (warm‐ and cool‐season graminoids and forbs). We conducted a factorial experiment in a continuously grazed site in the Flooding Pampa grassland (Argentina). Factors were seasons (summer, autumn, winter and spring), and environmental agents (mowing, shade, addition of phosphorus [P] and nitrogen [N]). N addition had the largest and most extended impact: it tripled aerial NPP in spring and summer but had no effect on below‐ground biomass. This positive effect was accompanied by higher N acquisition and higher soil N availability. Mowing increased aerial NPP in winter, increased root biomass in the first 10 cm during autumn and winter and promoted N and P uptake by plants. Shading did not affect aerial NPP, but stimulated N and P uptake by plants. P addition had no effect on aerial NPP, but increased shallow root biomass and its N content in spring, and tripled P accumulation in plant biomass. The three plant functional groups differentially accounted for these ecosystem‐level responses. Graminoids explained the greater biomass production of N‐fertilized plots and mowing tended to promote forbs. These results suggest that the environmental controls of aerial NPP in this grassland vary among seasons, differentially impact the major floristic groups, and affect the energy and nutrient transfer to herbivores.     

长期封育演替下典型草原植物群落生产力与多样性关系

封育是退化草地的重要恢复措施, 理解长期封育过程中草地群落生产力和植物多样性变化特征及两者间关系, 有助于草地植被的恢复管理与利用。该研究依托宁夏云雾山国家级自然保护区典型草原长期封育演替梯度, 选择持续放牧、封育9年、26年和34年的草地群落作为研究对象, 分析其地上生产力、物种多样性和功能多样性的变化特征及内在联系。结果表明, 封育显著提高典型草原植物群落的地上生产力、凋落物生物量、功能丰富度和功能离散度, 未改变草地群落的物种丰富度、Shannon-Wiener指数和功能均匀度, 但Simpson优势度指数和Pielou均匀度指数在长期封育(34年)后显著下降。此外, 封育对不同植物群落加权平均功能性状的影响存在差异。随机森林模型和方差分解结果显示, 群落加权平均功能性状对封育草地群落地上生产力变异的解释度高达70.70%, 其中植株高度是最主要的解释因子; 功能多样性的解释度为36.86%, 主要由功能丰富度贡献; 而物种多样性的解释度仅为14.72%。由此可见, 植物功能性状和功能多样性对草地群落地上生产力的贡献远高于物种多样性, 建议将其纳入植物群落恢复演替动态研究, 以便全面了解植物多样性与生态系统功能的关系, 为更好地实现生态恢复目标奠定基础。     

Interactive response of herbivores,soils and vegetation to annual burning in a South African savanna

Abstract Despite decades of research, the primary factors determining savanna structure remain elusive – a conundrum termed ‘the savanna problem’. After 47 years of annual burning in Terminalia woodland and Acacia/Combretum savanna on sandy, granite‐derived soils in the southern Kruger National Park, South Africa, a dense cover of trees and shrubs persists on some burnt plots and is largely absent from others. We postulated that intense browsing pressure by antelope and other herbivores prevents recruitment of trees in burnt plots and that herbivores concentrate on plots that are richest in nutrients. Herbivore abundance did not show a relationship with soil macronutrients and we consequently investigated micronutrient status. The reduction in tree cover as a result of annual burning was positively correlated with mass of herbivores (15–1500 kg) (r ² = 0.61, n = 8). This index of herbivore abundance was in turn positively correlated with total Zn (r ² = 0.64, n = 8). Other indices of herbivore abundance showed significant relationships with total clay content and total Mn. We suggest that herbivores concentrate on sites with greater clay content (possibly due to a greater availability of micronutrients), and that tree cover can remain relatively dense under a regime of annual burning if browsing pressure is not intense. The long‐term burn experiments in the Kruger National Park savanna provide a platform for unravelling the savanna problem. Determining possible interactions between soil properties, herbivory and fire is a step in this direction.