Relationship of Productivity to Species Richness in the Xinjiang Temperate Grassland

The relationship between species richness (SR) and aboveground net primary productivity (ANPP) is still a central and debated issue in community ecology. Previous studies have often emphasized the relationship of alpha diversity (number of species identity) to the mean ANPP with respect to the SR-ANPP relationship while neglecting the contribution of beta diversity (dissimilarity in species composition) to the mean ANPP and to the stability of ANPP (coefficient of ANPP: CV of ANPP). In this study, we used alpha and beta diversity, mean ANPP and the CV of ANPP collected from 159 sites and belonging to three vegetation types in the Xinjiang temperate grassland to first examine their trends along climatic factors and among different vegetation types and then test the relationship among alpha (beta) diversity and mean ANPP and the CV of ANPP. Our results showed that in the Xinjiang temperate grasslands, alpha diversity was positively and linearly correlated with MAP but unimodally correlated with MAT. Meanwhile, beta diversity was unimodally correlated with MAP but linearly correlated with MAT. Relative to desert steppe, meadow steppe and typical steppe had the highest alpha and beta diversity, respectively. Except for ANPP exhibiting a quadratic relationship with MAP, no significant relationship was found among ANPP, the CV of ANPP and climatic factors. ANPP and the CV of ANPP also exhibited no apparent patterns in variation among different vegetation types. Our results further showed that mean ANPP was closely associated with alpha diversity. Both linear and unimodal relationships were detected between alpha diversity and mean ANPP, but their particular form was texture-dependent. Meanwhile, the CV of ANPP was positively correlated with beta diversity. Our results indicated that in addition to incorporating alpha diversity and mean ANPP, incorporating beta diversity and the CV of ANPP could expand our understanding of the SR-ANPP relationship.     

Spatial variability of above‐ground net primary production in Uruguayan grasslands: a remote sensing approach

Question: How does above‐ground net primary production (ANPP) differ (estimated from remotely sensed data) among vegetation units in sub‐humid temperate grasslands? Location: Centre‐north Uruguay. Methods: A vegetation map of the study area was generated from LANDSAT imagery and the landscape configuration described. The functional heterogeneity of mapping units was analysed in terms of the fraction of photosynthetically active radiation absorbed by green vegetation (fPAR), calculated from the normalized difference vegetation index (NDVI) images provided by the moderate resolution imaging spectroradiometer (MODIS) sensor. Finally, the ANPP of each grassland class was estimated using NDVI and climatic data. Results: Supervised classification presented a good overall accuracy and moderate to good average accuracy for grassland classes. Meso‐xerophytic grasslands occupied 45% of the area, Meso‐hydrophytic grasslands 43% and Lithophytic steppes 6%. The landscape was shaped by a matrix of large, unfragmented patches of Meso‐xerophytic and Meso‐hydrophytic grasslands. The region presented the lowest anthropic fragmentation degree reported for the Rio de la Plata grasslands. All grassland units showed bimodal annual fPAR seasonality, with spring and autumn peaks. Meso‐hydrophytic grasslands showed a radiation interception 10% higher than the other units. On an annual basis, Meso‐hydrophytic grasslands produced 3800 kg dry matter (DM) ha^?1 yr^?1 and Meso‐xerophytic grasslands and Lithophytic steppes around 3400 kg·DM·ha^?1·yr^?1. Meso‐xerophytic grasslands had the largest spatial variation during most of the year. The ANPP temporal variation was higher than the fPAR variability. Conclusions: Our results provide valuable information for grazing management (identifying spatial and temporal variations of ANPP) and grassland conservation (identifying the spatial distribution of vegetation units).     

Are regional precipitation–productivity relationships robust to decadal-scale dry period?

降水-生产力的空间关系是否稳定不变？ 降水是全球陆地生态系统中植被生长和净初级生产力的主要驱动因素。因此,探究降水和生产力关系有助于深入了解气候变化如何改变生态系统功能。降水-生产力的空间关系在全球不同草地上非常相似,但在连续多年气候异常的情况下,这种关系是否会发生变化以及如何变化尚不清楚。本研究利用 利用中国北方温带草地长达10年低于多年平均降水的时期,基于遥感植被指数数据,量化了区域尺度上降水-植被生产力关系在持续多年的干湿期之间将如何变化。结果表明,在连续10年的干期,降水-生产力空间相关性急剧下降,而该空间关系的下降主要是由于不同草原类型对干旱的响应在空间上存在高度的异质性,即不同生态系统对干旱的响应程度存在差异。因此,如果未来气候变化进一步加剧全球草地的干旱,那么基于历史时期(平水期)得到的降水-生产力空间关系推测区域尺度植被生产力可能导致误差。     

Effects of climate warming on carbon fluxes in grasslands— A global meta‐analysis

Climate warming will affect terrestrial ecosystems in many ways, and warming‐induced changes in terrestrial carbon (C) cycling could accelerate or slow future warming. So far, warming experiments have shown a wide range of C flux responses, across and within biome types. However, past meta‐analyses of C flux responses have lacked sufficient sample size to discern relative responses for a given biome type. For instance grasslands contribute greatly to global terrestrial C fluxes, and to date grassland warming experiments provide the opportunity to evaluate concurrent responses of both plant and soil C fluxes. Here, we compiled data from 70 sites (in total 622 observations) to evaluate the response of C fluxes to experimental warming across three grassland types (cold, temperate, and semi‐arid), warming methods, and short (≤3 years) and longer‐term (>3 years) experiment lengths. Overall, our meta‐analysis revealed that experimental warming stimulated C fluxes in grassland ecosystems with regard to both plant production (e.g., net primary productivity (NPP) 15.4%; aboveground NPP (ANPP) by 7.6%, belowground NPP (BNPP) by 11.6%) and soil respiration (Rs) (9.5%). However, the magnitude of C flux stimulation varied significantly across cold, temperate and semi‐arid grasslands, in that responses for most C fluxes were larger in cold than temperate or semi‐arid ecosystems. In semi‐arid and temperate grasslands, ecosystem respiration (Reco) was more sensitive to warming than gross primary productivity (GPP), while the opposite was observed for cold grasslands, where warming produced a net increase in whole‐ecosystem C storage. However, the stimulatory effect of warming on ANPP and Rs observed in short‐term studies (≤3 years) in both cold and temperate grasslands disappeared in longer‐term experiments (>3 years). These results highlight the importance of conducting long‐term warming experiments, and in examining responses across a wide range of climate.     

Large‐scale pattern of biomass partitioning across China's grasslands

Aim To investigate large‐scale patterns of above‐ground and below‐ground biomass partitioning in grassland ecosystems and to test the isometric theory at the community level. Location Northern China, in diverse grassland types spanning temperate grasslands in arid and semi‐arid regions to alpine grasslands on the Tibetan Plateau. Methods We investigated above‐ground and below‐ground biomass in China's grasslands by conducting five consecutive sampling campaigns across the northern part of the country during 2001–05. We then documented the root : shoot ratio (R/S) and its relationship with climatic factors for China's grasslands. We further explored relationships between above‐ground and below‐ground biomass across different grassland types. Results Our results indicated that the overall R/S of China's grasslands was larger than the global average (6.3 vs. 3.7). The R/S for China's grasslands did not show any significant trend with either mean annual temperature or mean annual precipitation. Above‐ground biomass was nearly proportional to below‐ground biomass with a scaling exponent (the slope of log–log linear relationship between above‐ground and below‐ground biomass) of 1.02 across various grassland types. The slope did not differ significantly between temperate and alpine grasslands or between steppe and meadow. Main conclusions Our findings support the isometric theory of above‐ground and below‐ground biomass partitioning, and suggest that above‐ground biomass scales isometrically with below‐ground biomass at the community level.     

Comparative analyses of leaf anatomy of dicotyledonous species in Tibetan and Inner Mongolian grasslands

Knowledge of the leaf anatomy of grassland plants is crucial for understanding how these plants adapt to the environment. Tibetan alpine grasslands and Inner Mongolian temperate grasslands are two major grassland types in northern China. Tibetan alpine grasslands occur in high-altitude regions where the low temperatures limit plant growth. Inner Mongolian temperate grasslands are found in arid regions where moisture is the limiting factor. Few comparative studies concerning the leaf anatomy of grassland plants of the Tibetan Plateau and Inner Mongolian Plateau have been conducted. We examined leaf characteristics at 71 sites and among 65 species, across the alpine grasslands of the Tibetan Plateau and the temperate grasslands of the Inner Mongolian Plateau. We compared the leaf structures of plants with different life forms and taxonomies, and their adaptation to arid or cold environments. We explored relationships among leaf features and the effects of climatic factors (i.e., growing season temperature and precipitation) on leaf characteristics. Our results showed that (i) there were significant differences in leaf anatomy between Tibetan alpine and Inner Mongolian temperate grasslands. Except for mesophyll cell density, the values obtained for thickness of leaf tissue, surface area and volume of mesophyll cells were larger on the Tibetan Plateau than on the Inner Mongolian Plateau. (ii) Within the same family or genus, leaf anatomy showed significant differences between two regions, and trends were consistent with those of whole species. (iii) Leaf anatomy of woody and herbaceous plants also showed significant differences between the regions. Except for mesophyll cell density, the values obtained for the thickness of leaf tissue, and the surface area and volume of mesophyll cells were larger in herbaceous than in woody plants. (iv) Leaf anatomical traits changed accordingly. Total leaf thickness, thicknesses of lower and upper epidermal cells, and surface area and volume of mesophyll cells were positively correlated, while mesophyll cell density was negatively associated with those traits. (v) Growing season temperature had stronger effects on leaf anatomy than growing season precipitation. Although the communities in Tibetan and Inner Mongolian grasslands were similar in appearance, leaf anatomy differed; this was probably due to the combined effects of evolutionary adaptation of plants to environment and environmental stress induced by climatic factors.     

Regional grassland productivity responses to precipitation during multiyear above‐ and below‐average rainfall periods

There is considerable uncertainty in the magnitude and direction of changes in precipitation associated with climate change, and ecosystem responses are also uncertain. Multiyear periods of above‐ and below‐average rainfall may foretell consequences of changes in rainfall regime. We compiled long‐term aboveground net primary productivity (ANPP) and precipitation (PPT) data for eight North American grasslands, and quantified relationships between ANPP and PPT at each site, and in 1–3 year periods of above‐ and below‐average rainfall for mesic, semiarid cool, and semiarid warm grassland types. Our objective was to improve understanding of ANPP dynamics associated with changing climatic conditions by contrasting PPT–ANPP relationships in above‐ and below‐average PPT years to those that occurred during sequences of multiple above‐ and below‐average years. We found differences in PPT–ANPP relationships in above‐ and below‐average years compared to long‐term site averages, and variation in ANPP not explained by PPT totals that likely are attributed to legacy effects. The correlation between ANPP and current‐ and prior‐year conditions changed from year to year throughout multiyear periods, with some legacy effects declining, and new responses emerging. Thus, ANPP in a given year was influenced by sequences of conditions that varied across grassland types and climates. Most importantly, the influence of prior‐year ANPP often increased with the length of multiyear periods, whereas the influence of the amount of current‐year PPT declined. Although the mechanisms by which a directional change in the frequency of above‐ and below‐average years imposes a persistent change in grassland ANPP require further investigation, our results emphasize the importance of legacy effects on productivity for sequences of above‐ vs. below‐average years, and illustrate the utility of long‐term data to examine these patterns.     

Biomass allocation and productivity–richness relationship across four grassland types at the Qinghai Plateau

Aboveground biomass (AGB) and belowground biomass (BGB) allocation and productivity–richness relationship are controversial. Here, we assessed AGB and BGB allocation and the productivity–richness relationship at community level across four grassland types based on the biomass data collected from 80 sites across the Qinghai Plateau during 2011–2012. The reduced major axis regression and general linear models were used and showed that (a) the median values of AGB were significantly higher in alpine meadow than in other three grassland types; the ratio of root to shoot (R/S) was significantly higher in desert grassland (36.06) than intemperate grassland (16.60), alpine meadow (13.35), and meadow steppe (19.46). The temperate grassland had deeper root distribution than the other three grasslands, with about 91.45% roots distributed in the top 30 cm soil layer. (b) The slopes between log AGB and log BGB in the temperate grassland and meadow steppe were 1.09 and 1, respectively, whereas that in the desert grassland was 1.12, which was significantly different from the isometric allocation relationship. A competitive relationship between AGB and BGB was observed in the alpine meadow with a slope of ?1.83, indicating a trade‐off between AGB and BGB in the alpine meadow. (c) A positive productivity–richness relationship existed across the four grassland types, suggesting that the positive productivity–richness relationship might not be affected by the environmental factors at the plant location. Our results provide a new insight for biomass allocation and biodiversity–ecosystem functioning research.     

青藏高原草地植被覆盖变化及其与气候因子的关系

为揭示气候变化对青藏高原草地生态系统的影响及其生态适应机制,利用1982~1999年间的NOAA/AVHRR NDVI数据和对应的气候资料,研究了近20年来青藏高原草地植被覆盖变化及其与气候因子的关系。结果表明,18年来研究区生长季NDVI显著增加(p=0.015),其增加率和增加量分别为0.41% a^-1和0.001 0 a^-1。生长季提前和生长季生长加速是青藏高原草地植被生长季NDVI增加的主要原因。春季为NDVI增加率和增加量最大的季节,其增加率和增加量分别为0.92% a^-1和0.001 4 a^-1;夏季NDVI的增加对生长季NDVI增加的贡献相对较小,其增加率和增加量分别为0.37% a^-1和0.001 0 a^-1。3种草地(高寒草甸、高寒草原、温性草原)春季NDVI均显著增加(p<0.01;p=0.001; p=0.002); 高寒草甸夏季NDVI显著增加(p=0.027),而高寒草原和温性草原夏季NDVI呈增加趋势,但都不显著(p=0.106; p=0.087);3种草地秋季NDVI则没有明显的变化趋势(p=0.585; p=0.461; p=0.143)。3种草地春季NDVI的增加是由春季温度上升所致。高寒草地(高寒草甸和高寒草原)夏季NDVI的增加是夏季温度和春季降水共同作用的结果。温性草原夏季NDVI变化与气候因子并没有表现出显著的相关关系。高寒草地植被生长对气候变化的响应存在滞后效应。     

High land‐use intensity exacerbates shifts in grassland vegetation composition after severe experimental drought

Climate change projections anticipate increased frequency and intensity of drought stress, but grassland responses to severe droughts and their potential to recover are poorly understood. In many grasslands, high land‐use intensity has enhanced productivity and promoted resource‐acquisitive species at the expense of resource‐conservative ones. Such changes in plant functional composition could affect the resistance to drought and the recovery after drought of grassland ecosystems with consequences for feed productivity resilience and environmental stewardship. In a 12‐site precipitation exclusion experiment in upland grassland ecosystems across Switzerland, we imposed severe edaphic drought in plots under rainout shelters and compared them with plots under ambient conditions. We used soil water potentials to scale drought stress across sites. Impacts of precipitation exclusion and drought legacy effects were examined along a gradient of land‐use intensity to determine how grasslands resisted to, and recovered after drought. In the year of precipitation exclusion, aboveground net primary productivity (ANPP) in plots under rainout shelters was ?15% to ?56% lower than in control plots. Drought effects on ANPP increased with drought severity, specified as duration of topsoil water potential ψ < ?100 kPa, irrespective of land‐use intensity. In the year after drought, ANPP had completely recovered, but total species diversity had declined by ?10%. Perennial species showed elevated mortality, but species richness of annuals showed a small increase due to enhanced recruitment. In general, the more resource‐acquisitive grasses increased at the expense of the deeper‐rooted forbs after drought, suggesting that community reorganization was driven by competition rather than plant mortality. The negative effects of precipitation exclusion on forbs increased with land‐use intensity. Our study suggests a synergistic impact of land‐use intensification and climate change on grassland vegetation composition, and implies that biomass recovery after drought may occur at the expense of biodiversity maintenance.     

Soil nitrogen and carbon heterogeneity in woodlands and grasslands: contrasts between temperate and tropical regions

Aim  Soil resource heterogeneity is linked to several ecological processes including invasion of woody species into grasslands. Studies from the temperate zone have demonstrated greater soil heterogeneity beneath woody vegetation than beneath grasslands. Woody species have a more widespread and coarser root system than herbaceous species, and may have a competitive advantage in relatively heterogeneous soils. We tested the global generality of greater soil heterogeneity beneath woody vegetation.
Location  Global.
Methods  We used data from published literature for soil nitrogen and carbon heterogeneity from paired woodland and grassland sites around the world.
Results  Woodland and grassland soil heterogeneities from paired observations were strongly correlated. There was, however, significant geographical variability in the relationship. Soils were more heterogeneous in woodlands than grasslands in temperate areas, but the opposite was true for tropical habitats. Grassland soils were more heterogeneous at lower than higher latitudes. Woodland soil heterogeneity did not vary with latitude.
Main conclusions  The previously described high soil heterogeneity in woody vegetation compared to grasslands holds only for temperate regions. Consequently, the relationship between soil resource heterogeneity and vegetation type is dependent on the study region. Macroecological studies should test the generality of relationships between soil and vegetation at the global scale.     

Patterns of species density and productivity at different spatial scales in herbaceous plant communities

A major challenge in evaluating patterns of species richness and productivity involves acquiring data to examine these relationships empirically across a range of ecologically significant spatial scales. In this paper, we use data from herb‐dominated plant communities at six Long‐Term Ecological Research (LTER) sites to examine how the relationship between plant species density and above‐ground net primary productivity (ANPP) differs when the spatial scale of analysis is changed. We quantified this relationship at different spatial scales in which we varied the focus and extent of analysis: (1) among fields within communities, (2) among fields within biomes or biogeographic regions, and (3) among communities within biomes or biogeographic regions. We used species density (D=number of species per m²) as our measure of diversity to have a comparable index across all sites and scales. Although we expected unimodal relationships at all spatial scales, we found that spatial scale influenced the form of the relationship. At the scale of fields within different grassland communities, we detected a significant relationship at only one site (Minnesota old‐fields), and it was negative linear. When we expanded the extent of analyses to biogeographic regions (grasslands or North America), we found significant unimodal relationships in both cases. However, when we combined data to examine patterns among community types within different biogeographic regions (grassland, alpine tundra, arctic tundra, or North America), we did not detect significant relationships between species density and ANPP for any region. The results of our analyses demonstrate that the spatial scale of analysis – how data are aggregated and patterns examined – can influence the form of the relationship between species density and productivity. It also demonstrates the need for data sets from a broad spectrum of sites sampled over a range of scales for examining challenging and controversial ecological hypotheses.     

新疆草地净初级生产力(NPP)空间分布格局及其对气候变化的响应

分析植被物候与净初级生产力对气候变化的响应一直是研究全球变化的核心内容之一。新疆草地生态系统极为脆弱,对气候和环境变化的影响十分敏感,在新疆地区开展草地物候和净初级生产力及其对气候变化的响应有着独特的意义。基于遥感数据和野外台站实测数据,利用CASA模型模拟了新疆草地植被净初级生产力(NPP),阐述了2001—2014年新疆地区草地的NPP的空间格局及与气象因子的关系。(1)通过实测生物量精度检验表明,CASA模型基本可以反映新疆地区草地植被NPP。(2)2001—2014年新疆草地NPP平均值为102.49 gC m^-2 a^-1。不同草地类型的NPPA存在明显差异。其中,山地草甸平均NPP最高,达到252.37 gC m^-2 a^-1;温性草甸草原次之,为204.93 gC m^-2 a^-1。高寒荒漠和温性荒漠的平均NPP最低,分别为43.94 gC m^-2 a^-1,53.11 gC m^-2 ...     

Scale‐dependence of vegetation‐environment relationships in semi‐natural grasslands

Questions: Which environmental and management factors determine plant species composition in semi‐natural grasslands within a local study area? Are vegetation and explanatory factors scale‐dependent? Location: Semi‐natural grasslands in Lærdal, Sognog Fjordane County, western Norway. Methods: We recorded plant species composition and explanatory variables in six grassland sites using a hierarchically nested sampling design with three levels: plots randomly placed within blocks selected within sites. We evaluated vegetation‐environment relationships at all three levels by means of DCA ordination and split‐plot GLM analyses. Results: The most important complex gradient determining variation in grassland species composition showed a broad‐scale relationship with management. Soil moisture conditions were related to vegetation variation on block scale, whereas element concentrations in the soil were significantly related to variation in species composition on all spatial scales. Our results show that vegetation‐environment relationships are dependent on the scale of observation. We suggest that scale‐related (and therefore methodological) issues may explain the wide range of vegetation‐environment relationships reported in the literature, for semi‐natural grassland in particular but also for other ecosystems. Conclusions: Interpretation of the variation in species composition of semi‐natural grasslands requires consideration of the spatial scales on which important environmental variables vary.     

Desertification alters patterns of aboveground net primary production in Chihuahuan ecosystems

Abstract The Chihuahuan desert of New Mexico, USA, has changed in historical times from semiarid grassland to desert shrublands dominated by Larrea tridentata and Prosopis glandulosa. Similar displacement of perennial grasslands by shrubs typifies desertification in many regions. Such structural vegetation change could alter average values of net primary productivity, as well as spatial and temporal patterns of production. We investigated patterns of aboveground plant biomass and net primary production in five ecosystem types of the Jornada Basin Long‐Term Ecological Research (LTER) site. Comparisons of shrub‐dominated desertified systems and remnant grass‐dominated systems allowed us to test the prediction that shrublands are more heterogeneous spatially, but less variable over time, than grasslands. We measured aboveground plant biomass and aboveground net primary productivity (ANPP) by species, three times per year for 10 years, in 15 sites of five ecosystem types (three each in Larrea shrubland, Bouteloua eriopoda grassland, Prosopis dune systems, Flourensia cernua alluvial flats, and grass‐dominated dry lakes or playas). Spatial heterogeneity of biomass at the scale of our measurements was significantly greater in shrub‐dominated systems than in grass‐dominated vegetation. ANPP was homogeneous across space in grass‐dominated systems, and in most growing seasons was significantly more patchy in shrub vegetation. Substantial interannual variability in ANPP complicates comparison of mean values across ecosystem types, but grasslands tended to support higher ANPP values than did shrub‐dominated systems. There were significant interactions between ecosystem type and season. Grasslands demonstrated higher interannual variation than did shrub systems. Desertification has apparently altered the seasonality of productivity in these systems; grasslands were dominated by summer growth, while sites dominated by Larrea or Prosopis tended to have higher spring ANPP. Production was frequently uncorrelated across sites of an ecosystem type, suggesting that factors other than season, regional climate, or dominant vegetation may be significant determinants of actual NPP.     

Primary Productivity and Precipitation-Use Efficiency in Temperate Grassland in the Loess Plateau of China

Clarifying spatial variations in aboveground net primary productivity (ANPP) and precipitation-use efficiency (PUE) of grasslands is critical for effective prediction of the response of terrestrial ecosystem carbon and water cycle to future climate change. Though the combination use of remote sensing products and in situ ANPP measurements, we quantified the effects of climatic [mean annual precipitation (MAP) and precipitation seasonal distribution (PSD)], biotic [leaf area index (LAI)] and abiotic [slope gradient, aspect, soil water storage (SWS) and other soil physical properties] factors on the spatial variations in ANPP and PUE across different grassland types (i.e., meadow steppe, typical steppe and desert steppe) in the Loess Plateau. Based on the study, ANPP increased exponentially with MAP for the entire temperate grassland; suggesting that PUE increased with increasing MAP. Also PSD had a significant effect on ANPP and PUE; where more even PSD favored higher ANPP and PUE. Then MAP, more than PSD, explained spatial variations in typical steppe and desert steppe. However, PSD was the dominant driving factor of spatial variations in ANPP of meadow steppe. This suggested that in terms of spatial variations in ANPP of meadow steppe, change in PSD due to climate change was more important than that in total annual precipitation. LAI explained 78% of spatial PUE in the entire Loess Plateau temperate grassland. As such, LAI was the primary driving factor of spatial variations in PUE. Although the effect of SWS on ANPP and PUE was significant, it was nonetheless less than that of precipitation and vegetation. We therefore concluded that changes in vegetation structure and consequently in LAI and/or altered pattern of seasonal distribution of rainfall due to global climate change could significantly influence ecosystem carbon and water cycle in temperate grasslands.     

草原土壤有机碳含量的控制因素

基于374个高寒草原和温带草原土壤样品的测试结果,运用多元逐步回归分析模型定量评估了土壤环境因子对土壤有机碳(SOC)含量的影响.结果表明:高寒草原土壤有机碳含量(20.18 kg C/m2)高于温带草原(9.23 kg C/m2).土壤理化生物学因子对高寒草原和温带草原SOC含量(10 cm)变化的贡献分别是87.84％和75.00％.其中,土壤总氮含量和根系对高寒草原SOC含量变化的贡献均大于对温带草原SOC含量变化的相应贡献.土壤水分是温带草原SOC含量变化的主要限制性因素,其对SOC含量变化的贡献达33.27％.高寒草原土壤C/N比显著高于温带草原土壤的相应值,揭示了青藏高原高寒草原较高的SOC含量是由于较低的土壤微生物活性所导致.     

Contingent productivity responses to more extreme rainfall regimes across a grassland biome

Climate models predict, and empirical evidence confirms, that more extreme precipitation regimes are occurring in tandem with warmer atmospheric temperatures. These more extreme rainfall patterns are characterized by increased event size separated by longer within season drought periods and represent novel climatic conditions whose consequences for different ecosystem types are largely unknown. Here, we present results from an experiment in which more extreme rainfall patterns were imposed in three native grassland sites in the Central Plains Region of North America, USA. Along this 600 km precipitation–productivity gradient, there was strong sensitivity of temperate grasslands to more extreme growing season rainfall regimes, with responses of aboveground net primary productivity (ANPP) contingent on mean soil water levels for different grassland types. At the mesic end of the gradient (tallgrass prairie), longer dry intervals between events led to extended periods of below-average soil water content, increased plant water stress and reduced ANPP by 18%. The opposite response occurred at the dry end (semiarid steppe), where a shift to fewer, but larger, events increased periods of above-average soil water content, reduced seasonal plant water stress and resulted in a 30% increase in ANPP. At an intermediate mixed grass prairie site with high plant species richness, ANPP was most sensitive to more extreme rainfall regimes (70% increase). These results highlight the inherent complexity in predicting how terrestrial ecosystems will respond to forecast novel climate conditions as well as the difficulties in extending inferences from single site experiments across biomes. Even with no change in annual precipitation amount, ANPP responses in a relatively uniform physiographic region differed in both magnitude and direction in response to within season changes in rainfall event size/frequency.     

The role of linear mown firebreaks in conserving butterfly diversity: Effects of adjacent vegetation and management

Semi‐natural grasslands are vital for maintaining grassland butterflies in Japan, as well as in Europe. However, severe decline in these grassland environments has recently attracted attention to linear grasslands, such as firebreaks and power‐line corridors, as alternative habitats for grassland insects. We surveyed butterflies in an abandoned grassland and nearby linear mown firebreaks adjacent to different vegetation at the northern foot of Mt. Fuji, central Japan, over 5 successive years, particularly focusing on species on the 2012 Japanese Red List of Threatened Species (“red‐list” species). We found that the firebreaks were consistently higher in species richness and abundance of butterflies than the long‐term abandoned grassland, and that species composition differed among the firebreaks depending on conditions of the adjacent vegetation. The firebreaks surrounded by forests were mainly utilized by forest and edge species, whereas the firebreaks adjacent to the grassland were essential for conserving red‐list grassland species. Thus, only the mown firebreaks adjacent to the grassland were regarded as a high‐quality alternative habitat for many grassland butterflies, but the area was limited. Therefore, creating heterogeneity in the abandoned grassland by infrequent mowing could help conserve grassland butterflies, including red‐list species.     

降水变化对藏北高寒草原化草甸降水利用效率及地上生产力的影响

降水总量、分配方式及其发生时间共同决定了青藏高原植被生长的水分条件,而降水利用效率(PUE,地上生产力与降水量的比值)是评估降水与植被生产力关系的有效指标.本研究以藏北当雄高寒草原化草甸为研究对象,利用多年生物量采样数据与同期遥感EVI植被指数建立线性模型,反演了2000-2016年地上净初级生产力(ANPP),结合同时期气象数据,以生长季降水量(GSP)表征降水总体状况,改进的降水集度指标(PCI)表征生长季降水分配,降水重心(PC)表征降水集中时间,并结合生长季均温(GST),利用结构方程分析了气候因子对当雄草地降水利用效率和地上生产力的影响.结果表明: 当雄草地ANPP主要受生长季降水影响,GSP与ANPP呈显著正相关,而GST与PUE、ANPP无显著相关关系;PCI与PUE呈显著正相关,表明降水集中分布有利于PUE增加;PCI与ANPP相关的间接系数大于直接系数,表明PCI通过PUE影响ANPP;降水集中时间(PC)变化则对PUE和ANPP没有显著影响.在青藏高原显著的气候变暖背景下,降水量和降水集度的变化都将会对藏北高寒草地的地上生产力产生重要影响.