Spatial heterogeneity in species composition constrains plant community responses to herbivory and fertilisation

Environmental change can result in substantial shifts in community composition. The associated immigration and extinction events are likely constrained by the spatial distribution of species. Still, studies on environmental change typically quantify biotic responses at single spatial (time series within a single plot) or temporal (spatial beta diversity at single time points) scales, ignoring their potential interdependence. Here, we use data from a global network of grassland experiments to determine how turnover responses to two major forms of environmental change – fertilisation and herbivore loss – are affected by species pool size and spatial compositional heterogeneity. Fertilisation led to higher rates of local extinction, whereas turnover in herbivore exclusion plots was driven by species replacement. Overall, sites with more spatially heterogeneous composition showed significantly higher rates of annual turnover, independent of species pool size and treatment. Taking into account spatial biodiversity aspects will therefore improve our understanding of consequences of global and anthropogenic change on community dynamics.     

Effects of desertification on the C:N:P stoichiometry of soil,microbes, and extracellular enzymes in a desert grassland

为探讨荒漠草地沙漠化对“土壤-微生物-胞外酶”系统生态化学计量的影响机理, 该研究采用空间序列代替时间演替的方法, 研究了宁夏盐池荒漠草地沙漠化过程中土壤、土壤微生物及土壤胞外酶碳(C)、氮(N)、磷(P)生态化学计量的变异特征。结果表明: (1)随着荒漠草地沙漠化的不断加剧, 土壤C、N、P含量和土壤C:P、N:P均呈降低趋势, 而土壤C:N逐渐增加。(2)荒漠草地沙漠化过程中, 土壤微生物生物量C (MBC):微生物生物量P (MBP)、微生物生物量N (MBN):MBP和土壤β-葡萄糖苷酶(BG):N-乙酰氨基葡萄糖苷酶(NAG)逐渐降低, 而土壤BG:磷酸酶(AP)和NAG:AP基本表现为增加趋势。(3)随着荒漠草地沙漠化程度的加剧, 土壤微生物C利用效率CUE_C:N和CUE_C:P与土壤微生物N利用效率NUE_N:C和土壤微生物P利用效率PUE_P:C的变化趋势相反。(4)荒漠草地土壤、土壤微生物生物量和土壤胞外酶C:N化学计量(C:N, MBC:MBN, BG:NAG)与土壤、土壤微生物生物量和土壤胞外酶N:P化学计量(N:P, MBN:MBP, NAG:AP)显著负相关, 而土壤和胞外酶C:N化学计量(C:N, BG:NAG)与土壤和胞外酶C:P化学计量(C:P, BG:AP)显著正相关。土壤N:P与土壤MBN:MBP显著正相关, 而与土壤NAG:AP显著负相关。分析表明, 荒漠草地沙漠化过程中土壤微生物生物量及胞外酶活性随着土壤养分的变化而发生变化; 微生物-胞外酶C:N:P生态化学计量与土壤养分存在协变关系, 为理解荒漠草地土壤-微生物系统C、N、P循环机制提供理论依据。     

草地群落多样性和生态系统碳氮循环对氮输入的非线性响应及其机制

理解草地生态系统结构和功能对氮富集的响应及其机制有助于准确评估大气氮沉降等外源氮输入的生态效应。全球范围内建立的多水平氮添加实验为认识草地生态系统结构和功能对氮输入的非线性响应机制提供了有效途径。为了反映学术界基于多水平氮添加控制实验取得的主要研究进展,该文综述了草地群落多样性和生态系统碳氮循环过程对外源氮输入的非线性响应特征及其驱动机制。按照目前的研究,氮输入会导致草地植物物种多样性、功能多样性以及土壤细菌多样性下降,但真菌多样性的变化并不明显。地上和地下生产力对氮输入的响应趋势存在差异:地上生产力沿氮添加梯度呈“先上升后饱和”的变化规律,而根系生产量和根冠比呈下降趋势,根系周转速率则呈“先上升后下降”的单峰格局。不同碳分解过程对氮输入的响应也不尽相同:凋落物分解速率沿氮添加梯度表现出“指数衰减、线性增加或无显著变化”的多元响应,而土壤呼吸和CH₄吸收速率与施氮量的关系则以“低氮促进、高氮抑制”的单峰趋势为主。类似地,不同土壤碳组分对氮输入的响应存在差异:氮添加总体会导致草地土壤碳库和颗粒态有机碳含量增加,而矿物结合态碳含量随施氮量呈“增加、不变或下降”的多元响...     

Separating direct and indirect effects of global change: a population dynamic modeling approach using readily available field data

Two sources of complexity make predicting plant community response to global change particularly challenging. First, realistic global change scenarios involve multiple drivers of environmental change that can interact with one another to produce non‐additive effects. Second, in addition to these direct effects, global change drivers can indirectly affect plants by modifying species interactions. In order to tackle both of these challenges, we propose a novel population modeling approach, requiring only measurements of abundance and climate over time. To demonstrate the applicability of this approach, we model population dynamics of eight abundant plant species in a multifactorial global change experiment in alpine tundra where we manipulated nitrogen, precipitation, and temperature over 7 years. We test whether indirect and interactive effects are important to population dynamics and whether explicitly incorporating species interactions can change predictions when models are forecast under future climate change scenarios. For three of the eight species, population dynamics were best explained by direct effect models, for one species neither direct nor indirect effects were important, and for the other four species indirect effects mattered. Overall, global change had negative effects on species population growth, although species responded to different global change drivers, and single‐factor effects were slightly more common than interactive direct effects. When the fitted population dynamic models were extrapolated under changing climatic conditions to the end of the century, forecasts of community dynamics and diversity loss were largely similar using direct effect models that do not explicitly incorporate species interactions or best‐fit models; however, inclusion of species interactions was important in refining the predictions for two of the species. The modeling approach proposed here is a powerful way of analyzing readily available datasets which should be added to our toolbox to tease apart complex drivers of global change.     

Asynchronous responses of soil microbial community and understory plant community to simulated nitrogen deposition in a subtropical forest

Atmospheric nitrogen (N) deposition greatly affects ecosystem processes and properties. However, few studies have simultaneously examined the responses of both the above- and belowground communities to N deposition. Here, we investigated the effects of 8 years of simulated N deposition on soil microbial communities and plant diversity in a subtropical forest. The quantities of experimental N added (g of N m⁻² year⁻¹) and treatment codes were 0 (N0, control), 6 (N1), 12 (N2), and 24 (N3). Phospholipid fatty acids (PLFAs) analysis was used to characterize the soil microbial community while plant diversity and coverage were determined in the permanent field plots. Microbial abundance was reduced by the N3 treatment, and plant species richness and coverage were reduced by both N2 and N3 treatments. Declines in plant species richness were associated with decreased abundance of arbuscular mycorrhizal fungi, increased bacterial stress index, and reduced soil pH. The plasticity of soil microbial community would be more related to the different responses among treatments when compared with plant community. These results indicate that long-term N deposition has greater effects on the understory plant community than on the soil microbial community and different conservation strategies should be considered.     

Physiological and production responses of plant growth forms to increases in limiting resources in alpine tundra: implications for differential community response to environmental change

Physiological and growth measurements were made on forbs and graminoids following additions of water and N+water in a graminoid-dominated dry meadow and a forb-dominated moist meadow, to determine if the community-level response was related to differential responses between the growth forms. Graminoids had higher photosynthetic rates and lower transpiration rates and foliar N concentrations than forbs, and consequently maintained higher photosynthetic N- and water-use efficiencies. Photosynthetic rates, stomatal conductance, and transpiration rates increased significantly only in response to N fertilization and only in moist meadow species. The increase in photosynthetic rates was unrelated to variation in foliar N concentration, but instead correlated with variation in stomatal conductance. Growth based N-use efficiency was higher in moist meadow graminoids than in moist meadow forbs, but did not differ between the growth forms in the dry meadow. The moist meadow community had higher biomass and N standing crops, but the relative increase in these factors in response to N fertilization was greater in the dry meadow. Graminoids had a greater relative increase in biomass and N accumulation than forbs following N fertilization, but moist meadow graminoids exhibited a greater response than dry meadow graminoids. The difference in the growth response between the dry meadow and moist meadow graminoids to N fertilization was correlated with more conservative leaf gas exchange responses in dry meadow species, presumably related to a higher frequency of soil water deficits in this community. Community-level response to the resource additions was therefore mediated by the plant growth form response, corresponding with differences between the growth forms in physiological factors related to resource acquisition and use.     

Active versus passive restoration of tallgrass prairie in the U.S. Midwest: plant species diversity and assemblage,net primary production and soil carbon sequestration

We investigated the plant species diversity, community assemblage, net primary production and soil carbon sequestration in an old field (OF), which went through passive restoration with spontaneous secondary succession, and a restored prairie (RP), which went through active restoration with reintroduction of native plants. The passive restoration in OF did not attain as high diversity and richness of plant species as did in RP. Our NMS (nonmetric multidimensional scaling) ordination revealed a clear divergence of RP and OF vegetation with dissimilar species compositions to separate paths of succession trajectory. The spontaneous succession in OF has made very little progress due to a potentially strong inhibitory priority effect of invasive plants. The belowground biomass in the high-diversity RP was 1.3× higher than the low-diversity OF. We found no measurable difference in soil C sequestration between RP and OF at this time, possibly due to edaphic factors, lack of legumes, or both. Human intervention is needed for restoring abandoned croplands—highly disturbed, fragmented and isolated habitats—to tallgrass prairies in the U.S. Midwest. Our recommended intervention includes but is not limited to removal of exotic plants, further augmentation of native plants (particularly legumes), and periodic burns.     

基于盐分梯度的荒漠植物多样性与群落、种间联接响应

土壤盐分是影响干旱区荒漠植物群落动态的决定因素之一。基于样方调查和不同土壤盐分梯度下植物多样性指数及群落与种间关联的计算结果,分析干旱区荒漠群落植物多样性、群落联接性和种间关联对土壤盐分梯度的响应动态。结果表明,在土壤盐含量为0.03%-0.55% (S1)、0.61%-1.24% (S2)和1.41%-1.79% (S3)的盐分梯度上,(1)随土壤盐含量升高,群落生活型结构改变,草本比例减少,乔木比例增加;(2)植物多样性指数随土壤盐分增加而下降,低盐分梯度下,二者极显著正相关(P<0.01),中盐梯度下二者间呈部分显著负相关(P<0.05),高盐梯度下则转为以正相关为主(P>0.05);(3)群落联接性随土壤盐分梯度转变,在0.61%-1.24%的中度盐含量时正联接性最强(VR=1.89),高盐度含量下群落转为不显著的负联接,稳定性降低;(4)沿盐分升高梯度,种间的负相关种对数增加,正相关种对数减少,种间关联(相关)强度提高,正负相关种对比(PNR)与多样性指数呈显著正相关(P<0.05)。综上可知,干旱区荒漠植物多样性在土壤盐含量达到1.41%-1.79%水平时总体显著降低;土壤盐分水平显著影响植物群落和种间联接性,种间互利性随盐分梯度增加下降,物种趋于独立分布,并最终导致荒漠植物多样性降低。     

Effects of plant species diversity, atmospheric [CO2], and N addition on gross rates of inorganic N release from soil organic matter

A significant challenge in predicting terrestrial ecosystem response to global changes comes from the relatively poor understanding of the processes that control pools and fluxes of plant nutrients in soil. In addition, individual global changes are often studied in isolation, despite the potential for interactive effects among them on ecosystem processes. We studied the response of gross N mineralization and microbial respiration after 6 years of application of three global change factors in a grassland field experiment in central Minnesota (the BioCON experiment). BioCON is a factorial manipulation of plant species diversity (1, 4, 9 and 16 prairie species), atmospheric [CO₂] (ambient and elevated: 560 μmol mol^?1), and N inputs (ambient and ambient +4 g N m^?2 yr^?1). We hypothesized that gross N mineralization would increase with increasing levels of all factors because of stimulated plant productivity and thus greater organic inputs to soils. However, we also hypothesized that N addition would enhance, while elevated [CO₂] and greater diversity would temper, gross N mineralization responses because of increased and reduced plant tissue N concentrations, respectively. In partial support of our hypothesis, gross N mineralization increased with greater diversity and N addition, but not with elevated [CO₂]. The ratio of gross N mineralization to microbial respiration (i.e. the ‘yield’ of inorganic N mineralized per unit C respired) declined with greater diversity and [CO₂] suggesting increasing limitation of microbial processes by N relative to C in these treatments. Based on these results, we conclude that the plant supply of organic matter primarily controls gross N mineralization and microbial respiration, but that the concentration of N in organic matter input secondarily influences these processes. Thus, in systems where N limits plant productivity these global change factors could cause different long‐term ecosystem trajectories because of divergent effects on soil N and C cycling.     

氮添加对昆仑山高山草地土壤、微生物和植物生态化学计量特征的影响

全球范围内的氮沉降增加改变了生态系统氮(N)素循环过程,由此带来的生态学效应已成为当前研究的热点。以昆仑山高山草地生态系统2种优势植物黄花棘豆(Oxytropis ochrocephala)和针茅(Stipa capillata)为研究对象,开展人工氮肥添加试验,研究土壤-微生物-植物系统各组分生态化学计量特征对氮添加的响应特征。结果表明:①氮添加显著提高了土壤NH4^+-N和土壤NO3^--N含量(P<0.05),土壤全N、全磷(P)、速效P含量没有明显变化。②氮添加条件下针茅叶片N含量增加,P含量降低,而黄花棘豆N和P含量无明显变化。③土壤微生物量碳(MBC)和微生物量氮(MBN)随着施氮量的增加呈现出先增加后降低的趋势,当施氮量为6N·m^-2·y^-1时呈现出最高值。土壤NH4+-N含量与土壤微生物量N含量有显著的正相关关系(P<0.01)。综合分析表明,短期氮添加有利于土壤养分和微生物量的积累,促进植物和微生物养分吸收利用。2种优势植物的生态化学计量特征对氮沉降的响应不同,过量的氮输入将会造成植物生长受到P限制,氮沉降会改变昆仑山高山草地生态系统的生物地球化学循环过程。     

植物-土壤反馈与草地群落演替:菌根真菌和土壤病原菌的调控作用

由植物引起的根际土壤生物或非生物环境的改变能够反馈影响群落中不同植物的生长,直接改变共存植物的相对竞争关系,推动群落结构的动态变化。作为土壤生物群落的重要组成部分,土壤微生物在植物-土壤反馈关系中起到重要的调控作用,对解释植物群落的演替进程和方向有着重要的意义。在草地植物群落演替的早期阶段和外来物种入侵的过程中,宿主植物对丛枝菌根真菌（AMF）的依赖性较低,受本地病原菌的影响较小,一般不存在负反馈。在演替后期,植物对AMF更具依赖性,而积累的病原菌则产生较强的负反馈效应,从而促进群落物种共存和植物多样性,提高草地生产力和稳定性。研究微生物-植物反馈机制不仅有助于完善草地退化与恢复理论,还对退化草地恢复治理的实践有着指导意义。未来关于根际微生物-植物反馈在草地群落演替中的作用应该加强以下几方面的研究：（1）在实验方法上,开展专性微生物-植物反馈研究;（2）在测定指标上,进一步量化不同微生物在反馈关系中的功能差异;（3）在研究对象上,加强土壤微生物在植物群落水平的反馈研究;（4）在应用上,明晰植物-土壤反馈在退化草地恢复过程中的作用,指导草地管理实践。     

Biotic context and soil properties modulate native plant responses to enhanced rainfall

Background and Aims The environmental and biotic context within which plants grow have a great potential to modify responses to climatic changes, yet few studies have addressed both the direct effects of climate and the modulating roles played by variation in the biotic (e.g. competitors) and abiotic (e.g. soils) environment.Methods In a grassland with highly heterogeneous soils and community composition, small seedlings of two native plants, Lasthenia californica and Calycadenia pauciflora, were transplanted into factorially watered and fertilized plots. Measurements were made to test how the effect of climatic variability (mimicked by the watering treatment) on the survival, growth and seed production of these species was modulated by above-ground competition and by edaphic variables.Key Results Increased competition outweighed the direct positive impacts of enhanced rainfall on most fitness measures for both species, resulting in no net effect of enhanced rainfall. Both species benefitted from enhanced rainfall when the absence of competitors was accompanied by high soil water retention capacity. Fertilization did not amplify the watering effects; rather, plants benefitted from enhanced rainfall or competitor removal only in ambient nutrient conditions with high soil water retention capacity.Conclusions The findings show that the direct effects of climatic variability on plant fitness may be reversed or neutralized by competition and, in addition, may be strongly modulated by soil variation. Specifically, coarse soil texture was identified as a factor that may limit plant responsiveness to altered water availability. These results highlight the importance of considering the abiotic as well as biotic context when making future climate change forecasts.     

Impacts of soil temperature,phenology and plant community composition on invertebrate herbivory in a natural warming experiment

Species and community-level responses to warming are well documented, with plants and invertebrates known to alter their range, phenology or composition as temperature increases. The effects of warming on biotic interactions are less clearly understood, but can have consequences that cascade through ecological networks. Here, we used a natural soil temperature gradient of 5–35°C in the Hengill geothermal valley, Iceland, to investigate the effects of temperature on plant community composition and plant–invertebrate interactions. We quantified the level of invertebrate herbivory on the plant community across the temperature gradient and the interactive effects of temperature, plant phenology (i.e. development stage) and vegetation community composition on the probability of herbivory for three ubiquitous plant species, Cardamine pratensis, Cerastium fontanum and Viola palustris. We found that the percentage cover of graminoids and forbs increased, while the amount of litter decreased, with increasing soil temperature. Invertebrate herbivory also increased with soil temperature at the plant community level, but this was underpinned by different effects of temperature on herbivory for individual plant species, mediated by the seasonal development of plants and the composition of the surrounding vegetation. This illustrates the importance of considering the development stage of organisms in climate change research given the variable effects of temperature on susceptibility to herbivory at different ontogenetic stages.     

Responses of an old-field plant community to interacting factors of elevated [CO2], warming, and soil moisture

Aims: The direct effects of atmospheric and climatic change factors—atmospheric[CO₂], air temperature and changes in precipitation—canshape plant community composition and alter ecosystem function.It is essential to understand how these factors interact tomake better predictions about how ecosystems may respond tochange. We investigated the direct and interactive effects of[CO₂], warming and altered soil moisture in open-top chambers(OTCs) enclosing a constructed old-field community to test howthese factors shape plant communities. Materials and methods: The experimental facility in Oak Ridge, TN, USA, made use of4-m diameter OTCs and rain shelters to manipulate [CO₂] (ambient,ambient + 300 ppm), air temperature (ambient, ambient + 3.5°C)and soil moisture (wet, dry). The plant communities within thechambers comprised seven common old-field species, includinggrasses, forbs and legumes. We tracked foliar cover for eachspecies and calculated community richness, evenness and diversityfrom 2003 to 2005. Important findings: This work resulted in three main findings: (1) warming had species-specificeffects on foliar cover that varied through time and were alteredby soil moisture treatments; (2) [CO₂] had little effect onindividual species or the community; (3) diversity, evennessand richness were influenced most by soil moisture, primarilyreflecting the response of one dominant species. We concludethat individualistic species responses to atmospheric and climaticchange can alter community composition and that plant populationsand communities should be considered as part of analyses ofterrestrial ecosystem response to climate change. However, predictionof plant community responses may be difficult given interactionsbetween factors and changes in response through time.     

Photosynthetic responses of 13 grassland species across 11 years of free‐air CO2 enrichment is modest,consistent and independent of N supply

If long‐term responses of photosynthesis and leaf diffusive conductance to rising atmospheric carbon dioxide (CO₂) levels are similar or predictably different among species, functional types, and ecosystem types, general global models of elevated CO₂ effects can effectively be developed. To address this issue we measured gas exchange rates of 13 perennial grassland species from four functional groups across 11 years of long‐term free‐air CO₂ enrichment (eCO₂, +180 ppm above ambient CO₂) in the BioCON experiment in Minnesota, USA. Eleven years of eCO₂ produced consistent but modest increases in leaf net photosynthetic rates of 10% on average compared with plants grown at ambient CO₂ concentrations across the 13 species. This eCO₂‐induced enhancement did not depend on soil N treatment, is much less than the average across other longer‐term studies, and represents strong acclimation (i.e. downregulation) as it is also much less than the instantaneous response to eCO₂. The legume and C3 nonlegume forb species were the most responsive among the functional groups (+13% in each), the C4 grasses the least responsive (+4%), and C3 grasses intermediate in their photosynthetic response to eCO₂ across years (+9%). Leaf stomatal conductance and nitrogen content declined comparably across species in eCO₂ compared with ambient CO₂ and to degrees corresponding to results from other studies. The significant acclimation of photosynthesis is explained in part by those eCO₂‐induced decreases in leaf N content and stomatal conductance that reduce leaf photosynthetic capacity in plants grown under elevated compared with ambient CO₂ concentrations. Results of this study, probably the longest‐term with the most species, suggest that carbon cycle models that assume and thereby simulate long‐lived strong eCO₂ stimulation of photosynthesis (e.g.> 25%) for all of Earth's terrestrial ecosystems should be viewed with a great deal of caution.     

Origins of altruism diversity I: the diverse ecological roles of altruistic strategies and their evolutionary responses to local competition

Nature abounds with a rich variety of altruistic strategies, including public resource enhancement, resource provisioning, communal foraging, alarm calling, and nest defense. Yet, despite their vastly different ecological roles, current theory typically treats diverse altruistic traits as being favored under the same general conditions. Here, we introduce greater ecological realism into social evolution theory and find evidence of at least four distinct modes of altruism. Contrary to existing theory, we find that altruistic traits contributing to "resource-enhancement" (e.g., siderophore production, provisioning, agriculture) and "resource-efficiency" (e.g., pack hunting, communication) are most strongly favored when there is strong local competition. These resource-based modes of helping are "K-strategies" that increase a social group's growth yield, and should characterize species with scarce resources and/or high local crowding caused by low mortality, high fecundity, and/or mortality occurring late in the process of resource-acquisition. The opposite conditions, namely weak local competition (abundant resource, low crowding), favor survival (e.g., nest defense) and fecundity (e.g., nurse workers) altruism, which are "r-strategies" that increase a social group's growth rate. We find that survival altruism is uniquely favored by a novel evolutionary force that we call "sunk cost selection." Sunk cost selection favors helping that prevents resources from being wasted on individuals destined to die before reproduction. Our results contribute to explaining the observed natural diversity of altruistic strategies, reveal the necessary connection between the evolution and the ecology of sociality, and correct the widespread but inaccurate view that local competition uniformly impedes the evolution of altruism.     

Nutrient limitation of plant growth on the floodplain of the Narran River, Australia: growth experiments and a pilot soil survey

Water resource development has altered the hydrological regime on the Lower Balonne River in Queensland, Australia. Concerns have been raised about possible impacts to floodplain plant communities, which support a pastoral industry and a range of native fauna. Water and nutrients commonly limit plant growth in south central Queensland, where the climate is semi-arid and the soils are infertile. Floodplain plant productivity is boosted by inundation with water, but the role of flooding in nutrient provision is not known. Growth experiments and a pilot soil survey were conducted to help determine if soil nutrient deficiencies exist and if regular flooding is required to maintain floodplain soil fertility. Soils were sampled from areas representing three flood frequency classes: high, moderate, and low. Chemical extractions were performed as a surrogate for `bioavailable' nutrients. Soil nitrogen (N) but not phosphorus (P) limited the growth of seedlings of wheat (Triticum aestivum L. Gardia) based on responses to nutrient additions: plants supplied with N had greater shoot length and total biomass than plants without N. Clear evidence of an effect of flood frequency on fertility was not revealed. Neither soil P, soil N, nor plant growth varied significantly with flood frequency. However, this analysis had low statistical power. There were trends for greater biomass of seedlings grown on moderately flooded soils and thinner roots for seedlings grown on frequently flooded soils, but neither of these growth responses was clearly linked to nutrient limitation. Nevertheless, the possibility that flooding provides a nutrient subsidy to plants cannot be ruled out because of a number of factors, including the statistical power of this analysis and the possibility that short-term nutrient subsidies occur with floods.     

Press–pulse interactions: effects of warming,N deposition,altered winter precipitation,and fire on desert grassland community structure and dynamics

Global environmental change is altering temperature, precipitation patterns, resource availability, and disturbance regimes. Theory predicts that ecological presses will interact with pulse events to alter ecosystem structure and function. In 2006, we established a long‐term, multifactor global change experiment to determine the interactive effects of nighttime warming, increased atmospheric nitrogen (N) deposition, and increased winter precipitation on plant community structure and aboveground net primary production (ANPP) in a northern Chihuahuan Desert grassland. In 2009, a lightning‐caused wildfire burned through the experiment. Here, we report on the interactive effects of these global change drivers on pre‐ and postfire grassland community structure and ANPP. Our nighttime warming treatment increased winter nighttime air temperatures by an average of 1.1 °C and summer nighttime air temperature by 1.5 °C. Soil N availability was 2.5 times higher in fertilized compared with control plots. Average soil volumetric water content (VWC) in winter was slightly but significantly higher (13.0% vs. 11.0%) in plots receiving added winter rain relative to controls, and VWC was slightly higher in warmed (14.5%) compared with control (13.5%) plots during the growing season even though surface soil temperatures were significantly higher in warmed plots. Despite these significant treatment effects, ANPP and plant community structure were highly resistant to these global change drivers prior to the fire. Burning reduced the cover of the dominant grasses by more than 75%. Following the fire, forb species richness and biomass increased significantly, particularly in warmed, fertilized plots that received additional winter precipitation. Thus, although unburned grassland showed little initial response to multiple ecological presses, our results demonstrate how a single pulse disturbance can interact with chronic alterations in resource availability to increase ecosystem sensitivity to multiple drivers of global environmental change.