Response of soil nematodes to elevated temperature in conventional and no-tillage cropland systems

Aims

Nematodes are sensitive to environmental changes and are strongly affected by tillage practices. However, it remains unclear whether an increase in soil temperature in conventional tillage (CT) and no-tillage (NT) cropland systems would have a significant effect on nematode communities. The response of soil nematodes to increases in temperature will provide valuable information about probable changes in soil ecology under global warming.

Methods

A field experiment using infrared heaters to simulate climate warming was performed in North China. The impacts of predicted warming on the nematode community in CT and NT systems were measured during the growing season of maize.

Results

The results showed that the diversity of nematodes responded positively to warming in both tillage systems early in the maize growing season, though the diversity in NT declined due to warming late in the growing season. However, no significant warming effects were found on the total nematode density, individual feeding group density or functional indices. Compared to CT, NT presented a rather different nematode community that was characterized by a large nematode diversity, low fungal feeder density due to a strong decrease in Aphelenchoides, and high maturity indices.

Conclusions

Tillage is an important factor that influences the soil properties and nematode community. It is proposed that future global warming with soil temperature increasing approximately 1 °C will have only small effects on soil nematodes in the two tillage systems.     

Warming and oligotrophication cause shifts in freshwater phytoplankton communities

While there is a lot of data on interactive effects of eutrophication and warming, to date, we lack data to generate reliable predictions concerning possible effects of nutrient decrease and temperature increase on community composition and functional responses. In recent years, a wide‐ranging trend of nutrient decrease (re‐oligotrophication) was reported for freshwater systems. Small lakes and ponds, in particular, show rapid responses to anthropogenic pressures and became model systems to investigate single as well as synergistic effects of warming and fertilization in situ and in experiments. Therefore, we set up an experiment to investigate the single as well as the interactive effects of nutrient reduction and gradual temperature increase on a natural freshwater phytoplankton community, using an experimental indoor mesocosm setup. Biomass production initially increased with warming but decreased with nutrient depletion. If nutrient supply was constant, biomass increased further, especially under warming conditions. Under low nutrient supply, we found a sharp transition from initially positive effects of warming to negative effects when resources became scarce. Warming reduced phytoplankton richness and evenness, whereas nutrient reduction at ambient temperature had positive effects on diversity. Our results indicate that temperature effects on freshwater systems will be altered by nutrient availability. These interactive effects of energy increase and resource decrease have major impacts on biodiversity and ecosystem function and thus need to be considered in environmental management plans.     

基于物种多样性与生物量关系的草地群落稳定性对全球变暖的响应研究进展

全球变暖背景下物种多样性和生物量的空间变化格局及其对温度升高的响应是生态学研究的热点内容,是探究群落稳定性响应全球变暖的关键。物种分布是多个生态过程相互作用的产物,温度升高通过改变群落关键种的作用影响物种多样性,从而改变群落稳定性。关于草地群落稳定性对全球变暖的响应过程,国内外学者的相关研究存在很大差异。该文作者结合自己研究团队在青藏高原和黄土高原的研究成果,对近年来国内外有关草地群落物种多样性和生物量的空间变化格局及其对温度升高的响应、以及二者的相互作用关系等方面的研究进展进行了综述,并提出了草地群落稳定性对全球变暖响应研究的重点方向。     

Distinct patterns of soil bacterial and fungal community assemblages in subtropical forest ecosystems under warming

Climate change globally affects soil microbial community assembly across ecosystems. However, little is known about the impact of warming on the structure of soil microbial communities or underlying mechanisms that shape microbial community composition in subtropical forest ecosystems. To address this gap, we utilized natural variation in temperature via an altitudinal gradient to simulate ecosystem warming. After 6 years, microbial co-occurrence network complexity increased with warming, and changes in their taxonomic composition were asynchronous, likely due to contrasting community assembly processes. We found that while stochastic processes were drivers of bacterial community composition, warming led to a shift from stochastic to deterministic drivers in dry season. Structural equation modelling highlighted that soil temperature and water content positively influenced soil microbial communities during dry season and negatively during wet season. These results facilitate our understanding of the response of soil microbial communities to climate warming and may improve predictions of ecosystem function of soil microbes in subtropical forests.     

Warming alters community size structure and ecosystem functioning

Global warming can affect all levels of biological complexity, though we currently understand least about its potential impact on communities and ecosystems. At the ecosystem level, warming has the capacity to alter the structure of communities and the rates of key ecosystem processes they mediate. Here we assessed the effects of a 4°C rise in temperature on the size structure and taxonomic composition of benthic communities in aquatic mesocosms, and the rates of detrital decomposition they mediated. Warming had no effect on biodiversity, but altered community size structure in two ways. In spring, warmer systems exhibited steeper size spectra driven by declines in total community biomass and the proportion of large organisms. By contrast, in autumn, warmer systems had shallower size spectra driven by elevated total community biomass and a greater proportion of large organisms. Community-level shifts were mirrored by changes in decomposition rates. Temperature-corrected microbial and macrofaunal decomposition rates reflected the shifts in community structure and were strongly correlated with biomass across mesocosms. Our study demonstrates that the 4°C rise in temperature expected by the end of the century has the potential to alter the structure and functioning of aquatic ecosystems profoundly, as well as the intimate linkages between these levels of ecological organization.     

Temperature-driven regime shifts in the dynamics of size-structured populations

Global warming impacts virtually all biota and ecosystems. Many of these impacts are mediated through direct effects of temperature on individual vital rates. Yet how this translates from the individual to the population level is still poorly understood, hampering the assessment of global warming impacts on population structure and dynamics. Here, we study the effects of temperature on intraspecific competition and cannibalism and the population dynamical consequences in a size-structured fish population. We use a physiologically structured consumer-resource model in which we explicitly model the temperature dependencies of the consumer vital rates and the resource population growth rate. Our model predicts that increased temperature decreases resource density despite higher resource growth rates, reflecting stronger intraspecific competition among consumers. At a critical temperature, the consumer population dynamics destabilize and shift from a stable equilibrium to competition-driven generation cycles that are dominated by recruits. As a consequence, maximum age decreases and the proportion of younger and smaller-sized fish increases. These model predictions support the hypothesis of decreasing mean body sizes due to increased temperatures. We conclude that in size-structured fish populations, global warming may increase competition, favor smaller size classes, and induce regime shifts that destabilize population and community dynamics.     

The duality of stability: towards a stochastic theory of species interactions

Understanding the dynamics of ecological systems using stability concepts has been a key driver in ecological research from the inception of the field. Despite the tremendous effort put into this area, progress has been limited due to the bewildering number of metrics used to describe ecological stability. Here, we seek to resolve some of the confusion by unfolding the dynamics of a simple consumer-resource interaction module. In what follows, we first review common dynamical metrics of stability (CV, eigenvalues). We argue using the classical type II consumer-resource model as an example where the empirical stability metric, CV, hides two different, but important, aspects of stability: (i) stability due to mean population density processes and (ii) stability due to population density variance processes. We then employ a simple stochastic consumer-resource framework in order to elucidate (i) when we expect these two different aspects of stability to arise in ecological systems and, importantly, highlight (ii) the fact that these two different aspects of stability respond differentially, but predictably, to changes in fundamental parameters that govern biomass flux and loss in any consumer-resource interaction (e.g., attack rates, carrying capacity, mortality).     

Spatial scaling of consumer-resource interactions in advection-dominated systems

Ecologists studying consumer-resource interactions in advection-dominated systems such as streams and rivers frequently seek to link the results of small-scale experiments with larger-scale patterns of distribution and abundance. Accomplishing this goal requires determining the characteristic scale, termed the response length, at which there is a shift from local dynamics dominated by advective dispersal to larger-scale dynamics dominated by births and deaths. Here, we model the dynamics of consumer-resource systems in a spatially variable, advective environment and show how consumer-resource interactions alter the response length relative to its single-species value. For one case involving a grazer that emigrates in response to high predator density, we quantify the changes using published data from small-scale experiments on aquatic invertebrates. Using Fourier analysis, we describe the responses of advection-dominated consumer-resource systems to spatially extended environmental variability in a way that involves explicit consideration of the response length. The patterns we derive for different consumer-resource systems exhibit important similarities in how component populations respond to spatial environmental variability affecting dispersal as opposed to demographic parameters.     

Constrained proteome allocation affects coexistence in models of competitive microbial communities

Microbial communities are ubiquitous and play crucial roles in many natural processes. Despite their importance for the environment, industry and human health, there are still many aspects of microbial community dynamics that we do not understand quantitatively. Recent experiments have shown that the structure and composition of microbial communities are intertwined with the metabolism of the species that inhabit them, suggesting that properties at the intracellular level such as the allocation of cellular proteomic resources must be taken into account when describing microbial communities with a population dynamics approach. In this work, we reconsider one of the theoretical frameworks most commonly used to model population dynamics in competitive ecosystems, MacArthur’s consumer-resource model, in light of experimental evidence showing how proteome allocation affects microbial growth. This new framework allows us to describe community dynamics at an intermediate level of complexity between classical consumer-resource models and biochemical models of microbial metabolism, accounting for temporally-varying proteome allocation subject to constraints on growth and protein synthesis in the presence of multiple resources, while preserving analytical insight into the dynamics of the system. We first show with a simple experiment that proteome allocation needs to be accounted for to properly understand the dynamics of even the simplest microbial community, i.e. two bacterial strains competing for one common resource. Then, we study our consumer-proteome-resource model analytically and numerically to determine the conditions that allow multiple species to coexist in systems with arbitrary numbers of species and resources.Subject terms: Biodiversity, Microbial ecology, Microbial ecology, Bacterial physiology     

Does species richness drive community production or vice versa? Reconciling historical and contemporary paradigms in competitive communities

Studies examining the relationship between species richness and the productivity of ecological communities have taken one of two opposite viewpoints, viewing either productivity as a primary driver of richness or richness as a driver of productivity. Recently, verbal and graphical hypotheses have been proposed that attempt to merge these perspectives by clarifying the causal pathways that link resource supply, species richness, resource use, and biomass production. Here we present mathematical models that formalize how these pathways can operate simultaneously in a single ecological system. Using a metacommunity framework in which classic consumer-resource competition theory governs species interactions within patches, we show that the mechanisms by which resource supply influences species richness are inherently linked to the mechanisms by which species richness controls resource use and biomass production. Unlike prior hypotheses, our models show that resource supply can affect species richness and that richness can affect productivity simultaneously at a single spatial scale. Our models also reproduce scale-dependent associations between species richness and community biomass that have been reported elsewhere. By detailing the pathways by which resource supply, species richness, biomass production, and resource use are connected, our models move closer to resolving the nature of causality in diversity-productivity relationships.     

A Consumer-Resource Approach to Community Structure

Because all species are consumers and all, eventually, are consumedby other species, consumer-resource interaction is one of themost fundamental processes of ecology. Simple models that includethe direct mechanisms of consumer-resource interactions maythus be the fundamental building-block for models of communitystructure. These models are easily extended to include suchcomplexity as the effects of physical limiting factors, spatialheterogeneity in resource supply, fluctuating resource supply,and multiple trophic levels. Each such modification places constraintson the traits of species that can persist. Consumer-resourcemodels make predictions about many aspects of community structure,including species richness, species composition, species dominance,population dynamics, morphological or physiological traits ofspecies, and patterns of phenotypic variation within species.Thus, each model affords numerous opportunities to test andmodify or reject it. A review of a variety of communities suggeststhat much of the structure of each community can be explainedby a relatively simple consumer-resource model, but that differentelements of complexity may be important in different communities.     

Trade-offs in community properties through time in a desert rodent community

Resource limitation represents an important constraint on ecological communities, which restricts the total abundance, biomass, and community energy flux a given community can support. However, the exact relationship among these three measures of biological activity remains unclear. Here we use a simple framework that links abundance and biomass with an energetic constraint. Under constant energetic availability, it is expected that changes in abundance and biomass can result from shifts in the distribution of individual masses. We test these predictions using long-term data from a desert rodent community. Total energy use for the community has not changed directionally for 25 years, but species composition has. As a result, the average body size has decreased by almost 50%, and average abundance has doubled. These results lend support to the idea of resource limitation on desert rodent communities and demonstrate that systems are able to maintain community energy flux in the face of environmental change, through changes in composition and structure.     

Opening the black box of plant nutrient uptake under warming predicts global patterns in community biomass and biological carbon storage

The effect of climate change on the amount of carbon stored in the different biological compartments of complex natural communities is relevant for a range of ecosystem functions and services. Temperature‐dependency of many physiological and ecological processes drives this storage capacity. As opposed to other physiological rates, the temperature‐dependence of nutrient uptake by plants has, to date, not been thoroughly investigated and therefore was not explicitly included in food web models. In a meta‐study, we extracted experimental data to establish the temperature‐dependence of the parameters determining plant nutrient uptake. Overall, we found an increase in the maximum uptake rate, as well as the half‐saturation density. As the respiration rates of plants (biomass loss) increase more strongly than the nutrient uptake rates (driving biomass gain under nutrient limitation), our results suggest that warming should decrease plant biomass. We applied these temperature‐dependent nutrient uptake rates by plants to a model of a three‐level food‐chain composed of two nutrients, a plant pool, and an herbivore pool. Having established plant nutrient uptake rates based on real data to replace the previously used assumption of logistic growth, we were able to use realistic natural nutrient deposition rates as the input variables in this model. This mechanistic model approach allowed us to show the quantitative responses of natural communities to realistic fertilization rates for the first time. We ran the model under realistic nutrient supply scenarios based on deposition data from the literature, adding a scenario of anthropogenic fertilization. We found decreases in overall community biomass with increasing temperature, but the intensity of this decrease varied strongly depending on the nutrient supply scenario. Our findings highlight the importance of including other global change drivers besides warming, as they can mediate the temperature impact on changes in global carbon storage and thus biomass‐related ecosystem services.     

Robustness of size–structure across ecological networks in pelagic systems

The study of biomass size distributions has become an important tool for addressing aquatic ecosystem complexity and the consequences of anthropogenic disturbances. However, it remains unclear how changes in pelagic food web topology affect the biomass size–structure. Employing a dynamic multispecies bioenergetic consumer-resource model, we simulated biomass trajectories over time in 10,000 virtual networks of varying topology to address which food web properties are important in determining size–structure in pelagic systems. The slopes of the normalized biomass size spectra (NBSS) and Pareto’s shape parameter (γ) of our modeled communities are consistent with theoretically expected values for steady-state systems and empirical values reported for several aquatic ecosystems. We found that the main drivers of the NBSS slope and Pareto’s γ were the slope of the relationship between body mass and trophic level, the maximum trophic level of the food web, and the stability of total community biomass. Our analyses showed a clear conservative trend in pelagic community size–structure as demonstrated by the robustness of the NBSS slope and Pareto’s γ against most of the topological changes in virtual networks. Nevertheless, these analyses also caution that major disturbances in large-bodied or top-trophic level individuals may disrupt this stable pattern.     

Biomass and structure of planktonic communities along an air temperature gradient in subarctic Sweden

1. Air temperature will probably have pronounced effects on the composition of plankton communities in northern lake ecosystems, either via indirect effects on the export of essential elements from catchments or through direct effects of water temperature and the ice‐free period on the behaviour of planktonic organisms. 2. We assessed the role of temperature by comparing planktonic communities in 15 lakes along a 6 °C air temperature gradient in subarctic Sweden. 3. We found that the biomass of phytoplankton, bacterioplankton and the total planktonic biomass were positively related to air temperature, probably as a result of climatic controls on the export of nitrogen from the catchment (which affects phytoplankton biomass) and dissolved organic carbon (affecting bacterioplankton biomass). 4. The structure of the zooplankton community, and top down effects on phytoplankton, were apparently not related to temperature but mainly to trophic interactions ultimately dependent on the presence of fish in the lakes. 5. Our results suggest that air temperature regimes and long‐term warming can have strong effects on the planktonic biomass in high latitude lakes. Effects of temperature on the structure of the planktonic community might be less evident unless warming permits the invasion of fish into previous fishless lakes.     

Responses of moist non-acidic arctic tundra to altered environment: productivity, biomass, and species richness

In arctic Alaska, researchers have manipulated air temperature, light availability, and soil nutrient availability in several tundra communities over the past two decades. These communities responded quite differently to the same manipulations, and species responded individualistically within communities and among sites. For example, moist acidic tundra is primarily nitrogen (N)‐limited, whereas wet sedge tundra is primarily phosphorus (P)‐limited, and the magnitude of growth responses varies across sites within communities. Here we report results of four years of manipulated nutrients (N and/or P) and/or air temperature in an understudied, diverse plant community, moist non‐acidic tussock tundra, in northern Alaska. Our goals were to determine which factors limit above‐ground net primary productivity (ANPP) and biomass, how community composition changes may affect ecosystem attributes, and to compare these results with those from other communities to determine their generality. Although relative abundance of functional groups shifted in several treatments, the only significant change in community‐level ANPP and biomass occurred in plots that received both N and P, driven by an increase in graminoid biomass and production resulting from a positive effect of adding N. There was no difference in community biomass among any other treatments; however, some growth forms and individual species did respond. After four years no one species has come to dominate the treatment plots and species richness has not changed. These results are similar to studies in dry heath, wet sedge, and moist acidic tundra where community biomass had the greatest response to both N and P and warming results were more subtle. Unlike in moist acidic tundra where shrub biomass increased markedly with fertilization, our results suggest that in non‐acidic tundra carbon sequestration in plant biomass will not increase substantially under increased soil nutrient conditions because of the lack of overstory shrub species.     

淡水湖泊浮游藻类对富营养化和气候变暖的响应

水体富营养化和气候变暖是淡水生态系统面临的两大威胁。文章分别阐述了富营养化和气候变暖对淡水湖泊浮游藻类直接和间接效应, 并总结气候变暖可能通过影响水体理化性质、水生植物组成、食物链结构从而直接或间接改变浮游藻类生物量或群落结构。作者重点分析了气候变暖下湖泊生态系统蓝藻水华暴发机制, 比较了不同湖泊蓝藻对气候变暖和富营养化响应的异同点, 发现气候变暖和富营养化对湖泊生态系统影响存在相似性, 表现在均促进湖泊由清水-浊水稳态转变、增加蓝藻水华发生频率和强度。然而二者对湖泊浮游藻类影响的相对重要性取决于分层型湖泊和混合型湖泊的差异性、不同营养型湖泊和不同类群蓝藻组成差异性。作者认为, 开展气候变暖和富营养化下, 湖泊浮游藻类功能群响应研究亟待进行。     

Size‐based ecological interactions drive food web responses to climate warming

Predicting climate change impacts on animal communities requires knowledge of how physiological effects are mediated by ecological interactions. Food‐dependent growth and within‐species size variation depend on temperature and affect community dynamics through feedbacks between individual performance and population size structure. Still, we know little about how warming affects these feedbacks. Using a dynamic stage‐structured biomass model with food‐, size‐ and temperature‐dependent life history processes, we analyse how temperature affects coexistence, stability and size structure in a tri‐trophic food chain, and find that warming effects on community stability depend on ecological interactions. Predator biomass densities generally decline with warming – gradually or through collapses – depending on which consumer life stage predators feed on. Collapses occur when warming induces alternative stable states via Allee effects. This suggests that predator persistence in warmer climates may be lower than previously acknowledged and that effects of warming on food web stability largely depend on species interactions.     

Experimental whole‐stream warming alters community size structure

How ecological communities respond to predicted increases in temperature will determine the extent to which Earth's biodiversity and ecosystem functioning can be maintained into a warmer future. Warming is predicted to alter the structure of natural communities, but robust tests of such predictions require appropriate large‐scale manipulations of intact, natural habitat that is open to dispersal processes via exchange with regional species pools. Here, we report results of a two‐year whole‐stream warming experiment that shifted invertebrate assemblage structure via unanticipated mechanisms, while still conforming to community‐level metabolic theory. While warming by 3.8 °C decreased invertebrate abundance in the experimental stream by 60% relative to a reference stream, total invertebrate biomass was unchanged. Associated shifts in invertebrate assemblage structure were driven by the arrival of new taxa and a higher proportion of large, warm‐adapted species (i.e., snails and predatory dipterans) relative to small‐bodied, cold‐adapted taxa (e.g., chironomids and oligochaetes). Experimental warming consequently shifted assemblage size spectra in ways that were unexpected, but consistent with thermal optima of taxa in the regional species pool. Higher temperatures increased community‐level energy demand, which was presumably satisfied by higher primary production after warming. Our experiment demonstrates how warming reassembles communities within the constraints of energy supply via regional exchange of species that differ in thermal physiological traits. Similar responses will likely mediate impacts of anthropogenic warming on biodiversity and ecosystem function across all ecological communities.     

Linking phytoplankton community metabolism to the individual size distribution

Quantifying variation in ecosystem metabolism is critical to predicting the impacts of environmental change on the carbon cycle. We used a metabolic scaling framework to investigate how body size and temperature influence phytoplankton community metabolism. We tested this framework using phytoplankton sampled from an outdoor mesocosm experiment, where communities had been either experimentally warmed (+ 4 °C) for 10 years or left at ambient temperature. Warmed and ambient phytoplankton communities differed substantially in their taxonomic composition and size structure. Despite this, the response of primary production and community respiration to long‐ and short‐term warming could be estimated using a model that accounted for the size‐ and temperature dependence of individual metabolism, and the community abundance‐body size distribution. This work demonstrates that the key metabolic fluxes that determine the carbon balance of planktonic ecosystems can be approximated using metabolic scaling theory, with knowledge of the individual size distribution and environmental temperature.