Jonathan R. De Long

Contrasting Responses of Soil Microbial and Nematode Communities to Warming and Plant Functional Group Removal Across a Post-fire Boreal Forest Successional Gradient

Global warming is causing increases in surface temperatures and has the potential to influence the structure of soil microbial and faunal communities. However, little is known about how warming interacts with other ecosystem drivers, such as plant functional groups or changes associated with succession, to affect the soil community and thereby alter ecosystem functioning. We investigated how experimental warming and the removal of plant functional groups along a post-fire boreal forest successional gradient impacted soil microbial and nematode communities. Our results showed that warming altered soil microbial communities and favored bacterial-based microbial communities, but these effects were mediated by mosses and shrubs, and often varied with successional stage. Meanwhile, the nematode community was generally unaffected by warming and was positively affected by the presence of mosses and shrubs, with these effects mostly independent of successional stage. These results highlight that different groups of soil organisms may respond dissimilarly to interactions between warming and changes to plant functional groups, with likely consequences for ecosystem functioning that may vary with successional stage. Due to the ubiquitous presence of shrubs and mosses in boreal forests, the effects observed in this study are likely to be significant over a large proportion of the terrestrial land surface. Our results demonstrate that it is crucial to consider interactive effects between warming, plant functional groups, and successional stage when predicting soil community responses to global climate change in forested ecosystems.

Crossing the threshold: the power of multi-level experiments in identifying global change responses.

Crossing the threshold : the power of multi-level experiments in identifying global change responses.

A test of the hierarchical model of litter decomposition

Our basic understanding of plant litter decomposition informs the assumptions underlying widely applied soil biogeochemical models, including those embedded in Earth system models. Confidence in projected carbon cycle–climate feedbacks therefore depends on accurate knowledge about the controls regulating the rate at which plant biomass is decomposed into products such as CO2. Here we test underlying assumptions of the dominant conceptual model of litter decomposition. The model posits that a primary control on the rate of decomposition at regional to global scales is climate (temperature and moisture), with the controlling effects of decomposers negligible at such broad spatial scales. Using a regional-scale litter decomposition experiment at six sites spanning from northern Sweden to southern France—and capturing both within and among site variation in putative controls—we find that contrary to predictions from the hierarchical model, decomposer (microbial) biomass strongly regulates decomposition at regional scales. Furthermore, the size of the microbial biomass dictates the absolute change in decomposition rates with changing climate variables. Our findings suggest the need for revision of the hierarchical model, with decomposers acting as both local- and broad-scale controls on litter decomposition rates, necessitating their explicit consideration in global biogeochemical models.Accurate understanding of plant litter decomposition is vital to inform Earth system modelling. Here the dominant hierarchical model for plant litter decomposition is found to be wanting, and revisions are suggested.

Effects of elevation and nitrogen and phosphorus fertilization on plant defence compounds in subarctic tundra heath vegetation

Plant chemical and structural defence compounds are well known to impact upon herbivory of fresh leaves and influence decomposition rates after leaf senescence. A number of theories predict that al ...

Predicting the structure of soil communities from plant community taxonomy, phylogeny, and traits

There are numerous ways in which plants can influence the composition of soil communities. However, it remains unclear whether information on plant community attributes, including taxonomic, phylogenetic, or trait-based composition, can be used to predict the structure of soil communities. We tested, in both monocultures and field-grown mixed temperate grassland communities, whether plant attributes predict soil communities including taxonomic groups from across the tree of life (fungi, bacteria, protists, and metazoa). The composition of all soil community groups was affected by plant species identity, both in monocultures and in mixed communities. Moreover, plant community composition predicted additional variation in soil community composition beyond what could be predicted from soil abiotic characteristics. In addition, analysis of the field aboveground plant community composition and the composition of plant roots suggests that plant community attributes are better predictors of soil communities than root distributions. However, neither plant phylogeny nor plant traits were strong predictors of soil communities in either experiment. Our results demonstrate that grassland plant species form specific associations with soil community members and that information on plant species distributions can improve predictions of soil community composition. These results indicate that specific associations between plant species and complex soil communities are key determinants of biodiversity patterns in grassland soils.

Local plant adaptation across a subarctic elevational gradient

Predicting how plants will respond to global warming necessitates understanding of local plant adaptation to temperature. Temperature may exert selective effects on plants directly, and also indirectly through environmental factors that covary with temperature, notably soil properties. However, studies on the interactive effects of temperature and soil properties on plant adaptation are rare, and the role of abiotic versus biotic soil properties in plant adaptation to temperature remains untested. We performed two growth chamber experiments using soils and Bistorta vivipara bulbil ecotypes from a subarctic elevational gradient (temperature range: ±3°C) in northern Sweden to disentangle effects of local ecotype, temperature, and biotic and abiotic properties of soil origin on plant growth. We found partial evidence for local adaption to temperature. Although soil origin affected plant growth, we did not find support for local adaptation to either abiotic or biotic soil properties, and there were no interactive effects of soil origin with ecotype or temperature. Our results indicate that ecotypic variation can be an important driver of plant responses to the direct effects of increasing temperature, while responses to covariation in soil properties are of a phenotypic, rather than adaptive, nature.

How anthropogenic shifts in plant community composition alter soil food webs

There are great concerns about the impacts of soil biodiversity loss on ecosystem functions and services such as nutrient cycling, food production, and carbon storage. A diverse community of soil organisms that together comprise a complex food web mediates such ecosystem functions and services. Recent advances have shed light on the key drivers of soil food web structure, but a conceptual integration is lacking. Here, we explore how human-induced changes in plant community composition influence soil food webs. We present a framework describing the mechanistic underpinnings of how shifts in plant litter and root traits and microclimatic variables impact on the diversity, structure, and function of the soil food web. We then illustrate our framework by discussing how shifts in plant communities resulting from land-use change, climatic change, and species invasions affect soil food web structure and functioning. We argue that unravelling the mechanistic links between plant community trait composition and soil food webs is essential to understanding the cascading effects of anthropogenic shifts in plant communities on ecosystem functions and services.

Soil Biota as Drivers of Plant Community Assembly

Evidence is accumulating that belowground soil organisms are strong drivers of the aboveground plant community. In this chapter, we examine how soil communities influence plant community assembly through priority effects, soil legacy effects, and niche modification. We discuss how different functional groups of soil organisms drive competitive interactions, species coexistence, and species turnover. We then explore how primary and secondary successional trajectories can be altered by soil communities and delve into the mechanisms by which soil communities can affect ecosystem restoration and biodiversity conservation. Finally, we discuss the role of soil biota in plant invasion and range expansion and how soil biota interact with global environmental changes to affect plant community composition. We conclude by outlining knowledge gaps and propose potential avenues for addressing these gaps via upscaling of measurements, enhanced experimental design, and the utilization of plant and soil organism traits.

Plant Communities as Modulators of Soil Carbon Storage

Abstract In this chapter, we evaluate the role of various plant community attributes as determinants of soil carbon cycling and storage. We firstly consider how vegetation composition influences carbon uptake, the molecular forms and stabilization of soil carbon, and losses of carbon while highlighting contrasts across vegetation types. We then discuss the various roles of the soil microbial community in these processes, consider the importance of diurnal and seasonal cycles, and the potential effect of climate change on soil carbon cycling and storage. We also provide case studies to illustrate the mechanisms by which vegetation composition impacts soil carbon storage and identify important gaps in vegetation models that seek to predict soil carbon dynamics at regional and global scales.

Using plant, microbe, and soil fauna traits to improve the predictive power of biogeochemical models

ELF is supported by the NERC Soil Security Programme (NE/P013708/1); JRD and BGJ by the UK Biotechnology and Biological Sciences Research Council (BBSRC) (Grants BB/I009000/2 and BB/I009183/1). DJ receives partial support from the N8 AgriFood programme. This work was supported by a BBSRC International Partnering award (BB/L026759/1) to EB, DJ, RB and PS.