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The last few years have seen a substantial increase in research activity in the area of soil carbon (C) dynamics and into the role that soils play in the global C cycle and climate change. This interest has arisen because soils absorb and release greenhouse gases, including carbon dioxide and methane, and act as a major global C reservoir, storing some 80% of the Earth’s terrestrial C stock (IPCC 2007). Despite the importance of soils for C cycling, remarkably little is known about the factors that regulate the fluxes of C to and from soil, or about the role that interactions between plants and soil biota play in regulating soil C cycling (Högberg & Read 2006; Bardgett, Freeman & Ostle 2008; De Deyn, Cornelissen & Bardgett 2008).

This Journal of Ecology Special Feature, which consists of six papers, explores recent advances in understanding about the ways in which plant traits, and changes in vegetation composition and diversity, influence soil C dynamics via interactions with soils and their biota. It was generated by bringing together scientists with different expertise in ecosystem C dynamics at the 2008 Annual Meeting of the British Ecological Society, held at Imperial College London. Experts ranged from those working on plant physiological controls on C dynamics at local scales, to those exploring how major shifts in vegetation might feedback on soil C cycling at regional and global scales. The six papers address a wide range of questions about plant–soil interactions and the C cycle, and illustrate some of the major advances that have been made and challenges that remain in this rapidly growing field.

As highlighted by Chapin et al. (2009) in the first paper of this Special Feature, the last few years have witnessed an explosion of studies into the genetic, ecological and biogeochemical dynamics of C cycling processes in soils. These studies include investigations into plant and rhizosphere effects on soil respiration, effects of soil microbial communities on plant productivity and soil C turnover, and interactions among element cycles, for instance between nitrogen (N), phosphorus (P) and C. However, current models of the global C cycle seldom include these processes; rather, they simply treat net C emissions from ecosystems as the balance between net primary production (NPP) and heterotrophic respiration. In their paper, Chapin et al. (2009) challenge this approach by illustrating how recent advances in biogeochemical understanding of C cycling, especially in the area of soil microbial processes, could greatly improve the representation of ecosystem C dynamics in C cycle models. Moreover, they identify critical gaps in the modelling of ecosystem–climate feedbacks. These gaps include the role of nutrient and other controls that couple photosynthetic C input to respiratory C outputs, and the role of non-CO2 C fluxes that influence the climate system.

A similar theme is developed by Ostle et al. (2009), but in the context of dynamic global vegetation models (DGVMs), which are used to predict impacts of global change on terrestrial ecosystem C cycling and feedbacks to climate change. In their paper, Ostle et al. (2009) describe the general structure of DGVMs that use plant functional type classifications as a means to integrate plant–soil interactions into predictions, and illustrate how models have developed in recent years to enhance the simulation of soil C and N dynamics and impacts of global change in the form of drought and vegetation dynamics. Ostle et al. (2009) also identify ecological weaknesses within these models and the need to address these weaknesses through the evaluation of model representations of key plant–soil interactions.

The other four papers in this Special Feature report on experimental studies that address very different questions related to plant–soil interactions and carbon cycling. These papers can be broadly divided into two themes. The studies of De Deyn et al. (2009) and Klumpp et al. (2009) address how attributes of plant communities influence the input and cycling of C and N in soils, whereas the studies of Ayres et al. (2009) and Lang et al. (2009) consider controls on decomposition processes in natural ecosystems. These papers demonstrate the many forms of plant–soil interactions that regulate both the input of C to soils and its loss via decomposition processes. For instance, De Deyn et al. (2009) used model plant communities to examine the ways in which variations in plant species and functional group richness and composition influence the storage and loss of C and N from soil, showing that responses were related to the presence and biomass of certain plant species, notably N fixers and forbs. Klumpp et al. (2009) used a mesocosm approach coupled with stable isotope (13C-CO2) labelling to identify the sequence of events involved in grazer effects on soil carbon dynamics, including interactions between plant roots, microbial communities and soil organic matter fractions.

In terms of decomposition processes, Lang et al. (2009) examined links between decomposition rates and chemical traits of sub-arctic bryophytes, lichens and vascular plants, yielding important insights for understanding how shifts in vegetation composition, for instance caused by global change, might affect decomposition. Ayres et al. (2009) also studied controls on decomposition, but in their case they tested the idea of home field advantage, namely that leaf litter decomposes more rapidly beneath the plant species it is derived from than it does beneath different plant species. This ‘home field’ advantage has been observed in several previous studies, including a recent paper in the Journal of Ecology (Vivanco & Austin 2008). However, Ayres et al. (2009) show for the first time that soil communities actually specialize in decomposing the litter produced by the plant species above them. This observation illustrates the fine-tuning that can occur at local scales between plant species and their associated soil biota, with consequences for plant nutrient supply and ecosystem function.

The recent explosion of studies into the ecology and biogeochemistry of C cycling processes in soils has greatly advanced understanding, and the examples included in this Special Feature illustrate some of the major advances that have been made, and challenges that still remain, in this rapidly growing field. Perhaps the biggest challenge is that identified by Chapin et al. (2009), namely the need to use this advancing understanding of plant and soil microbial processes involved in C cycling to improve representation of ecosystem C dynamics in C cycle models, without rendering them too complex to make global-scale predictions (Ostle et al. 2009). We hope that the papers included in this Special Feature will help in tackling this challenge.

Acknowledgements

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  2. Acknowledgements
  3. References

We thank the British Ecological Society for the funding and organisation of the Thematic Topic that led to this Special Feature.

References

  1. Top of page
  2. Acknowledgements
  3. References