Plant-soil feedback

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Introduction

Plant–soil feedback: experimental approaches, statistical analyses and ecological interpretations. Journal of Ecology Volume 98, Issue 5, pages 1063-1073, 13 JUL 2010 DOI: 10.1111/j.1365-2745.2010.01695.x.

Definition

Plant influences on biotic and abiotic soil properties may alter the soil’s ability to support these same individuals, other individuals of the same species or other plant species. Changes to soil properties that are caused by plants, which in turn influence the performance of plants are termed ‘plant–soil feedbacks’ (Putten et al., 2013).

In plant-soil systems, a plant-induced change in the composition and activity of the soil’s biotic, physical or chemical properties, and/or the rates of ecosystem processes, directly affect the plants. Through changes in the demography of the plant population and/or the physiological activity of the individual plants, the plant’s effect on the soil conditions increases (positive feedback) or decreases (negative feedback) (Ehrenfeld et al., 2005).

Basic approaches

The basic idea of plant–soil feedback experiments is that plants first influence the composition of the soil community, which is called soil conditioning. Then, the effects of conditioning are evaluated by assessing soil effects on subsequent plant growth.

The earlier experiments testing plant–soil feedback effects were started from natural field-sampled soil. The strength of this method is that plants have influenced the soil for a long period of time under natural conditions. However, the weakness of this approach is that soils may differ in the composition of the soil community and abiotic properties.

A following developed approach was that plant species were grown in living soils to develop a soil community, which is the conditioning phase, followed by a test phase in which the growth response on changed biotic conditions was tested (Figure 1). The strength of this two-phase plant–soil feedback approach is that the effects are less dependent on possible side effects of local differences in abiotic soil conditions and that the plant species influencing the soil is controlled. But a potential weakness is that a different soil community may develop in pots under greenhouse conditions than in the field. And the growth responses in the feedback phase can be due to nutrient depletion in the first phase (Pernilla Brinkman et al., 2010).

History and importance

More than 2000 years ago in both Europe and Asia, it was known that fruit trees were subject to replanting failures when young trees were planted where conspecifics or congeners had grown. For more than 1000 years, humans have been aware of, and managed, plant–soil feedbacks in agriculture and horticulture. In agricultural settings, plant–soil feedbacks most often involves soil nutrient depletion or the build-up of species-specific, soil-borne pathogens. Rotational cropping systems were developed to reduce failures of crop establishment and to increase productivity. Ecologists have benefited greatly from insights into agricultural practices and the early knowledge about plant-pest and pathogen inter-actions (Putten et al., 2013).

Interest in plant–soil feed-backs has increased in the past 10 years. And many exciting results are released. Plant–soil feedbacks is becoming an important concept for explaining vegetation dynamics, the invasiveness of introduced exotic species in new habitats and how terrestrial ecosystems respond to global land use and climate change.

Factors that influence the results of plant-soil feedback

Physical factors

Water: The potential for feedback involving water comes from the capacity of plants to alter the distribution and amount of water in the soil, potentially affecting their growth and reproduction. These pathways can cause successional change driven by plant response to changing soil moisture conditions or by the maintenance of stable plant assemblages stemming from increased soil moisture.

Soil aggregation results from a variety of root-mediated processes, including wet-dry cycles enhanced by plant water uptake, the physical pressures exerted by roots growing through cracks, and the direct effect of roots and their associated mycorrhizae in binding soil minerals together. Roots affect aggregation through plant carbon (C)-based microbial growth, the production of plant and microbial mucilages, the presence of phenolic compounds in root exudates, and the overall input of SOM. Feedback between plants and the physical properties of soils arise from the promotion of aggregates by roots and root-associated microorganisms.

Soil temperature affects root growth, water availability, and microbial activity, thus affecting both nutrient cycling and soil respiration.

Chemical factors

pH: Plants are an important factor in the acidification of soils through several pathways including the generation of carbonic acid from root and root-supported microbial respiration, the leaching of organic acids, and imbalances in the uptake of positive and negative ions. It is generally presumed that the pathways of soil acidification involve feedbacks: plant-induced acidification promotes conditions under which only acidophiles can live.

Oxygen: Wetland plants are well known for their ability to release oxygen from their roots, thereby modifying the sequence of redox reactions that characterize anoxic soils. Wetland species vary greatly in the extent of root oxygen loss and their tolerance for reduced chemical conditions. These plant generated effects on soil chemistry are presumed to be part of a feedback cycle.

Carbon and nitrogen cycle: The interplay among plant species, plant communities, N and C cycling has generated more discussion of feedback in the soil-plant system than any other topic. Frequently proposed feedback mechanisms include the linkage of decomposition and mineralization rates, the linkage between chemical forms of N and their up-take by plants, competition between microbes and plants for N, and plant-mediated effects on ecosystem inputs and outputs. There are also multiple pathways of feedback between plants and soil C, operating over a wide range of temporal and spatial scales and often operating through complex (multifactor) pathways.

Niche

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Microbial processes

What microbial processes are important for this microbial interaction? Does this microbial interaction have some ecosystem-level effects? Does this interaction affect the environment in any way? Describe critical microbial processes or activities that are important in this interaction, adding sections/subsections as needed. Look at other topics in MicrobeWiki. Are some of these processes already described? Create links where relevant.

Key Microorganisms

What specific kinds of microbes are typically involved in this interaction? Or associated with important processes? Describe key groups (genera, species) of microbes that we find in this environment, and any special adaptations they may have evolved to survive in this environment. List examples of specific microbes that represent key groups or are associated with important processes found in this environment. Add sections/subsections as needed. Look at other microbe listings in MicrobeWiki. Are some of the groups of microbes from your environment already described? Create links to other MicrobeWiki pages where possible.

Current Research

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References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Edited by <your name>, a student of Angela Kent at the University of Illinois at Urbana-Champaign.