Experimental evidence that soil heterogeneity enhances plant diversity during community assembly

Williams, Brandon M.; Houseman, Gregory R.

doi:10.1093/jpe/rtt056

Cited by 49 publications

(64 citation statements)

References 43 publications

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“…We found a marginally significant positive effect of heterogeneity on invader establishment at the scale of individual plants, consistent with the theoretical prediction. These results are consistent with experimental tests manipulating soil texture, which found higher heterogeneity led to greater plant community diversity (Williams & Houseman ). If heterogeneity in the soil is plant‐induced, perhaps influenced by factors such as soil pathogens or soil texture, this might increase coexistence to a greater degree than nutrient heterogeneity.…”

Section: Discussionsupporting

confidence: 89%

Heterogeneity in plant–soil feedbacks and resident population dynamics affect mutual invasibility

Burns

Brandt

2014

Journal of Ecology

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Summary1. Understanding the mechanisms governing coexistence is a central goal in ecology and has implications for conserving and restoring communities, yet the high diversity in many plant communities is difficult to explain. Theory suggests that plant-soil feedbacks (PSF) can lead to frequency-dependent coexistence by suppressing conspecifics more than heterospecifics, potentially helping to explain high-diversity plant communities. In addition, species-specific population dynamics, including the rate at which individuals are replaced in a population or population turnover rate, may influence coexistence outcomes. 2. We have created a rigorous test of the coexistence predictions of theory by generating a soil heterogeneity experiment in the field and testing for mutual invasibility by establishing resident populations, then experimentally invading them. Experimental tests of mutual invasibility can demonstrate coexistence because, if species are able to invade one another's populations when at low density, they should exhibit long-term coexistence. We use pairs of congeners in this experiment that coexist at small spatial scales, sometimes within cm, at our field site. 3. We demonstrate that invader individuals established better in congener's soils than in conspecific soils, consistent with plant-soil feedback mediated coexistence. This effect was often mediated by competition with established resident plants. 4. Further, we show that soil heterogeneity interacted with the population turnover rate of the resident population to influence invasibility (P < 0.10), consistent with the theoretical prediction that a plant's population dynamics will interact with heterogeneity to influence coexistence. 5. Synthesis. Plant-soil feedbacks (PSF) can in theory lead to frequency-dependent coexistence, and reciprocally, negative feedback effects in glasshouse experiments are often consistent with this prediction. We provide the first field test of mutual invasibility structured by PSF, demonstrating that PSF can lead to coexistence when they create a patchy, or heterogeneous, soil environment. This work suggests that understanding the influence of PSF on diversity necessitates understanding the spatial scale at which soil heterogeneity emerges in the field. Thus, high diversity might be maintained in plant communities by heterogeneity created by plants' influence on the soil, and this outcome depends strongly on population dynamics.

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Section: Discussionsupporting

confidence: 89%

Heterogeneity in plant–soil feedbacks and resident population dynamics affect mutual invasibility

Burns

Brandt

2014

Journal of Ecology

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“…S3). This response is consistent with species sorting patterns found after two years of community assembly (Williams and Houseman ). However, species spatially associating with SPTs did not always correspond with differences in spatial aggregation between soil treatments, suggesting that aggregation was primarily influenced by endogenous processes.…”

Section: Discussionsupporting

confidence: 89%

“…, Hart and Marshall ). We found that after four years of community assembly, species richness in the homogenous and heterogeneous plots was equivalent despite a clear richness difference detected after two years of community assembly (Williams and Houseman ). Potentially, the development of endogenously driven spatial structure may have led to a convergence in species richness between the homogeneous and heterogeneous soil treatments.…”

Section: Discussionmentioning

confidence: 63%

“…). Multivariate analysis from Williams and Houseman () from the same plots indicated significantly higher soil variability in heterogeneous than homogenous plots. The individual strata differed in clay content (upper, 11.63% ± 0.23%; middle, 11.93% ± 0.22%; lower, 12.93% ± 0.31%; mixed, 11.88% ± 0.13%), organic matter (upper, 2.78% ± 0.08%; middle, 1.54% ± 0.05%; lower, 1.22% ± 0.04%; mixed, 1.81% ± 0.04%), and pH (upper, 5.59 ± 0.03; middle, 5.22 ± 0.02; lower, 5.09 ± 0.01; mixed, 5.35 ± 0.01; values are means ± 1 SE).…”

Section: Methodsmentioning

confidence: 94%

“…Here we define exogenous factors as those processes that are not dependent on the resident plant community and likely to include soil heterogeneity prior to plant colonization, immigration from outside the community, or disturbances. In this experiment soil heterogeneity was effectively introduced with significant differences in soil texture, organic content, and pH observed in the three soil patch types after plot establishment (Williams and Houseman ). We found that exogenous soil heterogeneity had small effects on spatial aggregation relative to endogenous processes.…”

Section: Discussionmentioning

confidence: 99%

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Effect of soil heterogeneity and endogenous processes on plant spatial structure

Schouten

Houseman

2019

Ecology

Self Cite

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Within communities, organisms potentially self‐organize through endogenous processes that create nonrandom spatial structure as they interact with one another or modify the abiotic environment. In contrast, exogenous processes such as environmental heterogeneity or variable immigration are thought to be dominant processes controlling these spatial patterns. Although both endogenous and exogenous processes likely occur, their relative importance is still largely unknown because of limited analytical tools and the lack of experimental evidence, particularly those that address exogenous sources of environmental heterogeneity. Here, we used a soil heterogeneity experiment to examine the relative effect of endogenous and exogenous processes on plant spatial structure after five years of community assembly. Soil heterogeneity was manipulated by splitting the vertical soil profile into three soil‐types that were randomly assigned to 40 × 40 cm patches within 2.4 × 2.4 m plots. Homogeneous plots were created by mixing all soils before filling each patch. Thirty‐four grassland species were then sown into all plots and allowed to grow for five years after which the location of all plants was mapped using a 5 × 5 cm grid. Results from point‐pattern spatial analysis indicated that, even in the absence of soil heterogeneity and with initial seed arrival, spatial structure was primarily generated by endogenous processes. Although soil heterogeneity increased species aggregation at certain scales, most of the spatial structure was created by endogenous processes. These results suggest that endogenous processes may be more important than expected for generating spatial structure and can develop much faster than anticipated.

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Soil heterogeneity increases plant diversity after 20 years of manipulation during grassland restoration

Baer

Adams

Scott

et al. 2019

Ecological Applications

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The “environmental heterogeneity hypothesis” predicts that variability in resources promotes species coexistence, but few experiments support this hypothesis in plant communities. A previous 15‐yr test of this hypothesis in a prairie restoration experiment demonstrated a weak effect of manipulated soil resource heterogeneity on plant diversity. This response was attributed to a transient increase in richness following a post‐restoration supplemental propagule addition, occasionally higher diversity under nutrient enrichment, and reduced cover of a dominant species in a subset of soil treatments. Here, we report community dynamics under continuous propagule addition in the same experiment, corresponding to 16–20 yr of restoration, in response to altered availability and heterogeneity of soil resources. We also quantified traits of newly added species to determine if heterogeneity increases the amount and variety of niches available for new species to exploit. The heterogeneous treatment contained a factorial combination of altered nutrient availability and soil depth; control plots had no manipulations. Total diversity and richness were higher in the heterogeneous treatment during this 5‐yr study due to higher cover, diversity, and richness of previously established forbs, particularly in the N‐enriched subplots. All new species added to the experiment exhibited unique trait spaces, but there was no evidence that heterogeneous plots contained a greater variety of new species representing a wider range of trait spaces relative to the control treatment. The richness and cover of new species was higher in N‐enriched soil, but the magnitude of this response was small. Communities assembling under long‐term N addition were dominated by different species among subplots receiving added N, leading to greater dispersion of communities among the heterogeneous relative to control plots. Contrary to the deterministic mechanism by which heterogeneity was expected to increase diversity (greater variability in resources for new species to exploit), higher diversity in the heterogeneous plots resulted from destabilization of formerly grass‐dominated communities in N‐enriched subplots. While we do not advocate increasing available soil N at large scales, we conclude that the positive effect of environmental heterogeneity on diversity can take decades to materialize and depend on development of stochastic processes in communities with strong establishment limitation.

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Experimental evidence that soil heterogeneity enhances plant diversity during community assembly

Cited by 49 publications

References 43 publications

Heterogeneity in plant–soil feedbacks and resident population dynamics affect mutual invasibility

Heterogeneity in plant–soil feedbacks and resident population dynamics affect mutual invasibility

Effect of soil heterogeneity and endogenous processes on plant spatial structure

Soil heterogeneity increases plant diversity after 20 years of manipulation during grassland restoration

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