Testing predictions of a three‐species plant–soil feedback model

Abstract

Summary 1.A growing number of experiments measure plant growth on soils cultivated by different species. Models show that the resulting plant-soil feedbacks (PSFs) can determine plant abundance and persistence; yet, quantitative tests of their importance in community dynamics are lacking.2. Here, we use the growth of eight plant species on 'self' and 'other' soils to parameterize a threespecies PSF model. Predictions from the parameterized model were compared to plant growth observed in a 3-month glasshouse experiment. Four types of three-species communities were simulated: native, non-native, nitrogen-fixing and non-nitrogen-fixing. Because the PSF model is founded on a competition model, removing PSF effects from the model allowed us to compare PSF model predictions to competition model predictions. 3. Mean plant biomass differed among soil types by 20% and differed among plant species by 101%. 4. The PSF model correctly predicted rank abundance in the four communities tested while the competition model correctly predicted rank abundance in the two communities with nitrogen-fixing plants. Furthermore, PSF model predictions of species abundances were closer to observed values than competition model predictions. Despite consistently improving upon the competition model, predictions from the PSF model were significantly different from observed values for three of four communities. Competition model predictions were different from observed values for all four communities. 5. Our three-species model described the plant and soil conditions that allow coexistence and competitive exclusion, but when parameterized with experimental data, no communities were predicted to result in long-term coexistence. 6. Synthesis. Results suggest that PSFs captured a mechanism of plant community development. However, because improvements in model predictions were consistently small, either PSFs were not a dominant mechanism determining plant community development or PSFs were underestimated by our experimental or modelling approaches. Further testing of PSFs and development of improved methods to measure PSFs are suggested.

Plant–soil feedbacks provide an additional explanation for diversity–productivity relationships

“…However, in contrast to previous continuous-time models [14,[16][17][18], we use a discrete-time approach that provides specific estimates of plant and soiltype biomass (e.g. A and SA; table 1) and is easily implemented in a spreadsheet.…”

“…The growth of each soil type is a function of the abundance and the growth of the plant that cultivates it. Finally, each plant grows at a rate that is specific to each soil type [18].…”

“…both positive and negative plant-soil interactions [14][15][16][17]). There is extensive conceptual and empirical support for the role of PSFs in processes of plant community development such as succession, invasion, abundance, persistence and diversity [14,16,18]. However, one problem for understanding the role of PSFs in diversityproductivity relationships is that current PSF models simulate plant proportional abundance, not plant biomass [15,16,18].…”

“…As a result, current PSF models do not provide insight into plant productivity. A second problem is that current models are limited to two-and three-species systems and so do not allow insight across a range of diversities [14,[16][17][18]. Finally, PSF models have not been parameterized and tested, so their importance to plant productivity and community development remains largely untested (but see Kulmatiski et al [18]).…”

Plant–soil feedbacks promote negative frequency dependence in the coexistence of two aridland grasses

“…Our competition modelling focusing on per capita effects also confirmed this result, showing the strongest self-limitation in B. gracilis inoculated with its own, live, rhizospheric microbes. Prior work correlating the strength of PSF with species relative abundance [12,13] as well as pairwise studies examining PSF under competitor present/absent scenarios [16][17][18]46] set the stage for PSF as a potential driver of plant community dynamics, but do not wholly demonstrate it as a stabilizing mechanism that increases self-limitation. In addition, while negative conspecific density-or distance-dependent effects on seedling survival found in Janzen-Connell studies may result in negative frequency dependence when considered intergenerationally, we found that soil communities are able to intensify intraspecific interactions within the same generation.…”