Plant-soil feedbacks quantified: model validation with experimental data shows the importance of plant-soil feedbacks to plant community development

Background/Question/Methods

Plant-soil feedbacks (PSFs) are rapidly gaining attention as a mechanism that can determine plant community development.  This reflects the fact that 1) experimental data shows that plant growth often differs on soils cultivated by different plant species and 2) models show that the resulting plant–soil feedbacks (PSFs) can determine plant abundance and persistence.  Yet, we are aware of no studies that take the important steps of parameterizing a PSF model with experimental data and validating model predictions against observed plant community development.  Here we use the growth of ten plant species on ‘self’ and ‘other’ soils to parameterize a three-species PSF model.  Predictions from the parameterized model were compared to plant growth observed in several greenhouse experiments and a five-year field experiment.  Twelve, three-species plant communities of four types 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.

Results/Conclusions

Mean plant biomass differed among soil types by 20% and differed among plant species by 80%.  The PSF model correctly predicted rank abundance in 10 of 12 communities tested while the competition model correctly predicted rank abundance only in 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 than observed values for eight of twelve communities.  Competition model predictions were different than observed values for all communities. 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.  Results provide what we believe to be the first example of a validated PSF model and indicate that PSFs captured a mechanism of plant community development.  Further testing of PSFs and development of improved methods to measure PSFs are suggested.