Plant-soil feedback (PSF) theory has been successfully applied to explaining patterns in plant communities, including species coexistence and plant succession. This theoretical framework has parallels with crop rotation and, given the success of this framework in natural communities, there is potential for plant-soil feedback theory to inform crop rotation practices. We tested this idea by collecting soil from six crop species, which were divided into two categories: non-mycorrhizal and mycorrhizal. The non-mycorrhizal species consisted of chard and two varieties of kale, while the mycorrhizal species included leeks, lettuce, and carrots. Seedlings of these species were inoculated with conspecific and heterospecific soils to test for PSF effects; the seedlings were then harvested after approximately two months to compare growth rates. From our samples, we also extracted and counted arbuscular mycorrhizal fungi (AMF) spores and identified them morphologically.
Results/Conclusions
The abundance of mycorrhizal fungi, as measured by spore counts, was approximately twice as high under mycorrhizal crop species as compared to non-mycorrhizal crop species (p = 0.01). However, among mycorrhizal and non-mycorrhizal species, variation in AMF abundance was not statistically significant (p = 0.2). Additionally, we found no evidence for changes in species composition of AMF communities (PERMANOVA, p = 0.2). Counts of individual taxa were highly variable; further research in the area is warranted. Even if community composition is not changing, the change in AMF abundance may be ecologically important due to the important role of AMF in maintaining soil health and sequestering soil carbon. Furthermore, past work has demonstrated that changes in AMF abundance through plant-soil feedbacks can cause changes in plant productivity in natural plant communities. We are currently analyzing data to test this hypothesis in our agricultural study system.