The influence of plant phylogenetic and functional relatedness on soil feedbacks
Soil microbes play an important role in plant ecology by altering plant competitive ability and resource limitations. Evolution produces variation in phenotypic traits among plant species (e.g. root morphology and chemistry, carbon allocation), which can shape associated soil microbial communities. The unique community harbored by one plant species can limit or promote the growth of another species. These plant-soil feedbacks are common in nature but despite their widespread importance, we lack an understanding of the causal factors driving their outcomes. In a growth chamber experiment we grew 8 focal plant species in soils previously conditioned by 50 heterospecific plants representing a spectrum of phylogenetic and phenotypic similarity between focal and soil-conditioning plant species. Using divergence time from a time-calibrated phylogeny and phenotypic distance calculated from a series of above and belowground measured plant traits we ask: Does the phylogenetic or phenotypic similarity among plant species predict the strength or direction of their soil feedback?
We found that focal plant species significantly differed in their growth response within a soil treatment and that each focal species differed significantly in their growth response across soil treatments. Overall we found a weakly positive but significant relationship between phylogenetic distance and feedback strength, where focal species produced increasingly more biomass when grown in soil conditioned by increasingly distant plant relatives. This relationship significantly varied across our 8 focal species however. We also found that several plant traits were important predictors of soil feedback strength and that they were independent of evolutionary history. These results aid our understanding of plant-soil feedbacks, a mechanism underlying terrestrial ecosystem structure and function. Additionally, these results indicate the importance of including both phylogenetic and phenotypic information when predicting the outcome of contemporary species interactions.