Phylogenetic Diversity of Arbuscular Mycorrhizal Fungal Communities Increases with Crop Age in Coffea arabica Plantations

Arbuscular mycorrhizal (AM) fungi are key soil microorganisms that establish a mutualistic symbiotic relationship with plants. The establishment of crops represents an environmental filter that usually reduces the diversity and variability of AM fungal communities, affecting the ecosystem stability and functionality. Despite several studies addressing these effects, the temporal development of these soil microbes since crop establishment has not been studied. We hypothesized that the negative effect of cropping practices in terms of reducing AM fungal richness, phylogenetic, and beta diversity will increase in time as far as the new dynamics progressively filter the AM fungal community composition. This research tested the impact of crop establishment and the role that time has in the progressive assembly of soil microbial communities. The AM fungal communities were characterized using terminal restriction fragment length polymorphism in coffee (Coffea arabica) plantations of different ages established in previous pristine tropical forest. We found that intraradical colonization and AM fungal phylogenetic diversity increased with plantation age. AM fungal richness was constant across time but a significant compositional turnover was detected. In relation to our initial hypothesis, these unexpected results face the current general view of the negative effects of crops on soil microbial diversity and highlight the need of studying temporal dynamics when assessing human impacts on soil biodiversity. Nevertheless, next steps would imply to put in context the found patterns by relativizing them to the original natural diversity inhabiting the studied areas.