Soil microbial community diversity and composition is affected by cover crop diversity

Background/Question/Methods

There has been a significant loss of biodiversity in agricultural ecosystems. The lack of aboveground diversity has been shown to reduce soil microbial diversity the main drivers of soil carbon and nutrient cycling, and ecosystem function. The implementation of cover crops is a proposed management strategy to increase agricultural diversity. In grassland ecosystems, an increase in aboveground diversity results in increased belowground diversity. However, it is unknown how increasing diversity over short time scales (i.e., cover crops) in agroecosystems impacts microbial communities and their function. This research investigates how six species of cover crops including oilseed, grass, and legume species affect microbial diversity and composition. Cover crops were planted individually and in combinations with increasing levels of diversity. Soil samples were collected for two field seasons, once before cover crop establishment and again prior to cover crop termination. Bacterial and fungal communities were assessed using 16S and ITS Illumina sequencing, respectively. We determined alpha- and beta-diversity, and differential abundance across our different treatments. Bacterial communities were also analyzed for the ratio of r strategists (copiotrophs) and K strategists (oligotrophs).

Results/Conclusions

Cover crop identity and diversity affected soil microbial community diversity and composition. Increasing cover crop species diversity from zero to six species increased alpha-diversity for both bacterial and fungal communities. Beta-diversity for bacteria and fungi also increased with increasing cover crop species diversity. However, individual cover crop treatments significantly affected microbial community composition. These differences, overall, were most apparent in treatments that included the oilseed and grass species. More specifically, Verrucomicrobia, Proteobacteria, Sordariomycetes, and Tremellomycetes relative abundance was greater in the oilseed and grass treatments. Oilseed and grass treatments also increased the abundance of r strategists. Increased soil microbial diversity means that there is a greater likelihood that more than one species will perform the same function. Since not all microbial species will be affected equally by a disturbance, this increases the chance for continued function after a disturbance leading to greater agro-ecosystem stability. Changes in community composition could impact soil functions and processes, including soil carbon sequestration, which can help mitigate climate change. An increase in r-strategists suggests greater nutrient availability, which has implications for crop growth.