Soil microbial communities form the backbone of the highly complex soil ecosystems underpinning global agricultural security. Gaining insights into how these communities respond to changes in aboveground plant biodiversity is important for both agroecologists and farmers as they can influence physical soil structure, drive nutrient cycling, and promote both plant growth and disease suppression in plants. Cover crops can improve soil health, but less is known about their effects on soil microbial community composition in semiarid cropping systems. These relationships will be important to quantify and understand as semiarid regions become warmer and drier due to climate change. This study focuses on a wheat-cover crop rotation in Havre, Montana that tests cover crop mixtures of zero (fallow), five, and seven species with three different termination methods (chemical, grazed, or hayed) under a warmer and drier treatment versus ambient conditions. Soil samples from the 2018 cover crop field were taken from each plot for metagenomic extraction and sequencing targeting the V3-V4 region of the 16S rRNA microbial gene. Sequence Variances along with Shannon’s diversity index were used to measure soil microbial community alpha diversity, while Bray-Curtis dissimilarity and non-metric multidimensional scaling ordination were used to assess beta diversity.
Results/Conclusions
Observed sequence variances did not vary among cover crop, termination, or climate treatments, except the grazed fallow plots had a slightly lower number of observed sequence variances. The seven species cover crop mixture terminated by haying had higher alpha diversity. The cover crop treatment accounted for most dissimilarity among soil microbial communities, while termination and climate conditions did not affect soil communities. Soil microbial communities from the fallow and seven species mixture were more dissimilar than microbial communities from the five and seven species mixtures. However, communities within the fallow treatment were more variable. Soil microbial communities clustered by cover crop treatment, with communities from the seven species cover crop mixture separated from the two other cover crop treatments. Cover crop termination methods and climate treatments did not explain clustering of soil microbial communities. Based on this work, the species composition of a cover crop mixture may be more influential in determining soil microbial community diversity than cover crop termination method.