Belowground response of prairie restoration and resiliency to drought

Abstract

Agricultural land use is a major threat to biodiversity and ecosystem functions in tallgrass prairies. However, there are proposed bioenergy systems that can use biomass harvested from restored tallgrass prairie, creating a potential free market incentive for landowners to restore prairies. These alternative management practices may alter associated soil microbial communities and their ecosystem services. We examined changes in soil microbial community structure, function, and resiliency to drought following two prairie restorations from row-crop agriculture and through subsequent succession in a fertilized and unfertilized tallgrass prairie. The soil microbial community structure was assessed through amplicon (16S and ITS) sequencing, function through potential extracellular enzyme activity, and resiliency indices were calculated for both microbial diversity measures and extracellular enzyme activity. We hypothesized that 1) distinct soil microbial communities in each management system will continue to develop over time reflecting the extent of divergence between the plant communities, due to the strong selective forces plant communities have on the soil microbiome. 2) Microbial extracellular enzymatic function will continue to diverge between the management systems across sampling years. 3) We will see increased resiliency to drought in the prairies potentially due to the greater diversity in this management system for the microbial and plant community, creating a possible enhancement in functional redundancy. Our experiment demonstrates that soil microbial communities continue to diverge from row-crop agriculture as prairie restoration progresses. Planted prairie bioenergy systems with higher plant diversity supported greater microbial diversity than corn systems. Corn monocultures were less resistant to drought stress, as evidenced by decreased microbial activity and richness. Prairies with increased microbial diversity exhibited increased functional resiliency than corn systems, as measured by cellulose-degrading enzyme activity. Prairies that received nitrogen fertilization maintained high microbial diversity and activity, even under drought. Our study demonstrates that diverse cropping systems may benefit from nitrogen fertilization to confer resiliency to disturbance events. Increasing resiliency, while maintaining productivity, is key to managing alternative crops that are sustainable systems for biofuel uses. Our multi-year study reveals the benefits of long-term experiments for capturing the dynamic range of microbial mediation of soil carbon and nutrients and the importance of resiliency in both developing sustainable management systems and modeling predictive biogeochemical models.