Anthropogenic disruption of the global nitrogen cycle is a major issue facing society. Humans have doubled the rate of nitrogen inputs into terrestrial systems with the goal of improving agricultural yields. While we know that N inputs are lost via leaching and GHG production, variability in time and space make it difficult to predict. Research needs to be done to understand where and how nitrogen inputs are interacting with the plant-soil agroecosystem, specifically the influence plants have on the microbial nitrogen metabolism in their surrounding soil. We hypothesize that this variability is a product of soil microbial community’s interactions with plant root systems. Here, we use Zea mays to examine the influence of plant developmental stage and distance from the plant on the activity of nitrogen-cycling, nitrifying, denitrifying, and metabolically active microbial communities. To address how plant phenology informed microbial activity, we sampled the root zones of multiple genotypes over the growing season, capturing the major developmental stages. From these samples we performed potential nitrification and denitrification assays to address changes in microbial function over time. In addition, spatial sampling was conducted in relation to distance from the plant to assess rhizosphere influence on nitrification, denitrification, and substrate utilization.
Results/Conclusions
In the root zone, we found that potential activity of nitrifying communities is correlated with plant demands for nitrogen as predicted by developmental stage, while potential activity of denitrifying communities constantly increases regardless of growth stage. Knowing this allows us to have a starting point for managing these ecosystem processes. Spatially, we see the suppression of both nitrification and denitrification activity in microbial communities closer to the root zone; while diversity of substrate utilization increases in proximity to the root zone. These results demonstrate that plants grown in a field are adding heterogeneity to the processing of nitrogen in the agroecosystem both through time and space. Understanding these processes is vital as researchers who model/measure nitrogen ecosystem fluxes and processes are ignoring this plant-generated gradient in the soil environment. With incorporation of these results we can gain an improved understanding and ability to maintain and use nitrogen sustainably.