Human activities have led to increased deposition of nitrogen (N) and phosphorus (P) into soils. Nutrient enrichment of soils is known to increase plant biomass and rates of microbial litter decomposition. However, interacting effects of hydrologic position and associated changes to soil moisture can constrain microbial activity and lead to unexpected nutrient feedbacks on microbial community structurefunction relationships. Examining feedbacks of nutrient enrichment on decomposition rates is essential for predicting microbial contributions to carbon (C) cycling as atmospheric deposition of nutrients persists. This study explored how long-term nutrient addition and contrasting litter chemical composition influenced soil bacterial community structure and function. We hypothesized that long-term nutrient enrichment of low fertility soils alters bacterial community structure and leads to higher rates of litter decomposition especially for low C:N litter, but low-nutrient and dry conditions limit microbial decomposition of high C:N ratio litter. We leveraged a long-term fertilization experiment to test how nutrient enrichment and hydrologic manipulation (due to ditches) affected decomposition and soil bacterial community structure in a nutrient-poor coastal plain wetland. We conducted a litter bag experiment and characterized litter-associated and bulk soil microbiomes using 16S rRNA bacterial sequencing and quantified litter mass losses and soil physicochemical properties. Results revealed that distinct bacterial communities were involved in decomposing higher C:N ratio litter more quickly in fertilized compared to unfertilized soils especially under drier soil conditions, while decomposition rates of lower C:N ratio litter were similar between fertilized and unfertilized plots. Bacterial community structure in part explained litter decomposition rates, and long-term fertilization and drier hydrologic status affected bacterial diversity and increased decomposition rates. However, community composition associated with high C:N litter was similar in wetter plots with available nitrate detected, regardless of fertilization treatment. This study provides insight into long-term fertilization effects on soil bacterial diversity and composition, decomposition, and the increased potential for soil C loss as nutrient enrichment and hydrology interact to affect historically lownutrient ecosystems.

Anthropogenic disturbances have led to increased deposition of nitrogen (N) and phosphorus (P) into soils. Nutrient enrichment of soils is known to increase plant biomass and also increase rates of microbial litter decomposition. Thus, examining plant-soil-microbial interactions and their influence on decomposition rates is essential for predicting microbial contributions to carbon (C) cycling as atmospheric deposition persists. This study explores how changes in organic C, nitrogen (N), and phosphorus (P) caused by long-term nutrient enrichment and known litter-type composition influence soil microbial community structure and function. It is hypothesized that long-term nutrient enrichment causes shifts in soil microbial community structure that lead to higher rates of litter decomposition. Further, plant litter with a lower C: N ratio (compared to high C:N ratio litter) is expected to decompose faster due to an available N source provided to nutrient-starved microbes. We leverage a long-term experimental fertilization and disturbance by mowing experiment to test how nutrient enrichment affects decomposition and soil bacterial community structure in a nutrient poor coastal plain wetland. In each of eight replicate mowed/fertilized and mowed/unfertilized plots, bags of two different litter types (high C:N ratio rooibos tea and low C:N ratio green tea) were buried for 111 days. We characterized litterassociated and bulk soil microbiomes using 16S rRNA bacterial sequencing and quantified litter mass losses. As predicted, the green tea litter decomposed faster than the rooibos tea litter.Results also revealed that distinct bacterial communities were involved in decomposing rooibos tea litter (higher C:N ratio) more quickly in fertilized compared to unfertilized especially under drier soil conditions, while decomposition rates of green tea litter (lower C:N ratio) were similar between fertilized and unfertilized plots. Bacterial community structure in part explained litter decomposition rates, and long-term fertilization and drier hydrologic status affected bacterial