Nutrient enrichment modifies soil bacterial and plant communities to influence wetland carbon storage potential

Background/Question/Methods

Wetland ecosystems are known for their carbon storage potential due to slow decomposition rates and high carbon fixation rates. However, nutrient addition from human activities affects carbon storage by changing the balance of fixed and respired carbon. Ongoing atmospheric deposition of nutrients could be changing wetland plant-microbe interactions in ways that tip the balance from carbon storage to loss. In this study, we hypothesized that because of increased organic carbon input into the soil from fertilization of a low nutrient ecosystem, both plant biomass and soil microbial diversity will increase. Increased soil nutrients and carbon resources provide energy to support increased microbial growth rates, which can result in wetland carbon losses. To address this hypothesis, we used community-level and soil chemical data from the long-term wetland ecology experiment at East Carolina University’s West Research Campus (established in 2003) to test the long-term effects of nutrient enrichment on wetland microbial communities and plant biomass. We collected soil cores from fertilized and unfertilized test plots, extracted genomic DNA from soil samples, and conducted 16S rRNA targeted amplicon sequencing to determine microbial community composition. In addition, we collected plant above and belowground biomass samples as well as measured soil physical and chemical properties.

Results/Conclusions

Results of this study revealed an increase in aboveground plant biomass, soil carbon, and bacterial diversity. In contrast, belowground plant biomass and microbial biomass were similar in fertilized and unfertilized plots. To further examine bacterial community changes to nutrient enrichment, we compared the relative abundance of fast growing copiotrophic and slow growing oligotrophic bacteria of a subset of taxa putatively identified as belonging to either life history strategy. These taxa-level results revealed a decrease in oligotroph relative abundance and little to no change in copiotroph relative abundance of a subset of bacterial taxa. If there is a community-wide shift in the proportion of oligotroph to copiotroph life history strategies, this would have a negative impact on organic carbon storage since oligotrophic bacteria respire less carbon than copiotrophic bacteria over the same amount of time. Taken together, this study provided evidence that long-term nutrient enrichment influences wetland soils in ways that decrease their carbon storage potential of important carbon sinks.