The Impact of Low Molecular Weight Organic Acids and Dissolved Organic Carbon On Microbial Biomass in a Loblolly Pine and Switchgrass Intercropped System.

Low molecular weight organic acids (LMWOAs), a component of dissolved organic carbon (DOC), have been linked to the availability of nutrients in the rhizosphere. Gaining knowledge in the quantity and types of these organic substances contributed by different plant species is also necessary for understanding both chemical and biological processes and competition between the microbial community and plants for carbon. LMWOAs, DOC and dissolved organic nitrogen (DON) were measured to evaluate the impact of intercropping switchgrass in a loblolly pine plantation in the lower coastal plain of eastern North Carolina. Correlations between chloroform fumigation and substrate-induced respiration (SIR) were also developed to access effects of these water-soluble organics on microbial biomass. Surface soil samples (0 – 15 cm) were taken from pine only, switchgrass only and the bed, interbed and boundary of pine-switchgrass intercropped treatments to analyze total carbon, total nitrogen, and microbial biomass. Soil solution for testing DOC, DON, and LMWOAs was extracted with the centrifuge drainage technique and from Amberlite XAD resins in the same treatments. We hypothesize that there will be significant differences in microbial biomass and these water-soluble organics due to the intercropping of loblolly pine and switchgrass. We also predict that microbial biomass and DOC will be significantly lower on the boundary between pine and intercropped switchgrass due to competition between the different plant species.