Abstract
Relations among microbes, plants, and soil function are complex and poorly understood. Studies of microbial communities by use of biomarkers (phospholipid fatty acids, PLFAs), revealed that the soil C/N ratio explained as much, or more, of the variation in microbial community as pH did. Microbial community composition and N mineralisation was strongly correlated. This may occur because plants adjust their plant belowground C allocation in relation to the N-supply; I found that tree-girdling, which terminates this flux, affected a fungal PLFA as much as high N-supply did. Here, I want to explore these relations in greater detail using modern molecular methods I learned during my postdoc-period in USA. I will compare a range of manipulative experiments, viz. a 37-year-old N-loading experiment, tree-girdling, and a new N-fertilization experiment, in which the photosynthates, and hence the belowground C flux, is labeled with 13C, with the variations in community structure occurring along a natural forest nutrient supply and plant productivity gradient. At these sites and experiments, I will use stable isotope probing methods to trace N and C from double-labeled amino acids into microbial biomass and specific PLFAs. In the large-scale canopy 13C labeling experiment I will have a unique opportunity to trace the labeled photosynthate C into the different functional groups in the soil. Molecular methods will provide information about the effects of treatments on species diversity.
Sweden