Resource limitation of soil organic matter decomposition

Microbial decomposition of soil organic material is a key process for the global carbon cycle. Decomposition processes may be limited by available resources, predominantly by carbon and nitrogen. Thus, increasing N input to terrestrial ecosystems by enhanced anthropogenic N deposition may strongly affect decomposition and thereby carbon release from soils. The proposed project aims at establishing the relationship between resource availability and microbial decomposition processes and at revealing the underlying mechanisms. We will examine how the modulation of carbon and nitrogen availability, e.g. through enhanced nitrogen deposition or reduced plant carbon input, alters microbially-driven ecosystem functions, either directly or by affecting microbial community composition. We hypothesise, (1) that microbial community composition is highly sensitive to varying resource availability, mainly because different microbial groups may be differentially limited by C and N availability, and (2) that microbial community changes have the potential to strongly affect extracellular enzyme activities (responsible for organic matter break down) and thereby decomposition rates. In order to test these hypotheses, we will conduct field experiments, in which we alter the carbon and nitrogen availability (by N fertilization and tree girdling, which cuts off the translocation of plant carbon to the soil) and analyse the effect of seasonal variation in soil nutrients. In these experiments we will monitor concomitantly decomposition processes and microbial community composition to clarify how input stoichiometry affects microbial structure function coupling. Furthermore we will conduct a sophisticated laboratory experiment testing different microbial communities for their functional response to substrate and nutrient addition and to identify functional groups responsible for the degradation of specific substrates. Finally, a new conceptual model will be developed, that, for the first time, allows us to model individual carbon and nitrogen limitation for different functional groups of microbes. This will enable us to reshape the current understanding of the regulation of decomposition processes through microbial community dynamics.

Microbial decomposition of soil organic material is a key process for the global carbon cycle. Decomposition processes may be limited by available resources, predominantly by carbon and nitrogen. Thus, increasing N input to terrestrial ecosystems by enhanced anthropogenic N deposition may strongly affect decomposition and thereby carbon release from soils. The proposed project aims at establishing the relationship between resource availability and microbial decomposition processes and at revealing the underlying mechanisms. We will examine how the modulation of carbon and nitrogen availability, e.g. through enhanced nitrogen deposition or reduced plant carbon input, alters microbially-driven ecosystem functions, either directly or by affecting microbial community composition. We hypothesise, (1) that microbial community composition is highly sensitive to varying resource availability, mainly because different microbial groups may be differentially limited by C and N availability, and (2) that microbial community changes have the potential to strongly affect extracellular enzyme activities (responsible for organic matter break down) and thereby decomposition rates. In order to test these hypotheses, we will conduct field experiments, in which we alter the carbon and nitrogen availability (by N fertilization and tree girdling, which cuts off the translocation of plant carbon to the soil) and analyse the effect of seasonal variation in soil nutrients. In these experiments we will monitor concomitantly decomposition processes and microbial community composition to clarify how input stoichiometry affects microbial structure function coupling. Furthermore we will conduct a sophisticated laboratory experiment testing different microbial communities for their functional response to substrate and nutrient addition and to identify functional groups responsible for the degradation of specific substrates. Finally, a new conceptual model will be developed, that, for the first time, allows us to model individual carbon and nitrogen limitation for different functional groups of microbes. This will enable us to reshape the current understanding of the regulation of decomposition processes through microbial community dynamics.