Edaphic factors contributing to soil microbial extracellular enzyme activities

Microorganisms participate in nutrient cycling through the expression of extracellular enzymes which are capable of oxidizing or hydrolyzing structural components of organic matter. The activity of these enzymes is important for degrading ligno-cellulose complexes of plant detritus and cellular constituents of extant microorganisms. As such, microbial activity is intrinsically linked to ecosystem scale processes such as decomposition. However, the activity of many enzymes can be dependant on the soil conditions and the availability of substrates. Increasing N deposition has been shown to negatively impact laccase activity and decomposition rates in temperate forests. Alternatively, microbes in nutrient limited systems often produce more enzymes to obtain resources that are in low abundance. Specific factors such as plant community, soil organic matter (SOM) and soil pH are likely to play a role in how microbes produce enzymes at both local and continental scales. At small scales, factors such as plant community, nutrient availability and other edaphic factors are likely to regulate microbial activity, while precipitation regime and soil pH may have a greater impact at regional and ecosystem scales. Litter chemistry may be regionally important when multiple species heterogeneously dominate the landscape but factors like soil pH may broadly define the EEA profile of diverse ecosystems. The first study examines the change of laccase gene diversity in response to N fertilization in a temperate northern oak forest soil. The second paper focuses on the effect of plant community and rainfall on EEA and soil chemistry in a semi-arid ecosystem. The final chapter attempts to define the edaphic factors that are predictive of soil EEA across ten ecosystems. The results show laccase gene diversity was not linked to changes in soil phenol oxidase activity with N fertilization, but EEA varied significantly with vegetation and rainfall in the semi-arid ecosystem. At the largest scale, soil pH, SOM and mean annual temperature explain system-to-system variation across a number of diverse plant communities and soil types.