Fungal community structure and microbial biomass in a semi-arid environment: Roles in root decomposition, root growth, and soil nitrogen dynamics

Although the roles of microbes in ecosystems have been well recognized, few studies have focused directly on the bottom-up effects of microbial activities on ecosystem processes. A challenge for contemporary ecology is to understand how spatial and temparal patterns in microbial community dynamics in soils are linked to above- and below-ground dynamics. To address this issue a field study was initiated within a sand shinnery-oak ecosystem in West Texas to examine spatial and temporal patterns in microbial community dynamics in soils and associated with decomposing roots.; Fungal community development did not differ spatially, but changed in response to moisture conditions of the decomposing roots. Although enzymatic activities of the decomposing roots were spatially variable, their heterogeneity did not alter root decomposition. Moreover, changes in the carbon quality of roots during decomposition also did not result in changes in the attendant fungal community. Temporally, soil microbial biomass in the shinnery-oak ecosystem was tightly coupled with soil nitrogen dynamics. Above-ground heterogeneity in stem density of shinnery-oak was found to significantly influence microbial biomass and soil nitrogen dynamics, but not the fungal community dynamics on decomposing roots. These results indicate that the hetergeneity in above-ground stem density significantly influences soil microbial community activities and microbial biomass.; Annual fine root production showed distinct seasonal patterns with 95% of fine root production occurring during July and September. Root growth occurred prior to significant immobilization of nitrogen in this system by microbial biomass. Furthermore, root growth began when available nitrogen pools were high. Root production was found to be significantly linked to temporally integrated microbial biomass and ectomycorrhizal colonization.; A manipulative experiment with water and nitrogen addition, showed that microbial biomass, soil nitrogen transformation dynamics, root production, and ectomycorrhizal colonization exhibited significant responses to water and nitrogen addition. The results suggest that microbial community dynamics, and below-ground processes within this semi-arid system are strongly water regulated and nitrogen limited.; Overall, soil microbial activities and biomass in this semi-arid ecosystem are linked to the above-ground heterogeneity in stem density. Spatially while variation in microbial community dynamics, does not affect root decomposition, soil microbial dynamics may regulate root production by influencing soil nitrogen dynamics.