Cox, S. B. 1999. Soil properties and microbial functional diversity of surface soils in the Luquillo Experimental Forest of Puerto Rico. Ph.D. Dissertation, Texas Tech University.
Microbial communities represent an important, yet poorly understood component of the biodiversity of tropical forest ecosystems. Nonetheless, methodological difficulties associated with sampling and identifying microbes prevents obtaining answers to many questions related to fundamental issues in microbial ecology. One such issue is whether or not patterns in soil microbial communities are discernible at broad spatial scales (e.g., hectares). I assessed microbial functional diversity (MFD) in the Luquillo Experimental Forest of Puerto Rico based on the differential catabolism of 95 carbon sources (Biolog method). Specifically, I: (1) examined the influence of extreme soil types associated with topography (ridges and riparian valleys) and soil nutrient characteristics in determining MFD, and (2) elucidated broad-scale patterns of MFD with respect to forest type (elevation) and landuse within a landscape modified by agricultural and forestry practices. I included abandoned pastures as a "forest type" in order to assess the impacts of clearcutting and cattle grazing on microbial diversity and nutrient status. Considerable spatial variation characterized soils of the LEF, and differences between sites within each combination of forest type and topographic position accounted for 11-60% of the total variation in soil properties. Considerable spatial variation also characterized indexes of MFD, and differences between sites within each combination of forest type and topographic position were significant in 22 of 28 analyses. Nevertheless, mean soil properties differed significantly among forest types, between topographic positions (ridge vs. valley), and between seasons (wet vs. dry). In contrast, indexes of MFD were not different among forest types and between topographic positions. Of the 14 soil characteristics examined, P, Ca, and pH accounted for unique variation in MFD, and when variation in MFD due to these dominant soil parameters was removed, the interaction between forest type and topography was significant for diversity, evenness, and richness, and approached significance for total activity. Mantel analyses and Metric Multi-Dimensional Scaling revealed that microbial communities of different forest types and topographic positions exhibited distinct profiles of substrate utilization; however, differences among forest types depended on topographic position. Functional diversity of bacterial communities does exhibit distinctive patterns at the scale of the entire LEF, with the soil environment mediating the mechanisms related to forest type, topography, and season.