USDA Forest Service / Purdue University West Lafayette, Indiana
Body of Abstract: Positive interactions between components of above- and belowground afforested forest plantations are critical to the optimal growth and development of fine hardwood trees. Within the Central Hardwoods Region (CHR), synergistic relationships between tree species and soil microbial community structure and function have received limited attention. As healthy soil microbes are integral to forest ecosystems, evaluation of their activities may lead to greater understanding of soil organic matter decomposition, nutrient cycling, and ecosystem functioning. Nonetheless, studies assessing linkages between tree species, microbial community structure, and microbial functioning have yet to received focused attention. Here, we examined soils from two perfectly aligned stands of black walnut (BW, Juglans nigra L.) and Northern red oak (RO, Quercus rubra L.) trees. Measurements of selected soil chemical properties, microbial community structure using ester-linked fatty acid methyl ester (EL-FAME), and soil enzymatic activities (EAs) allow us to elucidate the effects of tree species and seasonal changes on microbial nutrient cycling. Microbial communities showed a significant positive response to BW based upon soil EAs and microbial indicators compared to RO. As expected, seasonal comparisons revealed higher microbial activities during summer for both species. Gram-positive (GP) rather than gram-negative (GN) bacteria or actinomycetes dominated the bacterial community flora while fungi dominated soil microbial community structure with a fungal/bacterial ratio of 2.1. Some soil enzyme activities increased, ß-glucosidase and arylsulfatase, whereas those of ß-glucosaminidase and acid phosphatase decreased. Additionally, strong correlations were observed between acid phosphatase and mycorrhizal fungi. The differences observed in biological properties, specifically microbial communities and EAs, highlight the varied responses to BW and RO soil biology and subsequent soil ecosystem functions.