Landscape‐Level Patterns of Microbial Community Composition and Substrate Use in Upland Forest Ecosystems

northern Wisconsin, Christensen (1969) found evidence for such a relationship, wherein communities of soil The composition and diversity of biotic communities are controlled microfungi were correlated with the occurrence of forest by the availability of growth-limiting resources. Resource availability for microbial populations in soil is controlled by the amount and types vegetation (also see Christensen et al., 1962; Tresner et of organic compounds entering soil from plant litter. Because plant al., 1954). Notwithstanding these observations, we have communities differ in the amount and type of substrates entering a limited understanding of the manner in which the soil, we reasoned that the composition and function of soil microbial broader soil microbial community varies with plant comcommunities should differ with the dominant vegetation. We tested munity composition at a landscape-level scale. this idea by studying two sugar maple (Acer saccharum Marsh.)- Temporal patterns of root and leaf litter production, dominated and one oak (Quercus spp.)-dominated forest ecosystems combined with variation in the chemical composition in northern Lower Michigan that differ in rates of soil N cycling. We of these tissues, could influence the composition and used phospholipid fatty acid (PLFA) analysis to gain insight into function of soil microbial communities. Root litter typimicrobial community composition, and we used a subset of Biolog cally contains more N and lignin than leaf litter (Aber GN substrates found in root exudate to assess the metabolic capabilities soil microbial communities. Although microbial biomass did not et al., 1990; Vogt et al., 1986). The fact that roots and differ among ecosystems, principal components analysis of bacterial, leaves differ chemically could lead to changes in microactinomycetal, and fungal PLFAs clearly separated the microbial com- bial community composition and function, depending munities of the three ecosystems. Similarly, principal components on temporal variation in the proportion of leaf vs. root analysis separated microbial communities by differences in growth on litter entering soil. In sugar maple‐dominated forests, carbohydrates, organic acids, and amino acids. Discrimination among the greatest addition of root litter to soil occurs when microbial communities in the three ecosystems by PLFAs and sub- fine-root mortality peaks in early autumn (Hendrick and strate use occurred in spring, summer, and fall, but the individual Pregitzer, 1992), but substantial inputs also can occur PLFAs and substrates contributing to discrimination changed during throughout the growing season. Unlike the continuous the growing season. Our results indicate that floristically and edaphiinput of dead fine roots to mineral soil, the majority of cally distinct forest ecosystems also differ in microbial community composition and substrate use. This pattern was consistent across aboveground litter is deposited in late autumn. Seasonal the growing season and repeatedly occurred across relatively large variation in above- and belowground litter production land areas. could influence microbial community composition and function, depending on the types of substrates available for microbial metabolism.