Regional Assessment of Soil Microbial Functional Diversity of Douglas‐fir Forests

Extracellular enzyme activity (EEA) provides a functional fingerprint of soil microbial communities and can be an indicator of change following disturbance. This study examined the EEA of nine managed, Douglas‐fir [ Pseudotsuga menziesii (Mirb.) Franco] dominated forests in the Pacific Northwest of the United States. It assessed the variability of EEA both within and among sites and correlated EEA with environmental variables covered by the broad geographical range of the study sites. This characterization was linked with measures of community size, C and N cycling ability, and other soil properties, such as texture and nutrient status, to provide insights into extracellular enzyme production and microbial function. Principal components analysis and multiple response permutation procedure results indicated that EEA is highly variable among sites but much less variable within sites. It also revealed that the functional fingerprint of the soil tended to be more similar for soils within the same soil order. Additionally, the results implied that phosphatase and the C‐cycling enzymes β‐glucosidase and cellobiohydrolase are constitutive in these systems, whereas the N‐scavenging enzymes N ‐acetylglucosaminidase and leucine aminopepdidase are facultative. Furthermore, the N‐cycling EEA suggests an N limitation in these sites despite N fertilization. This characterization will be critical in assessing microbial community changes following timber harvest.