Microbial Carbon Cycling Along a Drainage Sequence In a New England Forested Watershed.

Soil drainage plays an important role in regulating microbial carbon (C) cycling and soil carbon dioxide (CO₂) emissions.  Imperfectly drained soils can occupy extensive areas of the landscape in northern forests, but microbial processing of C in these ecosystems is not well characterized compared to moderately well drained, upland soils.  Furthermore, these imperfectly drained soils could transition to a less oxygen depleted character in some landscape positions with altered precipitation and temperature regimes under a changing climate.  We examined indices of microbial C cycling across a range of three drainage classes under coniferous forest type in a New England watershed: moderately well drained, somewhat poorly drained, and poorly drained mineral soils.  At these sites we measured soil respiration, the activity of ß-glucosidase and phenol oxidase, and characterized differences in DOM using fluorescence spectroscopy.  These indices of microbial C cycling suggest that enzyme activities and C efflux in somewhat poorly drained soils are more similar to those in poorly drained soils than moderately well drained soils.  For instance, ß-glucosidase activities were 66-68% higher in both somewhat poorly and poorly drained soils compared with moderately well drained soils.  Our findings suggest that moisture stress in somewhat poorly drained systems is associated with decreased rates of microbial C cycling and CO₂ efflux, and could result in subsequent increases in soil C storage if these soils shift towards more moderately well drained conditions.