Seasonal partitioning of resource use and constraints on the growth of soil microbes and a forage grass in a grazed Arctic salt-marsh

Seasonal growth responses of plants and soil microorganisms to additions of nitrogen (N), phosphorus (P) and carbon (C) were examined in goose-grazed and exclosed plots in an Arctic salt marsh. Plants showed strong growth responses to N and NP additions but not to P. Nitrogen levels in the shoots and roots of Puccinellia phryganodes declined as summer progressed. Microbial biomass was low in spring in spite of N and P additions, likely due to C limitation, but values rose in autumn, independent of nutrient treatment, as dissolved organic carbon (DOC) increased. Glucose addition (C source) elicited a transitory increase in microbial biomass. Multiple plant defoliations by geese had a negative effect on microbial biomass, in spite of the presence of DOC and added N and P, possibly because hypersalinity restricted growth. Plants appear to limit soil inputs of C in summer and compete effectively for resources in contrast to autumn, indicating a temporal partitioning of resources.