Root decomposition across a barrier island chronosequence: Litter quality and environmental controls

Abstract

A root decomposition study using the litterbag approach was conducted along a dune and swale chronosequence on the Virginia Coast Reserve-Long Term Ecological Research Site in Virginia, USA to evaluate how environmental and substrate quality factors influence belowground decay and associated nutrient dynamics. Gradients in moisture levels and nitrogen availability associated with the chronosequence provided the experimental framework. Spartina patens roots were buried at all sites as a standard substrate to evaluate environmental influences. Roots native to each site were buried to evaluate community decay dynamics and the influence of litter quality. Spartina decay was reduced in the wet, anoxic soils of swale sites (k = 0.21–0.33 yr-1) relative to decay in dunes soils (k = 0.52–0.72 yr-1). Increasing soil nitrogen availability from younger to older sites had no effect on the rate of Spartina root decay. Native root decay across the Hog Island chronosequence exhibits certain trends expected in response to nitrogen limitation and moisture availability. Increased nitrogen content of root material corresponds to increased soil nitrogen availability. Among dune sites, native root decay increased in concert with increased root nitrogen (6 year k = 0.34 yr-1, 120 year dune: k = 0.97 yr-1). Litter quality, alone, does not explain this trend since Spartina roots decayed more slowly than native dune roots and had a higher initial nitrogen content. Among swales, increased moisture levels and associated soil anoxia inhibited native root decomposition and minimized the effects of litter quality on decay. In general, phosphorus was rapidly lost from decaying roots while nitrogen immobilization was low to nonexistent. The low nitrogen immobilization of decaying roots in a nitrogen limited ecosystem warrants further study and may reveal that belowground decay increases the rate of nutrient cycling relative to decay aboveground.