Monday, November 13, 2006 - 9:30 AM

Doc, Don, and Dop Production Across an Ecosystem Chronosequence: Root Litter Versus Leaf Litter.

Shauna Uselman, Robert Qualls, and Juliane Lilienfein. Univ of Nevada-Reno, NRES Dept, Mail Stop 370, Reno, NV 89557

Understanding production of dissolved organic matter (DOM) is important because DOM affects soil development, microbial activity, and ecosystem retention of C, N, and P.  Although DOM is increasingly recognized for its importance in ecosystem nutrient cycling, we know of no study that has examined DOM production from root litter.  In this study, we measured production of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) from root litter, leaf litter, and throughfall across a primary successional forest ecosystem chronosequence at the Mt. Shasta Mudflows Research Natural Area in northern California.  Freshly senesced root and leaf litter was exhaustively extracted and analyzed for DOC, DON, and DOP content, and then scaled to the ecosystem level using measurements of root and leaf litter production (over one and two years, respectively).  Throughfall fluxes were measured by analyzing concentrations and volumes of throughfall collections over two years.  In comparison to DOM production from litter, throughfall was generally the smallest source of DOM.  In comparing DOM production from root litter versus leaf litter, we found that although leaf litter was the largest source of DOC, root litter was the largest source of DON and DOP, both at the root/leaf level (amount solubilized per gram litter) and at the ecosystem level (g m-2 yr-1).  Furthermore, we found that the relative importance of root litter for ecosystem DOC, DON, and DOP production increased significantly during primary succession.  Our results suggest that root litter is a very important source of DOM, especially DON and DOP; therefore studies that do not measure DOM production from roots could seriously underestimate DOM production in forest ecosystems.