Submitted to: Ecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2008
Publication Date: 12/11/2008
Citation: Uselman, S.M., Qualls, R.G., Lilienfein, J. 2009. Production of Total Potentially Soluble Organic C, N, and P Across An Ecosystem Chronosequence: Root Versus Leaf Litter. Ecosystems. 12:240-260. Interpretive Summary: Dissolved organic matter (DOM) plays an important role in soil formation processes and nutrient retention in forested ecosystems. DOM originates from the water-soluble component of ecosystem net primary production (NPP), and few studies have quantified the total amount of DOM produced from aboveground NPP and no studies have done so for belowground NPP. The aims of this study were to quantify the major sources of total potentially water-soluble organic matter (DOMtps) from above- and belowground, compare total potentially water-soluble organic C, N and P (DOCtps, DONtps, and DOPtps), and examine patterns in DOMtps production during ecosystem development at the Mt. Shasta Mudflows ecosystem chronosequence. Results showed that DOMtps production from root litter was a very important source of DOMtps, and the importance of belowground relative to aboveground litter for DOCtps and DONtps production increased during ecosystem development. Thus, studies that do not measure belowground inputs could seriously underestimate total DOMtps production. The pattern of DOMtps production increased during ecosystem development for DOCtps and DONtps, but the pattern for DOPtps was unique. Production of DOCtps and DONtps were predominantly driven by changes in biomass production during ecosystem development, rather than by changes in litter solubility of different species. Generally, considerable proportions of the total C, N, and P in a variety of types of litter were water-soluble. We suggest that fine roots may play an increasingly fundamental role in the accumulation of soil organic matter during forest ecosystem development, because fine roots become more deeply distributed in the soil profile and contribute an increasing proportion of total DOMtps production during ecosystem development. Furthermore, we suggest that the water solubility of a substantial component of ecosystem NPP profoundly influences its fate, by affecting its potential for translocation and storage in mineral soil and loss from the ecosystem via leaching and/or microbial respiration.
Technical Abstract: Dissolved organic matter (DOM) plays several important roles in forest ecosystem development, undergoing chemical, physical and/or biological reactions that affect ecosystem nutrient retention. Very few studies have focused on gross rates of DOM production, and we know of no study that has directly measured DOM production from root litter. Our objectives were to quantify major sources of total potentially water-soluble organic matter (DOMtps) production, with an emphasis on production from root litter, to quantify and compare total potentially soluble organic C, N, and P (DOCtps, DONtps, and DOPtps) production, and to quantify changes in their production during forest primary succession and ecosystem development at the Mt. Shasta Mudflows ecosystem chronosequence. To do so, we exhaustively extracted freshly senesced root and leaf and other aboveground litter for DOCtps, DONtps, and DOPtps by vegetation category, and we calculated DOMtps production (g m-2 y-1) at the ecosystem level using data for annual production of fine root and aboveground litter. DOM production from throughfall was calculated by measuring throughfall volume and concentration over 2 years. Results showed that DOMtps production from root litter was a very important source of DOMtps in the Mount Shasta mudflow ecosystems, in some cases comparable to production from leaf litter for DONtps and larger than production from leaf litter for DOPtps. Total DOCtps and DONtps production from all sources increased early in succession from the 77- to the 255-year-old ecosystem. However, total DOPtps production across the ecosystem chronosequence showed a unique pattern. Generally, the relative importance of root litter for total fine detrital DOCtps and DONtps production increased significantly during ecosystem development. Furthermore, DOCtps and DONtps production were predominantly driven by changes in biomass production during ecosystem development, whereas changes in litter solubility due to changes in species composition had a smaller effect. We suggest that DOMtps production from root litter may be an important source of organic matter for the accumulation of SOM during forest ecosystem development.