Location: Great Basin Rangelands ResearchTitle: Quality of soluble organic C, N, and P produced by different types and species of litter: root litter versus leaf litter) Author
Submitted to: Soil Biology and Biochemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/8/2012
Publication Date: 11/13/2012
Citation: Uselman, S.M., Qualls, R.G., Lilienfein, J. 2012. Quality of soluble organic C, N, and P produced by different types and species of litter: root litter versus leaf litter. Soil Biology and Biochemistry. 54:57-67. Interpretive Summary: Dissolved organic matter (DOM) plays an important role in soil formation processes and nutrient retention in forested ecosystems, and the quality of DOM influences its fate. In this study, we emphasized the quality of DOM inputs from freshly senesced litter, which differs in quality from DOM percolating from lower soil horizons. By quality, we specifically mean components of DOM that are considered indicative of availability to microbes and/or roots, or involvement in chemical and/or physical reactions in soil. The dissolved organic carbon that is initially produced by freshly senesced litter may (1) be respired, (2) contribute to soil organic matter accumulation, or (3) be leached from the soil profile. The N and P in DOM may also be mineralized and recycled within the ecosystem. In this study, we investigated the effects of litter type (i.e. root litter, leaf litter, and other litter types) and species (i.e. five species of leaf litter) on several measures of the quality of DOM produced. We found that DOM from fine roots may be more prone to humification in some respects, which means that DOM originating from root litter is more likely to contribute to soil organic matter compared to DOM originating from leaf litter. Further, DOM originating from fine roots was also high in labile forms of dissolved N and P as compared to leaf litter. By labile, we mean components of DOM that are known to be readily available to microbes and/or roots. This suggests that a large portion of the soluble N and P in fine roots is likely to be rapidly recycled within the ecosystem. We also found that a considerable portion of the total P in leaf litter was water-soluble as inorganic P, which is readily available for plant and microbial uptake. Many of the inputs from freshly senesced litter are rapidly respired or recycled in soil, while DOM that leaches from lower soil horizons represents the remaining less easily decomposed fraction of DOM. Though some fractions of DOM are not found in high concentrations in soil solution (e.g. sugars), these components of DOM that are initially produced by fresh litter serve as an important energy source for microbial activity and contribute to the recycling of N and P within the ecosystem. In summary, we have shown that the quality of DOM from freshly senesced roots is important to carbon and nutrient cycling, but these inputs have previously been very little studied and their importance has not been widely recognized.
Technical Abstract: In forested ecosystems, the quality of dissolved organic matter (DOM) produced by freshly senesced litter may differ by litter type and species, and these differences may influence the amount of DOM that is respired versus that which may either contribute to soil organic matter accumulation or be leached from the ecosystem. In this study, we investigated the effect of litter type (including freshly senesced fine root, leaf, fine woody, and reproductive litter) and species (5 species of leaf litter) on several measures of the quality of DOM produced. We measured differences in solid litter chemistry (C, N, and P content) and differences in the content of dissolved organic C, N, and P (DOC, DON, and DOP, respectively), soluble monomeric carbohydrates, polyphenols, proteins, fractions of DOC, as well as UV absorbance. For most aspects of DOC quality, DOM from fine roots was less labile than DOM from leaf litter. In some respects, DOM from fine roots may be more prone to humification. However, in contrast to DOC quality, DOM originating from fine root litter and live fine roots was high in labile forms of dissolved N and P as compared to leaf litter. We also found that leaf litter with greater %N or %P content had higher DON or DOP content (and higher total soluble P content). A very high percentage, on average 72% (up to 89%) of the total P in leaf litter was water-soluble and mostly inorganic P. DOC content of leaf litter (in mg g-1 dry weight) was best predicted by a combination of soluble polyphenol, soluble monomeric carbohydrate, and %N contents of litter. DON content was best predicted by soluble protein and %P contents of litter; and DOP content was best predicted by soluble protein, soluble monomeric carbohydrate, and %P contents of litter. Given the increasing ratio of root to leaf litter production and shifting species composition during primary succession, our results suggest that some aspects of DOC quality reflect a decrease in labile forms of DOC originating from both above and belowground litter, whereas dissolved N and P showed an increase in labile forms.