Decomposition and nitrogen dynamics of red alder and Douglas-fir leaf litter in Oregon Coast Range riparian forests Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/m039k890x

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  • I examined factors regulating decomposition rates of red alder (Alnus rubra)) and Douglas-fir (Pseudotsuga menziesii) leaf litter in Coast Range riparian areas in western Oregon. Overall, this study was designed to examine the influence that leaf litter quality characteristics and decomposition site treatment have on decomposition rates, to provide a better understanding of how vegetation management can impact nutritional subsidies and nutrient cycles within these riparian systems. I employed the litterbag method to compare decomposition rates of litter with different initial chemistry in sites of different N availability. Specifically, this study investigates the role of litter source, riparian decomposition site, and how differences in N (both endogenous and exogenous) may influence the decomposition dynamics of red alder and Douglas-fir leaf litter. I addressed the following research questions: 1) How do the decomposition rates of red alder and Douglas-fir differ? 2) Do differences in chemical measures of initial litter quality (eg. N, Ca, lignin, cellulose, C:N) correlate with different rates of decomposition in Douglas-fir (8 different sources of Douglas-fir litter)? 3) Does dominance of a site by either red alder or Douglas-fir overstory) influence decomposition rates? 4) Does N fertilization increase the rate of litter decomposition under Douglas-fir overstories? Results suggest that red alder litter decomposes more rapidly than Douglas-fir litter under either canopy, but the difference in decomposition rates is greater under a red alder overstory than under a Douglas-fir overstory. N mineralization began immediately following placement of the red alder litter bags and more N was mineralized in red alder litter decomposing under red alder overstories than under Douglas-fir overstories. Compared to red alder, Douglas-fir litter decomposition did not vary by overstory treatment. Generally, Douglas-fir litter went through an immobilization period, with only high N litter mineralizing N under unfertilized Douglas-fir overstories. Both low- and high-N Douglas-fir litter immobilized more N under red alder overstories, and under fertilized Douglas-fir conditions. In fertilized plots under Douglas-fir overstories, high-N litter was still immobilizing N after two years. In contrast, low-N Douglas-fir litter immobilized N throughout the 2 year period under all treatments. This study indicates strong species-specific effect of overstory composition on riparian ecosystem processes. These effects can influence energy and nutrient budgets of riparian food webs, and suggest a need for broader consideration of potential impacts resulting from conversion of red alder to Douglas-fir dominated riparian area. Surprisingly, rates of Douglas-fir litter decomposition were negatively related to initial litter nitrogen concentrations across the range 0.7 – 1.4% N, contrary to patterns observed across species in other ecosystems. N fertilization exerted a minor influence on decomposition rates of Douglas-fir, with decomposition rates slower in fertilized Douglas-fir plots. These results highlight the complicated relationship between decomposition of high lignin litter and N availability and suggest that under such conditions decomposition can be dramatically reduced.
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  • description.provenance : Approved for entry into archive by Julie Kurtz(julie.kurtz@oregonstate.edu) on 2009-04-15T15:35:23Z (GMT) No. of bitstreams: 1 Matkins_Thesis_Final Manuscript_4.7.2009.doc: 1886720 bytes, checksum: d7a091c6b48c433a7a4d9c7d50fe363d (MD5)
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