Session: Biogeochemistry: New Paradigms In Biogeochem Cycling
Broad-scale patterns of litter chemistry throughout decomposition: chemical classes respond differently to litter characteristics and the decay environment
Wednesday, August 4, 2021
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Becky A. Ball, School of Mathematical and Natural Sciences, Arizona State University at the West Campus, Glendale, AZ, Lynn Christenson, Biology Department, Vassar College, Poughkeepsie, NY and Kyle Wickings, Cornell University
Becky A. Ball
School of Mathematical and Natural Sciences, Arizona State University at the West Campus Glendale, AZ, USA
Background/Question/Methods Decades of decomposition research have yielded rich information about litter mass loss and carbon dynamics, but relatively less is understood about the chemical dynamics of litter throughout decomposition, particularly micronutrients and the structural and metabolic compounds whose fragments are either broken down or incorporated into soil humus. While numerous studies quantify initial concentrations of these compounds, it’s possible that initial differences in litter chemistry do not persist throughout decomposition, with examples of both chemical convergence and divergence reported in the literature. Whether there are overarching patterns across plant functional types or ecosystems is difficult to test because few studies measure beyond initial chemistry, and do not cover a consistent array of chemical parameters to allow cross-study comparisons. We solicited archived litter decomposition samples from across the United States and analyzed a comprehensive and consistent set of litter nutrient, structural, and metabolic chemistry to identify overarching patterns across a wide variety of species from various plant functional types (PFT) and U.S. ecosystems throughout decomposition. We investigated patterns categorically for (1) nutrient elements, (2) carbon-based fiber compounds (measured by sequential acid digestion), and (3) structural and metabolic compounds (measured by py-GCMS) across decay stages, PFT, and geographic region. Results/Conclusions PFT was the dominant factor influencing the trajectory of nutrient and fiber chemistry over decay, but geographic region (the decay environment) was most influential for the structural and metabolic compounds. The regional differences in metabolic and structural chemistry persisted throughout decay, but nutrient chemistry converged across regions as decomposition proceeded, while fiber chemistry diverged over decay. PFTs, however, remained chemically distinct throughout decay for all three chemical categories. Individual chemical parameters, when analyzed alone rather than collectively by category, did not mirror the response of their chemical category. For example, while nutrients collectively converged across the regions, individual nutrient elements did not. Even in late-stage decay, region was still a significant factor for each individual nutrient element, though the nature of the differences were not necessarily the same as initial differences. Overall, there was more convergence of individual chemical parameters across PFTs than regions, with most parameters remaining distinct across regions. Thus, conclusions about the trajectories of litter chemistry throughout decay will depend upon the parameters being measured and whether they are viewed individually or collectively, but our results suggest a broad-scale pattern of persistent differences across PFTs throughout decay, with evidence for both convergence and divergence across geographic regions.