A general model of litter decomposition in the northern Chihuahuan Desert
Numerous empirical studies have described the pathways of mass, C and N flows during decomposition, but there remains a paucity of data on underlying mechanisms in arid ecosystems. In the northern Chihuahuan Desert, termites remove large quantities of litter and act as carbon and nitrogen sinks, contributing to low soil fertility. In their absence, decomposition at the soil surface is primarily driven by abiotic weathering, but studies suggest buried litter decay occurs through microbiological activities. We develop a general, synthetic model to examine the interactions between buried litter, decomposer microorganisms, and C and N pools in this ecosystem. Our goal is to explore the mechanisms underlying observed patterns of decomposition in arid systems using a modelling approach that balances simplicity with enough detail to suggest the reasons for system behavior. To this end, we utilize elements of existing models, interfacing microbial physiology and population dynamics with empirical observations of C and N pool dynamics, litter mass loss and changing C:N ratios. Good agreement was achieved between simulated and observed patterns of mass loss and nitrogen concentrations once a time lag describing the microbial colonization of litter was included. Model results indicate nutrient availabilities may be determined by relatively short-term carbon dynamics mediated by microflora since soil organic matter and nitrogen content are low. Model behavior also suggests decomposer organisms immobilize nitrogen from surrounding soils, accounting for the elevated quantities observed within decaying materials. Past hypotheses have proposed that soil flora and fauna partially decouple decomposition processes from abiotic constraints in this system. This study indicates that the pattern of microbial activities, accounting for the decomposition of buried materials in the absence of termites, is primarily determined by climatic conditions. © 1991.
Moorhead, DL; Reynolds, JF
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