Carbon and nitrogen dynamics during the decomposition of litter and roots of a Chihuahuan New Mexico USA desert annual Lepidium lasiocarpum

Parker, L.; Santos, P.; Phillips, J.; Whitford, W.

C and N dynamics were analyzed during the decompositon of litter and roots of the desert ephemeral pepperweed (L. lasiocarpum). Litter bags were treated with the insecticide chlordane and the fungicides benomyl and captan to eliminate or restrict groups of soil biota. The mass losses of buried litter (51, 39, and 25% for untreated, insecticide treated, and fungicide-insecticide-treated matieral, respectively) were higher than those of the respective root treatments (35, 18, and 15%) at 96 days. The mass loss of untreated material was correlated with numbers of detritivorous-fungivorous microarthropods, and only a small peprcentage of this loss was as CO2: 27 and 42% for litter and roots, respectively. In the absence of microarthropods a higher percentage of mass loss C could be accounted for as CO2: 33 and 76% for litter and roots, respectively, indicating that mass loss was due primarily to litter removal by microarthropod activity and not dependent on abiotic constrants such as soil moisture (r = 0.65. P less than 0.00l) than was mass loss when microarthropods were absent (r = 0.79, P less than 0.001). N the absence of microarthropods, mass loss was more closely coupled with biomass grazers, such as nematodies, which require free water for activity (r = 0.99, P less than 0.0001). Unlike mass loss, C mineralization was highest in untreated roots, suggesting a stimulation of microbial activity by microarthropods, while in untreated litter no stimulation was observed when compared to insecticide treatments. This difference was primarily a function of fungivorous microarthropod density,. with overgrazing occurring in the untreated litter. N budgets inicated the importance of microarthropods in the turnover of root N. In the presence of microarthropods 132% of the initial root N could be accounted for after 96 days, while in the absence of microarthropods 270% could be accounted for. This net immobilizatin of N was primarily in the soil organic fraction around the roots and was associated with fungal development. Data from this study reemphasize the importance of microarthropods as regulators of decomposition in deserts and suggest that predation by nematodes or protozoa on bacteria and fungi contributes to rate regulation. N flux data suggest decompositin of ephemeral roots with attendant N immobilization can reduce the N available to creosotebush, Larrea tridentata, thus reducing shrub production. Higher taxa of soil biota, i.e. nematodes and microarthropods, may thus be important regulators of N fluxes and of mass loss in decompositon.

Carbon and nitrogen dynamics during the decomposition of litter and roots of a Chihuahuan New Mexico USA desert annual Lepidium lasiocarpum

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