Carbon and Nitrogen Dynamics During the Decomposition of Litter and Roots of a Chihuahuan Desert Annual, Lepidium Lasiocarpum

Abstract

Carbon and nitrogen dynamics were analyzed during the decomposition of litter and roots of the desert ephemeral pepperweed (Lepidium lasiocarpum). We treated litter bags 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 fungicideinsecticide-treated material, respectively) were higher than those of the respective root treatments (35, 18, and 15%) at 96 d. The mass loss of untreated material was correlated with numbers of detritivorousfungivorous microarthropods, and only a small percentage of this loss was as C0 2 : 27 and 42% for litter and roots, respectively. In the absence of microarthropods a higher percentage of mass-loss carbon could be accounted for as C0 2 : 33 and 76% for litter and roots, respectively, indicating that mass loss was due primarily to litter removal by microarthropod activity and not to mineralization. Litter removal by microarthropods was less dependent on abiotic constraints such as soil moisture (r = 0.65, P < .001) than was mass loss when microarthropods were absent (r = 0.79, P < .001). In the absence of microarthropods, mass loss was more closely coupled with biomass of grazers, such as nematodes, which require free water for activity (r = 0.99, P < .0001).Unlike mass loss, carbon 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.Nitrogen budgets indicated the importance of microarthropods in the turnover of root nitrogen. In the presence ofmicroarthropods 132% of the initial root nitrogen could be accounted for after 96 d, while in the absence ofmicroarthropods 270% could be accounted for. This net immobilization of nitrogen was primarily in the soil organic fraction around the roots and was associated with fungal development.Data from this study re-emphasize 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. Nitrogen flux data suggest that when spring ephemeral plant production is high, decomposition of ephemeral roots with attendant nitrogen immobilization can reduce the nitrogen 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 nitrogen fluxes and of mass loss in decomposition.

Decomposition of leaf and root litter of Chihuahuan desert shrubs: effects of three years of summer drought

“…Whitford et al, 1982;Silva et al, 1985) suggest that the moisture insensitivity of decay of surface litter in the Jornada Basin is due to termites or other microarthropods transporting the material into the soil pool. When microarthropods and/or termites were removed, rates of mass loss from bags of leaf litter were reduced substantially Parker et al, 1984b), and the resulting mass loss was much more strongly related to levels of soil moisture (Whitford & Parker, 1989). However, we saw no obvious evidence of termite activity in the litter samples, and furthermore, the increase in the N content of the remaining litter, that we observed in both control and treatment litter during the first half of the study (Fig.…”

Decomposition of Avena sterilis litter under arid conditions

“…However, some decomposition studies have been performed in arid and semi-arid ecosystems with extreme ranges of moisture availability and many other climatic factors, mostly in North American deserts (Elkins & Whitford, 1982;Parker et al, 1984;Schaefer et al, 1985;Whitford et al, 1988), with only a few studies in the Negev Desert of Israel Steinberger et al, 1990). The North American studies, especially those conducted in the Chihuahuan Desert, have elucidated several surprising features of the decomposition rate in deserts: (1) the rate of organic matter decomposition is high and almost equal to that reported for the wet tropics (Schaefer et al, 1985); (2) the rate of decomposition is not correlated with lignin content or actual evapotranspiration (Whitford et al, 1981;Santos et al, 1984;Schaefer et al, 1985); (3) there is no relationship between the litter decomposition rate and litter quality (Schaefer et al, 1985); and (4) soil fauna accelerate the decomposition of buried litter but not surface litter (Parker et al, 1984). In addition, Berg (1984) and Offer et al (1992) suggested the possibility that soil nutrients, especially nitrogen, may play an important role in controlling the litter decomposition rate.…”

The effects of termites and straw mulch on soil nitrogen in a creosotebush (Larrea tridentata) dominated Chihuahuan desert ecosystem

“…The higher soil nitrogen on plots with no straw mulch and no termites resulted from the decomposition and mineralization of annual plant roots (Parker et al, 1984). Subterranean termites consume a large fraction of annual plant roots .…”