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We measured mass losses of both buried and surface litter of six litter types: leaves of the perennial evergreen shrub, Larrea tridentata, leaves of the winter deciduous perennials Fluorensia cernua, Prosopis glandulosa and Chilopsis linearis (a desert riparian species), an evergreen monocot, Yucca elata, and a mixture of annual plants. These species differed in lignin content and carbon-nitrogen ratios. There was no correlation between rates of mass loss and percent lignin, carbon-nitrogen ratio, or lignin-nitrogen ratio. The leaves of F. cernua and the mixed annuals exhibited the highest rates of mass loss. Surface litter of Y. elata, the mixed annuals and C. linearis exhibited higher mass loss than buried litter of the same species. The patterns of mass loss of buried and surface litter differed with buried litter mass loss occurring as a negative exponential and surface litter exhibiting low rates in winter and spring and high rates in summer. There was no correlation between mass loss in surface bags that were field exposed for 1 month and actual evapotranspiration (AET) but there was a correlation between AET and mass losses in buried litter. A model relating mass loss to AET and initial lignin content underestimated mass losses in all species examined.

We tested the hypotheses that rates of decomposition in a desert should be higher following single large rain events of 25 mm than evenly spaced 6 mm events and that supplemental rainfall should result in higher populations of soil biota. There were no significant differences in mass losses of creosotebush, Larrea tridentata, leaf litter on plots receiving water supplementation and no added water. On some sampling dates, there were higher mass losses in the 6 mm·week treatment. Weekly rainfall produced higher coefficients of variation in mass losses than the other rainfall regimes. A single event pulse compared with weekly pulses of rainfall during the normal "dry" period resulted in no differences in mass losses. Microarthropods and nematodes exhibited numerical responses to supplemental rainfall but the litter microflora did not. These studies provide direct experimental evidence that the conventional wisdom linking decomposition to rainfall in deserts is wrong. The studies also suggest that the effects of litter fauna on surface litter decomposition are minimal; therefore, future studies should focus on activites of the microflora.