Effect of increased soil moisture and reduced soil temperature on a desert soil arthropod community.

The effects of soil moisture and temperature on arthropod communities were experimentally examined in the northern Chihuahuan Desert of New Mexico. Shaded plots were established which lowered the soil temperature several degrees; some plots received artificial rainfall to increase soil moisture. Shading reduced soil temperature at 5-cm depth 7-10 C. Soil moisture at 5 cm accounted for most of the variation in surface activity of subterranean termites (r values between 0.3 and 0.7). Termites did not respond to temperature differences. When all soils were at field capacity, there was no difference in termite activity in shaded and unshaded plots. There were higher densities of microarthropods in litter bags on the shaded plots than on the unshaded plots. Numbers of microarthropods were an order of magnitude larger in litter bags on watered and shaded plots than on other plots. Lower litter temperatures apparently affect litter arthropods more than increased soil moisture. Shade had no effect on ant colonies but there were fewer colonies on the watered plots. There was between 40 to 50% mass loss from creosotebush leaf litter after 7 months on all plots. Water and soil temperature had no effect on decomposition rates. INTRODUCTION Temperature extremes and water availability are considered to be the most important factors limiting production, activity of desert organisms and ecosystem processes in deserts (Noy-Meir, 1973, 1974; Whitford et al., 1981, Whitford et al., 1983). The frequency, amount and seasonal occurrence of precipitation are thought to affect productivity, litter decomposition and behavior of soil biota (Whitford et al., 1981). Noy-Meir (1973) proposed a "pulse-reserve" hypothesis for desert organisms in which rainfall sets off a pulse of activity that is rapidly reduced, but some energy is stored "reserved" to await the next pulse. If desert organisms behave as predicted by the "pulse reserve" hypothesis, simulated rainfall events should trigger intense activity of various groups of soil organisms. Recent work indicates that moisture may not be as important as once thought as a regulator of the activity of soil biota. Whitford et al. (1982a) found no effect of rainfall on disappearance of leaf litter. They suggested that the desert soil decomposer community has evolved adaptations that allow those organisms to process surface litter independently of rainfall, and that soil temperature could be the most important parameter affecting the rate of litter removal. Hence, rates of decomposition in North American deserts are considerably greater than predicted based on the actual evapotranspiration and lignin content, which are good predictors of decomposition in more mesic environments (Whitford et al., 1983). Subterranean termites Gnathamitermes tubiformans are the most important processors of dead plant material and dung in the northern Chihuahuan desert (Johnson and Whitford, 1975; Whitford et al., 1982b). Termites are active aboveground during the rainy seasons, especially in the autumn, when they can be found in accumulations of litter or producing mud galleries on dead plant material (MacKay et al., 1985). Ettershank et al. (1980) reported that termites locate large food objects such as cow dung 'Send reprint requests to W. G. Whitford.