Litter decomposition in a sandy Monte desert of western Argentina: Influences of vegetation patches and summer rainfall

We tested the hypothesis that shrub canopies interact with monthly rain pulses to control litter decomposition in a sandy Monte desert, in Argentina. We assessed (i) the potential for litter decomposition of soils beneath the canopies of two dominant shrub species ( Larrea divaricata and Bulnesia retama, Zygophyllaceae R. Br . ) and from bare-ground microsites or 'openings'; (ii) litter decomposition at different spatial patches over the summer rainy season; and (iii) the interaction between vegetation patches and monthly rain pulses on short- term litter decomposition, or decomposition pulses. In a greenhouse experiment, we found buried litter decomposition to be higher in soils from under the canopies of a dominant shrub species compared with soils from openings and sterilized controls. This, and higher nutrient concentration under shrub soils, suggest undercanopy soils may support a microbial community capable of decomposing litter at higher rates than soils in bare openings. However, field trials showed that shrub patches did not affect leaf litter decomposition over the rainy season, at least for short periods. We found an interaction between shrub patches and incubation time at the end of the field experiment, with higher litter decomposition rates under B. retama canopies. In a monthly field experiment, we found monthly rain pulses significantly explained decomposition pulses, irrespective of patch type. Our findings support the hypothesis that shrub soils have a greater potential for litter decomposition, but this is not directly translated to the field possibly due to interactions with abiotic factors. Rain pulses create conditions for decomposition pulses to occur at shorter time scales, whereas rainfall may interact with a dominant shrub undercanopy to control litter mass loss over longer time scales.