Greenfall litter decomposition of three common species in the northern Chihuahuan Desert, 2010-2012

Soil organic carbon (SOC) is derived primarily from the decomposition of plant biomass. Animals that create greenfall, or green leaf litter, influence SOC dynamics by altering the phenological condition and, therefore, nutrient quality of plant litter. Animals that transport greenfall to a microsite with different microhabitat conditions from those where senesced litter would typically be found also influence SOC dynamics by altering the prevalence of various decomposition drivers. Microsite differences are particularly pronounced in arid and semi-arid ecosystems with heterogeneous vegetation cover. We investigated differences in decomposition between greenfall and senesced litter of three common Chihuahuan Desert plants from which animals frequently generate greenfall (Larrea tridentata, Sporobolus flexuosus, Yucca elata), using a litterbag study to quantify differences in mass, carbon (C), and nitrogen (N) losses between green and senesced leaves placed in shrub intercanopy and subcanopy microsites in a desert shrubland. We hypothesized that decomposition would be more rapid in 1) greenfall than naturally senesced litter, because of the higher nutrient concentration in green than senesced leaves, and 2) in intercanopy than shrub subcanopy microsites, because of increased exposure to decomposition drivers like soil-litter mixing and photodegradation in the less vegetated open area between shrub canopies. Using a litterbag study, we quantified differences in litter mass, C, and N losses between green and senesced leaves placed in shrub subcanopy and intercanopy (open) microsites. Measured variables include litter mass and litter ash, carbon, and nitrogen content. We found that there were significant differences in the nutrient concentration of green and senesced leaves of the same species, and that both litter condition and microsite affected decomposition rate. For two of the three litter species, greenfall decomposed more rapidly than senesced litter, and for all three species litter in intercanopy microsites decomposed more rapidly than in subcanopy microsites. Our results support that the creation and translocation of greenfall by animals is an important mechanism regulating the speed of decomposition and the transfer of C and nutrients from plant biomass into the soil.