ASPECT AND SPECIES INFLUENCES ON NITROGEN AND PHOSPHORUS ACCUMULATION IN ARIZONA CHAPARRAL SOIL-PLANT SYSTEMS

To improve understanding of nutrient relationships and factors affecting nutrient patterns in chaparral ecosystems a study was conducted to quantify the effect of aspect and shrub species on accumulation of N and P in a mature chaparral ecosystem. Components of shrub biomass, litter, and soil were sampled from 32 randomly selected soil-plant systems, eight each of Cercocarpus betuloides and Quercus turbinella on north and south aspects, and analyzed for N and P. Shrub species influenced dry matter accumulation, with Cercocarpus accumulating more biomass in leaves, stems, and litter than Quercus. Similarly, N concentration and accumulation were greater in Cercocarpus systems than in Quercus systems. This was attributed to the ability of Cercocarpus to form symbiotic relationships with actinomycetes capable of N fixation. Phosphorus accumulation was much greater in Cercocarpus biomass than in Quercus. Aspect significantly influenced P concentration of soil, with higher concentrations occurring on north than south aspects, which are subject to higher rates of erosion. About 40% of total N and 15% of total P in these systems are in the biomass, litter, and soil (0-2 cm); hence, the systems are especially vulnerable to loss by volatilization during prescribed fire or wildfire, and from erosion.