Aspect and species influences on nitrogen and phosphorus accumulation in Arizona chaparral soil‐plant systems

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Abstract
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.