Litter Decomposition Across an Air‐Pollution Gradient in the San Bernardino Mountains

Abstract

AbstractAir pollution may affect forest ecosystems by altering nutrient cycling rates. The objective of this study was to compare decomposition rates of L‐layer litter of ponderosa pine (Pinus ponderosa Laws.) and Jeffrey pine (Pinus jeffreyi Grev. & Balf.) collected from across an air‐pollution gradient in the San Bernardino Mountains in southern California. Litter from the more polluted western areas decomposed at a significantly (P = 0.01) faster rate than litter from plots in areas exposed to moderate or low pollution levels. The Shannon diversity index values for litter fungi were 1.41, 1.84, and 2.25 for plots in areas exposed to low, moderate, and high pollution levels. Nitrogen content of litter was greatest in the high pollution plots and was positively correlated with litter decomposition rate. Higher N and lower Ca content of litter at the more polluted western sites suggest that litter in the western plots originates from younger foliage than litter at the less polluted sites, possibly because of ozone (O3)‐induced needle abscission. Possible factors contributing to increased decomposition and fungal diversity in the western plots include: higher litter nutrient content because litter originates from younger foliage, higher soil N levels which may result in higher foliar N content, greater input of N from air pollution, and O3 damage to needles creating favorable sites for microbial decomposers.