Document: MIC-3-83-1

Effects of nitrogen deposition and ozone on three major plant species of the San Bernardino Mountains.

EATOUGH, M.* and T.D.PAINE

Univeristy of California, Riverside, CA 92521 USA ¹

Abstract:
This project examines the impact of ozone and nitrogen additions on arthropod herbivore communities of three major plant species in a xeric mixed conifer forest. In eastern forests, nitrogen saturation has been associated with forest decline. Because of differences in nitrogen cycling in western forests, high levels of nitrogen may be deposited without leading to decline. The impact of LA Basin emissions on surrounding forests may therefore be mediated by changes in foliar chemistry that are optimally examined by assessing herbivore populations. The effects seen in the herbivore community are expected to be associated with changes in C and N allocation of the plant, which may vary with plant species. The plant species used in this study each store carbon differently and may therefore be affected differently by ozone exposure. Treatments consisted of ambient ozone exposure and N fertilizer additions (control and 150 kg ha^-1 yr^-1) at two sites east of Los Angeles. The western-most site has historically been associated with high concentrations of ozone and high levels of nitrogen deposition while the more eastern site has received relatively low input from atmospheric ozone and nitrogen. Insects were extracted from foliage collected during the 1998 growing season. Richness for gross morphotaxa and the Shannon-Wiener diversity index were determined for each treatment level. Pteridium aquilinum herbivore diversity was lower with high atmospheric ozone exposure but increased with N additions, regardless of ozone exposure. Richness was significantly lower for the high ozone exposure with no added N. Quercus kellogii herbivore richness and diversity increased with N additions for low ozone exposure, but decreased with N additions under high ozone. Pinus ponderosa herbivore richness and diversity decreased with N additions for both low and high ozone exposure and were higher with high ozone exposure. This research indicates that insect communities in the San Bernardino forest are affected by anthropogenic pollution. As N emissions increase with growing populations in Southern California, we predict that community structures will further be altered.

Keywords: ozone, nitrogen deposition, insect diversity, herbivory, insect-plant interations

This abstract is being presented at: 3:30 PM in session:
Poster Session #15: Nutrient Cycling.