THE EFFECT OF ELEVATED ATMOSPHERIC CO2 ON LEAF LITTER DECOMPOSITION IN BEAVER CREEK, ARIZONA.

J.L. Moan, J.C. Marks, C.J. LeRoy, and C. Williamson. Department of Biology, Northern Arizona University, Flagstaff, Arizona 86011

Leaf litter is an important allochthonous energy source for stream ecosystems. It has been shown in previous studies that elevated atmospheric CO₂ affects leaf litter chemistry and decomposition. It is not known what effect this has on stream detritivore communities. In this experiment, leaves from 2 species of cottonwoods, Populus fremontii and P. angustifolia, grown in greenhouse chambers under elevated and ambient forced-air CO₂ conditions were collected and put in Beaver Creek, Arizona in litterbags. The decomposition rate of the leaves was measured. Leaves grown in elevated CO₂ showed a significantly slower decomposition than those grown in ambient conditions during the first harvest, but not for subsequent harvests. Significantly slower decomposition was observed for P. angustifolia for all four harvests. This suggests that atmospheric CO₂ may have an effect on early stages of leaf litter decomposition, but tree species has a greater overall effect. Invertebrate abundance in all treatments was found to decrease, but species richness increased. These differences can be attributed to a combination of leaf chemistry, microbial, fungal and invertebrate processing, microhabitat of streambed and greenhouse artifacts. This study is important because it strives to understand the effects of rising CO₂ in the Earth's atmosphere.