Tuesday, August 7, 2007: 1:30 PM
San Carlos I, San Jose Hilton
Individual plant species and their interactions with their environment determine litter quality and nutrient availability during decomposition. I examined implications of Pennisetum ciliare invasion on leaf and root litter decomposition. Pennisetum ciliare tissue decomposition was compared to the native grass Heteropogon contortus. The effects of three community types (P. ciliare dominated, H. contortus dominated, and diverse native) on decomposition rates of P. ciliare and H. contortus were compared to better understand effects of tissue chemistry vs. plant community on decomposition. There were distinct differences between root and shoot tissue decomposition rates. The exotic P. ciliare shoot tissue decomposed twice as fast (ANOVA, P < 0.001), had 33% higher Acid Detergent Lignin (ADL)% (ANOVA, P < 0.001), and 63% lower Carbon to Nitrogen ratio (C:N) (ANOVA, P < 0.001) than H. contortus shoot tissue. Root tissue of P. ciliare decomposed at only 77% the rate of H. contortus (ANOVA, P = 0.02). The exotic grass roots had a 40% higher N content (ANOVA, P = 0.016), an 11% lower Carbon content (ANOVA, P = 0.040), a 51% lower C:N (ANOVA, P < 0.001), 11% higher Acid Detergent Fiber % (ANOVA, P = 0.001), and 39% higher ADL%(ANOVA, P < 0.001) than H. contortus. Averaged across the two grass species, annual decomposition constants (k) of shoot tissue incubated beneath native diverse vegetation communities were 15 - 19% higher (Tukey's, P = 0.005 and P = 0.04, respectively) than the k for tissue decomposed under P. ciliare and H. contortus dominated communities. There was no community-based effect on root tissue decomposition rates. These results indicate that this exotic grass impacts decomposition and nutrient cycling in invaded areas primarily via the faster decomposition rates of its own shoot tissue, rather than by affecting decomposition rates of native litters via alteration of ecosystem function.
