Litter decomposition is a fundamental ecosystem process controlled by biotic and abiotic factors. The breakdown of organic matter derived from plants plays key roles in nutrient cycling, primary productivity, and maintaining biodiversity. Anthropogenic global change has potentially important implications for litter decomposition. Atmospheric N deposition from anthropogenic sources has doubled terrestrial N inputs globally. Since the availability of N in the soil is an abiotic factor known to affect decomposition, N deposition may alter decomposition rates. In the United States, Southern California has the highest rates of N deposition from fossil-fuel emissions. Increased N levels have been known to perpetuate the spread of invasive plant species, which in turn may alter litter decomposition by changing the type, quantity, and quality of litter found in ecosystems. California grasslands are endangered ecosystems that continue to decline as a consequence of plant invasion facilitated by N deposition. In this study, we employed a litter bag decomposition experiment to test how litter type (invasive versus native) and litter quality (added nitrogen versus ambient nitrogen) affect litter decomposition rates in an experimental California grassland.
Results/Conclusions
Results from this study indicate that both litter type (invasive versus native) and litter quality (added nitrogen versus ambient nitrogen) affected litter decomposition. Litter from Bromus hordeaceus, an invasive annual grass, had lower decomposition rates than litter from Stipa pulchra, a California native perennial grass. Litter quality results showed that B. hordeaceus litter had lower %N (and thus, higher C:N) than S. pulchra litter. Therefore, B. hordeaceus litter decomposed more slowly than S. pulchra litter due to lower litter quality. Litter with added N had higher decomposition rates than litter with ambient nitrogen since litter with added N had higher litter quality (higher %N and lower C:N). Therefore, N deposition increased both litter quality and decomposition rates. B. hordeaceus litter that decomposes slower can accumulate as thatch and may have implications for nutrient cycling, native recruitment, and the grass-fire cycle. In conclusion, invasion and N deposition affect litter decomposition rates differently in California grasslands.