PARENT SESSION
Oral Session 3: Biogeochemistry I: Litter and Decomposition.
Presiding: J Dilustro
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room A 107.
Nitrogen deposition alters soil and litter nutrient cycling in exotic annual grasslands of southern California.
Sirulnik, Abby*,1, Meixner, Thomas*,1, Fenn, Mark*,2, Allen, Michael*,1, Allen, Edith*,1, 1 University of California, Riverside, CA, United States2 USDA Forest Service, Riverside, CA, United States
ABSTRACT- Elevated nitrogen deposition may affect ecosystem processes in exotic annual grasslands that invade coastal sage scrub vegetation in southern California. Here we report our results on soil N mineralization and litter decomposition, including litter quality, mass loss, and impacts of elevated N on phosphatase activity. Added N affected nutrient cycling in the mineral soil as well as in litter. During some, but not all, of the in situ soil incubation periods, soil amended with N fertilizer had increased net mineralization rates and decreased N biomass. Litter of the dominant invasive exotic grass species, Bromus diandrus, at the high N deposition site, had greater percent P and N and lower percent lignin than from the low deposition site. B. diandrus from controlled conditions shows the same trend in litter quality. This litter was decomposed in a growth chamber on the surface of microcosms containing high and low N soil from a long-term field fertilization experiment. The decomposition experiment ran for 200 days until approximately 20% of litter remained. Mass loss and litter glucosidase activity results showed that litter quality and soil N accelerate B. diandrus decomposition. High N soil caused higher activity of acid phosphatase in litter and soil, suggesting that N fertilization could be affecting P cycling in these grasslands.
Key words: mineralization , grassland, nitrogen, decomposition