1. Results and discussion
Our results suggest that chronic N deposition causes a decline in litter decomposition.
A decline in microbial respiration and N demand in soil exposed to chronic N inputs could act to increase soil C storage and N availability in these semiarid shrublands.
Introduction
Atmospheric N deposition is estimated to be kgN ha-1 yr-1 in polluted southern Californian chaparral and coastal sage scrub.
Dry deposition accounts for 85-90% of anthropogenic N and accumulates on the surfaces of plants and soil during summer and fall.
N accumulation has the potential to alter soil C and N storage and cycling.
Hypothesis: Chronic N addition will increase initial rates of microbial respiration and N-mineralization.
Litter and soil C and N mineralization dynamics for a coastal sage scrub ecosystem exposed to chronic experimental N deposition
LaTeasha N. Edelman, Judy Garza, and George L Vourlitis
Department of Biological Sciences, California State University, San Marcos, CA, USA
Results and discussion
There was a significant soil x time interaction with microbial respiration. Soil exposed to added N had a higher initial, but a lower final, respiration rate.
Measuring CO2 efflux
Experimental design at SMER
Fenn et al. (2010) JEMA 91:
Salvia mellifera
This research was supported by the NSF-CAREER (DEB ), NIH-NIGMS-SCORE (S06 GM 59833), and USDA-NIFA-HSI ( ). Access to the Santa Margarita Ecological Reserve granted by San Diego State University is gratefully acknowledged.
Acknowledgements
Conclusions
Microbial respiration
N mineralization was significantly higher in soil exposed to added N.
Experimental N enrichment significantly increased litter N concentration and decreased litter C:N ratio; however, litter structural chemistry was not affect by N addition.
N mineralization
Total C mineralization was significantly depressed in soil exposed to added N, while N mineralization was significantly higher in soil exposed to added N. These data indicate that greater microbial growth in control soil increased microbial N demand
Methods
Plots (100 m2) at the Santa Margarita Ecological Reserve have received annual inputs of ambient (control, n = 4) or added N (50 kgN ha-1 yr-1; n = 4) since October 2002.
Soil cores (0-10 cm) and leaf litter of Salvia mellifera collected from added N and control plots were used in a factorial laboratory experiment with control and added N soil and litter as treatment factors (n = 4 per treatment combination).
N mineralization (NH4+ + NO3-) and microbial respiration was periodically measured over 28 weeks.