PS 8-75
The effects of added nitrogen deposition on net nitrogen mineralization and microbial biomass in semi-arid shurblands

Monday, August 5, 2013
Exhibit Hall B, Minneapolis Convention Center
Cloe S. Hentz, Department of Biological Sciences, California State University San Marcos, San Marcos, CA
George L. Vourlitis, Department of Biological Sciences, California State University, San Marcos, CA
Background/Question/Methods

Anthropogenic activity has significantly increased the levels of N in the atmosphere that eventually deposit onto semi-arid shrublands. The increased N deposition has altered litter and soil organic matter quality (C:N ratio) , and presumably, levels net N mineralization and microbial biomass. We expect that semi-arid shrublands exposed to high levels of added N will have increased levels of net N mineralization and microbial activity, and we have been measuring in situ rates of net N mineralization in plots exposed to ambient and elevated (50 kgN ha-1 yr-1) N addition.  Soil samples in the upper 10 cm layer were collected monthly and incubated in perforated PVC tubes over monthly intervals beginning in December 2012. 

Results/Conclusions

Net N mineralization and nitrification were quantified as the change in NH4 and NO3, respectively over the monthly interval, and microbial biomass was measured using chloroform fumigation.  Previous results revealed that N addition significantly increased NH4 and NO3 availability; however, it was unclear whether net mineralization or microbial N uptake was affected by exogenous N.  These data will help determine how N addition alters N cycling dynamics in the field and how interactions between N availability and soil moisture alter microbial activity in semi-arid shrublands.