Tuesday, November 14, 2006 - 8:30 AM
185-1

Litter Effects on DOC and DON Dynamics in a Sierran Conifer Forest.

William Horwath, Univ of California at Davis, LAWR, 3226 PES Bldg, Davis, CA 95616-8627, Victoria Nicholson, Univ. California Davis, One Shields Ave, Davis, CA 95616, and Robert Powers, PSW Research Station, 3644 Avtech Parkway., Redding, CA 96002.

Long-term (35-year old) shrub management and litter quality effects on dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) in ponderosa pine plantations were examined with field and laboratory incubations. Dual (13C and 15N) and single (either 13C or 15N) labeled Pinus ponderosa and Ceanothus integerrimus litter was added to soil where understory shrubs were absent or present for 35 y. The soil litter mixtures were incubated for 90 days in the lab and two years in the field to determine DOC and DON dynamics.  The contribution of mineralized carbon from litter and soil was determined through frequent 13CO2 headspace analysis. Our results indicate that shrub management affects all aspects of the C and N cycle (increases microbial activity, DOC production, and N mineralization).  Soils where shrubs were present (SP) respired an average of 3.32 mg C/g soil over the course of the lab incubation while soils where shrubs were absent (SA) respired only 2.56 mg C/ g soil.  DOC production in SP soils was increased over the incubation (average 29.8 g DOC/g soil) as compared to DOC production in the SA soils (average 23.87 g DOC/g soil). Nitrogen mineralization in the SP soil was lower (average 4.38 g N/g soil) than in the SA soil (average 5.89 g N/g soil).  Litter quality and diversity only showed significant effects on the N dynamics.  Adding high quality ceanothus litter to the soil led to a decrease in N mineralization (average 5.46 g N/g soil) as compared to low quality pine litter (average 6.55 g N/g soil).  Our results indicate a significant correlation (P<0.01) between CO2 and dissolved organic carbon (DOC) production showing that DOC production from litter was primarily controlled by microbial activity.  Net N mineralization was also significantly correlated (P<0.024) to respiration but appeared not tightly coupled to DOC.