PARENT SESSION
Oral Session 110: Biogeochemistry VII: Soil I and Nutrient Cycling I.
Presiding: K Lajtha
Thursday, August 5, 1:30 PM to 5:00 PM, Meeting Room A 106.
Episodic rewetting enhances carbon and nitrogen release from seasonally arid soils.
Miller, Amy*,1, Schimel, Joshua1, Meixner, Tom2, Sickman, James3, Melack, John1, 1 University of California, Santa Barbara, CA, USA2 University of California, Riverside, CA, USA3 University of New Orleans, New Orleans, LA, USA
ABSTRACT- The short-term pulse of carbon (C) and nitrogen (N) mineralization that accompanies the wetting of dry soils may dominate annual C and N production in many arid and semi-arid environments characterized by seasonal transitions. The effect that this C release, both as DOC and CO2, has on soil N dynamics may be substantial. We used a laboratory incubation to evaluate the impact of drying and rewetting frequency on soil carbon-nitrogen interactions, and the degree to which rewetting enhanced C and N release. Following repeated drying and rewetting of seasonally arid chaparral soils, cumulative respiration in rewet treatment soils was 2.2-3.7 times greater than from soils maintained at equivalent soil moisture. Net N mineralization and nitrification were likewise enhanced by rewetting in spite of significant reductions in nitrification potential. Extractable N (DIN + DON) ranged from 1% of total soil N in dry soils, to 10% of total N in frequently wetted soils, and was dominated by NO3- in all but the driest soils. Carbon (litter) addition significantly reduced N release, as expected, but also indicated that leaching losses of DON and DOC may be large and derived primarily from soil organic matter in undisturbed dry soils. These results, paired with field data showing a marked increase in N pools during the transition from summer drought to winter rains, indicate that the wetting of dry soils has the potential to significantly enhance C and N release and to disproportionately impact annual C and N budgets.
Key words: nitrification, DOC, chaparral, DON