HR: 1340h
AN: B43A-0242    [Abstracts]
TI: The Presence of Plants Alters the Effect of Soil Moisture on Soil C Decomposition in Two Different Soil Types
AU: * Dijkstra, F A
EM: dijkstra@ucsc.edu
AF: Dept. of Environmental Studies University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064
AU: Cheng, W
EM: wxcheng@ucsc.edu
AF: Dept. of Environmental Studies University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064
AB: While it is well known that soil moisture directly affects microbial activity and soil C decomposition, it is unclear if the presence of plants alters these effects through rhizosphere processes. We studied soil moisture effects on soil C decomposition with and without sunflower and soybean. Plants were grown in two different soil types with soil moisture contents of 45 and 85% of field capacity in a greenhouse experiment. We continuously labeled plants with depleted ¹³C, which allowed us to separate plant-derived CO₂-C from original soil-derived CO₂-C in soil respiration measurements. We observed an overall increase in soil-derived CO₂-C efflux in the presence of plants (priming effect) in both soils with on average a greater priming effect in the high soil moisture treatment (60% increase in soil-derived CO₂-C compared to control) than in the low soil moisture treatment (37% increase). Greater plant biomass in the high soil moisture treatment contributed to greater priming effects, but priming effects remained significantly higher after correcting for plant biomass. Possibly, root exudation of labile C may have increased more than plant biomass and may have become more effective in stimulating microbial decomposition in the higher soil moisture treatment. Our results indicate that changing soil moisture conditions can significantly alter rhizosphere effects on soil C decomposition.
DE: 0402 Agricultural systems
DE: 0428 Carbon cycling (4806)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0486 Soils/pedology (1865)
DE: 1884 Water supply
SC: Biogeosciences [B]
MN: Fall Meeting 2005