Tuesday, November 14, 2006 - 3:00 PM
202-14
Soil Moisture Alters Rhizosphere Effects on Soil C Decomposition in Two Different Soil Types.
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 a sandy loam and a clay loam 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 (up to 76% increase in soil-derived CO2-C compared to control) than in the low soil moisture treatment (up to 52% increase). The response to increased soil moisture content was greater in the sandy loam soil than in the clay loam soil. 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 become more effective in stimulating microbial decomposition in the higher soil moisture treatment and in the sandy loam. Our results indicate that rhizosphere processes can accelerate soil moisture effects on soil C decomposition.
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