HR: 12:05h
AN: B12B-08    [Abstracts]
TI: Effects of experimental drought on soil CO2 efflux in a Mediterranean Quercus ilex forest
AU: * Misson, L
EM: laurent.misson@cefe.cnrs.fr
AF: CNRS-CEFE, 1919 route de Mende, Montpellier, 34000, France
AU: Rocheteau, A
EM: alain.rocheteau@cefe.cnrs.fr
AF: CNRS-CEFE, 1919 route de Mende, Montpellier, 34000, France
AU: Rambal, S
EM: serge.rambal@cefe.cnrs.fr
AF: CNRS-CEFE, 1919 route de Mende, Montpellier, 34000, France
AU: Ourcival, J
EM: jean-marc.ourcival@cefe.cnrs.fr
AF: CNRS-CEFE, 1919 route de Mende, Montpellier, 34000, France
AU: Limousin, J
EM: jean-marc.limousin@cefe.cnrs.fr
AF: CNRS-CEFE, 1919 route de Mende, Montpellier, 34000, France
AU: Rodriguez, R
EM: raquel.rodriguez@cefe.cnrs.fr
AF: CNRS-CEFE, 1919 route de Mende, Montpellier, 34000, France
AU: Joffre, R
EM: richard.joffre@cefe.cnrs.fr
AF: CNRS-CEFE, 1919 route de Mende, Montpellier, 34000, France
AB: Mediterranean ecosystems are among the most heavily and early utilized by man, and as a result, are frequently severely impacted. Because of these anthropogenic perturbations as well as strong ecological constraints like long summer drought, Mediterranean ecosystems are predicted to be especially responsive to environmental changes. One scenario based on the output from four climate models suggests that temperatures could rise by over 4°C by 2100 over the Mediterranean Basin. Annual precipitation is projected to decline by 10 to 40% over much of Africa and South-eastern Spain, with smaller but significant changes elsewhere. The objectives of this research was (1) to better understand how such drought would influences soil carbon storage and soil respiration in forested ecosystems, (2) to test the interaction between soil water and soil temperature in controlling soil respiration, and (3) to examine the relationship between canopy photosynthesis and soil respiration in a seasonally dry evergreen ecosystem. To reach these objectives, drought was simulated since 2003 by continuously excluding 20% of throughfall using gutters below canopy in a Quercus ilex forest in south of France (MIND project). In 2005, soil respiration was continuously measured in a control and a dry plot using an automatic soil respiration system (Rayment, open system). Respiration showed a diurnal hysteresis: efflux was higher during the day than at night for the same temperature. This small hysteresis could not be explained by the progression of the heat front in the soil profile and was correlated with canopy photosynthesis derived from an Eddy-Covariance tower nearby (Carboeurope project). However, canopy photosynthesis only explained 17% of the diurnal variability of soil respiration, while temperature explained 80%. Seasonally, soil water content explained 80% of the variation in respiration in both treatments, temperature explaining 60% of the residuals. Soil water content and soil respiration were systematically lower in the dry plot. However, soil respiration in the dry plot was higher than in the control plot for the same soil water content, and soil respiration was the same in both plots at high soil water content. Thus, after 3 years of rain exclusion, soil respiration seems to have acclimated to dryer conditions. The apparent Q10 was not influenced by the throughfall exclusion. Soil respiration was modeled using soil water and soil temperature relationships calibrated in both plots. The model showed that respiration in the dry plot was similar than in the control plot in winter for high soil water content. Soil respiration was also almost equal in both plots in mid-summer, for very low soil water content. Only in spring, for medium soil water content, soil respiration was higher in the control plot. Thus annually, respiration was almost equal in both plots (5% lower in the dry plot). Consequences for soil carbon storage in Mediterranean forests in the future are discussed.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0418 Bioremediation
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0438 Diel, seasonal, and annual cycles (4227)
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting