Seasonal fluctuations in Vitis vinifera root respiration in the field

We studied the seasonal fluctuation of soil respiration (R-S), and its root-dependent (R-R) and basal (R-B) components, in a Vitis vinifera (Chardonnay) vineyard. The R-S components were estimated through independent field methods (y-intercept and trenching) and modeled on the basis of a Q(10) response to soil temperature, and fine and coarse root respiration coefficients. The effect of assimilate availability on R-R was assessed through a trunk girdling treatment. The apparent Q(10) for R-R was twice that of R-B (3.5 vs 1.6) and increased linearly with increasing vine root biomass. The fastest R-R of fine roots was during rapid fruit growth and the fastest R-R of coarse roots was immediately following fruit development. R-S was estimated at 32.6 kg ha(-1) d(-1) (69% as a result of R-R) for the hottest month and at 7.6 kg ha(-1) d(-1) (18% as a result of R-R) during winter dormancy. Annual R-S was low compared with other natural and cultivated ecosystems: 5.4 Mg ha(-1) (46% as a result of R-R). Our estimates of annual vineyard R-S are the first for any horticultural crop and suggest that the assumption that they are similar to those of annual crops or forest trees might lead to an overestimation.