Transpiration and stomatal behaviour of Quercus ilex plants during the summer in a Mediterranean carbon dioxide spring

摘要: Variations in the water relations and stomatal response of Quercus ilex were analysed under field conditions by comparing trees at two locations a Mediterranean environment during consecutive summers (1993 1994). We used heat-pulse velocity technique to estimate transpirational use 5 month period from June November 1994. At end sap flow measurements, harvested, foliage sapwood area measured. A distinct environmental gradient exists between sites with higher atmospheric CO 2 concentrations proximity natural spring. Trees spring site have been growing for generations elevated concentrations. both sites, maximum leaf conductance was related predawn shoot potential. The effects deficits on whole-plant transpiration summer drought severe. Leaf potential recovered after major rainfall September predrought values. Sap flow, decreased parallel increases hydraulic resistance, reaching minimum mid-summer. These relationships are agreement hypothesis control prevent desiccation damage but also avoid 'runaway embolism'. underwent less reduction resistance given value decrease caused limited tended be high than low vapour pressure deficit. Mean (and diurnal) flux consistently trees. degree varied among periods. had corresponding values either cross-sectional or area. Larger displayed smaller differences trees, strong association found latter supporting stem specific (SLA) not influenced site. results discussed terms plant organ whole-tree scale.