Nutrient limitations removal by fertilizations decreases nocturnal water loss in savanna trees.

BUCCI, S.J., SCHOLZ F.G. (ORADOR), GOLDSTEIN G., MEINZER F.C., FRANCO A.C.

Montreal

Simposio; IX International Congress of Ecology.; 2005

Nocturnal water loss has been studied in relatively few species because it is assumed that stomata are closed at night. However, under certain environmental conditions nocturnal transpiration can be relatively high. In Neotropical savannas soil nutrients availability is low and nocturnal temperatures and air saturation deficit (D) are high. We evaluated the occurrence and magnitude of nocturnal transpiration in some dominant woody species of savannas Brazil during the dry season as well as the effects of changes in soil nutrient availability on nocturnal water loss. Nocturnal sap flow contributed from 13 to 28 % of total daily transpiration and all species maintained their stomata partially open at night. Nighttime stomatal conductance (gs) represented about 30% of daily total gs. Leaf water potentials ( L) for covered (non-transpiring) leaves were less negative throughout the day than for freely transpiring leaves. At nighttime, ( L) differences between exposed and covered leaves ranged from 0.1 to 0.5 MPa, suggesting that predawn L was more negative than bulk soil estimated by predawn L of freely transpiring leaves. Nocturnal sap flow, gs and disequilibrium between leaf and soil Y decreased in trees fertilized with N and P. The potential adaptive significance, if any, of nocturnal stomata opening in savannas woody species is not clear, but it is possible that having stomata partially open during the early morning when incident light is increasing rapidly and air saturation deficit is still low, may enhance the water-use efficiency and permit additional carbon gain before stomata conductance is restricted. It appears that nocturnal transpiration can prevent equilibration between leaf and soil water potential at night and increase total daily nutrients uptake.