Removal of nutrient limitations by long-term fertilization decreases nocturnal water loss in savanna trees

SCHOLZ, FG, S.J. BUCCI, G. GOLDSTEIN, F.C. MEINZER, A.C. FRANCO AND F. MIRALLES-WELHEIM

TREE PHYSIOLOGY

Heron Publishing

Lugar: Victoria Canada; Año: 2007 vol. 27 p. 551 - 559

0829-318X

Under certain environmental conditions, nocturnal transpiration can be relatively high in temperate and tropical woody species.  We have previously shown that nocturnal sap flow accounts for up to 28% of total daily transpiration in woody species growing in a nutrient-poor Brazilian Cerrado ecosystem. In the present study, we assessed the impact of increased nutrient supply on nocturnal transpiration in three dominant Cerrado tree species to explore the hypothesis that in nutrient-poor systems, continued transpiration at night may enhance delivery of nutrients to root absorbing surfaces.  We compared nocturnal transpiration of individuals growing in unfertilized plots and plots to which nitrogen (N) and phosphorous (P) had been added twice yearly from 1998 to 2005.  Three independent indicators of nocturnal transpiration were evaluated: sap flow in terminal branches, stomatal conductance (gs), and disequilibrium in water potential between covered and exposed leaves (DYL).  In the unfertilized plots, about 25% of the total daily sap flow occurred at night.  Nocturnal sap flow was consistently lower in the N and P-fertilized plots, significantly so in the N treatment.  Similarly, nocturnal gs was consistently lower in fertilized than unfertilized plots where it sometimes reached values of 150 mmol m-2 s-1 by the end of the dark period.  Predawn gs and the percentage of nocturnal sap flow were linearly related.  Nocturnal DYL was significantly greater in the unfertilized plots than in N and P-fertilized plots.  The absolute magnitude of DYL increased linearly with the percentage of nocturnal sap flow.  These results are consistent with the idea that enhancing nutrient uptake by allowing additional transpiration to occur at night when evaporative demand is lower may avoid excessive dehydration associated with increased stomatal opening during the day when evaporative demand is high.