M.S. Alvarado-Barrientos, H. Asbjornsen, F. Holwerda
Fog occurrence has been shown to suppress transpiration (Et). On the other hand foggy conditions during which leaf wetness does not block stomatal gas exchange may enhance stomatal conductance, and so Et immediately after fog. Furthermore, although nighttime Et has been found to be prevalent for a wide range of species from cloud-affected forests, its magnitude relative to daytime Et has been reported to be generally small. Here, we report considerable variability in nighttime Et rates of Pinus patula trees associated to rapidly changing meteorological conditions typical for the dry season in the tropical montane cloud belt of the Eastern Sierra Madre, Mexico. Stand level tree Et was derived from sapflow measurements with the Heat Ratio Method in the stem of P. patula trees growing in contrasting stands and at different elevations within the cloud belt: 10-year-old reforestation at 2180 m a.s.l. and mature forest at 2470 m a.s.l. The dry-season range of nighttime Et for the young and mature forest was 0-0.08 and 0-0.06 mm h-1, respectively. Expressed as a proportion of dry-season daily totals, nighttime Et was high and variable (42±28 and 19±23% for the young and mature stand, respectively). This large variation was related to the wide range of air humidity, caused by the alternation of cold front intrusions bringing about fog events and high pressure weather characterized by dry nights with vapor pressure deficits up to 2 kPa. Shortly after the end of fog events without concurring rainfall, nighttime Et for the young stand was higher (although not significantly) and more variable than for fog-free nights. Climate change-related alterations in lifting condensation level that have been projected for tropical montane regions will also affect the dynamics of the inversion layer, and as shown here, nighttime Et may increase/decrease considerably depending on a lowering/rise of the cloud ceiling.
Alvarado-Barrientos, M.S., Asbjornsen, H. and Holwerda, F. (2013). IS NIGHTTIME TRANSPIRATION ENHANCED AFTER FOG EVENTS?. Acta Hortic. 991, 133-139
DOI: 10.17660/ActaHortic.2013.991.16
cloud forest, sap flow, inversion layer, leaf wetness, Pinus patula, visibility

Acta Horticulturae