O papel ecológico da neblina e a absorção foliar de água em três espécies lenhosas de Matas Nebulares, SP - Brasil / The ecological role of fog and foliar water uptake in three woody species from Southeastern Brazilian Cloud Forest

AUTOR(ES)
DATA DE PUBLICAÇÃO

2010

RESUMO

Fog deposition is an important water source in several terrestrial ecosystems. Fog water intercepted by the plants can run off to the soil or be absorbed by the leaves. However, very little is known about the ecological role of fog and the mechanisms and structures involved in foliar water uptake by woody species in tropical environments. In this context, we investigated the anatomical pathways involved in the process of foliar uptake of water and evaluated the consequences of this process in the ecophysiological performance, growth and survival of three common woody species from Brazilian cloud forests: Drimys brasiliensis, Eremanthus erythropappus e Myrsine umbellata. Greenhouse experiments using artificial fog enriched in deuterium and labelling experiments with fluorescent apoplastic tracers demonstrated that the three species absorbed water directly through their leaf surfaces. Leaf water uptake contributed to as much as 42% of total foliar water content in D. brasiliensis. Fog exposition caused reversals in sap flow and reduced nighttime transpiration for this species. Water diffused directly through leaf cuticles in all species. Tector trichomes of E. erythropappus and glandular peltate trichomes of M. umbellata are important pathways for water uptake in these species. After the cuticular barrier was transposed, solutions moved through apoplast routes at the epidermis and parenchyma in all species, reaching the xylem in E. erythropappus and accumulating on collector cells of M. umbellata. The high abundance of hidrofilic compounds found on leaf surfaces of D. brasiliensis and M. umbellata may have contributed to the great retention of solution with apoplastic tracers in the mesophyll of these species. Sprayed water on isolated branches caused an immediate increase in leaf water status in the three species, a benefit also observed in a long-term experiment. After two months, plants under the fog treatment improved leaf water potential, photosynthesis and stomatal conductance in relation to plants exposed to drought in a greenhouse experiment. Species responses to the treatments were different. D. brasiliensis had 100% mortality after a month under drought. Soil water content (SWC) of fogged plants was constant throughout the experiment, suggesting that fog water might have been used as the main water source for transpiration during this period. E. erytroppappus was the only species with similar growth and survival rates in all treatments and the beneficial effects of fog water was only observed after two months. For M. umbellata, SWC decreased substantially in the drought and fog treatments but no decrease in water potential, photosynthesis and stomatal conductance was observed. For this species, fog water deposition caused a decoupling of foliar water relations and gas exchange from soil water availability.We demonstrated that the three cloud forest woody species can absorb water directly through their leaves during fog deposition, allowing shoot rehidratation and improving ecophysiological performance, growth and survival when soils are dry.

ASSUNTO(S)

drimys brasiliensis eremanthus erythropappus myrsine umbellata apoplastic routes plants drimys brasiliensis eremanthus erythropappus myrsine umbellata stable isotopes isótopos estáveis traçadores apoplásticos plantas - relações hidricas

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