Toward the elucidation of eco-physiological processes in forests during and after rainfall

Abstract

Rainfall and fog are common in many regions worldwide, including the Japanese archipelago, and plant surfaces remain wet for more than 100 days annually in many areas. To date, most knowledge about plant processes such as photosynthesis, biomass partitioning, and growth is based on observations under ideal sunny conditions. A comprehensive understanding and prediction of plant responses in fluctuating environments requires investigating plant behaviors under both sunny and rainy conditions, but the quantification of physiological and physical processes in forests during rainfall can pose technical challenges. This review summarizes recent advances in elucidating physical and physiological phenomena within forests from the onset of rainfall to the immediate aftermath, focusing on trees and forests with complex three-dimensional structures. Wetting processes within the forest canopy can be estimated by analyzing throughfall drop size distributions. After leaf wetting, rainwater is absorbed by the leaves and assimilated into organic matter. Isotope labeling experiments have revealed that a substantial portion of leaf biomass that forms during and immediately after rainfall originates from absorbed water. Some studies of individual leaves have reported lower photosynthetic rates in forests during and immediately after rainfall, while analyses based on enclosed-path analyzers have revealed minimal decreases in overall forest gas exchange flux during rainfall events. We anticipate that integration of advanced technologies and cross-disciplinary information exchange will improve understanding of the diverse ecological phenomena occurring in forests on rainy days.