Canopy conductance and gas exchange of a Japanese cypress forest after rainfall‐induced wetness

Wet canopy photosynthesis in a temperate Japanese cypress forest

This study aimed to reveal the mechanism and significance of wet canopy photosynthesis during and after rainfall in temperate coniferous ecosystems by evaluating the influence of abaxial leaf interception on wet canopy photosynthesis. We used the eddy covariance method in conjunction with an enclosed-path gas analyser to conduct continuous ecosystem CO2 flux observations in a Japanese cypress forest within the temperate Asian monsoon area over 3 years. The observation shows that wet-canopy CO2 uptake predominantly occurred during the post-rainfall canopy-wet period rather than the during-rainfall period. Then, the measured canopy-wet net ecosystem exchange was compared with the soil-vegetation-atmosphere transfer multilayer model simulations under different parameter settings of the abaxial (lower) leaf surface wet area ratio. The multilayer model predicted net ecosystem exchange most accurately when it assumed the wet area ratio of the abaxial surface was 50% both during and after rainfall. For the wet canopy both during and after rainfall, the model overestimated CO2 uptake when it assumed no abaxial interception in the simulation, but underestimated CO2 uptake when it assumed that the entire abaxial leaf surface was wet. These results suggest that the abaxial surface of the Japanese cypress leaf is only partly wet to maintain stomatal openness and a low level of photosynthesis. These results allow for an evaluation of the effect of rainfall on forest carbon circulation under a changing climate, facilitating an improvement of ecosystem carbon exchange models.

Shower thoughts: why scientists should spend more time in the rain

Stormwater is a vital resource and dynamic driver of terrestrial ecosystem processes. However, processes controlling interactions during and shortly after storms are often poorly seen and poorly sensed when direct observations are substituted with technological ones. We discuss how human observations complement technological ones and the benefits of scientists spending more time in the storm. Human observation can reveal ephemeral storm-related phenomena such as biogeochemical hot moments, organismal responses, and sedimentary processes that can then be explored in greater resolution using sensors and virtual experiments. Storm-related phenomena trigger lasting, oversized impacts on hydrologic and biogeochemical processes, organismal traits or functions, and ecosystem services at all scales. We provide examples of phenomena in forests, across disciplines and scales, that have been overlooked in past research to inspire mindful, holistic observation of ecosystems during storms. We conclude that technological observations alone are insufficient to trace the process complexity and unpredictability of fleeting biogeochemical or ecological events without the shower thoughts produced by scientists' human sensory and cognitive systems during storms.

Diurnal Change of the Photosynthetic Light-Response Curve of Buckbean (Menyanthes trifoliata), an Emergent Aquatic Plant

Understanding plant physiological responses to high temperature is an important concern pertaining to climate change. However, compared with terrestrial plants, information about aquatic plants remains limited. Since the degree of midday depression of photosynthesis under high temperature depends on soil water conditions, it is expected that emergent aquatic plants, for which soil water conditions are always saturated, will show different patterns compared with terrestrial plants. We investigated the diurnal course of the photosynthetic light-response curve and incident light intensity for a freshwater emergent plant, buckbean (Menyanthes trifoliata L.; Menyanthaceae) in a cool temperate region. The effect of midday depression was observed only on a very hot day, but not on a moderately hot day, in summer. The diurnal course of photosynthetic light-response curves on this hot day showed that latent morning reduction of photosynthetic capacity started at dawn, preceding the apparent depression around the midday, in agreement with results reported in terrestrial plants. We concluded that (1) midday depression of emergent plants occurs when the stress intensity exceeds the species' tolerance, and (2) measurements of not only photosynthetic rate under field conditions but also diurnal course of photosynthetic light-response curve are necessary to quantify the effect of midday depression.