An investigation on leaf water economy traits in trees with varying cloud immersion in the Wayqecha Andes region

Abstract

Tropical cloud forests (TCFs) are characterized by high levels of humidity due to the frequent presence of clouds, creating a unique ecosystem type. With the imminent threats of climate change, land-use change and deforestation, understanding how cloud immersion affects plants' water economy is imperative for conservation. In this study, we investigate three key leaf water economy traits exhibited by 26 tropical tree species, foliar water uptake (FWU), minimum conductance (gmin) and leaf water retention angle, along a natural cloud gradient in the Wayqecha Andes region in Peru. Two other plots established by the Wayqecha Amazon Cloud Curtain Ecosystem Experiment (WACCEE) were used, where an artificial barrier reduces the fog levels received by the treatment plot in comparison to the control. For FWU measurements, all samples were subjected to standardized wetting treatment, where leaves were submerged for two hours under controlled conditions. Leaf water retention angle was measured by recording the angle at which water moves when the leaf is tilted. For gmin determination, leaves were dried for four hours while mass loss, relative humidity and temperature were recorded regularly. The results showed significant large species differences for the three traits, with mean values between species exhibiting a 15-fold difference for FWU, a twofold difference in leaf water retention angle and a nine-fold difference for gmin. There was no significant within species difference in trait values of trees growing in the different cloud regimes or under the experimental cloud removal plot. Community-weighted trait averages of FWU and gmin did not differ between High, Medium and Low cloud level plots in the cloud gradient. However, leaf water retention angle was higher in Low cloud level plots, suggesting an improved capture and use of intercepted water under potentially more water-limited conditions. This study indicates that FWU and gmin might not be the most important traits in shaping tree community composition under varying cloudiness levels, but that leaf surface characteristics influencing the retention of intercepted fog water may play a role.