Xeromorphic traits help to maintain photosynthesis in the perhumid climate of a Taiwanese cloud forest
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Previous flux measurements in the perhumid cloud forest of northeastern Taiwan have shown efficient photosynthesis of the endemic tree species Chamaecyparis obtusa var. formosana even under foggy conditions in which leaf surface moisture would be expected. We hypothesized this to be the result of ‘xeromorphic’ traits of the Chamaecyparis leaves (hydrophobicity, stomatal crypts, stomatal clustering), which could prevent coverage of stomata by precipitation, fog, and condensation, thereby maintaining CO2 uptake. Here we studied the amount, distribution, and composition of moisture accumulated on Chamaecyparis leaf surfaces in situ in the cloud forest. We studied the effect of surface tension on gas penetration to stomata using optical O2 microelectrodes in the laboratory. We captured the dynamics of condensation to the leaf surfaces with an environmental scanning electron microscope (ESEM). In spite of substantial surface hydrophobicity, the mean water film thickness on branchlets under foggy conditions was 80 µm (upper surface) and 40 µm (lower surface). This amount of water could cover stomata and prevent CO2 uptake. This is avoided by the clustered arrangement of stomata within narrow clefts and the presence of Florin rings. These features keep stomatal pores free from water due to surface tension and provide efficient separation of plant and atmosphere in this perhumid environment. Air pollutants, particularly hygroscopic aerosol, may disturb this functionality by enhancing condensation and reducing the surface tension of leaf surface water.
KeywordFog Clustered stomata Gas exchange LMA ESEM Xeromorphism
This work was supported by Deutscher Akademischer Austauschdienst (DAAD 56186816), Germany, Taiwan Ministry of Science and Technology (MOST: 102-2911-I-259-502) and Deutsche Forschungsgemeinschaft (BU 1099/7-1, 7-2). We thank Knut Wichterich for his help with the ESEM measurements, I-Ling Lai for advice.
Author contribution statement
SP, S-CC, and JB designed the study, SP, S-CC, DZ, and JB performed the field experiments, SP, MH, and JB designed and performed the ESEM studies, SP, DZ, HZ, and JB performed the O2 measurements, SP performed the statistical analysis, and SP, DZ, DAG, and JB performed the lab analysis and wrote the manuscript, with revision by all authors.
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