Fog Water Is Important in Maintaining the Water Budgets of Vascular Epiphytes in an Asian Tropical Karst Forests during the Dry Season

Yi Wu,Peili Fu,Liang Song,Huazheng Lu,Quan Chen,Junen Wu,Wenjie Liu,Su Li,Wenyao Liu,Youxin Shen,Pingyuan Wang

doi:10.3390/f9050260

Abstract

Fog may be an important source of water for forest vascular epiphytes on trees, because they lack direct access to sources of soil water, but little is known about the water use proportions from various sources and potential water uptake pathways in epiphytes. Here, we analyzed leaf carbon isotope ratios as a measure of water use efficiency (WUE), proportions of fog, rain, and soil water use, and foliar water uptake (FWU) in species of epiphyte and their host trees in a tropical karst dwarf forest in China during the dry season. We found that the WUE, as represented by leaf δ13C, was generally enriched in the epiphyte species compared to their host trees. Epiphytes used substantial proportions of fog water, whereas water use in the host trees was dominated by soil water. The leaves of epiphytes and host trees absorbed water following immersion in water for 3 h and FWU possibly related to foliar epicuticular structures, such as fungal endophytes. Our results show a divergence of water use strategies between epiphytes and their hosts and highlight the importance of fog water for epiphytes during the dry season and under a climate change scenario with a reduced occurrence of fog events.

Highlights

Occult precipitation, such as mist and fog, may be a primary source of water for canopy plants in forest ecosystems that are affected by periods of low rainfall [1]
There were no differences in the leaf carbon isotope ratios between the two host tree species (p = 0.5) or between the epiphytes, H. pottsii and B. delitescens (p = 0.6)
We found δ13 C-values typical for Crassulacean acid metabolism (CAM) in the epiphytes B. ambrosia, B. delitescens, and H. pottsii, whereas host trees had δ13 C-values typical for C3and these results are consistent with other studies of epiphytes that frequently had more enriched δ13 C compared with ground-rooted plants [11,18]

Summary

Introduction

Occult precipitation, such as mist and fog, may be a primary source of water for canopy plants in forest ecosystems that are affected by periods of low rainfall [1]. Fog water has been shown to be important for plants in forests subjected to seasonal droughts mediated by monsoons and canopy epiphytes that have no direct access to ground level water resources [3,4,5]. Fog mitigates drought stress in epiphytes by preventing desiccation and lengthening the photosynthetic period, and it has been suggested that epiphyte growth benefits from the interception of fog water [6,7,8]. Epiphytes are frequently drought stressed and use water more efficiently, as indicated by enriched δ13 C signatures compared to ground-rooted plants [11].

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Discussion

Conclusion