The prevalence and significance of foliar water uptake in tropical montane cloud forest plants

Background/Question/Methods

Foliar water uptake is a common phenomenon in plants from a range of ecosystems that experience frequent fog or cloud immersion. The resulting improvement in leaf water status has been demonstrated to enhance plant carbon balance and lead to increased growth and survival. In tropical montane cloud forests, where projected changes in climate are expected to include decreases in frequency, duration and timing of cloud cover, very little is known about the prevalence or functional significance of foliar water uptake. We studied patterns of foliar water uptake in seasonally dry pre-montane and montane cloud forests in Monteverde, Costa Rica. Our objectives were to 1) characterize the frequency of leaf wetting events associated with cloud immersion in each forest and determine whether such events were associated with foliar water uptake, as well as 2) compare the capacity for foliar water uptake in each forest.  

Results/Conclusions

Over the course of the dry season, the montane cloud forest experienced more leaf wetting events than the pre-montane forest. Moreover, the mean number of hours per day registering leaf wetness in the montane cloud forest (12.8 ± 1.3) was significantly higher than the premontane forest (2.8 ± 0.8). These events resulted in foliar water uptake, measured in situ by means of sap flow, in all 6 species at each forest. There was a significant, negative linear relationship between rates of foliar water uptake and improvement in leaf water potential (p < 0.01, r² = 0.55). However, the capacity for foliar water uptake, measured in the 12 most common species in each forest, was significantly higher in the montane cloud forest than the pre-montane forest. Our results suggest that the foliar water uptake is a common tropical montane cloud forest phenomenon that serves to improve plant water status during the dry season. While the two plant communities may respond differentially to leaf wetting events, projected changes in cloud cover will likely change the extent to which foliar water uptake alleviates dry season water stress.