Water acquisition via foliar water uptake in island and mainland chaparral shrubs

Background/Question/Methods

Recent studies have discovered that foliar water uptake FWU - the intake of water through a plant’s leaves to supplement water acquired by the roots - is an important water acquisition strategy for plants in California coastal redwood forests and tropical montane cloud forests.  However, work on FWU outside of these systems is extremely limited. Chaparral shrub communities from the California Channel Islands and the adjacent California mainland represent another system where FWU may be important. Recent work in this system suggests that summertime fog may provide important water inputs during seasonally hot, dry summers, especially for plants inhabiting the Channel Islands.  FWU is a potential mechanism allowing plants in this system to take advantage of frequent summertime fog events.

To assess and compare the capacity of island and mainland chaparral shrub species to perform FWU, leaf samples from congeneric species pairs (island vs. mainland) collected from the UC Berkeley Botanical Garden were tested using recently developed laboratory methods. In brief, leaf water potential was determined using a pressure chamber before and after being submerged in a water bath for 1 hour.  Increase in leaf water potential during the experiment was interpreted as evidence of the capacity for FWU.

Results/Conclusions

Preliminary results indicate that all island chaparral shrub species tested are capable of performing FWU (P < 0.05). Furthermore, paired comparisons of congeneric island and mainland species reveal a greater capacity for foliar water uptake in island plants (P < 0.05).  These findings suggest that the leaves of island plants are better equipped to capture water from summertime fog events compared to mainland relatives and that island plants may be locally adapted to the greater frequency of fog that characterizes the insular environment of the California Channel Islands.  These findings also have important implications for how island and mainland plant communities may respond to global climate change, which may alter the frequency of summertime fog in this system.  Additional work is underway to correlate FWU with other functional traits that will help us better understand the evolutionary trade-offs associated with this important water acquisition strategy.