Water availability is essential to terrestrial plants, especially tall canopy trees. Satellite observations at microwave frequencies make it possible to assess total canopy water content and plant stress. However, leaf surface water -- water coming from dew, fog and rainfall -- is often overlooked when interpreting changes in canopy water content. An increasing body of evidence, though, indicates that plants might rely more than originally thought on these nonconventional water sources.
In a recent study in New Phytologist, Xiangtao Xu, postdoctoral fellow, and Paul Moorcroft demonstrate the large contribution of leaf surface water to diurnal changes in satellite vegetation optical depth (VOD) data. The study found that leaf surface water accounts for over 60% of diurnal variations in canopy water content despite being less than 10% of the total pool of water in tropical forest canopy. The results confirm the assumed importance of leaf surface water dynamics from scarce ground observations. Commentary from New Phytologist.