Experimental cloud immersion and foliar water uptake in saplings of Abies fraseri and Picea rubens

Frequent cloud immersion events result in direct uptake of cloud water and improve plant water potentials during daylight hours in saplings of two dominant cloud forest species. In ecosystems with frequent cloud immersion, the influence on plant water balance can be important. While cloud immersion can reduce plant water loss via transpiration, recent advances in methodology have suggested that many species also absorb water directly into leaves (foliar water uptake). The current study examines foliar water uptake and its influence on daily plant water balance in tree species of the endangered spruce-fir forest of the southern Appalachian Mountains, USA. These mountain-top communities are considered relic, boreal forests that may have persisted because of the benefits of frequent cloud immersion. We examined changes in needle water content, xylem water potentials, and stable isotope values in saplings of the two dominant tree species, Abies fraseri and Picea rubens before and after a 24 h period of experimental cloud immersion. Both species exhibited foliar water uptake following immersion, evidenced by substantial changes in stable isotope values of extracted needle water that reflected the composition of the fog water. In addition, total needle water content improved 3.7-6.4 % following experimental submersion and xylem water potentials were significantly greater (up to 0.33 MPa) in cloud-immersed plants over control plants. These results indicate that foliar water uptake may be an adaptive strategy for utilizing cloud water and improving overall tree vigor in these most southerly distributed boreal species.