Foliar uptake of fog in the coast redwood ecosystem: a novel drought-alleviation strategy shared by most redwood forest plants
| Authors: | Emily Limm, Kevin Simonin, Tod Dawson |
| Year: | 2012 |
| Type: | General Technical Report |
| Station: | Pacific Southwest Research Station |
| Source: | In: Standiford, Richard B.; Weller, Theodore J.; Piirto, Douglas D.; Stuart, John D., tech. coords. Proceedings of coast redwood forests in a changing California: A symposium for scientists and managers. Gen. Tech. Rep. PSW-GTR-238. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture. pp. 273-281 |
Abstract
Fog inundates the coast redwood forests of northern California frequently during the summer months (May to September) when rainfall is largely absent (Azevedo and Morgan 1974, Byers 1953, Oberlander 1956). This maritime fog modifies otherwise warm and dry summer climate by increasing humidity, decreasing the air temperature, reducing solar radiation, and contributing water to the ecosystem through leaf wetness and fog drip (Fischer et al. 2008, Grubb and Whitmore 1966, Hutley et al. 1997, Williams et al. 2008). Fog water provides an important water subsidy for redwood forest plants that face high demand for water during the spring growing season and throughout the summer as soil moisture levels decrease (Dawson 1998, Ewing et al. 2009). In this study, we investigated how effectively fog water alleviates redwood forest plant drought stress during the summer and identified foliar uptake as a key mechanism promoting plant hydration following exposure to fog. Foliar uptake is the absorption of water into plant crowns by leaves and stems (Rundel 1982). It occurs in diverse taxa around the world directly through the leaf cuticle (Gouvra and Gammaikopoulos 2003, Slatyer 1960, Suarez and Gloser 1982, Vaadia and Waidel 1963, Yates and Huxley 1995), specialized water-absorbing trichomes (Benzing et al. 1978, Franke 1967), or hydathode channels in the leaf epidermis (Martin and von Willert 2000). Fog, light rain, and dew may contribute little or no water to the soil profile, but may wet leaves for hours at a time (Boucher et al. 1995, Breshears et al. 2008, Ewing et al. 2009). Plants with foliar uptake capacity can absorb this water whenever their crowns are wet. In this way, foliar uptake provides an efficient mechanism to hydrate photosynthetic tissue when water is available aboveground because the water does not need to be absorbed from the soil first and transported from the roots to the plant crown second (Simonin et al. 2009).
Given the frequent occurrence of fog in the coast redwood forest during the summer and the known contribution of fog to the annual water budget of redwood forest plants (Dawson 1998), we hypothesized that foliar uptake was a common water combination of glasshouse experiments using artificial fog chambers and field measurements, we studied (1) how many species in the redwood forest absorb fog water directly by foliar uptake, (2) geographical variation in the foliar uptake capacity of the dominant understory fern, Polystichum munitum, along the redwood forest range, (3) how foliar uptake influences the water status of P. munitum, and (4) how fog influences the seasonal timing and intensity of drought stress for understory plants.