Читать книгу North American Agroforestry - Группа авторов - Страница 96

Hydraulic lift is the process by which deep‐rooted plants transport or conduct water from deep within the soil and release it into the upper, drier regions of the soil. The process has been reported to be an appreciable water source for neighboring plants in some systems (Caldwell & Richards, 1989; Corak, Blevins, & Pallardy, 1987). This phenomenon can increase plant growth, in some cases, by increasing the availability of water for shallow‐rooted plants and has important implications for ecosystem nutrient cycling and net primary productivity (Horton & Hart, 1998).

In a tropical agroforestry context, numerous studies have shown that trees can benefit associated crop plants through hydraulic lift by increasing water availability during dry periods when water would otherwise be unavailable (Burgess, Adams, Turner, & Ong, 1998; Dawson, 1993; Ong et al., 1999; van Noordwijk, Lawson, Soumaré, Groot, & Hairiah, 1996). In temperate agroforestry systems, however, research documenting the hydraulic lift phenomenon is limited. Hydraulic lift in temperate systems has been reported in Quercus sp. and Pinus sp. (Asbjornsen, Shepherd, Helmers, & Mora, 2008; Espeleta, West, & Donovan, 2004; Penuelas & Filella, 2003). These species are commonly used in temperate agroforestry systems, indicating a potential for these genera to be used in agroforestry to positively impact water relations. For example, Espeleta et al. (2004) reported hydraulic lift in longleaf pine (Pinus palustris Mill.), a species commonly used in silvopastoral systems in the southeastern United States. They reported hydraulic lift in two oak species (Q. laevis Walt. and Q. incana Bartr.) as well. They concluded that the ability of these species to redistribute water from the deep soil to the rapidly drying shallow soil has a strong positive effect on the water balance of understory plants.