Environmental and Experimental Botany 68 (2010) 26–30 Contents lists available at ScienceDirect Environmental and Experimental Botany journal homepage: www.elsevier.com/locate/envexpbot Evaluation of hydraulic lift in cotton (Gossypium hirsutum L.) germplasm B.L. McMichael, Robert J. Lascano ∗ USDA-ARS, Cropping Systems Research Laboratory, 3810 4th St., Lubbock, TX 79415, USA article info Article history: Received 17 February 2009 Received in revised form 21 September 2009 Accepted 11 October 2009 Keywords: Cotton Roots Water uptake ET Water content abstract Hydraulic lift (HL) in plants is defined as the redistribution of water from wetter to drier soil through the plant roots in response to soil water potential gradients. Water is released from the roots into the dry soil when transpiration is low (night) and reabsorbed by the plant when higher transpiration rates are resumed (daylight). It was hypothesized that since HL is not of sufficient magnitude to meet total transpirational demands, there may be sufficient water transferred to maintain viable roots in the surface soil in anticipation of root water uptake for plant development from rain events before it is lost to water evaporation and/or runoff. Cotton (Gossypium hirsutum L.) plants of diverse genetic backgrounds were grown in a split-root container with roots of one plant divided between the two adjacent soil volumes. The soil in one container was allowed to dry while the adjacent soil container remained wet for the duration of the tests. Cotton transpiration was lowered by covering the plant with black cloth for several hours while changes in soil water content were measured in both containers using calibrated soil water sensors. Results showed that water was transferred from the wet to the dry soil through the root system at low transpiration rates. There was also an indication of genetic diversity in the magnitude of HL that may be due to differences in root resistance to water flow since total root length for a particular genotype was either smaller in the dry soil or similar to total root length in the wet soil. The amount of water transferred was small, but when integrated over a soil depth represented an amount ranging from 11% to 32% of corresponding daily evapotranspiration rates of 2–6 mm d -1 , respectively, which could presumably maintain root viability for additional root water uptake when made available. These results are important in dryland cotton production where additional transpiration represents increased lint yield and plant breeders may consider this trait in their selection of cotton germplasm with drought resistance. Published by Elsevier B.V. 1. Introduction The process whereby soil water is redistributed from wet soil layers deep in the profile to drier soil layers near the soil surface by the root systems of plants is termed hydraulic lift (HL) (Richards and Caldwell, 1987). This phenomenon has been reported to occur in a large number of plant species (Caldwell et al., 1998; Liste et al., 2008). They describe the HL process as the movement of water from the roots to the soil because of root xylem water potential becoming greater than the surrounding soil water potential when transpira- tion rates are low, i.e., <0.5 mm d -1 . In many cases the water that is transferred to the surrounding soil when transpiration is low, usu- ally at night, is reabsorbed by roots the following day to become a portion of the daily transpiration (Caldwell et al., 1998). Much of the work in HL investigations has been conducted using diverse plant material such as shrubs and trees under field condi- tions (Moreira et al., 2003). Some studies, however, have indicated ∗ Corresponding author. Tel.: +1 806 723 5238. E-mail address: Robert.lascano@ars.usda.gov (R.J. Lascano). that HL does occur in herbaceous species as well (Xu and Bland, 1993; Sekiya and Yano, 2004; Wan et al., 2000; Liste et al., 2008). Laboratory experiments have also been conducted to suggest the potential for HL and to document the extent of the phenomenon (Baker and Van Bavel, 1988). Furthermore, a number of studies have suggested that the occurrence of HL in one plant may benefit neighboring plants by moving water to the drier upper soil layers so that the neighbor plant may have access to the water, provided the neighbor plant has a relatively shallow root system (Sekiya and Yano, 2004). For example, an experiment by Hirota et al. (2004) showed that HL that occurred in a Markhamia (Markhamia lutea [Benth.] Schumann) tree successfully transferred sufficient water to neighboring rice (Oriza sativa L.) plants and allowed the rice to remain viable during a drying period. In contrast, the rice plants not associated with the tree roots desiccated during the same drying period. In some cases it has also been suggested that HL can account for a portion of the daily transpirational requirements of the plant. For example, Caldwell et al. (1998) estimated that 20–40% of the daily transpiration might be accounted for by HL. Also, Baker and Van Bavel (1988), demonstrated HL with cotton grown with a split- 0098-8472/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.envexpbot.2009.10.002