Roots generally absorb water from the soil and transport it above ground to the stem, branches, etc. Where the soil is too dry for water to be absorbed by the roots, the roots might actually lose water to the soil and risk being damaged if that situation persists. However, in some arid conditions where upper soil water levels may be very low and near-surface roots could otherwise subsequently become damaged, water absorbed by roots at depth may be transported upwards and released through those near-surface roots into the soil that surrounds them at night-time. During the following day that root-released water is taken up and transpired from those shallower roots. This phenomenon is known as hydraulic lift (HL) and can have substantial benefits to the plant doing the lifting (e.g. greater daily carbon gain, increased growth and increased nutrient uptake); in a coincidentally altruistic way, HL may also benefit neighbouring plants. It has also been postulated that HL might enhance nutrient availability to plants by stimulating microbially controlled nutrient cycling; experimental support for which notion has now been provided by Zoe Cardon et al. Working with sagebrush (Artemisia tridentata var. vaseyana), the team not only demonstrated increased rates of nitrogen cycling in surface soil layers around plants where HL was permitted, but also increased uptake of nitrogen into their inflorescences as seed was set. Or, in the words of John Stark (one of the study’s co-authors and professor at Utah State University’s Department of Biology and Ecology Center), ‘What we’re discovering is, through a process called hydraulic lift, plants also leak water into the bone-dry surface soil to release nutrients and stir microbial activity critical to the plants’ survival’. All of which just goes to show that whenever presented with a problem, Nature usually finds an elegant, even uplifting, solution. Sage bush, that there sagebrush.
[HL is nowadays better replaced by the term hydraulic redistribution, since it can occur/take place upwards (HL) and/or downwards (hydraulic descent); see, for example, Kevin Hultine et al.’s Tree Physiology article. For a review of water release through plant roots, see Iván Prieto et al.’s New Phytologist article – Ed.]