Hydraulic redistribution by plants and nutrient stoichiometry: Shifts under global change



Hydraulic lift, water movement from deep to upper soil layers by roots, is a widespread process in temperate and semi-arid environments. It can contribute 17–81% of total water transpired and favour the uptake of nutrients available mainly from soil organic matter decomposition (e.g. N). Downward siphoning, water movement from upper to deep soil layers, can represent 10–60% of total transpired water, favouring the uptake of nutrients supplied mainly from the leaching of bedrock minerals (e.g. P and K). These vertical water movements also can affect the N : P ratio of runoff waters when, in the case of hydraulic lift, they open the possibility for a given pulse of water to circulate multiple times across the N-rich upper soil layers. Plants, thus, affect the stoichiometry of nutrients in soils and groundwater not only through the physical protection of the soil and through the water uptake but also through water redistribution. Soil water redistribution can also play an outstanding role in the ecosystem responses to global change drivers. The increase in soil patchiness in current and future arid lands modifies runoff fluxes, hydraulic lift and downward siphoning, allowing plants to dispose of higher water and nutrient availabilities. The higher use of hydraulic lift and/or downward siphoning by alien species is a possible cause of alien plant success. Further mechanistic and quantitative research is thus warranted to discern the plant role in water and nutrient cycling and in the responses to global change. Copyright © 2014 John Wiley & Sons, Ltd.