WATER PARASITISM STEMMING FROM HYDRAULIC LIFT: A QUANTITATIVE TEST IN THE FIELD

Abstract

Hydraulic lift, a process involving efflux of water from the root system in dry soil layers at night, provides the opportunity for parasitism of the released water by roots of neighboring plants the following day. The potential for parasitism had been shown in earlier experiments by a transfer of deuterated water from shrub roots to neighboring tussock grass plants. In the present field study, the transpiration of entire grass tussocks was measured under controlled light, temperature, and humidity conditions resulting in a high evaporative demand during the daylight periods. After establishing a series of diel courses of transpiration, the neighboring shrubs were illuminated overnight in order to circumvent their hydraulic lift, while the tussocks experienced a normal dark period. No effect on transpiration rates of the grass tussocks was detected on the days following this night-lighting treatment. Thus, removing the nocturnal efflux of water by the shrub roots did not diminish the access of the grasses to water needed to meet their transpiration demand. These results suggest that a large net transfer of water from shrubs to the grasses did not occur under these circumstances. The potential for some water parasitism under particular aridland conditions is discussed.