Hydraulic lift is a passive phenomenon of water movement between disparate parts of the soil via plant root systems, driven by water potential gradients within the soil. Evidence for the phenomenon in numerous species and ecosystems is strong, and many studies have focused on its positive effect on plant water availability, transpiration, and growth. Studies have also suggested that the greater plant water availability in the soil resulting from hydraulic lift may lead to higher nutrient mobility and uptake by the roots, but direct experimental evidence for this hypothesis is lacking or inconclusive. Here, we use a common arid land grass species grown in split-pots to test whether mineralization and uptake of 15N-labeled litter in ingrowth cores are higher in plants performing hydraulic lift (HL treatment) compared to plants that are not (N treatment). We induced hydraulic lift by watering the bottom of the pots while withholding water from the top layer during the study (2 months). Hydraulic lift in N treatment was inhibited by placing plants under 24-hour light treatment. We included separate unvegetated controls for HL and N treatments, and a well-watered (W) treatment where both tops and bottoms of the split-pots were watered.
Results/Conclusions
Top layers of the split-pots were significantly wetter in W and HL treatments than in N treatment. W and HL treatments were also wetter than its unvegetated control but the difference was less pronounced for N treatment and its unvegetated control. Aboveground biomass, leaf %nitrogen, and leaf 15N‰ were higher in W and HL treatments compared with N treatment. No such differences were found for roots. Midday leaf water potential in HL treatments was higher than in N treatments, but did not differ significantly from that of W treatment. To our knowledge, this is the first direct evidence that hydraulic lift can enhance nutrient uptake, with important implications for plant community functions. Differences in physiological and biomass measurements between the HL and N treatments were large and significant, while the differences between HL and W treatments were less dramatic or statistically insignificant, indicating that hydraulic lift enabled plants in HL treatment to function similarly as plants in well-watered conditions for the duration of our experiment.
