Sagebrush Carrying Out Hydraulic Lift Enhances Surface Soil Nitrogen Cycling and Nitrogen Uptake into Inflorescences
Plant roots are conduits for water flow from soil to leaves and from wetter to drier soil. This hydraulic redistribution through root systems occurs in soils worldwide and can enhance stomatal opening, transpiration, and plant carbon gain. For decades, upward hydraulic lift (HL) of deep water through roots into dry, litter-rich, surface soil also has been hypothesized to enhance nutrient availability to plants by stimulating microbe controlled nutrient cycling, but this link has not been demonstrated in the field. Working in sagebrush-steppe, where water and nitrogen limit plant growth and reproduction and where HL occurs naturally during summer drought, Department of Energy scientists from the Marine Biological Laboratory slightly augmented deep soil water availability (HL+) to plants throughout the summer growing season. The treated sagebrush lifted greater amounts of water than control plants and had slightly less negative predawn and midday leaf water potentials. Soil respiration also was augmented under HL+ plants. At summer’s end, they observed increased rates of nitrogen cycling in surface soil layers around HL+ plants and increased nitrogen uptake into HL+ plants’ inflorescences as sagebrush set seed. These treatment effects persisted even though unexpected monsoon rainstorms arrived during assays and increased surface soil moisture around all plants. Simulation models from ecosystem to global scales have just begun to include effects of hydraulic redistribution on water and surface energy fluxes. Results from this field study indicate that plants carrying out HL also can substantially enhance decomposition and nitrogen cycling in surface soils.
Cardon, Z. G., J. M. Stark, P. M. Herron, and J. A. Rasmussen. 2013. “Sagebrush Carrying Out Hydraulic Lift Enhances Surface Soil Nitrogen Cycling and Nitrogen Uptake into Inflorescences,” Proceedings of the National Academy of Sciences (USA) 110, 18988-991. DOI:10.1073/pnas.1311314110.