Sagebrush carrying out hydraulic lift enhances surface soil nitrogen cycling and nitrogen uptake into inflorescences

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 110; no. 47; pp. 18988 - 18993
• Main Authors: Cardon, Zoe G., Stark, John M., Herron, Patrick M., Rasmussen, Jed A.
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences 19-11-2013; NATIONAL ACADEMY OF SCIENCES; National Acad Sciences
• Subjects: Analysis of Variance; Artemisia - metabolism; Artemisia - physiology; Biological and medical sciences; Biological Sciences; Biological Transport - physiology; Flowers - metabolism; Fundamental and applied biological sciences. Psychology; Hydraulics; Inflorescences; Isotopes; Moisture; Nitrogen; Nitrogen Cycle - physiology; Nitrogen Isotopes - pharmacokinetics; Plant growth; Plant physiology and development; Plant roots; Plants; Soil - chemistry; Soil depth; Soil ecology; Soil hydraulic properties; Soil microorganisms; Soil water; Soil water content; Utah; Water - metabolism; United States; North America; Utah; America; Seed production; Fodder shrub; Inflorescence; Hydraulic conductivity; Compositae; Nitrogen; Nutrient uptake; Artemisia tridentata; Rhizosphere; Soils; Nitrogen cycle; Water regime; Steppe; Dicotyledones; Angiospermae; Flowering; Spermatophyta; seed production; flowering; rhizosphere
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1311314110

Plant roots serve as conduits for water flow not only from soil to leaves but also 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 microbially controlled nutrient cycling. 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, we slightly augmented deep soil water availability to 14 HL+ treatment plants throughout the summer growing season. The HL+ sagebrush lifted greater amounts of water than control plants and had slightly less negative predawn and midday leaf water potentials. Soil respiration was also augmented under HL+ plants. At summer’s end, application of a gas-based ¹⁵N isotopic labeling technique revealed increased rates of nitrogen cycling in surface soil layers around HL+ plants and increased uptake of nitrogen 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 can also substantially enhance decomposition and nitrogen cycling in surface soils.