Journal
NEW PHYTOLOGIST
Volume 215, Issue 4, Pages 1451-1461Publisher
WILEY
DOI: 10.1111/nph.14693
Keywords
drylands; hydraulic lift; mesquite (Prosopis velutina); photosynthesis; sap flow; woody plant encroachment
Categories
Funding
- NSF [EAR 1417101, EAR 1417444, EAR 1331408, EAR 1331906, ACI 1261582]
- Marie Curie International Outgoing Fellowship within the 7th European Community Framework Programme
- DIESEL project [625988]
- Water, Environmental, and Energy Solutions (WEES) initiative at the University of Arizona Institute of the Environment
- University of Arizona Office of the Vice President of Research
- Philecology Foundation of Ft. Worth, Texas
- Department of Energy's Office of Science
- Directorate For Geosciences
- Division Of Earth Sciences [1417444] Funding Source: National Science Foundation
- Division Of Earth Sciences
- Directorate For Geosciences [1417101] Funding Source: National Science Foundation
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A long-standing ambition in ecosystem science has been to understand the relationship between ecosystem community composition, structure and function. Differential water use and hydraulic redistribution have been proposed as one mechanism that might allow for the coexistence of overstory woody plants and understory grasses. Here, we investigated how patterns of hydraulic redistribution influence overstory and understory ecophysiological function and how patterns vary across timescales of an individual precipitation event to an entire growing season. To this end, we linked measures of sap flux within lateral and tap roots, leaf-level photosynthesis, ecosystem-level carbon exchange and soil carbon dioxide efflux with local meteorology data. The hydraulic redistribution regime was characterized predominantly by hydraulic descent relative to hydraulic lift. We found only a competitive interaction between the overstory and understory, regardless of temporal time scale. Overstory trees used nearly all water lifted by the taproot to meet their own transpirational needs. Our work suggests that alleviating water stress is not the reason we find grasses growing in the understory of woody plants; rather, other stresses, such as excessive light and temperature, are being ameliorated. As such, both the two-layer model and stress gradient hypothesis need to be refined to account for this coexistence in drylands.
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