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Climate models predict that water limited regions around the world will become drier and warmer in the near future, including southwestern North America. We developed a large-scale experimental system that allows testing of the ecosystem impacts of precipitation changes. Four treatments were applied to 1600 m2 plots (40 m × 40 m), each with three replicates in a piñon pine (Pinus edulis) and juniper (Juniper monosperma) ecosystem. These species have extensive root systems, requiring large-scale manipulation to effectively alter soil water availability.  Treatments consisted of: 1) irrigation plots that receive supplemental water additions, 2) drought plots that receive 55% of ambient rainfall, 3) cover-control plots that receive ambient precipitation, but allow determination of treatment infrastructure artifacts, and 4) ambient control plots. Our drought structures effectively reduced soil water potential and volumetric water content compared to the ambient, cover-control, and water addition plots. Drought and cover control plots experienced an average increase in maximum soil and air temperature at ground level of 1-4° C during the growing season compared to ambient plots, and concurrent short-term diurnal increases in maximum air temperature were also observed directly above and below plastic structures. Our drought and irrigation treatments significantly influenced tree predawn water potential, sap-flow, and net photosynthesis, with drought treatment trees exhibiting significant decreases in physiological function compared to ambient and irrigated trees.  Supplemental irrigation resulted in a significant increase in both plant water potential and xylem sap-flow compared to trees in the other treatments. This experimental design effectively allows manipulation of plant water stress at the ecosystem scale, permits a wide range of drought conditions, and provides prolonged drought conditions comparable to historical droughts in the past – drought events for which wide-spread mortality in both these species was observed. Water potential measurements were used to monitor the water stress of the two target species across the four treatment regimes.  Sampling for water potentials occurred twice daily.  One set of samples was collected hours before dawn and another set was collected at mid-day.  The predawn readings provided the “least-stressed†tree water content values as they were collected after the trees had returned to equilibrium over the evening and had yet to start transpiring.  The mid-day values, collected after tree-level respiration had been occurring for hours and when the daily temperatures were highest, represented the opposite “most-stressed†scenario. To gauge the effect of the irrigation treatment on the water content of the trees, we sampled water potentials just before and just after irrigation events.  Â
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Repeat leaf water potential data from oaks at Sedgwick Reserve, CA.
Data from repeated measurements of predawn and midday water potentials on Quercus agrifolia and Quercus douglassi trees at Sedgwick Reserve, CA, USA from 2022 - 2024. The data includes the following columns: Column name Description individual_id Unique numeric ID for individual tree site Name of site location, represents a spatially distinct group of trees species Quercus agrifolia and Quercus douglassii date date of data collection, in YYYYMMDD pd_md Indicates whether measurements were taken at predawn (pd, 1-3 hours before sunrise) or midday (md, within 1.5 hours of solar noon) water_potential_mean Mean water potential measurements for each tree/date/time (MPa). water_potential_sd Standard deviation of water potential measurements for each tree/date/time (MPa) water_potential_n Number of water potential measurements for each tree/date/time latitude Location of individual tree, latitude in decimal degrees longitude Location of individual tree, longitude in decimal degrees coord_system EPSG:4326-WGS 84 For details on collection methods, see: Boving I, Allen J, Brodrick PG, Chadwick KD, Trugman A, Anderegg LDL. The Unstable Relationship Between Drought Status and Leaf Water Content Complicates the Remote Sensing of Tree Drought Stress. Glob Chang Biol. 2025 Apr;31(4):e70188. doi: 10.1111/gcb.70188. PMID: 40249004; PMCID: PMC12007071.
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- PAR ID:
- 10637450
- Publisher / Repository:
- Zenodo
- Date Published:
- Edition / Version:
- 1.0.0
- Subject(s) / Keyword(s):
- water potential ecophysiology oaks
- Format(s):
- Medium: X
- Location:
- Zenodo
- Right(s):
- Creative Commons Attribution 4.0 International
- Institution:
- UC Santa Barbara
- Sponsoring Org:
- National Science Foundation
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