title: Prevalence and magnitude of groundwater use by vegetation: a global stable isotope meta-analysis.
abstract: The role of groundwater as a resource in sustaining terrestrial vegetation is widely recognized. But the global prevalence and magnitude of groundwater use by vegetation is unknown. Here we perform a meta-analysis of plant xylem water stable isotope (δ2H and δ18O, n = 7367) information from 138 published papers - representing 251 genera, and 414 species of angiosperms (n = 376) and gymnosperms (n = 38). We show that the prevalence of groundwater use by vegetation (defined as the number of samples out of a universe of plant samples reported to have groundwater contribution to xylem water) is 37% (95% confidence interval, 28-46%). This is across 162 sites and 12 terrestrial biomes (89% of heterogeneity explained; Q-value = 1235; P < 0.0001). However, the magnitude of groundwater source contribution to the xylem water mixture (defined as the proportion of groundwater contribution in xylem water) is limited to 23% (95% CI, 20-26%; 95% prediction interval, 3-77%). Spatial analysis shows that the magnitude of groundwater source contribution increases with aridity. Our results suggest that while groundwater influence is globally prevalent, its proportional contribution to the total terrestrial transpiration is limited.
authors.affiliation: Global Institute for Water Security and School of Environment and Sustainability, University of Saskatchewan, Saskatoon, Canada.
authors.forename: Jaivime
authors.initials: J
authors.lastname: Evaristo
authors.affiliation: Global Institute for Water Security and School of Environment and Sustainability, University of Saskatchewan, Saskatoon, Canada.|School of Geosciences, University of Aberdeen, Aberdeen, Scotland, United Kingdom.|Department of Forest Engineering, Resources and Management, Oregon State University, Corvallis, Oregon 97330 USA.
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: McDonnell
mesh_terms: D004784:Environmental Monitoring; D060587:Groundwater / Q000032:analysis* / Q000737:chemistry; D007554:Isotopes; D018521:Plant Physiological Phenomena; D018526:Plant Transpiration; D011891:Rain; D052584:Xylem / Q000737:chemistry
chemical_list: D007554:Isotopes