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A pool‐weighted perspective on the two‐water‐worlds hypothesis
Author(s) -
Dubbert Maren,
Caldeira Maria C.,
Dubbert David,
Werner Christiane
Publication year - 2019
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.15670
Subject(s) - soil water , xylem , environmental science , groundwater , ecosystem , precipitation , water content , stable isotope ratio , water flow , hydrology (agriculture) , soil science , environmental chemistry , ecology , chemistry , geology , botany , biology , geography , geotechnical engineering , physics , quantum mechanics , meteorology
Summary The ‘two‐water‐worlds’ hypothesis is based on stable isotope differences in stream, soil and xylem waters in dual isotope space. It postulates no connectivity between bound and mobile soil waters, and preferential plant water uptake of bound soil water sources. We tested the pool‐weighted impact of isotopically distinct water pools for hydrological cycling, the influence of species‐specific water use and the degree of ecohydrological separation. We combined stable isotope analysis (δ 18 O and δ 2 H) of ecosystem water pools of precipitation, groundwater, soil and xylem water of two distinct species ( Quercus suber , Cistus ladanifer ) with observations of soil water contents and sap flow. Shallow soil water was evaporatively enriched during dry‐down periods, but enrichment faded strongly with depth and upon precipitation events. Despite clearly distinct water sources and water‐use strategies, both species displayed a highly opportunistic pattern of root water uptake. Here we offer an alternative explanation, showing that the isotopic differences between soil and plant water vs groundwater can be fully explained by spatio‐temporal dynamics. Pool weighting the contribution of evaporatively enriched soil water reveals only minor annual impacts of these sources to ecosystem water cycling ( c . 11% of bulk soil water and c . 14% of transpired water).