Evidence of hydraulic lift in a young beech and oak mixed forest using 18O soil water labelling |
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Authors: | Marion Zapater Christian Hossann Nathalie Br??da Claude Br??chet Damien Bonal Andr?? Granier |
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Institution: | (1) INRA, UMR 1137 INRA-UHP Forest Ecology and Ecophysiology Unit, 54280 Champenoux, France;(2) INRA, UMR 1137 INRA-UHP Forest Ecology and Ecophysiology Unit, Technical Platform for Functional Ecology, 54280 Champenoux, France; |
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Abstract: | Hydraulic lift (HL) by tree roots in a young, broad-leaved, mixed temperate European forest was investigated during the 2008
growing season by injecting 18O-enriched soil water at a depth of 75–90 cm under drought conditions experimentally imposed in a rain-exclusion system. Based
on sap flow, leaf water potential, 2-D root distribution measurements, soil isotope profiles, and xylem water isotope composition,
water acquisition and use by two tree species, beech (Fagus sylvatica) and oak (Quercus petraea) was compared. We showed that, unlike oak, beech experienced a marked decrease in sap flow and predawn leaf water potential
with increasing soil drought. This behaviour was logical considering the shallower root system in beech than in oak. Six days
after 18O-labelling, we observed isotopic enrichment in the shallower soil layers. Since the intermediate soil layers did not display
any enrichment, our results clearly pointed to hydraulic lift by tree roots. The superficial enrichment that was observed
in the vicinity of oak trunks and the increase in the isotopic signature of xylem sap in the oak trees but not in the beech
trees confirmed the predominant role of oak in the hydraulic lift at our site. Even though facilitation for water acquisition
among species was not observed here, our results suggest a potential positive contribution of species like oak toward maintaining
species diversity in mixed forest ecosystems submitted to severe drought events. |
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