Aguilera, Mónica

Ferrio Díaz, Juan Pedro

Gil Pelegrín, Eustaquio

Martín Gómez, Paula

Pemán García, Jesús

citaREA Repositorio Electrónico Agroalimentario

Geophysical Research AbstractsVol. 16, EGU2014-13404, 2014EGU General Assembly 2014© Author(s) 2014. CC Attribution 3.0 License.Uncoupling between soil and xylem water isotopic composition: how todiscriminate mobile and tightly-bound water?Paula Martín Gómez (1), Mònica Aguilera (1), Jesús Pemán (1), Eustaquio Gil Pelegrín (2), and Juan PedroFerrio (1)(1) Universitat de Lleida, Crop and Forest Sciences-AGROTECNIO Center, Spain (paula.martin@pvcf.udl.cat), (2) Unidad deRecursos Forestales, Centro de Investigación y Tecnología Agroalimentaria de Aragón, Zaragoza, SpainAs a general rule, no isotopic fractionation occurs during water uptake and water transport, thus, xylem waterreflects source water. However, this correspondence does not always happen. Isotopic enrichment of xylem waterhas been found in several cases and has been either associated to “stem processes” like cuticular evaporation 1 andxylem-phloem communication under water stress 2,3 or to “soil processes” such as species-specific use of contrast-ing water sources retained at different water potential forces in soil. In this regard, it has been demonstrated thatmobile and tightly-bound water may show different isotopic signature 4,5. However, standard cryogenic distillationdoes not allow to separate different water pools within soil samples. Here, we carried out a study in a mixed adultforest (Pinus sylvestris, Quercus subpyrenaica and Buxus sempervirens) growing in a relatively deep loamy soil inthe Pre-Pyrenees. During one year, we sampled xylem from twigs and soil at different depths (10, 30 and 50 cm).We also sampled xylem from trunk and bigger branches to assess whether xylem water was enriched in the distalparts of the tree. We found average deviations in the isotopic signature from xylem to soil of 4h 2h and 2.4h inδ18O and 18.3h 7.3h and 8.9h in δ2H, for P.sylvestris, Q.subpyrenaica and B.sempervirens respectively. Xylemwater was always enriched compared to soil. In contrast, we did not find clear differences in isotopic compositionbetween xylem samples along the tree. Declining the hypothesis that “stem processes” would cause these uncou-pling between soil and xylem isotopic values, we tested the possibility to separate mobile and tightly-bound waterby centrifugation. Even though we could separate two water fractions in soils close to saturation, we could notrecover a mobile fraction in drier soils. In this regard, we welcome suggestions on alternatives to separate differentsoil fractions in order to find the correspondence between soil and xylem water.References1. Dawson, T. E. & Ehleringer, J. R. Isotopic enrichment of water in the “woody” tissues of plants: Implications forplant water source, water uptake, and other studies which use the stable isotopic composition of cellulose. (1993).2. Cernusak, L. a, Farquhar, G. D. & Pate, J. S. Environmental and physiological controls over oxygen and carbonisotope composition of Tasmanian blue gum, Eucalyptus globulus. Tree Physiol. 25, 129–46 (2005).3. Bertrand, G. et al. Determination of spatiotemporal variability of tree water uptake using stable isotopes (δ 18 O,δ 2 H) in an alluvial system supplied by a high-altitude watershed, Pfyn forest, Switzerland. Ecohydrology (2012).doi:10.1002/eco.13474. Tang, K. & Feng, X. The effect of soil hydrology on the oxygen and hydrogen isotopic compositions of plants ’source water. 185, (2001).5. Brooks, J. R., Barnard, H. R., Coulombe, R. & McDonnell, J. J. Ecohydrologic separation of water betweentrees and streams in a Mediterranean climate. Nat. Geosci. 3, 100–104 (2009).AcknowledgementsThis study was funded by RESILFOR project (AGL 2012-40039-C02-02) and FPU fellowship from the SpanishMinistry of Science and Innovation (FPU12/00648). We thank Instituto de Formación Agroambiental de Jaca andUnidad de Salud de los Bosques de Aragón for their support on field work and we feel very grateful to MiguelÁngel Lázaro for climbing the studied trees, José María Alcaire for one year of rain collection and Pilar Sopeñaand Mª Josep Pau for laboratory analysis. Helpful comments by Jordi Voltas on statistical analysis have improvedthe quality of the work.

Uncoupling between soil and xylem water isotopic composition: how to discriminate mobile and tightly-bound water?

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Uncoupling between soil and xylem water isotopic composition: how to discriminate mobile and tightly-bound water?

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citaREA Repositorio Electrónico Agroalimentario