Patricia Brito1, Thorsten E E Grams2, Rainer Matysssek2, Maria S Jimenez1, Agueda M Gonzalez-Rodríguez1, Walter Oberhuber3, Gerhard Wieser4. 1. Department of Botany, Ecology and Plant Physiology, Universidad de La Laguna (ULL), C/Astrofísico Francisco Sánchez s/n, E-38207 La Laguna, Tenerife, Spain. 2. Ecophysiology of Plants, Department of Ecology and Ecosystem Management, Technische Universität München, Von-Carlowitz-Platz 2, 85354 Freising, Germany. 3. Institute of Botany, Leopold-Franzens-Universität Innsbruck, Sternwartestraße 15, 6020 Innsbruck, Austria. 4. Department of Alpine Timberline Ecophysiology, Federal Research and Training Centre for Forests, Natural Hazards and Landscape (BFW), Rennweg 1, A-6020 Innsbruck, Austria.
Abstract
KEY MESSAGE: Intrinsic water-use efficiency of Pinus canariensis (Sweet ex Spreng.) growing at a semi-arid treeline has increased during the past 37 years. Tree-ring width by contrast has declined, likely caused by reduced stomatal conductance due to increasing aridity. CONTEXT: Rising atmospheric CO2 concentration (Ca ) has been related to tree growth enhancement accompanied by increasing intrinsic water-use-efficiency (iWUE). Nevertheless, the extent of rising Ca on long-term changes in iWUE and growth has remained poorly understood to date in Mediterranean treeline ecosystems. AIMS: This study aimed to examine radial growth and physiological responses of P. canariensis in relation to rising Ca and increasing aridity at treeline in Tenerife, Canary Islands, Spain. METHODS: We evaluated temporal changes in secondary growth (tree-ring width; TRW) and tree ring stable C isotope signature for assessing iWUE from 1975 through 2011. RESULTS: Precipitation was the main factor controlling secondary growth. Over the last 36 years P. canariensis showed a decline in TRW at enhanced iWUE, likely caused by reduced stomatal conductance due to increasing aridity. CONCLUSION: Our results indicate that increasing aridity has overridden the potential CO2 fertilization on tree growth of P. canariensis at its upper distribution limit.
KEY MESSAGE: Intrinsic water-use efficiency of Pinus canariensis (Sweet ex Spreng.) growing at a semi-arid treeline has increased during the past 37 years. Tree-ring width by contrast has declined, likely caused by reduced stomatal conductance due to increasing aridity. CONTEXT: Rising atmospheric CO2 concentration (Ca ) has been related to tree growth enhancement accompanied by increasing intrinsic water-use-efficiency (iWUE). Nevertheless, the extent of rising Ca on long-term changes in iWUE and growth has remained poorly understood to date in Mediterranean treeline ecosystems. AIMS: This study aimed to examine radial growth and physiological responses of P. canariensis in relation to rising Ca and increasing aridity at treeline in Tenerife, Canary Islands, Spain. METHODS: We evaluated temporal changes in secondary growth (tree-ring width; TRW) and tree ring stable C isotope signature for assessing iWUE from 1975 through 2011. RESULTS: Precipitation was the main factor controlling secondary growth. Over the last 36 years P. canariensis showed a decline in TRW at enhanced iWUE, likely caused by reduced stomatal conductance due to increasing aridity. CONCLUSION: Our results indicate that increasing aridity has overridden the potential CO2 fertilization on tree growth of P. canariensis at its upper distribution limit.
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