An increase in frequency, intensity and duration of drought events affects forested ecosystems. Trees react to these changes by adjusting stomatal conductance to maximize the trade-off between carbon gains and water losses. A better understanding of the consequences of these drought-induced physiological adjustments for tree growth could help inferring future productivity potentials of boreal forests. Here, we used samples from a forest inventory network in Canada where a decline in growth rates of black spruce (Picea mariana (Mill.) B.S.P.) and jack pine (Pinus banksiana Lamb.) occurred in 1988-1992, an exceptionally dry period, to verify if this growth decline resulted from physiological adjustments of trees to drought. We measured carbon and oxygen isotope ratios in growth rings of 95 spruces and 49 pines spanning 1985-1993. We used 13C discrimination (Δ13C) and 18O enrichment (Δ18O) as proxies for intrinsic water use efficiency and stomatal conductance, respectively. We studied how inter-annual variability in isotopic signals was linked to climate moisture index, vapor pressure deficit and annual snowfall amount. We found significantly lower Δ13C values over 1988-1990, and significantly higher Δ18O values in 1988-1989 and 1991 compared to the 1985-1993 averages. We also observed that a low climatic water balance and a high vapor pressure deficit were linked with low Δ13C and high Δ18O in the two study species, in parallel with low growth rates. The latter effect persisted into the year following drought for black spruce, but not for jack pine. These findings highlight that small differences in physiological parameters between species could translate into large differences in post-drought recovery. The stronger and longer lasting impact on black spruce compared to jack pine suggests a less efficient carbon use and a lower acclimation potential to future warmer and drier climate conditions.

Centre d'étude de la forêt Université du Québec à Montréal C P 8888 succ Centre ville Montréal QC H3C 3P8 Canada; Department of Forest Ecology Faculty of Forestry and Wood Sciences Czech University of Life Sciences Prague Kamýcká 129 Praha 6 Suchdol 165 00 Czech Republic; Natural Resources Canada Canadian Forest Service Laurentian Forestry Centre 1055 du P E P S P O Box 10380 Stn Sainte Foy Québec QC G1V 4C7 Canada

Centre d'étude de la forêt Université du Québec à Montréal C P 8888 succ Centre ville Montréal QC H3C 3P8 Canada; Institut de recherche sur les forêts Université du Québec en Abitibi Témiscamingue 445 boul de l'Université Rouyn Noranda QC J9X 5E4 Canada

Centre d'étude de la forêt Université du Québec à Montréal C P 8888 succ Centre ville Montréal QC H3C 3P8 Canada; Natural Resources Canada Canadian Forest Service Laurentian Forestry Centre 1055 du P E P S P O Box 10380 Stn Sainte Foy Québec QC G1V 4C7 Canada

Forest Management Silviculture Group Institute of Terrestrial Ecosystems Department of Environmental Systems Science ETH Zurich 8092 Zurich Switzerland

Max Planck Institute for Biogeochemistry Department of Biogeochemical Processes Hans Knöll Str 10 07745 Jena Germany

Natural Resources Canada Canadian Forest Service Laurentian Forestry Centre 1055 du P E P S P O Box 10380 Stn Sainte Foy Québec QC G1V 4C7 Canada; Centre d'étude de la forêt Université du Québec à Montréal C P 8888 succ Centre ville Montréal QC H3C 3P8 Canada

Citace poskytuje Crossref.org

Responses of stem growth and canopy greenness of temperate conifers to dry spells