科研之友
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摘要
Winter-drought induced forest diebacks in the low-latitude margins of species%26apos; distribution ranges can provide new insights into the mechanisms (carbon starvation, hydraulic failure) underlying contrasting tree reactions. We analysed a winter-drought induced dieback at the Scots pine%26apos;s southern edge through a dual-isotope approach (Delta C-13 and delta O-18 in tree-ring cellulose). We hypothesized that a differential long-term performance, mediated by the interaction between CO2 and climate, determined the fates of individuals during dieback. Declining trees showed a stronger coupling between climate, growth and intrinsic water-use efficiency (WUEi) than non-declining individuals that was noticeable for 25 years prior to dieback. The rising stomatal control of water losses with time in declining trees, indicated by negative Delta C-13-delta O-18 relationships, was likely associated with their native aptitude to grow more and take up more water (suggested by larger tracheid lumen widths) than non-declining trees and, therefore, to exhibit a greater cavitation risk. Freeze-thaw episodes occurring in winter 2001 unveiled such physiological differences by triggering dieback in those trees more vulnerable to hydraulic failure. Thus, WUEi tightly modulated growth responses to long-term warming in declining trees, indicating that co-occurring individuals were differentially predisposed to winter-drought mortality. These different performances were unconnected to the depletion of stored carbohydrates.
- 出版日期2013-8
