Abstract
The current scenario of global warming has resulted in considerable uncertainty regarding the capacity of forest trees to adapt to increasing drought. Detailed ecophysiological knowledge would provide a basis to forecast expected species dynamics in response to climate change. Here, we compare the water balance (stomatal conductance, xylem water potential, needle osmotic adjustment) of Abies pinsapo, a relict drought-sensitive Mediterranean fir, along an altitudinal gradient. We related these variables to soil water and nutrient availability, air temperature, atmospheric water potential, and vapour pressure deficit during two consecutive years. Our results indicate that A. pinsapo closed stomata rapidly over a very narrow range of soil water availability and atmospheric dryness. This isohydric response during water stress suggests that this relict conifer relied on the plant hormone abscisic acid to maintain closed stomata during sustained drought, instead of needle desiccation to passively drive stomatal closure, needle osmotic adjustment or a plastic response of the xylem to different levels of water availability. Both the soil and foliar nutrient contents suggest that the studied populations are not limited by nutrient deficiencies, and drought was stronger in the warmer low-elevation areas.
Highlights
IntroductionConsiderable literature on recent forest decline draws attention to a direct link between climate change and the water relations of trees
Water stress is a major determinant of plant species distribution
Pinsapo populations to ensure survival [11]. For both the populations, vapour pressure deficit values close to 1.5 kPa were related to near-complete stomatal closure; this threshold was reached at soil water contents of about 10%
Summary
Considerable literature on recent forest decline draws attention to a direct link between climate change and the water relations of trees Extreme climatic events, such as drought, are among the main drivers of forest dynamics and are usually related to forest decline of drought-sensitive tree species [1,2,3,4]. Drought-induced tree decline has been reported for several ecosystems and is usually focused on isohydric tree species, such as relict Mediterranean mountain conifers [4]. This tree die-off is mainly characterized by declining growth patterns, increases in defoliation and extensive death [1,2,3]
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