Regulation of Water Use in the Southernmost European Fir (Abies pinsapo Boiss.): Drought Avoidance Matters

Abstract

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 OPEN ACCESS Forests2015, 62242 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.

Carbon Limitation and Drought Sensitivity at Contrasting Elevation and Competition of Abies pinsapo Forests. Does Experimental Thinning Enhance Water Supply and Carbohydrates?

“…Indeed, the timing of this sequential reduction, in functions, such as gas exchange and growth, has been largely related to recent events of forest decline and mortality worldwide [11,[16][17][18][19]. Nonetheless, the functional and structural dynamics of these critical processes in response to competition are still not well understood.We focused on the hydraulic characteristics and seasonal patterns of sap flow density (SFD), gas exchange, secondary growth, and non-structural carbohydrate (NSC) of the drought-sensitive fir Abies pinsapo Boiss [20][21][22][23]. We assumed that xylem vulnerability to embolism places a physical limit for A. pinsapo tolerance to water shortage while the dynamics of NSC would be related to drought sensitivity, for the extent of isohydric regulation of the water potential, as well as the persistence of the drought [13,14,19].…”

“…We assumed that xylem vulnerability to embolism places a physical limit for A. pinsapo tolerance to water shortage while the dynamics of NSC would be related to drought sensitivity, for the extent of isohydric regulation of the water potential, as well as the persistence of the drought [13,14,19]. Specifically, an increase in NSC concentrations should be expected beneath moderate drought, assuming growth ceases before photosynthesis, whereas NSC concentrations should decay under extreme drought conditions [10][11][12].According to this general framework, we focused on low elevation stands, as they are subjected to higher than average drought conditions [20]. Here, we investigated the effects of experimental thinning, aimed to diversify the stand structure and reduce tree-to-tree competition, modulating drought stress in the remaining trees [23].…”

“…Specifically, we aimed: (1) To quantify the hydraulic conductivity and resistance to the cavitation of A. pinsapo trees under contrasting competition (thinned versus control) and elevation (low versus high elevation);(2) to quantify seasonal dynamics of SFD, gas exchange, secondary growth, and NSC content; and (3) to evaluate the relationships between the microclimate and carbon and water balances, and to what extent competition modulates them.Forests 2019, 10, 1132 3 of 17 buried at 0.30 m. A detailed description of the instrumentation can be found in [23]. Vapor pressure deficit (VPD, kPa) was estimated using T and RH data [20,23].…”

“…We focused on the hydraulic characteristics and seasonal patterns of sap flow density (SFD), gas exchange, secondary growth, and non-structural carbohydrate (NSC) of the drought-sensitive fir Abies pinsapo Boiss [20][21][22][23]. We assumed that xylem vulnerability to embolism places a physical limit for A. pinsapo tolerance to water shortage while the dynamics of NSC would be related to drought sensitivity, for the extent of isohydric regulation of the water potential, as well as the persistence of the drought [13,14,19].…”

Untitled

“…El tipo de suelo para la profundidad 0-40 cm es arcilloso limoso, con 0.9 g·cm -3 de densidad aparente, 7.60 de pH, 0.14 dS m -1 have allowed plants to be able to minimize water loss by evapotranspiration (Striker, 2012), allowing them to maintain tissue water status (Donoso et al, 2015). The above mentioned is essential for native trees and shrubs species in northeastern Mexico to present adaptation physiological mechanisms (González-Rodríguez et al, 2016), because of water deficit and high temperatures (Warren et al, 2011), such as the reduction of foliar water potential as water availability decreases in soil until it is maintained over a threshold (Sánchez-Salguero et al, 2015). Therefore, the regulation of foliar water potential is one of the mechanisms that determines plants' ability to survive in this type of regions (Fleta-Soriano & Munné-Bosch, 2016).…”