Báo cáo khoa học: Water relations of European silver fir (Abies alba Mill) in 2 natural stands in the French Alps subject to contrasting climatic conditions

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Báo cáo khoa học: "Water relations of European silver fir (Abies alba Mill) in 2 natural stands in the French Alps subject to contrasting climatic conditions" article Original Water relations of European silver fir (Abies alba Mill) in 2 natural stands in the French Alps subject to contrasting climatic conditions P Guicherd Université Joseph-Fourier, Centre de Biologie Alpine, BP 53, 38041 Grenoble cedex 9, France 30 November 1992; accepted 26 January 1994) (ReceivedSummary — This paper reports on the diurnal and seasonal variations in water potential, stomatal con-ductance, and transpiration of twigs from silver fir in a mesohygrophilic stand of the external French Alps,and in a mesoxerophilic stand in the inner French Alps where this fir grows near its ecological limits.In both stands, predawn needle water potential was always 0.2-0.4 MPa below the potential of thedriest soil layer. In the first one, it was maintained at about -0.4 MPa. Maximum stomatal conduc-tance and maximum transpiration, which could reach 200 mmol/m and 1 mmol/m respectively, /s 2 /s, 2occurred at the same time which corresponded to minimum leaf water potential. In the dry stand,predawn needle water potential never dropped below -1.14 MPa, yet a general browning of olderneedles was already observed. The decrease of predawn needle water potential was accompanied bythe decrease of maximum stomatal conductance and transpiration to 15% of their highest value, whichreached 150 mmol/m and 1 mmol/m respectively, at this stand. Maximum stomatal conduc- /s 2 /s, 2tance occurred in general before UT 07.00, and maximum transpiration 5-6 h later, irrespective ofpredawn needle water potential. Furthermore, in both stands, stomata closed at vapor pressure deficitvalue as low as 0.3 kPa. This extremely early reaction to water stress exhibited by European silver firis consistent with its well-known sensitivity to atmospheric humidity and soil water availability. It indi-cates a strong avoidance strategy, which we have hitherto attributed only to species better adapted todrought.Abies alba Mill European silver fir / Alps / stomata / water potential / water deficit =Abbreviations and units: E transpiration (mmol (H E maximal transpiration (mmol /s); O)/m 2 max = =/s);O)/m2s(H G stomatal conductance (mmol(H G maximal stomatal conductance /S); O)/m 2 smax = =(mmol(H Lp soil-to-leaf hydraulic conductance (mmol/m PFD photon flux /s/-MPa); 2/s);O)/m2 = =density (μE/m VPD vapor pressure deficit (kPa); &I leaf water potential (MPa); y minimum /s); 2 Imin = = psi; =leaf water potential (MPa); ψ predawn needle water potential (MPa); ψ soil water potential (MPa); = s = pΔψ ψ &p (MPa). Imin psi; - =Résumé — Comportement hydrique du sapin pectiné (Abies alba Mill) dans 2 stations desAlpes françaises climatiquement contrastées. L’article décrit les variations diurnes et saisonnièresdu potentiel hydrique foliaire, de la conductance stomatique et de la transpiration de rameaux desapin dans une station mésohygrophile des Alpes externes, et dans une station mésoxérophile des Alpesinternes en limite écolog ...