Báo cáo khoa học: Influence of soil drying on leaf water potential, photosynthesis, stomatal conductance and growth in two black pine varieties

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Báo cáo khoa học: "Influence of soil drying on leaf water potential, photosynthesis, stomatal conductance and growth in two black pine varieties" Original article drying on leaf water potential, Influence of soil photosynthesis, stomatal conductance and growth in two black pine varieties Gérard Lévy Gilbert Aussenac b , c François Lebourgeois a Bernard Clerc François Willm c , c Équipe a phytoécologie, Unité d’écophysiologie forestière, Inra Nancy, Champenoux, France 54280 b sol et nutrition, Unité d’écophysiologie forestière, Inra Nancy, Équipe 54280 Champenoux, France Unité d’écophysiologie forestière, Inra c Équipe bioclimatologie, Nancy, 54280 Champenoux, France accepted 20 October 1997) 12 June 1997; (ReceivedAbstract - The aim of this study was to examine the influence of long-term soil water deficit ongrowth and physiological processes of two black pine varieties (Pinus nigra ssp. laricio var. ssp. laricio var. Calabrica). Three-year-old seedlings grown in largesCorsicana and Pinus nigra ) 3 m were subjected to a prolonged summer drought (99 days from the endboxes (volume: 1.62of June until the end of September) and photosynthesis (A), stomatal conductance (g water sta- ), wtus and growth were measured. No marked differences arose between Corsican and Calabricanpines feature to drought. At least in their juvenile stage, both varieties exhibited a ’drought-avoidance strategy’ characterized by an efficient stomatal control of transpirational water loss. Thisresult is consistent with previous studies on Pinus nigra and confirm the water stress adapta-tion of this collective Mediterranean species. Because a significant decrease of g (about 30 %) w the data suggested that predawn water potentialwas observed with no obvious variation in , wp Ψwas not the best indicator to precociously detect water stress. However, both A and g reduced wto nearly zero as soon as the threshold value of Ψ = -1.6 MPa was reached (respective values wp0.5 μmol m s and 11 mmol m s Because most fine roots were within the upper 40 cm of -2 -1 -2 -1).the soil, a superficial soil desiccation has probably induced rapid stomatal closure, triggered bya biophysical and/or biochemical signal from the desiccated roots to the leaves. Embolism seemsnot to be responsible for the effect of drought on physiological processes, because the minimum observed at the end of the drying cycle (-2.5 MPa) remained higher than the thresh-value wp of Ψ inducing a significant xylem cavitation for these varieties (-4 MPa). Summer drought sig-oldnificantly reduced annual stem diameter (-20 %) and needle length (-25 %), but not stem elon-gation. Total elaborated dry weight was reduced about 45 %. Seedlings grown in the dry regime* Correspendence and reprintsE-mail: lebourgeois@nancy.inra.frreduced belowground growth proportionally more than aboveground growth, causing a signifi-cant decrease in the R/S ratio. Such a result, which diverges with classical models of wholeplant biomass partitioning, might be partially explained by seasonal pattern in the root growth whichtypically has its most important peak in mid-summer, period of maximum drought in our study.With the parameters studied here, the expression of the genetic characteristics bet ...