Báo cáo lâm nghiệp: "Responses of photosynthesis and stomatal conductance to atmospheric humidity in some mediterranean Abies specie"

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Responses of photosynthesis and stomatal conductance to atmospheric humidity in some mediterranean Abies species J.M. Guehi J. Bouachrine’ 1 2 Zimmermann E. 1 Dreyer R. ! Laboratoire de Bioclimatologie-Ecophysiologie Forestiere, Station de Sylviculture et Production, INRA, Centre de Nancy, F-54280 Seichamps, France, and Lehrstuhl 2 fOr Pfanzenökologie, Universität Bayreuth, Postfach 3008, D-8580 Bayreuth, F.R.G. sessed under controlled environmental condi- Introduction tions with an open gas-exchange measurement system on intact or excised shoots of different Leaf gas-exchange has long been shown mediterranean coniferous species. Stomatal to be sensitive to changes in the water conductance (g! and intercellular C0 concen- 2 vapor mole fraction difference between the tration (Ci) were calculated from the gas- exchange data using classical equations (see leaf and the air (Aw ) (Sandford and Jar- Guehl and Aussenac, 1987). Prior to dw being vis, 1986; Schulze, 1986). It has been pro- increased, the short-term response of gas- posed (Guehl and Aussenac, 1987; Grieu exchange to increasing ambient C0 concen- 2 et al., 1988) that decreasing C0 assimila- 2 tration (C was assessed, and the corre- ) a tion in response to increasing Aw is not sponding A(Ci) functions were determined, thus allowing the analysis of C0 assimilation in 2 only due to stomatal closure, but could be, terms of mesophyll photosynthetic capacity at least partially, a consequence of altered (demand function, see Fig. 1) and diffusional mesophyll photosynthetic capacity. How- limitation of C0 supply to the chloroplasts 2 ever, that interpretation is not consensual (supply function). The A(CiJ functions were also used to determine the marginal water cost of (Terashima et al., 1988). We report herein C0 assimilation (DEJDA) (Guehl and Aussenac, 2 results providing further evidence for the 1987) and to examine the gas-exchange regu- existence of a mesophyll effect in re- lation with respect to the optimization theory of sponse to increasing Aw in some mediter- Cowan and Farquhar (1977). ranean Abies species. The study was also aimed at determining whether the different species examined exhibit differences in Results and Discussion their water use efficiencies. Increasing Aw resulted in markedly low- ered A (Fig. 1 a) and g (Fig. 1 b) in seed- s Materials and Methods lings of Abies nordmanniana. Stomatal closure was efficient enough for the Responses of C0 assimilation rate (A) and 2 E (dw) response to exhibit a maximum at transpiration rate (E) to varying dw were as-
tion (Terashima et al., 1988), was shown about Aw = 12 Pa-kPa- (Fig. 1c), thus 1 in the second phase of the experiment in supporting the postulate (Schulze, 1986) which Aw was returned near its initial low that alterations of leaf water status are not level. During that phase, A recovered par- involved in the responses of A and g to s tially, with the data points remaining A Analyzing the data in an A vs Ci graph w approximately on the same supply func- (Fig. 1d, closed symbols) showed, as had tion (Fig. 1d, open symbols), thus indi- already been found for other coniferous cating that the recovery of A was almost species (Guehl and Aussenac, 1987; fully accounted for by a recovery of meso- Grieu et aL, 1988), that the experimental phyll photosynthesis. Fig. 2 gives a further points did not remain on the initial demand example of uncoupling between diffusional function. That such a reponse pattern and mesophyll photosynthetic processes actually denotes an effect of 3w on the in response to increasing Aw: Pinus pinea mesophyll photosynthetic capacity, and is seedlings, having a leaf diffusional struc- not an artifact due to improper Ci calcula-
fundamentally different from that vation regions of the Mediterranean area. ture not of the Abies exhibited a pure stomatal re- A. cephalonica, and A. marocana had the sponse (constant D function) of A to d highest A values for a given Aw. These 2 w between 10.0 and 22.0 Pa-kPa-!. species had !also the lowest EZ4 and Significant differences in the gas- 818A ratios (Fig. 4) and, furthermore, 818A was constant with Aw, which indi- exchange response to dw (Fig. 3) were found in a comparative study on 4 Abies cates optimization between C0 assimila- 2 species originating from different high ele- tion and transpirational water losses
in three coniferous species. Physiol. and Farquhar, 1977). In A. nord- (Cowan change Plant. 73, 97-104 manniana and A. alba, E/A and 818A Guehl J.M. & Aussenac G. (1987) Photosynthe- were higher and optimization was not sis decrease and stomatal control of gas achieved. These results are in good exchange in Abies alba Mill. in response to agreement with the growth performances vapor pressure difference. Plant Physiol. 83, of the studied species in southern France. 316-322 Sandford A.P. & Jarvis P.G. (1986) Stomatal responses to humidity in selected conifers. Tree Physiol. 2, 89-103 References Schulze E.D. (1986) Carbon dioxide and water vapor exchange in response to drought in the atmosphere and in the soil. Annu. Rev. Plant Cowan I.R. & Farquhar G.D. (1977) Stomatal Physiol. 37, 247-274 function in relation to leaf metabolism and envi- Terashima I., Wong S.C., Osmond C.B. & Far- ronment. Symp. Soc. Exp. Biol. 31, 471-505 quhar G.D. (1988) Characterization of non-uni- form photosynthesis induced by abscisic acid in Grieu P., Guehl J.M. & Aussenac G. (1988) The effects of soil and atmospheric drought on pho- leaves having different mesophyll anatomies. Plant Cell Physiol. 29, 385-394 tosynthesis and stomatal control of gas ex-