Báo cáo lâm nghiệp: resistance of two Douglas fir species (Pseudotsuga menziesii (Mirb.) Franco and Pseudotsuga macrocarpa (Torr.) Mayr.): relative importance of water use efficiency and root growth potentia

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: resistance of two Douglas fir species (Pseudotsuga menziesii (Mirb.) Franco and Pseudotsuga macrocarpa (Torr.) Mayr.): relative importance of water use efficiency and root growth potential...
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Báo cáo lâm nghiệp: "resistance of two Douglas fir species (Pseudotsuga menziesii (Mirb.) Franco and Pseudotsuga macrocarpa (Torr.) Mayr.): relative importance of water use efficiency and root growth potentia" resistance of two Douglas fir species (Pseudo-Droughttsuga menziesii (Mirb.) Franco and Pseudotsuga macro-carpa (Torr.) Mayr.): relative importance of water useefficiency and root growth potential J.M. GuehlG. Aussenac, P. GrieuLaboratoire de Bioclimatologie et Ecophysiologie Forestière, Station de et de Produc- Sylviculturetion, INRA Centre de Nancy, Champenoux, 54280 Seichamps, France !Introduction maintained at 4.6 Pa!KPa-!, and 2) in response to increasing d4V in well-watered plants. The measurements were performed with an assimi-In order to optimize the choice of species lation chamber in which air temperature, ambient C0 concentration, photosynthetic 2for reforestation in regions subjected to photon flux density and water vapor pressuresummer water shortage, it is important to were controlled. Analyzing the data trough Adetermine which physiological compo- vs Intracellular C0 molar fraction (Ci) graphs, 2nents may be involved in their drought could determine stomatal and mesophyll we components of changes in A (Prioul et al.,adaptation. Therefore, we have carried out 1984; Jones, l!185). The gas exchange re-this study aimed at comparing the ecophy- sponse to zH!Vwas also examined with respectsiological behavior of 2 Douglas fir spe- the optimization theory of Cowan and tocies: Pseudofsuga menziesii (Mirb.), origi- Farquhar (1977).nating from a relatively wet coastal In a second experiment (Grieu and Ausse-zone (Ashford, WA, U.S.A., 300 m eleva- nac, 1988), non-destructive measurements of the number of growing roots and root elonga-tion) and Pseudotsuga macrocarpa (Torr.) tion were made on 3 mo old seedlings of the 2Mayr., growing under drier conditions (CA, species grown in root boxes.U.S.A., 1315 m elevation). ResultsMaterials and Methods Data of Fig. 1 a show that the peak rates ofCarbon dioxide assimilation rate (A), stomatalconductance (g! and transpiration rate (E) A were higher in P. menziesii than inwere measured on 2 yr old seedlings: 1) during P. macrocarpa. After an initial increase,a soil water depletion cycle (the water status of mesophyll photosynthesis remained un-the plants was determined by predawn water changed over a wide predawn waterpotential measurements), while the leaf-to-airwater vapor pressure difference (4 W) was potential range in both species, while g s reduced. At higher soil drought, a dra-wasmatic decline of mesophyll photosynthesiswas noted starting from -1.5 MPa in P.macrocarpa and -1.9 MPa in P. menzie-sii. In both species, stomatal conductanceand especially mesophyll photosynthesiswere dramatically decreased, as d W wasincreased (Fig. 1 b). P. macrocarpa had the highest and themost unstable - and thus non-optimal values of aEf7A in response to in--creasing AW (Fig. 2a). P. macrocarpaalsohad the highest c7Elc?A at high water poten-tial (Fig. 2b). Growth of the pre-existent roots wasmore important in P. macrocarpa than inP. menziesii and growth of the new rootswas similar in both species (Fig. 3).Furthermore, P. macrocarpa explored thedeep soil layers more quickly tha P. men-ziesii (Fig. 4.).Conclusions exchange rates and exhibited the gas least conservative water economy.Unexpectedly, in the present comparative The P. high drought adaptation ofstudy the results show that the drought-resistant P. macrocarpa had the lowest macrocarpa seems to be due mainly to 80 n - fI menziesii, Pseudotsuga macrocarpa et Cedrus and soilefficient root growth exploration atlantica. Ann. Sci. For. 45, 117-124abilities, whereas, surprisingly, no adapta- Grieu P., Guehl J.M. & Aussenac G. (1988) Thetion f ...