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Báo cáo lâm nghiệp: "Variability of stomatal conductance in the crown of a maritime pine (Pinus pinaster Ait.)"

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Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: Variability of stomatal conductance in the crown of a maritime pine (Pinus pinaster Ait.)...

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Nội dung Text: Báo cáo lâm nghiệp: "Variability of stomatal conductance in the crown of a maritime pine (Pinus pinaster Ait.)"

Variability of stomatal conductance in the crown of a maritime pine (Pinus pinaster Ait.) D. Loustau Moussa F. El Hadj with the technical assistance of M. Sartore and M. Guedon with echnic sistance a nd Station de Recherches Forestières de Pierroton, Laboratoire de Sylviculture et d’Ecologie, INRA, Domaine-de-I’Hermitage, 33610 Cestas, France For each of the 30 shoots, measurements Introduction made on a pair of needles of a single fas- were cicle of the shoot. Measurements of the whole sample were made on 5 d, from 07:00 to 19:00 Stomatal response of conifers to environ- (U.T.), between June 2, and August 30, 1988. mental variables, such as air water vapor An automatic steady state porometer (LICOR deficit, has been reported by many 1600) was used with a chamber of 63 cc inter- authors (Whitehead et al., 1984; Sandford nal volume. g was expressed in cm/s, on a s total leaf area basis. and Jarvis, 1986). Variations of stomatal conductance (g related to needle age ) s of tem- the experiment, hourly During means perature, relative humidity, wind speed and irra- and situation in the canopy have also diance were calculated from micrometeorologi- been described (Leverenz et al., 1982; cal measurements made 2 m above the Tan ef al., 1977). canopy. Hourly means of canopy transpiration were also computed from sap flow measure- In order to estimate a general pattern of ments (Granier, 1985) on a sample of 10 pines stomatal conductance (g in the crown of ) s (including the s
As had been noticed during previous position, branch orienta- Effects of whorl tion, age of needle and interactions years, the ratio of canopy transpiration to were tested using ANOVA. When significant potential evapotranspiration (PET) (Pen- effects were detected, means at each man-Monteith) dropped from 0.75 in June to 0.44 in late summer. level were compared with Duncan’s test. Linear regression of g on air water No significant difference in g was found s s vapor deficit D (Pa) and irradiance Ir between morning and evening. But be- ) 2 (W-m- for spring and late summer re- tween 9:00 and 16:00, significant effects sulted in the following equation: spring (all (< 0.05) were shown for each of the 3 data before the beginning of the dry pe- selected features (Table I). riod): 9s =0.15-(0.95x10!x0)+(1.6x10! Late summer x Ir) (N=542; r = 0.52). 2 significant decrease of g There was a s Late summer (data after the beginning of the day, but no significant dif- during the dry period): ferences in g in terms of whorl position, s 0.08 - (0.34 x 10! x D) (0.38 s g x + = branch orientation or needle age could be 4 10- x Ir ) (N= = 11; r )0.3 3 2 1. detected. Variations related to needle features Discussion and Conclusions Spring Because of the diurnal pattern of the variance of g all subsequent analyses Variations in g over a growing season , s s show a seasonal pattern with 2 contrasted were conducted on data divided into 3 time periods (before 09:00, 09:00-16:00, periods, before and after the beginning of and after 16:00 h). the dry period.
In the pre-drought period, the stomatal tion. Stomatal closure could be general response to air water vapor deficit and throughout the crown and would explain irradiance explains 52% of the total g the absence of any stratification. s variation; g decreases as D increases, s and increases with Ir, as observed by many authors (Sandford and Jarvis, 1986; Tan et al., 1977; Running, 1979). References In midday, when g variance and mean s are high, the general pattern of stomatal Granier A. (1985) Une nouvelle m6thode pour conductance of a pine shows significant la mesure du flux de s6ve brute dans le tronc differences related to needle age, whorl des arbres. Anri. Sci. For. 42, 81-88 position and branch orientation. Position Leverenz J., Deans J.D., Jarvis P.G., Milne R. & effects probably reflect a micrometeoro- Whitehead D. (1982) Systematic spatial varia- tion of stomatal conductance in a Sitka spruce logical stratification within the crown, and plantation. J. Appl. EcoL 19, 835-851 age effects could be related to the physio- logical development of the needle. Cumu- Running S.W. (1979) Environmental and phy- siological control of water flux through Pinus lated effects of environmental variables contorta. Can. For. Res. . J 10, 82-91 and needle features explained 75% of the Sandford A.P. & Jarvis P.G. (1986) Stomatal total variation of g,. responses to humidity in selected conifers. During the drought period, the mean Tree Physiol. 2, 89-103 and variance of g were much lower and s Tan C.S., Black A.A. & Nnyamah J.U. (1977) showed only a slight decrease during the Characteristics of stomatal diffusion resistance course of the day. Variation in vapor deficit on a Douglas fir forest exposed to soil water deficits. Can. J. For. Res. 7, 595-604 and irradiance explained only 33% of the variation of g No stratification could be Whitehead D., .larvis P.G. & Waring R.H. (1984) . s Stomatal conductance, transpiration and resis- shown in the crown at any time of the day. tance to water uptake in a Pinus sylvestris Soil water deficit is assumed to be the spacing experiment. Can J. For. Res. 14, 692- main limiting factor for needle transpira- 700

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