TAILIEUCHUNG - Báo cáo lâm nghiệp: "Drought and photosystem II activity in two Mediterranean oaks"

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế, đề tài: "Drought and photosystem II activity in two Mediterranean oaks. | Ann Sci For 1996 53 255-262 Elsevier INRA 255 Original article Drought and photosystem II activity in two Mediterranean oaks M Méthy c Damesin s Rambal Centre d ecologie fonctionnelle et evolutive CNRS BP 5051 34033 Montpellier cedex 01 France Received 15 November 1994 accepted 18 July 1995 Summary The responses of photosystem II PS II to drought were analysed on two Mediterranean oak species Quercus ilex and Q pubescens using the chlorophyll fluorescence pulse-amplitude-modulation technique. The maximal PS II photochemical efficiency Fv Fm of the evergreen Q ilex and the deciduous Q pubescens oaks was only affected when leaf predawn water potential was lower than -4 MPa. This value is rarely observed on mature trees growing in the field but can be undergone by young seedlings during drought periods hence confirming the stability of PS II. Whatever the irradiance drought resulted in both species in lower values of PS II photochemical efficiency in a light-adapted state AF Fm due to stomatai closure and or a direct inhibition of the dark reactions of photosynthesis. Diurnal decreases of Fv Fm of 30 min dark-adapted leaves were greater for lower predawn water potential a recovery was observed in the late afternoon. The reversible decreases in the diurnal time-courses of maximal fluorescence led US to assume the onset of protective mechanisms from permanent photodamages in Q ilex and to a lesser extent in Q pubescens. fluorescence I photoinhibition photosystem III Quercus I water stress Resume Sécheresse et activité du photosystème II Chez deux chênes méditerranéens. La réponse du photosystème II PS II à la sécheresse a été analysée sur deux espèces de chênes mediterraneans Quercus ilex etQ pubescens par la technique de la fluorescence chlorophyllienne pul-sée. L efficaclte photochimique maximale du PS II FJFj de Q ilex sempervirent et de Q pubescens caducifolie n a été affectee que pour un potentiel hydrique de base inferieur à -4 MPa. Une telle valeurn .

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