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Các kỹ thuật huỳnh quang diệp lục và trao đổi khí đã được sử dụng để so sánh các đặc điểm quang hợp của loài Dầu Cát -Dipterocarpus. cf. condorensis (đặc hữu hẹp) và loài Sến-Shorea roxburghii (thông thường) tại Khu BTTN Tà Kóu - Tỉnh Bình Thuận. Kết quả khảo sát đã góp phần giải thích nguyên nhân phân bố hẹp của Dầu Cát . Dầu Cát có hiệu suất quang hợp tương tự như Sến ở các khu vực cả hai loài cùng mọc nơi có mực nước ngầm sâu (> 20m), nhưng có hoạt động quang hợp cao hơn ở nơi mực nước ngầm cạn ( | TAÏP CHÍ PHAÙT TRIEÅN KH&CN, TAÄP 14, SOÁ T6 - 2011 EXPLAINING RARITY OF THE NARROWLY ENDEMIC DIPTEROCARPUS CF. CONDORENSIS BY IN SITU PHYSIOLOGICAL MEASUREMENTS Le Buu Thach(1), Christa Critchley(2) (1) Institute of Tropical Biology, Vietnam. (2) The University of Queensland, Australia (Manuscript Received on October 05th 2011, Manuscript Revised December 25th 2011) ABSTRACT: Comparative physiological attributes, obtained by chlorophyll fluorescence and gas exchange techniques, of restricted Dipterocarpus cf. condorensis and widespread Shorea roxburghii species that are actually co-located in Ta Kou Nature Reserve - Binh Thuan Province, provided essential information for understanding rarity of D. condorensis. The narrowly endemic D. condorensis had similar photosynthetic performance to the locally abundant S. roxburghii in more common habitats in which ground water tables are deep (>20m), but had significantly higher photosynthetic activities in its specific habitat, where the ground water level is shallow (20m) and are not usually burnt. Figure 1. Forests dominated by D. condorensis It can be therefore assumed that the occur at low elevation (2-50 m), adjacent to wetland environmental conditions for the two species in forest dominated by Melaleuca cajeputi (left), and their natural habitats are identical. The deeper are burnt frequently. ground water level in the forest dominated by These two species grow in dry open forests with climatic conditions characteristic of S. roxburghii can be considered equivalent to the water stress treatment. tropical monsoonal climates: average annual The present case temperatures of 26-27oC, annual rainfall of physiological 1100 to 1500 mm, dry season lasting 5-6 condorensis and months (i.e. from November to April) in which association there are 3-4 months with no rain. For this dominance. Le 2007 [4] suggested that reason, drought conditions are inherent in this physiological data, obtained by .