关键词: 地宝兰属, 气孔特征, 光合日变化, 光响应曲线, CO₂响应曲线, 叶绿素

Abstract: To explore leaf anatomical structures and photosynthetic characteristics of Geodorum plant, the anatomical structure of leaves, daily variation of photosynthesis, light response curve, CO₂ response curve, chlorophyll content and other indexes of the narrowly endangered Geodorum eulophioides and widely spread G. densiflorum and G. attenuatum were measured. The results were as follows:(1)Three species of Geodorum did not have spongy and fenestrated tissue differentiation in their chloroplasts, and stomata were distributed only in the lower epidermis. Compared with G. densiflorum and G. eulophioides, G. attenuatum had a greater leaf thickness and smaller stomatal density, exhibiting structural characteristics that were more adaptable to low light environments.(2)The daily changes of net photosynthetic rate(P_n)of three species of Geodorum showed a “bimodal” curve, and the photosynthetic “lunch break” was mainly caused by non-stomatal limitation. The daily mean values of P_n and water use efficiency(WUE)showed that G. attenuatum > G. densiflorum > G. eulophioides, which indicated that G. eulophioides had a weaker ability of accumulating photosynthesis products, and its adaptive capacity to the arid environment was probably poorer.(3)Three species of Geodorum were all shade plants. G. densiflorum had the smallest light compensation point(LCP)and the largest light saturation point(LSP), and had a wider range of adaptation to light intensity; G. attenuatum had a high maximum net photosynthetic rate(P_max)and apparent quantum efficiency(AQY), and its photosynthetic capacity was stronger; G. eulophioides had the smallest P_max and the potential maximum net photosynthetic rate(A_max), and its photosynthetic capacity and CO₂ utilization capacity were weaker.(4)The chlorophyll a(Chl a), chlorophyll b(Chl b)and total chlorophyll(Chl)contents of G. densiflorum and G. attenuatum were significantly(P<0.05)higher than those of G. eulophioide.(5)There were significant(P<0.05)correlations between the leaf thickness, mesophyll thickness, chlorophyll content, and P_max of three species of Geodorum. It was concluded that the photosynthetic capacity and adaptability of G. eulophioides were poorer compared with G. densiflorum and G. attenuatum, which might be greatly related to its endangerment; appropriate shading and increased CO₂ concentration favored photosynthesis in three species of Geodorum. The results of this study provide a reference for the analysis of the endangered causes of G. eulophioides and the conservation of germplasm resources of three Geodorum species.

Key words: Geodorum, stomatal characteristics, daily variation of photosynthesis, light response curve, CO₂ response curve, chlorophyll