Acclimation of Lamina Mass Per Unit Area, Photosynthetic Characteristics and Dark Respiration to Growth Light Regimes in Four Tropical Rainforest Species
四种热带雨林树种幼苗比叶重,光合特性和暗呼吸对生长光环境的适应

The morphological and physiological acclimation to three growth light regimes were explored in seedlings of four tropical rainforest tree species during the foggy and cool season in 2000 at Xishuangbanna, Yunnan province, China. The main purpose was to determine whether plasticity of photosynthetic capacity and lamina mass per unit area (indicating leaf thickness) was greater in light-demanding species than that in shade-tolerant species, and to determine the relative importance of morphological and physiological acclimation. In seedling stage, the two species, Anthocephalus chinensis (Lam.) Rich.ex Walp. and Linociera insignis C. B. Clarke, are high light-demanding, and the two other species, Calophyllum polyanthum Wall. ex Choisy and Barringtonia macrostachya (Jack) Kurz, were shade-tolerant, according to the seedlings distribution of the four species in rainforest. The growth light regimes used in this study were 50%, 25%, and 8% of the full sunshine, respectively. The 50% relative irradiance is much stronger than that measured in tropical rainforest, and 25% and 8% relative irradiance correspond with those measured in very large and small forest gaps, respectively. The typical rainforest understory light intensity was not used in this study because high light-demanding species could not grow well at this weak light intensity. All the seedlings of the four species could acclimate to the low growth light regimes used in this study through decreasing lamina mass per unit area, lamina area based photosynthetic capacity and dark respiration rate, light saturation point, light compensation point, and chlorophyll a/b ratio, and through increasing lamina area based chlorophyll content. Lamina area based respiration rates and photosynthetic capacity of the two shade-tolerant species were lower than those of the two light-demanding species. The plasticity of photosynthetic capacity and lamina mass per unit area of the two light-demanders was higher than that of the two shade-tolerant. For the two light-demanders, with the growth light eregimes increasing lamina area based chlorophyll content decreased, and lamina area based and chlorophyll based carboxylation efficiency increased significantly. This means that the two light-demanders increased the allocation proportion of lamina nitrogen to Rubisco, while decreased the nitrogen allocation to chlorophyll. Compared with the two light-demanders, under the low growth light regimes the two shade-tolerant was higher in lamina area based chlorophyll content, and was lower in chlorophyll a/b ratio, lamina area based photosynthetic capacity and dark respiration rates, light saturation point, light compensation point, and the increment of their lamina area based photosynthetic capacity was not significant with the increase of growth light regimes. This indicates that the capacity of acclimation to low light regimes for the two shade-tolerant was stronger than that for the two light-demanders, but the capacity of