四种亚高山针叶林树种的表型可塑性对不同光照强度的响应

Plasticity responses of 4 tree species in subalpine-coniferous-forest to different light regimes

以青藏高原东缘亚高山针叶林群落演替后期种岷江冷杉、演替中后期种粗枝云杉和青榨槭、及先锋树种红桦为材料,研究了不同光强下生长的4种树苗生长、生物量分配、叶片形态和光合特性,探讨植物幼苗的形态和生理特征的表型可塑性与光适应的关系。结果表明:(1)弱光环境中生长的4种植物的基茎、相对生长速率、叶片厚度、根重比、最大净光合速率、光饱和点、光补偿点、暗呼吸速率较低,而比叶面积、地上/地下生物量、茎长/茎重、叶重比和茎重比较高。(2)大部分光环境下岷江冷杉幼苗的最大净光合速率和暗呼吸速率低于粗枝云杉,青榨槭幼苗的最大净光合速率和暗呼吸速率略低于红桦。(3)高光强下生长的粗枝云杉和红桦幼苗的相对生长速率分别大于岷江冷杉和青榨槭,但在低光强下则与之相反。(4)粗枝云杉和红桦幼苗的11种可塑性指数平均值则分别大于岷江冷杉和青榨槭。岷江冷杉适应弱光环境的能力略强于粗枝云杉和红桦,但适应强光的能力较差。生理适应的可塑性指数大于形态适应的可塑性指数,表明前者在4种植物幼苗光适应方面起到了重要的作用。研究结果支持树种的生理生态特性决定了其演替状况和生境选择的假说。

The morphological and physiological acclimations to six light conditions were investigated in seedlings of four tree species （ Abies faxoniana, Picea asperata, Acer davidii and Betula albo-sinensis） in subalpine coniferous forests, in Eastern Qinghai-Tibet Plateau, China. Four species are at different successional serals with A. faxoniana as late successional species, P. asperata and A. davidii as mid-late successional species, B. albo-sinensis as a pioneer tree species. The main purpose was to compare the difference in the responses of the plasticity of photosynthetic characteristics to different growth light gradients among the studies species. The growth light regimes designed in this study were 100% , 55% , 40% , 25% 15% and 7% of the full sun light, respectively. The results were： （ 1 ） All seedlings of the four species under the low growth light conditions applied in this study showed decreasing in root collar diameter, relative growth rate （RGR）, leaf thickness, root mass ratio （root dry mass/ seedling dry mass ）, leaf area based photosynthetic capacity and dark respiration rate, light saturation point and light compensation point, but increasing in leaf area per unit mass, above- / under- ground mass, specific stem length （ stem length/stem dry mass） , leaf mass rate （ leaf mass/seedling mass） and stem mass rate （ stem mass/seedling mass） ; （2） Under most light conditions leaf area-based photosynthetic capacity and respiration rates of A. faxoniana were lower than those of P. asperata, while A. davidii had higher values in those parameters when compared to B. albo-sinensis ; （3） For P. asperata and B. albo-sinensis seedlings, the relative growth rates （RGRs） were higher than those of A. faxoniana and A. davidii as the growth light regimes increased. However, under the low growth light regimes RGRs of A. faxoniana and A. davidii seedlings were higher than those of the other two species; and （4） The means of phenotypic plasticity index of the eleven morphological and physiological parameters of P. asperata and B. albo-sinensis were higher than those of A. faxoniana and A. davidii, respectively. All of which indicate that A. faxoniana had stronger capacity of acclimation to low light regimes than P. asperata and B. albo-sinensis did, but the capacity of acclimation to high light regimes of the shadetolerant species was poorer than that of the two early successional seral speeies. The index of physiological plasticity was higher than that of morphological plasticity, suggesting that morphological plasticity was an important acclimation characteristic for growth light regimes for the four subalpine coniferous tree species. The results in this paper also support the hypothesis that ecophysiological traits of tree species determines their successional status and associated habitats for their seedlings.