格氏栲幼苗叶绿素荧光和非结构性碳水化合物积累对种子散布位置的响应

植物种子从母树掉落形成土壤种子库时,凋落物或土壤是其最初接触的物理环境,种子所处位置(种子在凋落物上层、土壤表层或凋落物下层)影响了幼苗天然更新进程。模拟格氏栲种子在凋落物上层(种子下层铺垫2和4 cm凋落物)、土壤表层(无凋落物)及凋落物下层(种子上层覆盖2、4、6和8 cm凋落物)等3种不同散布位置,探讨种子散布位置对幼苗叶绿素荧光特性、非结构性碳水化合物、比叶面积、叶干物质含量和养分含量的影响。结果表明:不同散布位置的幼苗单位面积的叶氮含量与可溶性糖、非结构性碳水化合物含量呈显著正相关,与比叶面积呈显著负相关。适宜凋落物覆盖(2和4 cm)的幼苗通过提高叶绿素相对含量、可溶性糖含量、非结构性碳水化合物含量、叶干物质含量和单位面积的叶氮含量和叶磷含量,降低比叶面积等的资源获取策略来实现自身快速生长需求。无凋落物和深层凋落物覆盖(6和8 cm)的幼苗采取高单位重量的叶氮含量和比叶面积,低叶干物质含量和非结构性碳水化合物含量的资源保守型策略以截获更多有效光资源,进而弥补深层凋落物带来的郁闭环境,降低幼苗因“碳饥饿”而死亡的几率。下层铺垫凋落物的幼苗通过在叶片储藏淀粉,降低叶片光合组织消耗能量(低PSⅡ最大光化学效率)等维持幼苗生长。熵值法综合分析表明,浅层凋落物覆盖(2 cm)对格氏栲幼苗生长的促进作用最为显著,未来可通过调节天然林凋落物层厚度以促进格氏栲幼苗生长与更新。

Responses of chlorophyll fluorescence and non-structural carbohydrate accumulation of Castanopsis kawakamii seedlings to seed dispersal positions

When seeds fallen from the mother trees, their initial contact physical environment was litter or soil. The dispersal positions of seeds (seeds positioned on top of the litter, the soil surface and beneath the litter) determine the process of their natural regeneration. We simulated three different dispersal positions of Castanopsis kawakamii, including seeds positioned on top of the litter (2 and 4 cm litter was placed below the seed layer), soil surface (without litter), and seeds beneath the litter (2, 4, 6 and 8 cm litter covers in the upper layer of seeds). We examined the effects of seed dispersal position on the chlorophyll fluorescence characteristics, non-structural carbohydrate, specific leaf area, leaf dry matter content and nutrient content of seedlings. The results showed that leaf nitrogen content per area of seedlings had significantly positive correlation with soluble sugar content, non-structural carbohydrate content, and negative correlation with specific leaf area across different dispersal positions. Seedlings of the moderate litter cover (2 and 4 cm) adopted resource acquisitive strategies by increasing relative chlorophyll content, soluble sugar content, non-structural carbohydrate content, leaf dry matter content, leaf nitrogen content and phosphorus contents per area, and decreasing specific leaf area to achieve their demands for rapid growth. Seedlings grew on soil surface and beneath the deep litter (6 and 8 cm) adopted the resource conservative strategies with higher leaf nitrogen content per mass and specific leaf area, lower leaf dry matter content, and non-structural carbohydrate content to intercept more effective light resources to compensate for the shady environment brought by deep litter. This would further decrease the probability of seedling mortality due to ‘carbon starvation'. Seedlings under litter layer stored starch in leaf, and reduced the energy consumption of photosynthetic tissues (low PSⅡ maximum photochemical efficiency) to maintain seedling growth. Comprehensive analysis of entropy method indicated that low amount of litter cover (2 cm) significantly promoted seedling growth of C. kawakamii. In the future, we could regulate the thickness of litter layer to promote the growth and regeneration of C. kawakamii seedlings in natural forest.