长白山阔叶红松林不同演替阶段林下红松幼苗能量与养分季节动态

为了解林下红松幼苗生长和养分存储季节动态,以长白山原始阔叶红松林(原始林)和次生杨桦林(次生林)林下2年生红松幼苗为对象,研究林下光合有效辐射(PAR)、幼苗生物量、非结构性碳水化合物(NSC)、全氮(N)和全磷(P)等指标的季节变化,分析两林分林下光照的季节动态及其差异对红松幼苗生长和养分积累的影响。结果表明: 原始林和次生林林下月PAR累积量季节变化都呈“双峰”型,夏季为郁闭期,两林分林下光线弱。春季和秋季为阔叶树无叶期,林下光照条件变好,且次生林林下光照明显好于原始林;原始林和次生林红松幼苗的生物量、NSC、全N和全P浓度的季节动态与林下光照的季节变化基本一致,在春季和秋季表现为显著增加,在夏季呈下降趋势。春季幼苗的淀粉浓度增加,夏季淀粉和可溶性糖浓度均逐渐降低,到8月达到最低值,秋季可溶性糖浓度显著升高。春季和秋季次生林林下幼苗的生物量和NSC浓度整体上均显著高于原始林,而夏季两林分差异不显著。因此,春季和秋季的林下光照条件差异是影响原始林和次生林中红松幼苗养分积累和生长更新差异的主要原因。

Seasonal dynamics of energy and nutrients of Pinus koraiensis seedlings in different successional stages of broadleaved Korean pine forest in Changbai Mountain,China.

We examined the seasonal variations of growth and nutrient accumulation of two-year-old Korean pine (Pinus koraiensis) seedlings in the primary broadleaved Korean pine forest (primary forest) and poplar birch forest (secondary forest) in Changbai Mountain. The seasonal changes of photosynthetically active radiation (PAR), seedling biomass, nonstructural carbohydrate (NSC), total nitrogen (N), and total phosphorus (P) were measured in both forests. The effects of understory light and its seasonal variations in both forests on the growth and nutrient accumulation of understory Korean pine seedlings were also explored. The results showed that the seasonal variations of monthly cumulative PAR under both forests showed a double-peak pattern. In summer, light conditions under the two forests were poor because of the closed canopy. In spring and autumn, light conditions were better due to the deciduous characteristics of canopy broadleaved trees, with light conditions under the secondary forest being obviously better than that of the primary forest. The seasonal variations of biomass, NSC, total N and total P concentrations of Korean pine seedlings in the primary and secondary forests were basically consistent with that of understory light. All those variables increased significantly in spring and autumn, and decreased in summer. In spring, starch concentration increased. In summer, starch and soluble sugar concentrations decreased gradually, and touched bottom in August. In autumn, soluble sugar concentration increased significantly. The biomass and NSC concentration of seedlings under secondary forest were significantly higher than those under primary forest in spring and autumn, but without difference in summer. Therefore, the diffe-rence of understory light conditions in spring and autumn between the two forests might be the key factor driving nutrient accumulation, growth and regeneration of Korean pine seedlings.