长白山林线主要木本植物叶片养分的季节动态及回收效率

植物叶片养分含量的季节动态和回收效率对植被生态系统的养分循环和植物生长策略具有重要意义。以长白山高山林线上分布的3种主要木本植物——岳桦(Betula ermanii),牛皮杜鹃(Rhododendron aureum)和笃斯越橘(Vaccinium uliginosum)为研究对象,通过测定叶片中N、P、K、Ca、Mg、Fe等6种养分元素含量,分析在林线处植物叶片养分含量的季节动态及其与土壤养分含量的关系。结果表明岳桦和笃斯越橘叶片中养分元素的季节动态基本一致,即:N、P、K含量在生长季内逐渐降低,而Ca的含量逐渐增加;Mg在生长季旺盛期最低,而Fe含量却最高。牛皮杜鹃作为常绿灌木,叶片养分的季节动态与其余两种植物明显不同,表现为在生长季初期6种养分元素含量最低。岳桦和笃斯越橘植物叶片中N、P、K、Fe都有一定程度的回收,但笃斯越橘叶片的养分回收率更高,反映了笃斯越橘更能适应相对贫瘠的环境。3种林线植物叶片中养分含量与土壤养分并不存在显著的相关性,说明长白山林线上土壤中养分的分布没有对林线上3种主要的木本植物的生长和分布产生直接的影响。

Seasonal dynamics and resorption efficiencies of foliar nutrients in three dominant woody plants that grow at the treeline on Changbai Mountain

Seasonal dynamics of foliar nutrient concentrations and resorption efficiencies are key ecological indicators of the strategies of nutrient utilization in vegetation ecosystems at the alpine treeline. In the present study, we examined the strategies of nutrient utilization in three dominant woody plants, namely, Betula ermanii, Rhododendron aureum, and Vaccinium uliginosum, which were growing patchily at the treeline on Changbai Mountain. We compared the foliar nutrient resorption efficiencies of N, P, K, Ca, Mg, and Fe. We found that B. ermanii and V. uliginosum exhibited similar seasonal patterns of foliar nutrient utilization. In each species, we observed a decrease in foliar N, P, and K, but an increase in foliar Ca, during the growing season. The concentration of foliar Mg was the highest in the middle of growing season; by contrast, the concentration of foliar Fe was the lowest in the middle of growing season. The evergreen shrub R. aureum exhibited markedly different foliar nutrient dynamics. In this species, the concentrations of all six foliar nutrients were the lowest at the start of the growing season. The nutrient resorption efficiencies of foliar N, P, K, and Fe were higher in V. uliginosum than in B. ermanii, suggesting that the former species shows a higher degree of acclimation to the harsh environment and barren soil at the alpine treeline. We determined no significant correlations between soil nutrient contents and foliar nutrient concentrations in any of the three species, implying that the edaphic nutrient feathers at the treeline do not directly influence the distribution and growth of these three woody plants on Changbai Mountain.