随山地垂直带海拔上升,环境恶化会影响到植物生物量的绝对量和相对量的分配,进而影响到生态系统的碳平衡。测定了位于长白山北坡海拔1900m树线交错带的两个林分:长白落叶松混交林和岳桦林的生物量分配和净生产力,并与低海拔相似林分进行了比较,探讨树线特殊环境下树木的生长反应和生态系统的碳投资策略。树线交错带林分生物量和生产力都出现急剧降低,冠层树干生物量比例急剧降低,而枝、叶生物量比例有显著增加。而根系比例和地下/地上生物量比在两种林分表现出不同的反应,树线落叶松混交林出现急剧增加,而树线岳桦林与低海拔岳桦林相比没有显著差别。枝、叶生物量比例增加,特别是叶生物量分配增加有利于在树线恶劣环境的碳吸收和碳平衡,是对树线交错带大风、积雪等恶劣气候的可塑性适应,树木在树线出现多分枝、矮曲生长型。树线地带落叶松混交林和岳桦林的净生产量也出现急剧降低,但根系生产量比例则较低海拔同类林分高,有利于对土壤中水分和养分的吸收。

Increasing severity of environment and altitude in mountain ecosystems can affect relative and absolute biomass-allocation patterns in plants.Biomass allocation and net primary productivities were examined in two alpine treeline stands,i.e.Larix Changbaiensis mixed forest and Betula ermanii forest(1900 m a.s.l)on the Changbai Mountains in Northeast China.The biomass and their productivity were measured based on average standard tree with canopy and quadrat-harvesting method for shrub layer and herb layer.The total biomass and net primary production(NPP)of the Larix Changbaiensis mixed forest were 15.16t/ha and 1.68t/(ha·a)respectively,with 3.72,10.34 and 1.1t/ha of biomass allocation and with 0.43,0.46 and 0.79t/(ha·a)of NPP in canopy,shrub and herb layers as well.And the total biomass and NPP of the Betula ermanni forest were 19.44t/ha and 2.58t/(ha·a)respectively,with 5.14,12.68 and 1.62t/ha of biomass and 0.80,0.56 and 1.23t/(ha·a)of NPP in canopy,shrub and herb layers respectively.In comparison with counterparts at lower altitudes,the relative and absolute stem mass decreased significantly with increasing altitude,the ratio of branch and leaf mass to total arbor biomass increased with altitude for larch and birch.However,root ratio and root to shoot ratio present different responses.Root ratio of larch increased a lot but birch had no significant difference.The increase of leaf ratio is favorable for carbon uptake and carbon balance in severe environment at treeline ecotone.Variation in stem mass was caused by multi-stem plasticity and krummholz due to snow accumulation and heavy wind.Net primary productivities of larch mixed forest and birch forest decreased sharply at treeline in comparison with lower altitudinal stands,whilst the ratio of root production was much higher than that of lower altitude.This made it profitable to take water and nutrients in soil.