Inter-relationships between Forest stand structure and nitrogen dynamics in Siberian taiga

在相对密度条件下，一般植物种群生物量随林分密度的降低呈可预测的递增趋势。这种定量关系被称为“自我稀释规则”。然而，对生长在永久冻土上的西伯利亚落叶松林的数据分析表明，林分密度的减少与地上生物量在恒定值上趋于稳定有关，这违背了生态学的“常识”。我们认为，永久冻土限制了夏季可解冻冻土的深度，导致土壤营养物质的限制，从而限制了可获得的地上生物量的价值。我们把这种现象称为“生物量限制假说”。以落叶松为研究对象，通过对照施肥试验，研究了氮肥对落叶松森林氮素动态和结构功能的影响。我们证实了永久冻土上的落叶松林是一个氮动态模式很难准确描述的生态系统。氮矿化总体水平很小，空间差异很大。此外，土壤微生物对矿化氮的吸收也可能导致矿化氮的固定化。4个季节的氮肥施用均使部分森林地面植物的氮素浓度增加；然而，落叶松林的结构没有变化。结果表明，氮素是该森林树木生长的限制性营养元素。本研究结果发表在国际会议论文集和科学期刊上。在不久的将来还将发表更多的论文。目前的研究结果正以专著的形式发表在德国出版社Springer-Verlag的《生态学研究丛书》上。它的手稿已接近完成。

Biomass increases gradually in a predictable pattern with decrease in stand density in general plant populatioins when growing in relatively dense condition. This quantitative relationship is called the "Self-thinning rule." However, data analysis from larch stands of Siberia that grow on permafrost show that decrease in stand density is associated with leveling-off of aboveground biomass at constant values, which is against the "common sense" in ecology. We consider that the permafrost limits the depth of frozen soil that can be thawed in the summer, leading to limitation of sail nutrients, thus limiting the value of the attainable aboveground biomass. We termed this phenomenon "the biomass limitation hypothesis." This research investigated the changes in nitrogen dynamics and that in forest structure and function that are associated with a controlled fertilization experiment in larch forests with nitrogen fertilizers.We confirmed that the larch forests on permafrost are ecosystems where the patterns of nitrogen dynamics are rather difficult to described accurately. The general levels of nitrogen mineralization are very small, and their spatial variation was very large. Also immobilization of mineralized nitrogen was suggested to have occurred due to uptake of mineralized nitrogen by soil micro-organisms. Four seasons of nitrogen fertilization showed increase in nitrogen concentration of some forest floor plants ; however, the structure of larch forests was unchanged. It was strongly indicated that nitrogen is a limiting nutrient element for tree growth in this forest. Results of the present investigation were published in proceedings of international conferences and in scientific journals. Additional papers are also being published in the near future. Findings of the present research are being published as a monograph in the Ecological Studies Series of Springer-Verlag, a German publisher. Its manuscript is near-completion.