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

一般植物种群在相对密集条件下，生物量随林分密度的降低而逐渐增加，并呈现出可预测的规律。这种定量关系被称为“自稀规则”。然而，对西伯利亚生长在永久冻土上的落叶松林的数据分析表明，林分密度的下降与地上生物量的稳定有关，这与生态学中的“常识”相悖。我们认为，永久冻土层限制了冻土的深度，可以在夏季解冻，导致限制帆营养物质，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”。“本研究调查了氮素动态的变化以及在落叶松林中与氮肥控制施肥试验相关的森林结构和功能的变化。我们证实，永久冻土上的落叶松林是氮素动态模式很难准确描述的生态系统。氮矿化的总体水平很小，空间变异很大。此外，矿化氮的固定化被认为是由于土壤微生物对矿化氮的吸收而发生的。四季施氮均使部分林下植物的氮素浓度增加，但落叶松林的结构没有变化。这强烈表明，氮是该森林树木生长的限制性营养元素。目前的调查结果已在国际会议记录和科学期刊上发表。在不久的将来还将发表更多的论文。本研究的结果作为专著发表在德国出版商Springer-Verlag的生态研究系列中。其手稿已接近完成。

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.