温带落叶松人工林根桩养分源/汇效应及形成机制

In Temperate area, a great number of stumps have been left after plantation logging. However, the effect and mechanism of residual stumps on maintaining nutrient and carbon balance of ecosystem is unclear. Larch pure plantation takes up the biggest proportion of total plantation in northeast hilly area and has the longest management history. Based on larch pure plantation in northeast China treated by different vegetation modifications, nutrient managements, time series and logging ways (intermediate thinning, gradually cutting, clear cutting), we investigate the decomposition difference between underground and aboveground stump; and further quantify spatial and temporal variation of stump nutrient and soil nutrient, and the contribution of carbon and nitrogen of stump to soil carbon and nitrogen, by measuring the number and volume of stump, bulk density, temperature and humidity, chemical component, organic carbon composition, microbial community structure, carbon and nitrogen mineralization rate and stable isotope composition, and bryophyte of both stump and soil, etc. Combining the method of locating observation and spatial series representing temporal series, the effect and its timeliness of stump on different nutrients source-sink and bryophyte will be verified; at the same time, the evolution law of microbial community structure and microbiological mechanisms of stump nutrient source-sink during stump decomposition will be clarified. The expected outcomes of this project could provide scientific reference for temperate plantation nutrient management and long-term productivity improvement.

针对温带人工林经营作业后形成的大量根桩(桩头、桩基、根兜、主根和侧向粗根)对维系生态系统养分平衡的功能不清、作用机制不明等问题，以东北山地人工林中面积最大、经营历史最长的落叶松纯林为对象，在植被调控和营养管理试验的基础上，采用定位观测与时空替代相结合的方法，通过对各时间序列上间伐、渐伐和皆伐后人工更新林地内根桩的体积和数量以及根桩与微域土壤的容重、温湿度、化学成分、有机碳组成、微生物群落结构与多样性、酶活性、微生物量碳和氮、碳氮稳定同位素组成和根桩附生苔藓植物等指标的调查、取样及分析，探讨根桩地上与地下不同组份间分解规律差异性，量化根桩和土壤养分含量时空变异和根桩碳、氮对土壤有机碳和全氮贡献，辨析根桩各组份对各类养分的源/汇效应与时效性以及苔藓植物作用和影响，阐明根桩分解过程中微生物群落演变规律，揭示根桩养分源/汇效应的微生物学机制，为温带人工林营养管理与长期生产力提升提供科学依据。

根桩作为粗木质残体的重要组成部分，对维持森林生态系统养分平衡具有重要作用。本研究以落叶松人工林根桩为对象，建立了根桩加性生物量模型，分析了根桩分解的过程及其微域土壤养分的变化；分别以落叶松纯林和不同二代林中落叶松根桩及微域土壤为对象，对比研究了不同二代人工林内落叶松根桩及微域土壤的养分含量、微生物学特征及土壤酶活性的变化。研究发现，Dis-ML模型的建立对根桩各组分和总生物量的拟合程度较好；根桩腐烂分解过程是从桩头开始由上到下，从直径2-5cm侧根开始由外向里进行；根桩腐烂Ⅰ－Ⅱ级分解缓慢，腐烂Ⅲ级时分解迅速，到腐烂Ⅳ级时质量损失率高于Ⅲ级但不显著。二代人工林因建群种不同会影响落叶松根桩的分解，尤其是在落叶松和樟子松二代林中落叶松根桩的直径2-5cm粗根分解显著快于白桦和水曲柳。落叶松根桩对落叶松人工纯林和水曲柳、落叶松人工混交林微域土壤的全磷含量有明显提升作用，但在水曲柳、落叶松人工混交林中落叶松根桩对土壤全磷含量影响的水平范围、垂直深度均比在落叶松人工纯林中的大。落叶松根桩可以提高落叶松人工纯林内的微域土壤的磷素有效性，而在水曲柳、落叶松人工混交林中，落叶松根桩通过改变微域土壤的HCl-P和NaHCO3-Po含量提高了林地的供磷水平。细菌群落组成与结构对二代人工林内落叶松根桩组分分解的影响要比真菌群落明显，其丰富度和多样性指数均大于真菌群落。伯克霍尔德菌属和中间根瘤菌属是造成落叶松和樟子松二代林中落叶松根桩组分的分解快于水曲柳和白桦二代林的主要细菌属，革耳菌属和木霉属则是落叶松和樟子松二代林中根桩组分的分解快于水曲柳和白桦二代林的主要真菌属。研究成果为系统研究粗木质残体对人工林生态系统养分平衡及管理奠定了理论基础。