退化落叶松人工林近自然化改造对土壤微生物及养分的影响

Effects of close-to-nature transformation of degenerated larch(Larix gmelinii) plantation on soil microbes and soil nutrients

落叶松人工纯林生产力和地力下降是目前林业生产亟待解决的问题,尤其是第2代人工林,通过近自然化改造是否能提高土壤肥力,改善土壤微生物多样性及养分,缺乏深入的研究。本文对第2代落叶松人工纯林近自然化改造2年内土壤微生物群落的多样性和结构变化以及土壤养分变化进行了调查。结果显示:林隙大小与土壤微生物多样性有较强的相关性,小林隙(25m2)土壤微生物多样性比大林隙(100m2)高;改造后第1年,小林隙土壤微生物多样性显著提高,Shannon指数、丰富度指数和均匀度指数均高于大林隙和对照(未间伐);第2年各处理间差异不显著;2年的3个指数比较发现,Shannon指数和丰富度指数均是第1年明显高于第2年,而均匀度指数变化相反,说明第1年土壤微生物的物种多样性较高但分布不均匀。在种类遗传相似性方面,小林隙与对照更为接近,大林隙可能由于小气候变化较大致使土壤微生物变化较剧烈。改造后第1年土壤养分含量显著增加,尤其是有效P,大林隙增幅达80%,小林隙达52%,有效N的含量也有所增加,有效K含量增加不明显。第2年土壤养分含量有所下降,但大、小林隙下降的格局不同,大林隙有效P含量下降极显著,小林隙养分下降不显著。本研究为近自然化改造的可行性及其科学实施提供了依据。

The decline of the productivity and soil fertility of larch（Larix gmelinii） plantation is an urgently addressed issue in forestry production.Especially for the second generation larch plantation,whether its close-to-nature transformation can improve the soil fertility,soil microbial diversity,and soil nutrient contents is lacked of in-depth study.In this paper,an investigation was made on the effects of close-to-nature transformation of the second generation larch plantation on the soil microbial diversity and structure as well as the soil nutrient contents within two years of the transformation.The results showed that there was a close correlation between gap size and soil microbial diversity.After the first year of transformation,the soil microbial diversity in small gaps（25 m2） had a significant increase,with the Shannon index,richness index,and evenness index being higher than those in large gaps（100 m2） and the control（no-thinning）.In the second year of transformation,less difference was observed in the three indices among the three treatments.The Shannon index and richness index were higher in the first year than in the second year,while the evenness index was in adverse,suggesting that in the first year of transformation,soil microbial diversity was higher but in uneven distribution.The soil microbial genetic similarity in small gaps was similar to that in the control;while in large gaps,this similarity was significantly different from the other two treatments,because of the greater changes of microclimate conditions in large gaps resulting in an intense change in soil microbial diversity.In the first year of transformation,soil nutrient contents had a significant increase.The soil available P content in large gaps was increased by 80%,and that in small gaps was increased by 52%;soil available N content was also increased;while soil available K content had less increase.In the second year,soil nutrient contents were decreased,but the decrements differed between large gaps and small gaps.The soil available P content had a significant decrease in large gaps,but the soil nutrient contents had less decrease in small gaps.This study provided evidences for the feasibility and scientific implementation of close-to-nature forest management.