土壤微生物对黄花蒿凋落物或青蒿素的响应

黄花蒿主要通过植株残体向土壤释放化感物质,影响土壤肥力和生产力。本试验开展了土壤微生物对黄花蒿凋落物和青蒿素的响应研究。结果表明,在土壤中添加黄花蒿凋落物和青蒿素,真菌数量增加,但显著降低放线菌、自生固氮菌、硝化细菌和亚硝化细菌的数量,不利于土壤有机质矿化,生物固氮和硝化作用。黄花蒿凋落物和青蒿素降低微生物熵,增大代谢熵,说明土壤微生物代谢受到干扰,活性降低。此外,黄花蒿凋落物和青蒿素还使土壤微生物标记性磷脂脂肪酸总量和种类以及细菌、放线菌和原生动物标记性磷脂脂肪酸减少,选择性地抑制了土壤微生物的繁殖生长。在黄花蒿凋落物、青蒿素和对照(不加凋落物和青蒿素)的土壤中,微生物种群结构差异显著,黄花蒿凋落物和青蒿素降低微生物多样性和均匀度指数。因此,在大规模集约化种植黄花蒿的过程中,进入土壤的凋落物抑制有益微生物生长繁殖,改变土壤微生物群落结构,种群减少,密度降低,这可能是黄花蒿抑制后茬和周围植物生长,进而造成减产的重要原因之一。

Responses of soil microorganisms to Artemisia annua leaf litter or artemisinin

Artemisia annua releases many kinds of allelochemicals into soils via dead plant residues,either by rain leaching or root exudation.Dead leaves of A.annua contribute more than 80% of the total artemisinin that enters soils during the growth period of A.annua.Allelochemicals released by the dead leaves reduce the growth and yields of succeeding and adjacent crops.Soil microbes play roles in nutrient transformation,organic matter recycling,toxicant decomposition,and hormone efflux,and thus,are important for plant growth and development.However,little is known about the effects of these allelochemicals on soil microorganisms.In these experiments,artemisinin and A.annua leaf litter were each added to soil and changes in microbial bio-mass and community structure were evaluated.The growth and reproduction of culturable microorganisms in soils showed wide variations in response to A.annua leaf litter or artemisinin.For example,the number of fungi increased but the numbers of actinomycetes,azotobacteria,nitrobacteria,and nitrite bacteria significantly decreased in soils containing A.annua leaf litter or artemisinin.The results suggested that both leaf litter or artemisinin inhibited organic matter mineralization,nitrogen bio-fixation,mobilization of phosphorus and po-tassium,and nitrification.The soil microbial quotient decreased,while the metabolic quotient increased,after A.annua and artemisinin were added to soils.This result indicated that artemisinin and other allelochemicals in the leaf litter interfered with the metabolism of soil microorganisms.The types and total contents of signa-ture phospholipid fatty acids of microbes such as actinomycetes and protozoa decreased in soils containing leaf litter or artemisinin.The diversity and evenness indices of the microbial community also decreased,suggesting that the soil microbial ecosystem deteriorated as the densities of various microbial groups decreased.Therefore, artemisinin and allelopathic chemicals released from A.annua leaf litter affect the microbial community struc-ture in soils,and may pose a risk to soil ecosystems in the areas where A.annua is widely cultivated.Further research is required to clarify the mechanisms by which allelopathic chemicals from A.annua change the struc-ture of microbial communities in soil.