巨桉人工林挥发性单萜对土壤生物的作用

Scientists increasingly recognize that large-scale development of commercial plantations will have ecological effects when they supply increasing global demands for wood. Allelopathy has been recognized as one of the most important mechanisms causing the problems. However, the mechanisms of the of plantations' allelopathy have not been studied widely and deeply, especially the mechanisms of allelochemicals on soil biota. Recently, most of the studies of allelopathy focus on aqueous allelochemicals; studies of volatile allelochemicals mainly volatile monoterpenes still focus on the direct allelopathy by air on the accepters due to the low water-solubility. That could not satisfy the demand of plantation management and sustainable development. However, allelochemicals of volatile monoterpenes could be released from different part of plants and could be achieved by both air and soil media. Based on the volatile monoterpenes identified in Eucalyptus grandis plantations of previous study, the soils in abandoned arable land in the vicinity of Eucalyptus grandis plantaions in SW Sichuan province were collected. The effects of exogenous adding volatile monoterpenes allelochemicals on soil microbe community structure and soil fauna were studied by PCR-DGGE technology and earthworm (Eisenia fetida) ecological toxicology. The present study would objectively and widely explain the allelopahy mechanism of Eucalyptus plantations and provide critical recommendations for the management and sustainable development of Eucalyptus grandis afforested on the agricultural lands in southwestern China.

人工林在满足人类对木材需求的同时也带来了一系列人类普遍关注的生态问题，化感作用被认为是造成这些问题的主要作用机制之一。目前人工林化感作用机制研究仍不深入，尤其缺乏化感物质对土壤生物的作用机制研究。人工林化感作用机制更多关注水溶性化感物质，而挥发性物质主要是单萜类化合物，由于其较低的水溶性多数研究还局限在其经空气为载体的直接作用，这不能满足人工林经营和管理的需要。本课题以巨桉人工林为例，在前期对土壤中存在的单萜类化感物质鉴定的基础上，以巨桉人工林附近的弃耕地土壤为研究对象，以外源添加化感物质结合PCR-DGGE及生态毒理实验的研究方法，进行外源化感物质添加对土壤微生物群落特征及对赤子爱胜蚓（Eisenia fetida）的生态毒理研究。该研究将全面揭示我国西南地区退耕还林主要树种巨桉人工林化感作用机制，对巨桉人工林科学合理经营及可持续发展具有重要指导意义。

人工林在满足人类对木材需求的同时也带来了一系列人类普遍关注的生态问题，化感作用被认为是造成这些问题的主要作用机制之一。本项目在前期发现一个年龄序列巨桉人工林生物多样性呈现1-3年升高，4-5年稳定此后又升高的动态变化的基础上。结合前期对土壤中存在的单萜类化感物质鉴定的基础上，以弃耕地土壤为研究对象，以外源添加化感物质结合PCR-DGGE、高通量测序和生态毒理实验研究了巨桉人工林根际土壤中存在的8种挥发性有机化合物对土壤微生物群落结构特征及对赤子爱胜蚓（Eisenia fetida)生态毒理的影响。研究结果显示，1）赤子爱胜蚓在decane, 2,4-dimethyl heptane和2,2,4,6,6-pentametyl heptane在高浓度时表现显著回避行为; 蚯蚓的存活率随着时间和浓度的升高降低, Octane, 2,4-dimethyl heptane 和3,3-dimethyl octane作用较强；多数物质抑制了蚯蚓体重，但在7d处理后，octane, 2,2,4,6,6-pentametyl heptane和2,4-di-tert-butylphenol的低浓度时蚯蚓体重有所增加；随着浓度增加，蚯蚓的AChE, GST和SOD活性呈现被抑制和促进; 随着浓度的增加，octane, 2,2,4,6,6-pentametyl heptane, 2,4-di-tert-butylpheno赤子爱胜蚓的表皮和肠道结构在14d处理后有显著损伤；彗星实验显示, VOC处理彗尾DNA含量（%）相比于对照显著增加，然而尾动量和彗尾长度除了Octane, undecane和decane均有显著增加。2）选择其中有显著作用的物质发现，随着浓度增加，VOC对植物受体的种子萌发和幼苗及酶活性有抑制有作用；3）VOC处理下促进了土壤中假单胞菌比例、而对硝化细菌、乳酸菌、芽孢杆菌、硝化螺旋菌和光合细菌等有抑制作用。能抑制一些有害真菌如煤炱菌、瓜甲基囊菌，促进了一些有益真菌如酵母菌。总体来看，2,4-dimethyl heptane, 2,2,4,6,6-pentametyl heptane和2,4-di-tert-butylphenol是巨桉人工林根际土壤中对植物及土壤生物具有较强作用的挥发性化合物，但在自然生态系统中化感潜力的表达将受到环境因子的影响。