对映-贝壳杉烷型二萜类化合物对土壤纤毛虫群落的毒性效应

Toxic effects of ent-kaurane diterpenoids on soil ciliate communities

选取小陇山自然保护区麻沿林区的土壤纤毛虫并通过盆栽实验从纤毛虫的群落结构、丰度和食性三方面研究了对映-贝壳杉烷型二萜类化合物对纤毛虫群落的毒性作用。纤毛虫群落结构采用"非浸没式培养法"进行分析,物种鉴定采用活体观察和蛋白银染色法,同时采用直接计数法分析土壤纤毛虫的丰度。共鉴定到纤毛虫88种,隶属于3纲11目29科42属,其中对照组75种;分析表明二萜化合物可导致土壤纤毛虫群落结构的衰退演替;双因子方差分析显示纤毛虫物种数在二萜化合物各浓度处理组间呈现极显著差异(F5,9=137.776,P<0.01),并在不同时间处理组间呈显著差异(F5,9=2.607,P<0.05);线性回归分析显示土壤纤毛虫总物种数随着二萜类化合物浓度的升高有下降趋势,具有良好的直线线性关系(R2=0.9521)。当二萜类化合物浓度超过32.5 mg/kg时土壤纤毛虫优势种由膨胀肾形虫、长篮环虫、大口薄咽虫和长圆膜袋虫演替为膨胀肾形虫、长篮环虫、苔藓膜袋虫、水藓薄咽虫和大弹跳虫,且C/P系数从小于1变为大于1,当施药浓度超过62.5 mg/kg时,优势种演替为大弹跳虫、小尖毛虫、有肋薄咽虫和一种前口虫。同时,分析还显示肾形目对二萜化合物有较高的耐受能力,下毛目、前口目和篮口目对二萜类化合物有一定的耐受能力。对纤毛虫食性研究发现二萜类化合物对纤毛虫的影响还与纤毛虫的食性有关,尤其对肉食性纤毛虫危害最大。比较分析显示,在相同暴露时间,不同施药浓度下土壤纤毛虫丰度与对照组相比均有极明显的降低,而同一施药浓度,随着暴露时间逐渐延长,纤毛虫的数量逐渐回升,但即使土壤中二萜类化合物残留浓度很低,也对纤毛虫群落有显著的抑制作用。非参数多个独立样本检验分析结果表明各浓度组间纤毛虫的丰度存在极显著差异。结果表明,不同浓度的对二萜化合物对土壤纤毛虫群落结构在种类组成和丰度方面均成具有强烈的扰动作用。

Soil ciliates are an important component of microfauna and play a crucial role in the functioning of microbial food webs by mediating the flux of both substances and energy in many soil ecosystems.As they response to the changes of environmental conditions more quickly than other organisms,they have increasingly been used as a robust bio-indicator in bioassessment of soil environments.In order to obtain a better understanding on the toxicity of ent-kaurane diterpenoids to the soil ciliates,the effects of this toxin on the community structure,abundance and feeding habit of soil ciliates were detected.The bioassay of ent-kaurane diterpenoids on soil ciliate communities was conducted using a pot simulation test in the Mayan Forest Region of the National Nature Reserve of Xiaolongshan.The ent-kaurane diterpenoids were mixed with the soil at arrange of concentrations： 0,2.5,12.5,22.5,32.5,42.5,52.5,62.5,72.5 and 82.5 mg/kg dry soil.Three replicates were carried out for each treatment.The pots were treated in a greenhouse for 60 days,during which the ciliate community structures were evaluated using the non-flooded Petri dish method and the abundance of ciliates were estimated using direct counting method.Ciliate species were identified using living observation and silver impregnation.The residue concentrations of ent-kaurane diterpenoids and the abundance of ciliates were measured at the time interval of 1,3,8,15,30 and 60 days.A total of 88 species were identified,belonging to 42 genera,29 families,11 orders and 3 classes,of which 75 taxa were found in the samples of control.Analyzes using two-factor ANOVA showed that the effects of ent-kaurane diterpenoids on the numbers of ciliate species represented significant differences among the treatments with a arrange of toxin concentrations（F5,9=137.776,P0.01） and that the samples within different exposure time（F5,9 =2.607,P0.05）.The regression analyses demonstrated that species number of ciliates decreased with increasing concentrations of diterpenoids.This finding suggested that the toxin diterpenoids may resulted in a degraded succession in community structure of soil ciliates.Both dominant species and C/P quotient were changed at the concentrations of ent-kaurane diterpenoids more than 32.5mg/kg,i.e.,the ciliate communities were dominated by Colpoda inflata,Cyrtolophosis elongata,Leptopharynx eurystoma and Cyclidium oblongum,followed by Colpoda inflata,Cyrtolophosis elongata,Cyclidium muscicola,Leptopharynx sphagnetorum and Halteria grandinella,and the C/P quotient were changed into the values more than one that indicates the community structures were strongly disturbed.However,Halteria grandinella,Oxytricha minor,Leptopharynx costatus and Frontonia sp.dominated the communities at the concentrations of ent-kaurane diterpenoids more than 62.5mg/kg.The analyses of the ciliate feeding habits suggest that the diterpenoids represented a significant inhibition on carnivores.Furthermore,it was also shown that Colpodida presented high tolerance to ent-kaurane diterpenoids,compared to Hypotrichida,Prostomatida and Nassulida.Otherwise,the abundances of soil ciliates definitely decreased at different concentrations of diterpenoids within the same exposure time compared with the control,while the cell number of ciliates represented an increased trend with extending exposure time at same toxin concentration.The growth of ciliates can be inhibited even at considerably low residual concentrations of diterpenoids.K-independent sample of nonparametric tests indicated that there were significant differences in the abundance of ciliates among the treatments at different toxin concentrations.These findings suggest that the community structures of soil ciliates were strongly disturbed at different concentrations of diterpenoids in terms of both species composition and abundance.