基于cDNA克隆的亚热带阔叶林和针叶林生态系统担子菌漆酶基因多样性及其群落结构研究

作为木质素降解的关键酶之一,漆酶在森林生态系统养分循环过程中占有重要的地位。通过构建cDNA克隆文库,从mRNA水平上研究了亚热带喀斯特原生林(常绿落叶阔叶混交林)和红壤马尾松林(针叶林)凋落物层(O层)及表土层(A层,0—20 cm)中担子菌漆酶基因多样性及其群落结构。结果发现,O层担子菌漆酶基因多样性、丰富度和均匀度均以原生林远远高于马尾松林,而A层与O层的趋势相反;同一森林生态系统,原生林土壤O层中担子菌漆酶基因多样性和种群丰富度高于土壤A层,而马尾松林则O层明显低于A层。"目"分类地位上,伞菌目在两森林生态系统中占绝对优势,且在马尾松林O层中比例高达90.2%;原生林O层和马尾松林A层中存在丰富的多孔菌目和钉菇目;红菇目仅在原生林A层中检测到,且比例为12.4%。群落结构上,与原生林O层和马尾松林A层相比,原生林A层和马尾松林O层含漆酶基因的担子菌种群分布极不均匀,分别存在1和2个绝对优势种群(克隆子数占各克隆库20%以上),且分别与伞菌属、小菇属和侧耳属有较高的氨基酸相似性。此外,两森林土壤中漆酶活性、碳、氮、木质素含量均以原生林显著高于马尾松林,且O层显著高于A层。这些结果表明亚热带阔叶林和针叶林不同土壤层位中降解木质素的担子菌漆酶基因多样性和群落结构有着极大的差异,而这种差异与微生物底物的可利用性、多样性以及土壤pH等因素的综合作用密切相关。

Diversity and community structure of basidiomycete laccase gene from subtropical broad-leaved and coniferous forest ecosystems based on cDNA cloning

Decomposition of forest litter regulates the cycling of nutrients in forest ecosystems and influences the net carbon storage for terrestrial ecosystems.Laccase enzyme mainly produced by basidiomycetes plays a central role in lignin degradation and thus contributes to the cycling of soil organic matter.Compared to many studies of basidiomycetous laccase gene diversity in pure broad-leaved or coniferous forests,comparative data on diversity of this gene from different forest types are still rare,especially from forests exhibiting significant differences in vegetation and soil types.This study investigated the diversity and community structure the basidiomycete laccase gene in litter(O horizon) and surface soil(A horizon,0 to 20 cm) from subtropical karst primeval forest(a mixed evergreen and deciduous broad-leaved forest) and artificial masson pine forest in red soil(a coniferous forest) by constructing cDNA libraries at mRNA level.The diversity,richness and evenness of the laccase gene were higher in the primeval forest than those in the masson pine forest for the O horizon,while the reverse trend in these indices was observed for the A horizon.For the same forest ecosystem,the values of the aforementioned indicators from O horizon were correspondingly higher,but apparently lower,than those from A horizon in the primeval forest and the masson pine forest,respectively.With regard to taxonomy at the order level,Agaricales accounted for 90.2% of the clone library for the O horizon of the masson pine forest,and dominated both horizons of the two forests.Polyporales and Gomphales were abundant in the O horizon of the primeval forest and A horizon of the masson pine forest.Russulales was only detected in the A horizon of the primeval forest,accounting for 12.4% of the clone library.Regarding the community structure,the distributions of basidiomycetous populations containing the laccase gene in the A horizon of the primeval forest and O horizon of the masson pine forest were more uneven than those in the O horizon of the primeval forest and A horizon of the masson pine forest.One and two absolutely dominant basidiomycetous species(accounting for ≥20% of the total clones in each clone library),showing high amino acid similarity to Agaricus sp.,Mycena sp.and Pleurotus sp.,were found in the O horizon of the primeval forest and A horizon of the masson pine forest,respectively.Moreover,the laccase activity and the contents of carbon,nitrogen and lignin were significantly higher in the primeval forest than those in the masson pine forest,and were significantly higher in the O horizon than those in the A horizon of a same forest.These results indicate that there are great discrepancies in basidiomycetous laccase gene diversity and community structure in different soil horizons between subtropical broad-leaved forest and coniferous forest in China.These discrepancies may derive from intricate effects closely related to the availability and diversity of microbe-utilized substrates and soil pH.