冻融循环对亚高山森林土壤微生物生物量及群落结构的影响

Effects of Freeze-thaw Cycles on Soil Microbial Biomass and Community Structure in Subalpine Forests

土壤冻融循环过程释放的碳和养分是维持亚高山森林冬季土壤微生物活性的重要保障。为了解冻融循环对土壤微生物群落的影响,以川西亚高山针叶林、阔叶林和针阔混交林土壤为对象,采用微缩实验研究了冻融循环(-5℃冻结12 h,5℃解冻12 h为一个冻融循环,共80次)对土壤微生物群落磷脂脂肪酸(PLFAs)含量和结构的短期影响。结果表明:土壤微生物群落对冻融循环响应随林型不同而存在差异。与5次冻融循环相比,3种林型的细菌、真菌、革兰氏阳性菌(G^+)和革兰氏阴性菌(G^-)的PLFAs含量在经80次冻融循环后均出现降低,混交林、针叶林和阔叶林细菌PLFAs含量分别降低71.9%、73.7%和74.6%,真菌PLFAs含量降低55.5%、75.4%和84.7%,G^+PLFAs含量降低77.1%、68.8%和73.7%,G^-PLFAs含量降低70.6%、78.1%和78.8%。冻融循环显著影响阔叶林的真菌/细菌比值,林型对真菌/细菌比值和G^+/G^-影响不显著。Shannon-Wiener多样性指数和Pielou均匀度指数在混交林中随冻融循环次数增加而逐渐增加,在针叶林和阔叶林中则呈现降低趋势,且均受冻融循环显著影响。冗余分析(RDA)显示,冻融过程中土壤养分有效性与微生物生物量和群落结构显著相关。全球变暖导致冬季冻融循环格局变化可通过改变土壤养分有效性影响亚高山森林土壤微生物生物量和多样性。

The released carbon and nutrients from soil as affected by freeze-thaw cycle are important guarantees for maintaining winter soil microbial activity in subalpine forests.In order to understand the effects of freeze-thaw cycles on the structure of soil microbial community,soils in a coniferous(Abies faxoniana)forest,broadleaf(Betula albosinensis)forest and mixed forest in subalpine forests of western Sichuan were taken as study objects.The short-term response of the phospholipid fatty acid(PLFAs)contents and structure of microbial communities to freeze-thaw cycle was studied in microcosms.A total of eighty times of freeze-thaw cycle were performed to the microcosms,with which a freeze-thaw cycle was treated as the soil being in below 5℃for 12 h and followed being in above 5℃for 12 h.The results showed that the response of soil microbial communities to freeze-thaw cycles varied with forest type.Compared to the five times of freeze-thaw cycle,the abundances of the bacteria,fungi,gram-positive bacteria(G+)and gram-negative bacteria(G.)PLFA were reduced in all forest soil after the eighty times of freeze-thaw cycle;the bacterial PLFA abundances of the mixed,coniferous and broadleaf forests were reduced by 71.9%,73.7%and 74.6%,respectively;the corresponding decreases in the fungal PLFA abundances were 55.5%,75.4%and 84.7%,the G+PLFA abundances were 77.1%,68.8%and 73.7%and the G.PLFA abundances were 70.6%,78.1%and 78.8%,respectively.Freeze-thaw cycle significantly affected the fungi/bacteria ratio of the broadleaf forest,while forest type had no significant effect on the ratio of fungi/bacteria and G+/G..Both the Shannon-wiener diversity index and Pielou evenness index were significantly affected by the freeze-thaw cycle,and the Shannon-wiener diversity index and Pielou evenness index increased with the increase of freeze-thaw cycle in the mixed forest,but which decreased in the coniferous forest and broadleaf forest as the freeze-thaw cycle proceeded.The redundancy analysis(RDA)suggested that soil nutrient availability was significantly correlated with the microbial biomass and community structure during the study period.These results indicate that changes in the freeze-thaw cycle patterns during the winter period as affected by global warming can influence soil microbial biomass and diversity in subalpine forests by altering soil nutrient availability.