2种立地条件下沙棘林地土壤中细菌多样性比较

Comparison of Bacterial Diversity in Forest Soils of Hippophae rhamnoides Growing in Two Different Sites

利用高通量测序技术对陕西省中部和北部2个中国沙棘林地(永寿县马坊镇马坊林场和榆林市榆阳区转龙湾乡)表层(5~20 cm)土壤中细菌的特征区域进行检测,对比分析了2个林地土壤细菌群落结构和组成,并分析弗兰克氏菌科各细菌属的相对丰度与年平均降雨量和主要土壤营养因子之间的关系,以阐明环境条件对沙棘林地表层土壤中弗兰克氏菌群落的影响。结果表明,转龙湾林地土壤中细菌菌群丰富度指数(Ace指数和Chao1指数)高于马坊林地,而2个地区的细菌群落多样性指数(Shannon指数和Simpson指数)差异不大。从马坊和转龙湾林地土壤中分别获得89467条和85279条测序序列,可归类为2658条和2887个操作分类单元(operational taxonomic unit,OTU),其对应的细菌分属于26个门66个纲144个目275个科474个属和30个门75个纲164个目322个科584个属;2个林地在门和纲组成上的一致性分别达到83%和78%;在细菌目和科的分类水平上,2个林地土壤细菌群落中相对丰度较高的细菌目的组成、以及这些目所含的主要细菌科的组成高度相似,但各菌目以及同一菌目中各菌科的相对丰度在不同林地之间存在明显差异。弗兰克氏菌目(Frankiales)细菌在马坊和转龙湾2个林地中的相对丰度均比较低,分别只有0.44%和0.76%;从2个林地土壤中共获得弗兰克氏菌目下的20条OTU代表序列(其中共有序列19条),分属于7个科12个属;弗兰克氏菌科(Frankiaceae)弗兰克氏菌属(Frankia)在土壤营养条件较好、降雨量较多的马坊林地土壤中的相对丰度占该目细菌的5.57%,显著高于土壤营养条件较差、降雨量较少的转龙湾林地(相对丰度在该目中为0.77%)。据此,可计算出弗兰克氏菌属在2个沙棘林地土壤整个细菌群落中的相对丰度分别仅为0.011%和0.002%。弗兰克氏菌属的相对丰度与土壤全N和碱解N含量以及年平均降雨量呈显著正相关。综上所述,不同立地条件下沙棘林地表层土壤中细菌群落组成差别不大,但各类细菌的相对丰度差别较大;具有固N能力的弗兰克氏菌属细菌的相对丰度很低,而在降雨较为充沛、以及土壤有机质和矿质营养条件较为丰富的立地条件下,其相对丰度显著高于降雨较为稀少和土壤较为贫瘠的立地条件。

Bacterial diversity in forest soils(in depth of 5-20 cm)of Hippophae rhamnoides growing in central and northern Shaanxi Province(Mafang Forestry Station in Yongshou county and Zhuanlongwan in Yuyang District in Yulin city)was determined and analyzed by high-throughput sequencing technology,and the relationships between the relative abundance of Frankia with mean annual rainfall and main soil nutrition factors were evaluated to explain the influences of environmental conditions on the bacterial community structure,and to provide a theoretical reference for the forestry production practice.The results showed that the community richness indexes(Ace index and Chao1 index)of Zhuanlongwan site were higher than Mafang site,but there was no significant difference in the community diversity indexes(Shannon index and Simpson index)between the two sites.A total of 89467 and 85279 sequences,belonging to 2660 operational taxonomic units(OTUs)representative sequences and 2893 OTUs representative sequences,were obtained from the soils of the two sites respectively,which belonged to 26 phyla,66 classes,144 orders,275 families,474 genera;and 30 phyla,75 classes,164 orders,322 families,584 genera,respectively.At the level of order and family,the components of the soil bacteria at the level of order and family with higher relative abundance in the two sites were highly similar,but their relative abundances of the orders and families obviously differed from the two sites.The relative abundances of Frankiales in the two sites were relatively low,accounting for 0.44%and 0.76%,respectively.A total of 20 OTU representative sequences of Frankiales were obtained from the two sites,belonging to 12 genera of 7 families.Among that,the dominant family in the two sites was Geodermatophilaceae,and the dominant genus was Blastococcus.The relative abundance of Frankia in Frankiales was 5.57%in Mafang and 0.77%in Zhuanlongwan,so in the whole bacterial community of the both forest soils,the relative abundances were only 0.011%and 0.002%,respectively.The relative abundance of Frankia was significantly correlated with the contents of the total nitrogen and the alkali-hydrolyzabale nitrogen and the mean annual rainfall.In conclusion,the components of the bacterial community in the two forest soils did not differ significantly.However,the relative abundances of various bacteria were significantly different.The relative abundances of nitrogen-fixing bacteria Frankiales were rather low.However they were relatively richer in the good site conditions(such as plentiful rainfall,high contents of soil organic and inorganic nutrients)rather than poor site conditions(such as little rainfall,poor soil).