摘要:土壤理化性质是微生物群落结构变化和空间分布的主要驱动力，揭示土壤与微生物之间关系是当前生态学和土壤学的研究热点之一。在大小胡杨树冠下少有植物生长的区域，测定距离树干不同位置（距离大胡杨树干0-3 m和3-6 m，距离小胡杨树干0-3 m，以及距离大小胡杨树干至少9 m以上；分别简写为DB_{0-3 m}，DB_{3-6 m}，DS_{0-3 m}和CK）的土壤理化性质和土壤微生物的群落组成，之后运用微生物群落组间差异分析、典范对应分析和Spearman相关分析等方法，探讨胡杨树冠下土壤理化性质与微生物群落分布组成之间的关系。结果显示：（1）在4个采样位置，细根生物量、土壤含水量、有机质、全氮、全磷和总盐均在DB_{0-3 m}最高，DB_{3-6 m}居中，DS_{0-3 m}和CK的含量最低（DB_{0-3 m}≥DB_{3-6 m}≥DS_{0-3 m}≥CK）（P<0.05）。DB_{0-3 m}的这些理化性质的含量分别是DS_{0-3 m}的3.97、1.13、3.71、3.03、1.49和1.95倍；相反，土壤容重在4个采样位置没有显著性差别（P>0.05）；（2）纲水平上，丰度排名前十的细菌和真菌分布组成在4个采样位置明显不同。细菌方面，Rhodothermia和γ-变形菌纲为DB_{0-3 m}的优势纲（相对丰度为0.27和0.28），拟杆菌纲为其他3个位置的优势种（在DB_{3-6 m}、CK和DS_{0-3 m}的相对丰度为0.37、0.26和0.26）。真菌方面，粪壳菌纲为DB_{0-3 m}和DS_{0-3 m}的优势纲（相对丰度为0.27和0.10）。座囊菌纲为DB_{3-6 m}和CK的优势纲（相对丰度为0.09和0.16）；（3）细菌和真菌群落组成在4个采样位置存在显著差异。DB_{0-3 m}的真菌和细菌群落组成和DB_{3-6 m}较相似， DS_{0-3 m}和CK的真菌和细菌群落组成较为相似；（4）典范对应分析与Spearman分析结果表明，胡杨树冠下土壤微生物的群落组成受到土壤盐分、细根生物量、含水量、有机质、全氮和全磷的影响。其中，土壤盐分的影响最大。综合可知，在胡杨树冠下，土壤微生物群落的组成于胡杨树干下不同距离的位置上存在差异，它是胡杨和土壤之间物质交换、营养流动及微生物的生境选择共同作用的后果。土壤微生物群落组成在空间上的变化，可以负向影响树冠下幼苗的萌发和生长。在一定程度上，这种负向作用使得胡杨树冠下少有植物生长。



Abstract:Soil physiochemical properties are considered as the main driving force for the changes of community and spatial distribution of soil microorganisms. Exploring the relationship between soil physiochemical properties and soil microorganisms is one of the hot topics in ecology and soil science. In this study, changes of soil physicochemical properties and the composition of soil microbial community were measured along four distances from two types of Populus euphratica's trunk (big and small mature individuals) under their crown. Four distances included two positions that far from big Populus euphratica's trunk within 3 m (DB_{0-3 m}) and ranged from 3 to 6 m (DB_{3-6 m}), the position far from small Populus euphratica's trunk within 3 m (DS_{0-3 m}), and control group (CK) that distance from both big and small Populus euphonicus's trunk at least larger than 9 m. Then, differences in microbial communities, canonical correspondence analysis and Spearman correlation analysis were used to explore relationships between soil physicochemical properties and distribution of soil microorganisms. The results showed that (1) among four sampling positions, fine root biomass, soil water content, soil organic matter, total nitrogen, total phosphorus and total salinity were the highest in DB_{0-3 m}, the middle in DB_{3-6 m}, and the lowest in DS_{0-3 m} and CK (DB_{0-3 m} ≥ DB_{3-6 m} ≥ DS_{0-3 m} ≥ CK) (P<0.05). The contents of these soil physicochemical properties in DB_{0-3 m} were 3.97, 1.13, 3.71, 3.03, 1.49 and 1.95 times of these in DS_{0-3 m}, respectively. On the contrary, soil bulk density did not show the significant difference among four sampling positions (P>0.05). (2) At the class level, spatial distributions of the top 10 bacteria and fungi in abundance were significantly different in the four sampling positions. In bacteria, Rhodothermia and γ-metamorphosis were the dominant class in DB_{0-3 m} (their relative abundances were 0.27 and 0.28, respectively), while Bacteroides were the dominant class in other positions (relative abundances were 0.37, 0.26, and 0.26 in DB_{3-6 m}, CK, and DS_{0-3 m}, respectively). In fungi, Sordariomycetes were the dominant class in DB_{0-3 m} and DS_{0-3 m} (relative abundances were 0.27 and 0.10, respectively), while Dothideomycetes were the dominant class in DB_{0-3 m} and DS_{0-3 m} (relative abundance were 0.09 and 0.16, respectively). (3) There were significant differences in bacterial and fungal community composition among four sampling positions. The fungal and bacterial communities in DB_{0-3 m} were similar to those of DB_{3-6 m}, while which were similar between DS_{0-3 m} and CK. (4) The results of typical correspondence analysis and Spearman analysis showed that the community composition of soil microorganisms was mainly affected by soil salinity, fine root biomass, soil water content, soil organic matter, total nitrogen and total phosphorus. Compared with other factors, soil salinity had the greatest contribution to the change of community composition of soil microorganisms. To sum up, the composition and spatial distribution of soil microbial community vary along distances from Populus euphratica's trunk, which is the result of the joint actions of material exchange and nutrient flow between plant root and soil, and habitat selection of soil microorganism. To some degree, the changes of composition and distribution of soil microbial community negatively affect the germination and growth of seedlings. As a result, this negative effect makes less plant growth under the crown of Populus euphratica.





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