不同深度土壤控水对稻田土壤微生物区系及细菌群落多样性的影响

为研究不同深度土壤控水对壤土稻田土壤水势、微生物区系和细菌群落多样性的影响，通过土培池栽试验，在水稻生育后期设置土壤深度0~5 cm（S05）、0~10 cm（S10）和0~15 cm（S15）控水处理，以保持水层为对照，分析了不同深度控水处理下5 cm、10 cm、15 cm深土壤水势与土壤微生物区系、细菌群落多样性的变化。结果表明：土壤5 cm、10 cm、15 cm深度的水势随着控水深度增加而降低，S05控水处理主要影响上层（5 cm）土壤水势，S10控水处理影响上、中层（10 cm）土壤水势，S15控水处理土壤水势随土层深度的增加而升高。花后8 d和32 d，S05控水处理上层土壤细菌数量显著高于S10、S15控水处理；花后16~24 d，S05控水处理中层、下层（15 cm）土壤细菌数量均显著高于S15控水处理；土壤水势与水稻生育后期中、下层土壤细菌数量呈极显著正相关关系。S05控水处理10 cm、15 cm土层的细菌丰富度Chao指数均显著高于S15控水处理及CK。3个控水处理中，5 cm土层细菌的多样性Shannon指数以S05控水处理最低。优势细菌菌群分析发现，优势群落主要为变形菌门、绿弯菌门、酸杆菌门、拟杆菌门，四者总相对丰度在80%以上；S15控水处理中层土壤变形菌门相对丰度低于S05和S10控水处理。3个控水处理土壤样品中优势纲（相对丰度大于2%）达15个，主要包括α-变形菌纲、β-变形菌纲、δ-变形菌纲、厌氧绳菌纲等，这4个纲的总相对丰度在47%以上，其中厌氧绳菌纲相对丰度最高；上层土壤中S05控水处理的β-变形菌纲相对丰度显著低于S10和S15控水处理。因此，不同深度土壤控水对壤土土壤水势、细菌数量存在影响，改变了细菌的多样性及丰富度，对土壤细菌优势菌种类无显著影响。

Influence of water controlling depth on soil microflora and bacterial community diversity in paddy soil

Soil water potential as one of the main indexes of irrigation during alternation of wetting and drying process, has been widely applied in rice production and scientific research. To investigate the influence of soil water potential on soil micoflora and bacterial community diversity, 3 treatments of soil water controlling depth[0-5 cm (S05), 0-10 cm (S10) and 0-15 cm (S15)] were set in a pool-culture experiment. Dilution-plate method and the technology of high-throughput sequencing on Illumina Miseq platform were used to detect the numbers of fungi, bacteria and actinomycetes, and bacterial community structure and diversity under different treatments (CK, keeping 2 cm surface water layer). The results showed that soil water potential decreased with the increase of water controlling depth. The treatment of S05 mainly affected soil water potential of the upper soil layer (5 cm), while the treatment of S10 affected soil water potential of the top and middle soil layer (5 cm and 10 cm). Soil water potential of S15 treatment enhanced with the increase of soil layer depth. Soil bacteria number at the upper layer (5 cm) under S05 treatment was higher than that under S10 and S15 treatments at 8 and 32 days after rice flowering, while that at the middle and lower soil layer (10 cm and 15 cm) under S05 treatment was higher than that under S15 treatments at 16-24 days after rice flowering. Soil water potential was significantly correlated with soil bacterial number at the late period of rice growth. The bacterial community structure was profiled by sequencing the V4 16S rDNA gene. A total of 1 124 229 sequences were obtained, and 9 020 OTUs (Operational Taxonomic Units) were generated at 3% cutoff level. The richness (Chao index) of bacterial community at the 10 cm and 15 cm soil layers under S05 treatment were significantly higher than that under S15 and CK treatments. The diversity of bacterial community (Shannon index) in 5 cm soil layer was lowest under S05 treatment. The dominant bacteria phylums were Proteobacteria, Chloroflexi, Acidobacteria, and Bacteroidetes, whose relative abundance were more than 80%. The relative abundance of Proteobacteria of the 10 cm soil under S15 treatment was less than that under S05 and S10 treatments. Fifteen predominant classes (relative abundance > 2%) were found in these samples, in which the total relative abundance of Alphaproteobacteria, Betaproteobacteria, Deltaproteobacteria, and Anaerolineae was above 47%. Anaerolineae was the most abundant class. The relative abundance of Betaproteobacteria in 5 cm soil layer under S05 treatment was less than that under S10 and S15 treatments. Therefore, water controlling depth in loam influenced soil water potential and soil microbial number, and then affected the diversity and abundance of bacterial community. The water controlling depth of 0-5 cm in loam was helpful to improve the soil bacterial number and diversity at the 10 cm and 15 cm soil layers.