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 depth0-5 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.