| The soil fertility plays important role in the food safety and the sustainable development of agriculture. Fertilization is the key factor of influencing crop yields. Therefore, it is necessary to find out the critical value of fertilization for maintaining the soil fertility and avoiding soil contamination from over use of fertilizers. In order to address and monitor the effect of straw returning and different fertilizer combination on the soil quality, the Soil and Fertilizer Institute of Sichuan Academy of Agricultural Sciences established straw returning and fertilization combination experiments on paddy soil in Xigao town and Lianshan town, Guanghan city, Sichuan province, China, since2002. The impact of the different fertilizer treatments with or without straw returning on soil physiochemical properties and crop yields were studied extensively. Based on the previous works, the pour plate count method was used to study the impact of different fertilizer combination and straw returning on the soil viable microbial counts. Chemical analysis was employed to determine the influence of straw returning and different fertilizer combination on soil microbial biomass carbon and nitrogen and soil enzyme activities. Then, the denaturing gradient gel electrophoresis (DGGE) molecule fingerprint method was applied to study the community structure of bacteria, fungi, nitrogen fixation genes nif H, ammonium oxidizing bacterial and ammonia oxidizing archaea. The results are summarized as the following.(1) The results of different fertilizer combination and straw mulching on soil microbial counts, biomass and soil enzyme activities showed that straw mulching with additional adequate NPK significantly increased the number of soil microbes, SMBC, SMBN, invertases, urease and phosphatase, but decrease the activities of polyphenoloxidase compared with CK (no straw mulching)(P≤0.01) at rice ear initiation stage and after rice harvest; then these indicators in the treatments of no potash fertilizer plus straw mulching(SNP), low nitrogen fertilizer plus straw mulching(SNL) and no phosphate fertilizer plus straw mulching were lower than that introduced straw mulching plus adequate NPK, however, the polyphenol oxidase activity were significantly opposite. (2) The study on soil bacterial community and diversity affected by straw mulching and fertilization indicated that at rice ear initiation stage and after rice harvest, the bacterial diversity index of straw mulching plus adequate NPK treatment was significantly higher than the groups of CK without straw, low N plus straw mulching and no P plus straw mulching (P≤0.01), but there was not significant difference compared with treatment of no K plus straw mulching (P>0.05) at0-10cm soil depth; soil bacterial diversity was higher of straw mulching plus adequate NPK treatment than groups of CK without straw, low N, no P or no K plus straw mulching at10-20cm soil depth (P≤0.01). Sequencing results showed that the dominant bacteria in groups with treatment of straw mulching including Duganella of Betaproteobacteria, Rhodoplanes and Magnetospirillum of Alphaproteobacteria, Chloroflexi, Caldilineaceae, Anaerolineaceae Gemmatimonadetes, Acidobacteria and Nitrospirae. The dominant bands of CK were falling in the class Duganella of Betaproteobacteria, Chloroflexi, Rhodoplanes and Magnetospirillum of Alphaproteobacteria, Firmicutes.(3) The results about the impact of straw mulch and fertilization on the soil fungi community and diversity showed that at rice ear initiation stage straw mulching with addition of adequate NPK treatment had higher diversity index than CK without straw at0-10cm and10-20cm soil depth (P≤0.01). After rice harvest the diversity index of straw mulching with addition of adequate NPK treatment was not significantly different with CK at0-10cm soil depth (P≥0.05). The diversity index of straw mulching with addition of adequate NPK treatment was significantly lower than CK at10-20cm soil depth (P≤0.01). The dominant bands of DGGE patterns were sequenced and the results showed that the dominant species of straw mulching treatment were falling in class of Acremonium, Emericellopsis, Aspergillus, Cladosporium, Rhodotorula, Pleurotus and Mortierella. While the dominant species of CK were Ascomycota, Sordariomyceta. It indicated that the measure of straw returning can increase the diversity and change the community structure of soil fungi. (4) The results about the impact of straw mulch and fertilization on the soil nifH gene diversity showed that at rice ear initiation stage and after rice harvest the straw mulching plus adequate NPK treatment had higher diversity index of nifH gene than the CK both at0-10cm and10-20cm soil depth (P≤0.01). DGGE bands sequencing further revealed that the14closely related species were niJH gene fragment of uncultured bacteria with the dominant community falling in the class of Proteobacteria in Betaproteobacteria. The dominant nitrogen-fixing microbial of straw mulching treatment were uncultured Burkholderia, Pseudacidovorax, Azospira and Ideonella. The dominant species of CK were Pseudacidovorax and Azospira.(5) The results about the impact of straw mulching and fertilization on the soil ammonia-oxidizing bacteria community and diversity showed that at rice ear initiation stage the straw mulching plus adequate NPK treatment had the higher diversity index of ammonia-oxidizing bacteria than the CK, the low N or no P plus straw mulching treatments (P≤0.01), but it had no significant difference with no K plus straw mulching treatment (P≥0.05)at0-10cm soil depth. The straw mulching plus adequate NPK treatment had the higher diversity index of ammonia-oxidizing bacteria than the CK at10-20cm soil depth (P≤0.01). After rice harvest the diversity index of straw mulching with addition of adequate NPK treatment was significantly higher than CK at0-10cm and10-20soil depth. The analysis of sequencing derived from DGGE showed very simple phylogeny of the advantageous ammonia oxidizing bacteria. The dominant ammonia-oxidizing bacteria of straw mulching treatment and CK both were Nitrosospira and Nitrosomonas of beta-Proteobacteria.(6) The results about the impact of straw mulch and fertilization on the soil ammonia-oxidizing archaea community and diversity showed that at rice ear initiation the straw mulching plus adequate NPK treatment had the higher diversity index of ammonia-oxidizing archaea than the CK without straw at0-10cm and10-20soil depth (P≤0.01). After rice harvest the straw mulching plus adequate NPK treatment had the higher diversity index of ammonia-oxidizing archaea than the CK without straw (P≤0.01), but it had no significant difference with no K, no P and low N plus straw mulching treatments. The dominant bands of DGGE patterns were sequenced and the results showed that all the ammonia oxidizing archaea belonged to the uncultured Crenarchaeota.(7) The results of different fertilizer combination and straw burying on soil biomass and soil enzyme activities showed that straw buried into the soil with addition of adequate NPK and only NPK treatments significantly increased the SMBC and SMBN compared with CK(no fertilizer treatment)at rice ear initiation stage and after rice harvest (P≤0.01). Then, the straw burying with addition of adequate NPK treatment significantly increased the activities of invertases, urease, phosphatase and polyphenoloxidase (P≤0.01)(8) The study on soil ammonia-oxidizing bacteria community and diversity affected by straw burying and fertilization indicated that at rice ear initiation stage the CK with no fertilization treatment had the lower diversity index of ammonia-oxidizing bacteria than the NPK fertilization treatment. The diversity index of NPK fertilization treatment was lower than straw burying with addition of adequate NPK treatment at0-10cm and10-20soil depth. After rice harvest diversity index of no fertilization treatment was significantly lower than NPK fertilization treatment at0-10cm and10-20soil depth. The diversity index of NPK fertilization treatment was not significantly different with straw burying with addition of adequate NPK treatment at0-10cm and10-20soil depth. The analysis of sequencing derived from DGGE showed that the dominant ammonia-oxidizing bacteria of straw burying treatment and CK both were Nitrosospira and Nitrosomonas of Betaproteobacteria.(9) The study on soil ammonia-oxidizing archaea community and diversity affected by straw burying and fertilization indicated that at rice ear initiation stage and after rice harvest CK without fertilization had the lowest diversity index of ammonia oxidizing archaea, while NPK with straw burying had higher diversity index than the NPK treatment0-10cm and10-20soil depth. The sequences were divided into two fractions:water and soil by phylogeny tree. Similar strains came from the plateau, wetlands, cultivated soil, protected arable land and lake sediments. The sequence of all dominant bands analysis showed that all the ammonia oxidizing archaea belonged to the uncultured Crenarchaeota.In conclusion, straw returning and fertilization can significantly increase the number of soil microbes, SMBC, SMBN, invertases, urease and phosphatase; enrich the diversity and community structure of bacteria, fungi, nifH gene, ammonia oxidizing bacteria and ammonia oxidizing archaea; further benefit substance transformation and formation of soil fertility. Thus the research provides a scientific basis for straw returning. |
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