Effects Of Replacing Chemical Fertilizers With Bio-organic Fertilizers On Rhizosphere Of Wheat

Wheat is one of China’s main food crops.Therefore,ensuring a sustained and steady increase in wheat production is related to the country’s food security.In the past few decades,traditional agriculture has increased food production through excessive fertilization and watering,which has caused serious waste of resources and environmental pollution.The replacement of some chemical fertilizers by bio-organic fertilizers has the potential to not be ignored in improving soil fertility,promoting soil nutrient cycling,regulating rhizosphere microflora,and improving the yield and quality of agricultural products.In this experiment,winter wheat was used as the research object,using physiological and biochemical methods,high-throughput sequencing technology and yield statistics to explore the effects of different ratios of organic fertilizer substitution on content of rhizosphere soil nutrients,soil enzyme activities,wheat yield indicators,rhizosphere bacterial community structure and function,and root transcriptome.In order to improve the traditional fertilization mode,promote the reduction of chemical fertilizers and increase efficiency,and provide theoretical support for the large-scale application of biological organic fertilizers.The results of the study are as follows:(1)Taking winter wheat as the research object,five treatments were set up,including: no fertilization(CK),conventional fertilization(NPK),90%conventional fertilization rate plus bio-organic fertilizer(90%NPK+M),80%NPK+ M,70%NPK+M.(1)The results showed that the wheat yield index,soil nutrient content and soil enzyme activity were the lowest in the treatment without fertilization(CK).Compared with conventional fertilization(NPK),the yield of 90%NPK+M and 80%NPK+M treatments increased significantly by 8.9% and 6.1%,and there was no significant difference in plant height,grain number per spike,and 1000-grain weight.Compared with NPK treatment,after bio-organic fertilizer replaced chemical fertilizer,the nutrients content of wheat rhizosphere soil and soil enzyme activities increased.Among them,the content of soil organic matter,total nitrogen,available phosphorus,and available potassium increased by 5.8% ～17.4%,5.5% ～ 12.4%,1.1% ～ 16.2%,11.1% ～ 19.2%,respectively;the activities of rhizosphere soil urease,invertase and neutral phosphatase increased by:1.5% ～ 19.0%,4.8% ～ 9.7%,18.3% ～ 33.7%.The analysis found that 90%NPK+M treatment improved the above-mentioned physical and chemical properties and enzyme activities most significantly.(2)Considering the results of wheat rhizosphere soil nutrients content and enzyme activities,it was found that 90%NPK+M treatment had the best effect,so four groups of CK,NPK,90%NPK+M,70%NPK+M were selected to treat rhizosphere soil 16 S r RNA high-throughput sequencing to study the changes of bacterial community structure in rhizosphere soil after organic replacement of chemical fertilizers.The results showed that NPK treatment had the lowest soil bacterial community diversity index.After replacing chemical fertilizers with bio-organic fertilizers,the bacterial community αdiversity index increased,and the Chao1 and ACE indexes increased significantly.Sphingomonas,Lysobacter,Nitrospira,Massilia and other functional bacteria genera with growth promotion and biological control effects were enriched in the rhizosphere soil.The results of RDA analysis showed that invertase and phosphatase were the most important factors affecting the bacterial community in the rhizosphere of wheat.(3)Three treatment conditions of CK,NPK,and 90%NPK+M(MNPK)were selected for indoor pot experiment.After 15 days,wheat root samples were taken for transcriptome sequencing to study the effect of chemical fertilizer organic substitution on wheat root transcriptome.The CK vs MNPK group has the most differentially expressed genes(DEGs),9 680 up-regulated and 3 656 down-regulated;8 473 up-regulated and 2 559 down-regulated in the CK vs NPK group;720 up-regulated and 434 down-regulated in the NPK vs MNPK group,The 16 644 DEGs identified were analyzed for GO and KEGG functional enrichment.The GO enrichment results showed that NPK and MNPK treatments promoted biological processes such as DNA/RNA,cell membrane and other biomacromolecule synthesis pathways,and in vivo material transportation,which is consistent with the phenomenon that MNPK treatment of wheat roots grows best.KEGG enrichment results showed that plant hormones,secondary metabolites and nutrient metabolism pathways are still significantly enriched pathways.Changes in the expression of DEGs in these pathways may be responsible for the phenotypic changes of wheat root growth.Bio-organic fertilizer has significant effects on wheat root carbohydrate metabolism,cofactor metabolism,macromolecule synthesis,ion transport across membranes and signal transduction.(4)In summary,the reasonable substitution of bio-organic fertilizers for chemical fertilizers can improve soil nutrients availability and enzyme activities,enrich functional microorganisms with biological control and growth-promoting effects,enhance crop rhizosphere effects,and ultimately promote crop yields;At the molecular level,bio-organic fertilizer promotes the development of wheat roots by affecting the secretion of endogenous hormones,secondary metabolites and carbohydrate metabolism of wheat roots,and ultimately increases wheat yield.Therefore,this study provides a theoretical basis for promoting the reduction of chemical fertilizers and increasing the efficiency,and promoting the large-scale application of bio-organic fertilizers on food crops.