Mechanism Of Reduction Of Nitrogen With Biochar On Rhizosphere Environment And Root Development Of Cotton

Excessive use of nitrogen and low nitrogen efficiency are main limiting factors for advancing quality and efficiency of cotton fields in in Xinjiang gray desert soil.Cotton stalk carbonization instead of recycled straws into soil has become a feasible way.Biochar as a carrier to improve root system architecture and increase crop nitrogen efficiency provides a paradigm for solving the above problems.However,the research on water loss and temperature changes under the condition of reducing nitrogen with biochar is still disagreeable;The research conclusions on the species composition and diversity of rhizosphere nitrogen-metabolizing microorganism remain far apart on the divisive subject,whether promotes root development and improves the efficiency of nitrogen assimilation in cotton is not clarified.So the application model of nitrogen with biochar in cotton field of Xinjiang gray desert soil could not be accurately evaluated.Therefore,cotton was taken as the research object,using pot experiment and indoor analysis,combined with infrared spectroscopy,microscope observation,microplate reader,root scanner,high-throughput sequencing technologies,and using nonlinear equation fitting,redundant analysis,structural equation model,enzyme-linked immunoassay,generalized linear model and other analysis methods.From rhizosphere environment,cotton root morphology and root system architecture analysis,from the regulation of cotton rhizosphere environment by reduction of nitrogen with biochar;reduction of nitrogen with biological application biochar's regulation of root morphology and physiology,and the response of anatomical structure to reduction of nitrogen with biochar,and the response of key nitrogen metabolism enzymes and genes to reduction of nitrogen with biochar,these 4 aspects were to explore reduction of nitrogen with biochar effects on cotton rhizosphere environment and root development;which reveal the mechanism of reduction of nitrogen with biochar to regulate the nitrogen assimilation efficiency of cotton roots,and provide a theoretical reference for the effective and reasonable utilization of nitrogen reduction combined with biochar in Xinjiang cotton fields,with a view to perfect performance nitrogen is combined with biochar to achieve the effect of improving cotton quality and efficiency.The main results are as follows:(1)Compared with the treatment without adding nitrogen and biochar(T₀)and the traditional fertilization treatment(T₁),in 0?10 cm soil layer,soil temperature rised significantly(p<0.05)under 50%nitrogen reduction combined with 2%biochar(T₃)treatment,and it increased by 2.1±0.3?and 2.0±0.2?,respectively,the temperature of other treatments was not increase significant(p>0.05);compared with T₀treatment,in the 10?20 cm soil layer reduction of nitrogen by 20%with 1%biochar(T₂)treatment increased the soil temperature significantly(p<0.05),an increase of 2.6±0.5?,other treatments did not increase the temperature significantly(p>0.05);Compared with T₁treatment,the temperature change of each treatment in the 10?20 cm soil layer was not significant(p>0.05).Compared with T₁ treatment,the coefficient of variation of the quality water content and temperature of the biochar treatment was reduced by 6.05%and 1.33%,respectively.The soil moisture evapotranspiration of each treatment of 0?10 cm and 10?20 cm soil layer with reduction of nitrogen with biochar was kept constant,maintaining at19.1±0.9 mm and 17.9±0.7 mm,respectively.In T₁ treatment,water evapotranspiration increased exponentially with the increase of soil temperature.(2)Compared with T₀ treatment,both traditional fertilization and nitrogen reduction combined with biochar application had significant effects on rhizosphere soil NO₃^-(p<0.05),and T₂ treatment had the largest increase,NO₃^-increased 23.8 times,NH₄⁺increased 2.1times,and T₂ treatment was significantly greater than T₁ treatment.T₂ treatment increased the urease activity in the rhizosphere of very fine roots by 1.68 times.The relative abundance of Nitrosomonas nitrosa in extremely fine roots and fine rhizosphere soils was the highest in the treatment of nitrogen reduction combined with biochar,and the relative abundances of Nitrosomonas in extremely fine roots and fine rhizosphere soils were respectively introduced.In 35.5%?72%and 28.2%?62.3%,followed by very fine root and fine rhizosphere soil Nitrosospira between 7.4%?27.5%and 12.5%?36.5%,very fine root and fine rhizosphere soil Betaproteobacteria ranged from 4.0%to 16.9%and 2.1%to 10.4%,respectively.In T₁ treatment of very fine root and fine rhizosphere soil,the relative abundance of Betaproteobacteria was 20.6%and 32%,respectively,the relative abundance of Nitrosomonas was 22.5%and 27.5%,and the relative abundance of Nitrospira was 16.4%and 26.5%,respectively.Archaea did not exist in the rhizosphere of cotton treated with nitrogen reduction and biochar application,while Crenarchaeota(relative abundance 58.9%)and Archaea(relative abundance 40.5%)were dominant in the rhizosphere of cotton treated with T₀.Compared with T₁ treatment,reduction of nitrogen with biochar increased the root length density of 0?10 cm,and provided sufficient ecological niche for microorganisms.The corresponding analysis of the removal trend showed that the contribution of mineral nitrogen,urease activity and root length density to cotton N agronomic efficiency was 76.3%,and the root length density in 0?10 cm soil layer and NH₄⁺concentration in 10?20 cm soil layer had significant effects on cotton N agronomic efficiency(p<0.01).(3)Nitrogen reduction with biochar changed the branching angle(geotropism)of cotton fine roots and very fine roots.The former tended to stretch horizontally,while the latter tended to be more diversified,and the branching angle of the latter was introduced.At 60°-80°,it has a longer root system.Correspondence analysis of detrend indicated that the change of root system configuration is closely related to root geotropism,and the influence of fine root geotropism is the most significant.Root hormone level analysis showed that compared with T₁ treatment,auxin(Indoleacetic acid,IAA),cytokinin(CK),salicylic acid(Salicylic acid,SA),fine root SA and Abscisic acid(ABA)at very fine root content increased significantly(p<0.05)in T₂ treatment.CK did not increase significantly(p>0.05),the ratio of IAA/ABA content increased significantly(p<0.05),and other treatments did not increase significantly(p>0.05)in T₂ treatment.Compared with T₁ treatment,the root senescence time of the treatment with reduced nitrogen and biochar was delayed from 2to 14 days,and the mortality rate was reduced by 3.7%to 9.0%.This is related to the protection of soluble proteins or alcohol and phenolic hydroxyl groups in the biochar.Biochar addition at 0?10 cm soil layers is conducive to the release of the above functional groups.The non-linear fitting equation showed that with the increase of root age,the root nitrogen utilization and energy consumption of the T₁ treatment and the nitrogen-reducing with biochar decreased by 0.0934±0.034 and 0.0896±0.0002 mol N·mol^-1 O₂,respectively,because of biochar reduced root nitrogen consumption.The structural equation model showed that humin in the soil has the highest contribution to reducing root mortality,its contribution is-0.392,and the contribution of nitrogen reduction with biochar to root turnover is 0.764,which slowed down fine-root turnover rate.(4)Compared with T₀ treatment,the thickness of fine roots and very fine roots under the treatment of reduction of nitrogen with biochar was significantly reduced(p<0.05).At T₁and T₅ treatments of fine roots and very fine roots,the ratio of vascular bundle to root diameter decreased,and the vascular bundle diameters of fine roots and very fine roots were increase in T₂ and T₄ treatments.Compared with the T₁ treatment,the diameter of the fine root vascular bundles in the T₄ treatment increased significantly(p<0.05),while the other treatments did not increase significantly(p>0.05).Compared with T₀ treatment,the proportion of fine root cortex in T₂ and T₅ treatments increased significantly(p<0.05).Compared with T₀ treatment,no matter whether biochar was adding or not,most of the very fine roots are three prototypes,and compared with T₁ treatment,reduction of nitrogen with biochar treatment resulted in the variation of fine root xylem and the appearance of three or six prototypes.Further transcriptome analysis showed that compared with T₁ treatment,the root amino acid transport function gene(Glutamine Dumper3,GDU3),adenosine triphosphate bisphosphatase gene,cyclin gene(CYC)of T₄ treatment were significantly higher than that of T₁ treatment.CYC was significantly up regulated(p<0.05),while ethylene response binding factor(APETALA2,AP2)was significantly down regulated(p<0.05),and while other treatments were not significantly up regulated(p>0.05).According to the gene changes,it was speculated that reducing nitrogen combined with biochar accelerated organic nitrogen transport,prolonged cell proliferation cycle,and slowed down root aging.(5)Compared with the T₀ treatment,at 0?10 cm soil layer,very fine root nitrate reductase(NR),glutamine oxoglutarate synthetase(GOGAT),glutamic pyruvic transaminase(GPT),glutamate dehydrogenase(GDH)activity and glutamine(GPT)activity and Gln concentration increased or significantly increased(p<0.05)under the biochar priming.High-throughput sequencing showed that compared with T₀ treatment,glutamate dehydrogenase2 gene(gdh2)decreased by 1.69 and ammonium transporter1 gene(ammonium transporter1,AMT1;1)decreased by 1.69 in T₁ treatment.The AMT1;1expression level decreased-1.15?-4.10 in reduction of nitrogen and biochar treatment group.The expression of gdh2 was upregulated 2.60?3.91 times in fine root,the expression of gdh2 was increased 1.06?1.55 times in very fine root.The expression of Glutamate dehydrogenase3(gdh3)was increased 1.78?5.00 times.The expression levels of the above transcription factors were significantly changed(p<0.05).These data revealed at the molecular level that nitrogen reduction combined with biochar increased the NH₄⁺absorption efficiency,and the synergistic expression of gdh2 and gdh3 in roots could further improve the NH₄⁺assimilation efficiency.In summary,reduction of nitrogen with biochar optimizes the rhizosphere environment,increases the abundance of nitrosomonas in the soil nitrogen-metabolizing microorganism,and increases nitrate nitrogen concentration and urease activity in the rhizosphere.Nitrogen reduction combined with biochar also significantly promoted hormone synthesis.Under the synergistic effect of coupled NO₃^-and NH₄⁺signals,GDU3,APY,CYC transcription factors were up regulated,AP2 transcription factors were down-regulated,and so the development of cotton roots was-regulated.The improvement of nitrogen efficiency is to reduce nitrogen and apply biochar to promote root development,reduce root mortality,reduce root absorption of nitrogen and energy consumption,increase NR activity of very fine roots and fine roots,fine root GDH activity,and the up-regulation of AMT1;1,gdh2 and gdh3.This conclusion provides a theoretical basis for evaluating the effect of reduction of nitrogen with biochar in the cotton agro-ecosystem.