Effect Of Different Genotypes,Consecutive Ratooning And Nitrogen Fertilizers On Sugarcane Rhizosphere Bacterial Community Composition And Structure

Rhizobacteria play a crucial role among soil and plant microbiome association by enhancing and impacting plant physiology by various means.The microbial community in the rhizosphere and their interaction with the root system,in general,influences plant productivity.However,until now,limited literature has been reported regarding rhizosphere microbiome alterations among sugarcanes caused by different genotypes,consecutive ratooning and N-fertilizers rate.In this study,the effect of various cane varieties on rhizosphere microbiome alterations was determined by field experiment conducted in 2019.The experiment included eighteen cultivars,and the results illustrated that most of the rhizosphere microbiomes of these genotypes exhibited similar bacterial compositions.However,the evaluated genotypes harbored a significant effect and difference in the abundance of operational taxonomic units and bacterial composition in the rhizosphere compartments.Alpha diversity analysis on the rhizosphere microbiome showed a significant difference in the bacterial diversity（Shannon index,P<0.001）and OTU richness（Chao1,P<0.001）.The Principal Coordinate Analysis（PCo A）and hierarchical cluster analysis revealed that the genotype replicated samples grouped,indicating their similarity.The genotypes also differed significantly in root structure and soil properties.A significant genotypic effect（P<0.05）was found in the root traits except for rooting depth.The soil chemical properties were significantly different among the evaluated genotypes.Furthermore,brix content was strongly correlated with the total root length（TRL）and rooting depth.Genotypes（FN-1702,GUC-3,ZZ-13,ZZ-10,ZZ-6）were the best performing and distinct in bacterial diversity,root structure,soil parameters,and brix content.Based on results compiled from 1^st experiment,two genotypes were evaluated in the next experiment in consecutive ratooning.One of the genotypes was among the better performing in terms of bacterial composition and diversity,while the second one was among the low performing genotypes.Knowledge gap relating to the interaction between rhizosphere microbiome and ratooning crop,particularly the impact of different sugarcane cultivars on the rhizosphere microbiome in consecutive ratooning,requires additional research.Therefore,the field experiment was continued in 2020 to evaluate the response of two different sugarcane cultivars,viz ZZ-1 and ZZ-13,in consecutive ratooning towards the rhizosphere microbial community and cane morphological characters.Significant changes in the rhizosphere microbiome were observed in the second ratooning over the years.Several important genera were observed in high abundance during the second ratooning,including Burkholderia,Sphingomonas,Bradyzhizobium,and Acidothermus.Cultivar ZZ-13 caused more alterations in the rhizosphere microbiome than ZZ-1,resulting in a more favorable rhizosphere environment for sugarcane growth.Soil chemical properties varied significantly（P<0.05）among the two years for sugarcane rhizosphere soil,except AK（available potassium）.Compared to 2019,the soil nutrients increased effectively in 2020.These findings suggested that a sugarcane cropping strategy based on ratooning could effectively increase soil fertility.The ZZ-13 cultivar performed better regarding the number of roots,total root length,and root depth.Enzymatic activity was observed to be increasing with ratooning,though the effect was statistically non-significant.There were significant differences between the genotypes and year for the number of stalks,and yield was significant for genotypes,years,and genotype×year.Cane morphological traits among genotypes varied significantly（P<0.05）except for plant height and brix%among the years.Single stalk weight in ZZ-13 and ZZ-1 increased by 9.33 and 25.8%,respectively,in 2020.The cane yield in ZZ-13 and ZZ-1 decreased by 21 and 5%in 2020;respectively;however,the cane yield was significantly different between the years,genotypes and genotype×year with ZZ-13 the better performing.Based on the field experiments during the two years,ZZ-13 genotype was subjected to different nitrogen application rates in the next experiment（2021）to evaluate its effect on rhizosphere microbiome,soil physiochemical properties,cane yield and most importantly,to investigate appropriate/optimum rate of nitrogen fertilizer for the Guangxi region.The different treatment combinations were CK（no fertilizers）,L(Low,100 N kg ha^-1),M(Medium,150 N kg ha^-1)and H(High,200 N kg ha^-1).The results of the field experiment conducted in2021 illustrated that Medium(150 kg ha^-1)nitrogen application significantly altered the rhizosphere bacterial community,soil properties,and sugarcane yield.The richness and evenness of the bacterial community were observed more in M treatment than CK.In M treatment important bacterial phyla Acidobacteria and Proteobacteria increased by 47 and 71%,respectively;and at the genus level,Acidothermus and Bradyrhizobium increased by 77.2 and 30.3%,respectively compared to CK.Principal component analysis（PCA）and cluster analysis further confirmed the level of differences among the treatments.Spearmen correlation heatmap showed that environmental factors such as p H,AP（available phosphorous）,AK（available potassium）,and SCAT（soil catalase）were the key factors impacting sugarcane rhizosphere microbiome composition.Compared to Ck,number of nodes,plant height,and sugar content were statistically and significantly（P<0.05）increased in M treatment by 15.66,7.66,and 6%,respectively,except number of nodes which was statistically significant in L treatment.Furthermore,compared to Ck,the sugarcane yield per hectare varied from 4 to 25%under different fertilizer rates,with M treatment being the most productive.Different fertilizers rate increase soil p H value by 29and 10%in H and M treatment,respectively,as compared to Ck.Similarly,SOC,AN,AP,and AK were enhanced by 35.8,25.9,13.4,and 9.54%in M treatment,respectively,as compared to CK.Soil enzymes activities,including SCAT,SUE,and SACP were also improved in M treatment by 90.8,67.75,and43.05%over CK.Though the high and low nitrogen application alters the bacterial community and sugarcane plant performance but the medium nitrogen application appears to be ecofriendly,productive and appropriate nitrogen application rate that could be further used in the Guangxi region.Taken together,our study provides considerable deep understanding of rhizosphere interaction in sugarcane including soil nutrients and enzymatic activity having potential role in basic sugarcane activities that ultimately helped to maintain/improve their yield capacity and interaction with microbiome.Moreover,the present study provides comprehensive insight of different sugarcane cultivars,consecutive ratooning and use of chemical（nitrogen）fertilizers with their functional importance in rhizosphere microbiome,and significant involvement in cane yield performance.