| The planting area and total output of apple production in China rank first in the world.Despite the apple yield increased continuously in China,the current unit area yield under farmer practices remained low compared to other apple producing countries.The soil organic matter(SOM)content of apple orchard in China is much lower compared to the USA and Europe.Many studies have shown that as important indicators of soil fertility and productivity,soil organic matter,soil enzyme,and microbial community and diversity are closely related to each other.The application of bio-organic fertilizer(BOF)in orchards increased soil quality and productivity through improving soil chemical fertility such as SOM content and biological fertility including soil enzyme activity and soil microbial community composition and diversity.In this study,field fertilization experiments were conducted in apple orchards for 9 consecutive years(2008-2016)with three treatments:(?)control without fertilization(CK);(?)chemical fertilization(CF);and(?)BOF.We studied how fertilization treatments influence apple yield,soil physical and chemical properties,soil enzyme activity,soil microbial biomass,soil microbial community and soil nitrogen cycling genes in order to reveal the characteristics of the soil microbial community in apple orchard with high and stable yield and how BOF application is beneficial to improve the apple yield.The following results were obtained:1.The application of BOF increased the apple yield.The apple yield in BOF treatment increased from 2009 to 2016 consistently,while the apple yield decreased yearly in CK treatment.In the CF treatment,apple yield fluctuated during 2009-2016.During the 9 years,the average apple yield per year in BOF was 74.95Mg ha-1,which was 181.3%and 83.8%higher than that in the CK(26.65Mg ha-1)and CF(40.79Mg ha-1)treatments,respectively.The BOF treatment increased the content of soluble sugar,reducing sugar and Vc in apple,and decreased the content of apple titratable acid resulting in the highest sugar and acid ratio among all the treatments.Compared with CK and CF treatments,the soluble sugar content of apple in BOF treatment increased by 13.2%and 6.3%respectively,the content of reducing sugar increased by 53.9%and 5.9%,respectively,and the contents of Vc increased by 17.0%and 10.2%,respectively,but the titratable acid decreased by 8.6%and 2.3%,respectively.2.BOF application increased apple yield by increasing the soil organic matter and total nutrient content and slowing down the decline in soil pH.Compared to CK,CF and BOF treatments decreased soil pH by 0.22 and 0.13 at 0-20cm soil depth,respectively,by 0.66 and 0.37 at 20-40cm soil depth,respectively,and by 0.66 and 0.46 at 40-60cm soil depth,respectively.Compared to CK,both BOF and CF increased the content of SOM,(total nitrogen)TN,(total phosphorus)TP and(total potassium)TK in all the soil layers from 0-60cm.However,the increases of the content of SOM,TN,TP and TK after BOF treatment were significantly higher than those under CF treatment except for the TP at 0-20cm and 40-60cm soil depth:at 0-20cm soil depth,the SOM,TN,TP and TK in BOF treatment increased by 4.34g kg-1,0.50g kg-1,0.17g kg-1 and 4.47 g kg-1,respectively,while in CF treatment they increased by 3.12g kg-1,0.33g kg-1,0.24g kg-1 and 1.84g kg-1,respectively;at 20-40cm soil depth,they increased by 4.53g kg-1,0.58g kg-1,0.24g kg-1 and 4.86g kg-1 in BOF treatment,respectively,while in CF treatment they increased by 3.02g kg-1,0.41g kg-1,0.17g kg-1 and 2.18g kg-1 respectively;at 40-60cm soil depth,they increased by 2.78g kg-1,0.38g kg-1,0.11g kg-1 and 3.18g kg-1,respectively,while in CF treatment they increased by 0.82g kg-1,0.20g kg-1,0.25g kg-1 and 2.06g kg-1,respectively.3.BOF application increased apple yield through increasing soil microbial biomass and enzyme activities.Compared to CK and CF treatments,the BOF treatment significantly increased the amount of SMB-C,while no significant difference was observed between CK and CF treatments.At 0-20cm,20-40cm and 40-60cm soil depths,compared to CK treatment,the BOF treatment increased the SMB-C content by 102.3%,85.1%and 97.1%,respectively,the SMB-N content by 71.5%,66.1%and 89.7%,respectively,and the SMB-P content by 71.9%,37.9%and 33.5%,respectively,in addition,compared to CK,the SMB-C,SMB-N and SMB-P content after BOF treatment increased more rapidly than that in CF treatment.?t 0-60cm soil depths,compared to CK and CF treatments,the BOF treatment significantly increased the activity of N-acety-?-glucosaminidase,(3-cellobiosidase,sulfatase,?-xylosidase,?-glucosidase,a-glucosidase,invertase and catalease.Compared to CK,both BOF and CF treatments increased the abundance of nitrogen cycling genes(nifH,amoA,nirK,nirS,narG and nosZ),though the abundance of denitrofication associated genes(nirK,nirS,narG and nosZ)were all lower in BOF treatment compared to CF treatment.4.High microbial diversity,the increase in the interaction between microbial taxa and the stability of microbial networks are the guarantee of sustainable apple production with high and stable yield.BOF treatment significantly increased the abundance of 16S and 18S rRNA genes and both bacterial and fungal diversity compared to CK and CF treatments.BOF application significantly changed the bacterial and fungal community composition at all the soil depths from 0-60cm by increasing the relative abundance of the copiotroph taxa such as Proteobacteria,Bacteroidetes,Alpha-and Gamma-proteobacteria,the beneficial microbes taxa such as Pseudomonadales,Xanthomonadales,Sphingomonadales,Bacillus,Pseudomonas and Lysobacter,the organic C and N fixing microbial taxa(Rhodospirillales),as well as the fungal taxa Ascomycetes,Basidiomycetes,Lecanicillium and Ilyonectria,but reduced the relative abundance of the oligotroph taxa such as Acidobacteria,Chloroflexi,Sphaerobacter and Acidobacteria Gp4 and Gp6.Both of the fertilization treatment and soil depth significantly contributed to the variation of soil bacterial and fungal community composition.Further analysis revealed fertilization treatment was the main factor trigerred the bacterial community shift while the soil depth was the major contribution to the soil fungal community variations.Compared to CF and CK treatment,the soil bacterial and fungal network in BOF treatment had more closely linked nodes resulted in more complex bacterial and fungal networks and beneficial microbes(Pseudomonas)played more important role in network.Regression analysis showed that the increases of abundance of Proteobacteria,Bacteroides,Bacillus,Lysobacter,Pseudomonas,Lecanicillium and Ilyonectria in soil might be beneficial to the increase of apple yield.In summary,BOF treatment led to high and stable yield in apple production through increasing soil chemical fertility such as soil organic matter and total nutrient content,and soil bio-fertility reflected on soil microbial biomass and soil enzyme activity.In addition,BOF application triggered soil microbiome shift resulted in a more complex and efficent community with more copiotroph and beneficial microbes in soil,which was important to the sustainable apple production with high and stable yield.As a result,BOF application plays important role in improving soil productivity and is recommended in apple production. |
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