| The formation factors of continuous cropping obstacle are very complex,which is including plant autotoxicity,and the dissimilation of microorganism,physiochemical characteristics,and nutrients in the rhizosphere.Meanwhile,the interaction of various factors might lead to a reduction of the yield output.Crop rotation is an effective way to maintain soil habitat balance.However,there is lack of the mechanism and technology researches on how to restore and alleviate soil degradation through regulating the soil micro-ecosystem under different rotation systems.This has limited the potential of farming system on the improvement of soil ecosystem stability.Based on a long-term experiment and the traditional soil science and microbiology method in combination with 454 sequencing technology,the study investigated the difference of microbial community structure,bacterial and fungal diversity and enzymic activity under no cultivation,crop rotation and continuous cropping of potato.Furthermore,the GC-MS technology was applied to analysis the influence of rotation on the composition and cumulative-effect of rhizosphere secretion of potato in comparison with the continuous cropping.The main results are as follows:(1)Compared with continuous cropping,the yield and water use efficiency of potato rotation with wheat and pea preceded were improved significantly.On average,the rotation increased yield by 23.49%(wheat preceded)and 25.46%(wheat preceded)in 2013 and by 29.08%(pea preceded)and 26.73%(wheat preceded)in 2015.Similarly,the increased values for water use efficiency were 15.21% and 13.24% in 2013,and 15.30% and 10.90% in 2015.And the rotation increased yield by 31.42% and WUE by 18.74%(wheat and pea preceded)in 2014.(2)The rotation system had significantly high values of bacteria index of Chao1,ACE,Shannon and np Shannon than that of continuous cropping.Compared with continuous cropping,the number of Alphaproteobacteria,Betaproteobacteria,Gammaproteobacteria and Deltaproteobacteria was reduced in the rotation cropping soil.In addition,the number of Sphingomonas was increased significantly in pea preceded rotation compared with the wheat preceded rotation.(3)Different cropping patterns had a significant influence on soil fungal population structure and its dominant status.Compared with continuous cropping,the rotation and no cultivation systems significantly reduced the index of Chao1 and ACE,while increased the richness of Basidiomycota and the number of Eurotiomycetes,Pezizomycetes and Agaricomycetes.There appeared some harmful pathogens in all of the tested soil,such as Phoma,Penicilliu,Myrothecium,Fusarium,and Verticillium,etc.The number of Phoma,Myrothecium and Verticillium was reduced significantly in rotation and no cultivation soil.Also,there appeared some beneficial fungi,such as Aspergillus and Chaetomium,which were improved significantly in rotation and no cropping soil.(4)Among different soil microorganism groups,bacteria were predominant,actinomyces the next and fungi the least in the field experiment.As the soil is weak alkaline,among soil microbial flora formation,percentage of bacteria to total microbe is 43-90%(the dominant species),followed by actinomyces with 6-57%,and the least is fungi with 0.2-5.6% of total microbe.The rotation cropping significantly increased the quantity of microorganisms and bacteria,but reduced the quantity of fungi.The variation of soil bacteria quantity during potato growth period among four planting patterns followed the sequence: W-P-W-P > G-P-G-P > P-P-P-P > no cultivation.This indicated that crop rotation could improve the amount of microorganism,and the wheat preceded rotation would increase the quantity of soil bacteria.Compared with the treatment of W-P-W-P,the treatment of G-P-G-P would increase the quantity of soil fungi by 58.33%,39.02% and 68.18%.This indicated that the pea preceded would increase the quantity of soil fungi.(5)Compared with continuous cropping,rotation increased the soil invertase and urease activity,all the differences were statistically significant.In rotation cropping soil,the catalase activity was declined compared with 2-years continuous cropping,while it was improved compared with the 3-years and 4-years continuous cropping.Nevertheless,the polyphenol oxidase activity in rotation soil is increased compared with the 2-years continuous cropping,presented the tendency of high-low-high-low compared with the 3-years continuous cropping,but deceased compared with the 4-years continuous cropping.There was a significantly negative correlation between catalase activity and the activity of sucrase and urease,and the number of fungi.Whereas,the significantly positive correlation between the number of fungi and microorganism was revealed in this study.This implied that rotation cropping improved the soil eco-environment,inspired metabolic activity of the enzymes,and reduced the destruction of hydrogen peroxide on crop in the rhizosphere.Undoubtedly,crop rotation is important in improving the quality of degraded soil caused by continuous cropping.(6)There were 17 compounds of root exudates identified under different planting patterns of potato.The main components of potato root exudates including alkanes,esters,amines,organic acids,and alkaloid,and with alkanes(counting 22.13% of the total amount),esters(counting 6.70%)and organic acids(counting 6.08%)were the dominant components.Compared with rotation cropping,the root exudates species in soybean and continuous potato intercropping and the continuous sole potato cropping was increased by 13.79% and 17.24%,the relative contents of alkanes was increased by 52.17% and 52.60%,and the relative contents of organic acids was increased by 65.41% and 14.79%.The relative amount of aminoethane,N-Ethyl morpholine,and dibutyl phthalate detected in the root exudates of potato were 1.46%?2.87% and 5.00% in continuous cropping,however,no one of them were detected in rotation soil.Compared with rotation cropping,the contents of N,N-diethyl-acetamide in intercropping and continuous cropping were increased by 123.29% and 47.95%,the contents of hexadecanoic acid were increased by 23.18% and 40.00%,and the contents of octadecanoic acid were increased by 27.36% and 39.80%,respectively The results indicated that rotation potato with soybean could reduce the species and content of root exudates component of potato.The compounds of hexadecanoic acid,octadecanoic acid,dibutyl phthalate and N,N-diethyl carbamate have been confirmed as allelochemicals of potato root exudates,as they significantly inhibited potato growth. |
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