Effects Of Potato Continuous Cropping On Rhizosphere Micro-Ecological Environment And Its Biological Roles

Long-time continuous cropping potato has been one of the big problems thatrestrict the yield and serious pests and diseases, a field experiment was carried out inJingtai Tiaoshan Farm in Gansu Province in2010, the rotation cropping field is CK(continuous cropping potato for zero years, L0), the rest is the continuous croppingpotato from one year to five years (L1-L5), starting from the point of view of therhizosphere micro-ecological, using the PCR-DGGE molecular fingerprintingtechniques to study rhizosphere microbial community composition, bacteria andfungal population structure changes and root physiological activity change are thecharacteristic rhizosphere micro-ecological environment change, and after therhizosphere micro-ecological environment change, the leaf protective enzymesactivity and malondialdehyde content, the biological traits of plants and yield in thecondition of continuous cropping potato. A preliminary study on the effect and themechanism of potato continuous cropping obstacles to provide a theoretical basis toreduce the potato cropping obstacles. The main results were as follows:1. Effects of potato continuous cropping on the rhizosphere micro-ecologicalThe number of culturable rhizosphere microorganisms had significantlydifferent response for potato continuous cropping. bacterial response was sensitive,actinomycetes response was a little lag. With the continuous cropping yearsincreasing, the number of bacteria and actinomycetes decreased in the potatorhizosphere soil, while the number of fungi increased significantly; The ratio ofbacteria and fungi (B/F-value) decreased with the continuous cropping yearsincreasing, from rotation cropping L0for114.22×10~3to continuous cropping potatofor5years L5for1.08×10~3, potato continuous cropping made the rhizosphere fromthe "bacterial" type to "fungi" type.The results for DGGE were as follows, continuous cropping potato maderhizosphere bacteria and fungi population structure change significantly: continuouscropping potato significantly reduced the numbers of individuals of the bacteriadominant populations in rhizosphere soil,the numbers of visible bands were the most in L0, which were68the operational taxonomic unit (OTU), other treatmentswere much less than L0, the numbers of visible bands were significantly reducedafter continuous cropping three years, compared with CK, continuous cropping three,four and five years were respectively reduced19.12%,41.18%and29.41%.Continuous cropping significantly increased the numbers of individuals of the fungidominant populations, compared with CK, the OTU of continuous croppingtreatments from one to five years were increased by38%,38%,31%,46%and77%respectively. All the above illustrated that continuous cropping potato causedselective adaptation of rhizosphere soil microorganisms, which enriched somepopulations or reduced certain populations. The cluster analysis showed that, thesimilarity of bacterial and fungal population structure were higher in the adjacentcontinuous cropping years, with the continuous cropping years increasing, however,the similarity of each treatment is becoming less and less.From the sequencing results of the fungal DGGE bands, with the increase ofcontinuous cropping years, the number of the potato rhizosphere soil-bornepathogens Fusarium oxysporum and Fusarium solani increased significantly, whileChaetomium globosum, as a biocontrol species, was reduced significantly incontinuous cropping five years. Potato continuous cropping caused pathogen fungalpopulations become the dominant microbial populations in rhizosphere.The total absorbing area and actively absorbing area of roots were significantlyreduced by the continuous cropping potato. Compared with L0, the total absorbingarea of roots of L2and L4were respectively reduced26.07%and51.18%, and theactively absorbing area of roots were respectively reduced17.14%and48.57%inthe budding stage. The total absorbing area of roots were respectively reduced27.10%and80.06%, the actively absorbing area of roots were respectively reduced32.68%and85.37%in the tuber expansion stage, and the difference was significantbetween treatments. And root vigor displayed a decreasing trend, in the buddingstage, the results are as follows: L2＞L0＞L4, and the difference was significantbetween treatments. In the tuber expansion stage, the results are as follows: L0＞L2 ＞L4, compared with L0, L2and L4were respectively reduced5.25%and69.29%.Therefore, when the continuous cropping was mild, root vigor of potato had notsignificantly been reduced, even which was increased in the nutritional growthperiod.2. Effects of potato continuous cropping on the plant biological rolesPotato leaf SOD, POD and CAT activity were increased with the advance of thegrowth period. In the budding stage, SOD and POD activity were both increasedwith the continuous cropping years increasing, CAT activity first was increased andthen was decreased. To the tuber enlargement stage, leaf SOD and CAT activitieswere as follows: continuous cropping for three years＞continuous cropping for fiveyears＞CK, and the difference was not significant between treatments, POD activityof continuous cropping treatments were less than CK. MDA content was increasedwith the advance of the growth period, and which was also increased with thecontinuous cropping years increasing, and the cell membrane peroxidation effect ofthe leaf was increased.Growth of potato was restraibed under the condition of continuous cropping,such as plant short, Per plant main stems were reduced, the biomass of each organwere decreased with the continuous cropping years increasing, The tuber number ofper plant was little affected, however, per plant tuber weight was significantlyreduced, the ultimate expression was that the tuber yield had a significant reduction.In conclusion, the potato rhizosphere microorganisms community compositionand population structure had a change significantly under the condition ofcontinuous cropping, the number of the potato rhizosphere soil-borne diseasepathogens was significantly increased, but the number of biocontrol strain wasreduced obviously, the rhizosphere micro-ecological environment destruction, whichhindered the normal metabolic activity of plant system, the growth of potato wasrestrained eventually, the ultimate result was that the tuber yield had a significantreduction.