| The peanut(Arachis hypogaea L.)is one of the most important oil crops in China,accounting for a third of China's oil market,and it is the main oil and economic crop in the hilly red soil regions of southern China.However,long term continuous cropping of peanut leads to a significant reduction in the yield and quality of peanut,which seriously restricts the sustainable development of peanut industry in China.Our previous research indicated that an endophytic fungus,Phomopsis liquidambari(B3),which was isolated from the inner bark of Bischofia polycarpa,can produce 3-indoleacetic acid,abscisic acid,and vitamin B1 in vitro.Further studies showed that this endophytic fungus could efficiently decompose plant litter,accelerating soil organic carbon and organic nitrogen cycle,promoting biodegradation of phenolic acid allelochemicals 4-hydroxybenzoic acid and ferulic acid.As well,application of this fungus to soil of peanut consecutive monoculture significantly improved soil quality,increased the number of peanut nodules,significantly improved peanut yield.Further studies found that intercropping with medicinal plants Atractylodes lancea and adding B3 treatments significantly reduced soil mycete colony forming units,enhanced bacterium colony forming units,furtherly improved the peanut production.These results indicated that the endophytic fungus B3 has great potential in alleviating peanut continuous cropping obstacle and promoting increase of peanut production,whereas the mechanisms that involved are largely unknown.Thus,from the aspects of plant physiology and soil science,we investigated the effects of B3 alleviating peanut continuous cropping obstacles and promoting the absorption of trace elements,and explained the potential mechanisms of this effects caused by B3.First of all,a pot experiment was conducted to study the effects of the endophytic fungi B3 and A.lancea powder on rhizosphere soil microflora,enzyme activity,and available trace elements under continuous peanut cropping.The results showed that strain B3 and A.lancea powder significantly increased peanut straw and pod yield by 14.11%and 10.28%,respectively,relative to B3 treatment alone.B3 treatment significantly increased peanut root nodules as well as straw and pod yield relative to the control,which was grown under conventional fertilizer treatment.There were no significant differences in peanut root length and branch numbers between the treatments and the control.In addition,the B3 treatment significantly increased the number of culturable bacteria and actinomycetes,in peanut rhizosphere soil at seed,podding,and mature growth stages than did the control.The B3 and A.lancea powder treatment resulted in a significantly larger population of culturable fungi and actinomycetes at seed,flowering,and mature growth stages than the control.16S rDNA PCR-DGGE analysis showed that the B3 and A.lancea powder treatment significantly changed the soil bacteria community structure at seed,seedling,flowering,and mature growth stages and increased bacterial diversity during the seedling,flowering,and podding growth periods compared with the control,as estimated by the Shannon and band number indices.The B3 and A.lancea powder and B3 treatments markedly increased the activities of soil urease and sucrase during the flowering and podding growth periods,which promote material cycle and energy flow in the monoculture peanut ecosystem.It is worth noting that B3 and A.lancea powder activated essential trance elements(Mo,B,Fe,Zn,and Mn)in peanut rhizosphere soil at various growth stages and dramatically promoted absorption of Mo,B,and Fe in peanut leaves and kernels,particularly Mo and Fe.Secondly,we established a research system in a growth cabinet to obtain endophyte-infected(E+)and uninfected(E-)peanut seedlings.With the system we investigated the effects of B3 on the absorption and accumulation of iron and molybdenum in peanut plants,and revealed the underlying mechanisms that involved.The results showed that B3 significantly promoted the growth of peanut under the consecutive monoculture conditions,B3 treatment increased the peanut biomass and overground height by 47.83%and by 25.66%on the 5 DAI,respectively.Similarly,B3 treatment significantly facilitated the growth of peanut root.Compared with E-treatment,the main root lengths and activities of E+treatment peanut were increased by 43.96%and 17.65%on the 20 DAI,respectively.Moreover,the fungal endophyte significantly increased the chlorophyll contents and nitrate reductase(NR)activities in E+peanut leaves,on the whole growth period,NR activities were significantly higher than E-treatment peanut,maintaining at 20.59%to 38.46%level.Further study found that the endophytic fungus B3 significantly up-regulated the transcript levels of ferric reductase oxidase AhFRO1 and iron-regulated transporter AhIRT1,in addition,the accumulation of iron in the E+peanut plant were also significantly increased.B3 treatment significantly the transcript level of AhMOT1 related to molybdenum uptake,and increased the molybdenum contents in E+peanut root,shoot and leaves.Furthermore,the low-molecular weight organic acids in peanut rhizosphere soil were significantly affected by B3,the contents of citric acid in the whole growth period were significantly higher than the E-group,and the contents of oxalic acid and formic acid in the late growth stage were significantly higher than the E-group.Finally,in order to verify the potential of the endophytic fungus B3 in the practical peanut production under consecutive monoculture condition,we used the pig excreta from the local pig farm to product organic fertilizer,and the same time added endophytic fungus B3 and A.lancea powder to product the special organic fertilizer for peanut.We investigated the effects of the special organic fertilizer for peanut on the peanut plant with continuous cropping obstacle.The results indicated that the special organic fertilizer significantly increased the number of tillers,fresh weight of pod and plant fresh biomass by 26.92%,44.16%and 55.78%,respectively.In addition,the special organic fertilizer for peanut significantly changed the soil bacteria and fungus community structure,increased bacteria community diversity and reduced the fungal community diversity,as estimated by the Shannon and band number indices.In all,the special organic fertilizer for peanut has great potential to alleviate peanut continuous cropping obstacle. |
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