Microbial Community Characteristics Of Acidified Tie Guanyin Tea Soils With Different Ratooning Ages And Improvement Measures

Tea plants(Camellia sinensis(L.)0.Kuntze)are perennial shrubs,and are important cash crops in China.However,long-term tea cultivation practices can result in soil acidification,and negatively affect the tea yield and quanlity,which have become the major problems in the sustainable production of tea orchards.Many studies suggested that the imbalance of soil rhizhospere microecology is one of the important factors causing continuous cropping obstacle.Therefore,it is important to study the rhizosphere soil microbial diversity and community structure of tea orchards with different ratooning ages,which is helpful to understand the biological process in the rhizosphere of tea plants,and can provide scientific bases for tea orchard management.This study investigated the effects of ratooning continuous cropping of Tie Guanyin tea plants on the rhizospheric soil nutrition,enzymatic activities,and microbial diversity and community structure using the system biology methods such as Biolog(community level physiological profiling),PLFA(phospholipid fatty acid),and high-throughput sequencing.In addition,application of biochar and sheep manure were suggested to improve the rhizospheric microecology,and to accelerate the growth of tea plants by mehods of laboratory incubation and field experiment.The main conclusions are listed as follows:(1)Photosynthesis,bud characteristics,and chemical compositions of tea plants with different ratooning ages were investigated in this study.Results showed that the net photosynthetic rate,the intercellular CO2 concentration,and the stomatal conductance in the 20-year tea orchards remarkably decreased by 13.3%,17.06%,and 42.5%than in the 10-year tea orchards.The sprout density,hundred-sprout weight,and tea yield in 20-year tea orchards were significantly decreased than in the 10-year tea orchards.In addition,the contents of coffee alkali,amino acid,tea polyphenol and chatechin in the 20-year tea orchards were significantly decreased than in the 1-and 10-year tea orchards.In sum,after 20 years of ratooning continuous cropping,the growth,yield and chemical quality of Tie Guanyin tea plants showed a downward trend.(2)Tea_orchards with different ratooning ages showed signifieant differences in soil nutrition.Soil pH decreased significantly by 0.8,1.34 and 1.08 pH units from the wasteland to the 1-,10-,and 20-year tea soils respectively.Soil organic carbon,total nitrogen,total potassium,available nitrogen,and available potassium were present in the highest amounts in the 10-years soils,followed by 1-and 20-year soils.However,total phosphorus and available phosphorus had the highest amounts in the 1-year soil,and ranked in order of 1 year>10 years>20 years.The invertase,urease,phosphomonoesterase,and catalase activities in the 20-year soils significantly decreased by 43.63%,67.12%,48.28%,and 34.00%,respectively,compared with those in the 10-year soils.Therefore,the long-term ratooning continuous cropping of tea plants led to soil acidification,and significant decreases in soil nutrition and enzymatic activities.(3)The results from BIOLOG and PLFA analysis showed that long-term ratooning continuous cropping of tea plants produced a significant effect on rhizospheric microbial carbon metabolic activity and diversity,and microbial community composition.The CLPP analysis indicated a significant decrease of 27.86%and 16.98%in the average well color development and richness index,respectively,in the 20-year soils compared with the 10-year soils.Long-term ratooning continuous cropping tended to result in higher utilization of phenolic compounds and carboxylic acids than other substrates in the 10-and 20-year soils.PLFA analysis revealed that the total PLFA concentrations ranged from 13.68 nmol g-1 to 62.47 nmol g-1,which were significantly higher in the 1-and 10-year soils than in the 20-year and control soils.Stress in dicators(i.e.,saturated/monosaturated fatty acids)significantly increased in the 10-and 20-year soils than in the 1-year soils,implying higher nutritional or physiological stresses in microorganisms in the 10-and 20-year tea soils.Redundancy analysis indicated that the soil organic carbon and available phosphorus had high correlations with the variation in soil microbial community composition.(4)High-throughput sequencing was employed to evaluate the response of the soil microbial communities to long-term consecutive monoculture of tea plants.Compared with the control soil,OTU,Shannon index,Chaol and ACE index of bacterial community in the tea rhizosphere soils were significantly decreased;however,no significant difference was observed among the 1-,10-and 20-year tea soils.In contrast,these richness and diversity indices of fungal community significantly decreased with the long-term continuous cropping,1 year>10 years>20 years>0 year.In addition,Gammaproteobacteria,Alphaproteobacteria,Acidobacteria and Actinobacteria were the main phyla in the tea orchard soils and accounted for more than 60%of the bacterial sequences.Ascomycota and Basidiomycota were the main phyla in the tea orchard soils and accounted for 53.4%?90.8%and 8.3%?17.6%of the fungal sequence.Furthermore,we found that long-term ratooning continuous cropping of tea plants led to a signifieant decrease in the relative abundance of beneficial bacteria,such as Pseudomonas,Rhodanobacter,Bradyrhizobium,Mycobacterium and Sphingomonas in the 20-year tea orchard soils.However,there was a significant increase in the relative abundance of potential pathogens Alternaria in the 10-and 20 years tea orchards.The study demonstrated that long-term ratooning continuous cropping resulted in the decrease of the diversity of rhizosphere soil microbial community,and the alteration of microbial composition with more plant benifical bacteria and fewer fungal pathogens.(5)The amelioration effects of different biomass materials applied to acidic tea orchard soils were in order of sheep manure>biochar>wheat straw/rice straw with the laboratory incubation experiments.Field plot experiments showed that the application of 40 t hm-2 biochar,and 7.5 t hm-2 sheep manure can increase soil pH and soil nutrition in the acidic tea orchards,improve the rhizopheric microecology,and significantly enhance tea production.The biochar and sheep manure treatments significantly increased the carbon metabolic activity(AWCD)of the microorganism in the rhizosphere soils,sheep manure>biochar>control.The total PLFA concentrations in the biochar and sheep manure treatments were significantly increased by 20.87%and 47.51%than the control soils.qRT-RCR analysis indicated that sheep manure treatments increased the number of beneficial bacteria Pseudomonas,and decreased the number of potential pathogens Alternaria.Biochar treatments had no effect on the number of Pseudomonas and Alternaria.In short,application of biochar and sheep manure treatments can improve the rhizospheric soil micro-environment of tea plants,and accelerate the growth of tea plants.The above-mentioned results indicated that long-term ratooning continuous cropping of tea plants could lead to serious soil acidification,nutritional imbalance,the decline of rhizospheric soil microbial diversity,and the deterioration of the rhizosphere microecological environment.The application of biochar and sheep manure can increase the soil pH and nutritional level,improve microbial community composition and structure,and accelerate the growth of tea plants.