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Soil Aggregate-associated Microbial Characteristics In Tea Plantations Of Western Sichuan,China

Posted on:2019-04-30Degree:DoctorType:Dissertation
Country:ChinaCandidate:S Q WangFull Text:PDF
GTID:1360330596962948Subject:Ecology
Abstract/Summary:PDF Full Text Request
In the last century,the sharp increase of the population pressure has led to land degradation from overgrazing and deforestation.Consequently,not only ecological environments were severely destroyed,but also current and future soil productivity capacities were drastically decreased in the areas of Western Sichuan,China.To solve these situations,the Chinese government has implemented a variety of conservation projects to restore the degraded ecosystems.Among them,the conversion of wastelands to tea(Camellia sinensis L.)plantations is a key practive in the sustainable development of agriculture in the areas of Western Sichuan.During tea planting,soil physical and chemical properties are significantly influenced by the fertilization,litter decomposition,and root secretions.In order to adapt to the dynamics of soil environments,soil microorganisms must modify their own structure and function.Thus,soil microbial activity and community diversity can reflect the environmental stress of soil quality.As the basic unit of soil structure,the formation and stability of soil aggregates have a profound impact on the living environments of soil microorganisms.Understanding the relationships between soil microorganisms and aggregates are helpful to reveal the response mechanisms of soil microbial characteristics to tea plantation age.In this study,the microbial characteristics were analyzed in soil aggregates,which were collected at the 0-20 cm depth in four tea plantations with different ages(16-,23-,31-,and 53-years)at the long-term agricultural experimental site of Sichuan Agricultural University.A dry-sieving procedure was adopted to separate soil aggregates into four fractions,including >2,2-1,1-0.25,and <0.25 mm.These results could provide a soil-focused theoretical basis for the sustainable development of tea plantations.(1)There was a significant decline in the concentrations of soil aggregate-associated organic C and total N corresponding with the decrease of the aggregate size regardless of tea plantation age.However,the concentrations of aggregate-associated available nutrients(including N,P,and K)displayed an inverse trend.Although long-term tea planting brought various benefits,such as the accumulation of soil organic C,total N,and available N and P,soil available K was susceptible to leaching loss in the process of tea planting.As main carriers of soil organic C and nutrients,the >2 mm fractions had relatively high stocks of these elements in all the tea plantations.Notably,the variations in soil aggregate-associated organic C and nutrient stocks differed with the aggregate size duringtea planting.For example,in the early stage(from 16-to 23-years),tea cultivation contributed to a significant increase in organic C stock in the whole-soil,and this change was primarily reflected in the >2 mm fractions.In the later stage(from 23-to 53-years),however,the increase in organic C stock in the whole-soil was primarily reflected in the1-0.25 mm fractions.(2)In all the tea plantations,the higher levels of soil microbial biomass C and N,basal respiration,and substrate induced respiration were observed in the >2 mm fractions,indicating that there fractions were of great importance in soil C cycle and nutrient release.In contrast,the lower levels of soil microbial biomass and respiration were found in the<0.25 mm fractions,thus contributing to maintain the soil organic C and nutrients.During tea planting,soil microbial biomass and respiration in the 23-year-old tea plantation were highest in all the tea plantations,suggesting that the relatively suitable soil environments in this tea plantation were beneficial for the development of soil microorganisms.Meanwhile,the response of soil microbial biomass and respiration to tea plantation age in the >0.25 mm fractions was more sensitive in contrast to the <0.25 mm fractions.(3)In general,the >2 mm fractions were associated with the highest activities of soil?-glucosidase,invertase,urease,and protease,while the lowest activities were observed in<0.25 mm fractions,regardless of tea plantation age.However,the activities of soil polyphenol oxidase and acid phosphatase were evenly distributed in the different size fractions.The percentage contribution of enzyme activities in the >2 mm fractions to the whole-soil was 37.43%-52.57% across the four tea plantations,suggesting that these fractions were the primary carriers of soil enzymes in the present ecosystem.Moreover,soil C-and N-cycling enzyme(including ?-glucosidase,invertase,urease,and protease)activities associated with the >2 mm fractions were significantly increased in the first23-years of tea planting.These results indicated that young tea plantations in the early stage had limitations with respect to the potential for soil organic matter sequestration;however,as the tea plantations matured under the present system of management,the soil organic matter sequestration has improved.(4)Based on the phospholipid fatty acid biomarker technology,we found that not only soil microbial biomass(including bacteria,fungi,actinomycetes,and arbuscular mycorrhizal fungi)but also their diversity was highest in the >2 mm fractions regardless of tea plantation age,indicating that these fractions had a complex microbial community structure,thus providing biological buffering and prohibiting the dominance of individualorganisms via competition or predation.The 23-year-old tea plantation provided relatively suitable soil environments for the development of microbial communities,and subsequently induced an increase of soil microbial biomass and diversity.Notably,soil microbial quotient(the ratio of soil microbial biomass C to organic C)and pH were important drivers of the variations in soil microbial communities during tea planting.Also,tea plantation age affected the microbial biomass and diversity via altering soil aggregate distribution.As the main group of soil microorganisms,bacteria accounted for46.84%-72.40% of the total microbial biomass.Thus,the dynamics of soil bacteria could reflect the overall changes of soil microbial communities.(5)Based on the high-throughput sequencing,we observed that the Proteobacteria,Actinobacteria,Chloroflexi,and Acidobacteria were the dominant groups of soil bacterial communities in all the tea plantations.The relative abundance of Proteobacteria and Actinobacteria,which were identified as a type of copiotrophic taxa,increased significantly during the first 23-years of tea planting.Subsequently,there was a significant decrease that corresponded with the tea plantation age.Differently,the relative abundance of Chloroflexi and Acidobacteria,which were identified as a type of oligotrophic taxa,increased continuously with the increasing age of tea plantations.As shown in redundancy analysis,the two most important contributors(microbial quotient and pH)explained the most of changes in the composition of soil bacterial communities during tea planting.In all the tea plantations,the highest levels of soil bacterial community richness and evenness appeared in the >2 mm fractions.Meanwhile,the highest diversity of soil aggregate-associated bacterial communities was observed in the 23-year-old tea plantation,suggesting that the relatively suitable soil environments in this tea plantation were beneficial for the development of soil bacterial communities.(6)Based on the Biolog Eco MicroPlates,we showed that the highest levels of soil bacterial metabolic activity and diversity appeared in the >2 mm fractions regardless of tea plantation age,suggesting that the formation and stability of these aggregate fractions played an important role in maintaining the functional diversity of soil bacterial communities.The 23-year-old tea plantation provided relatively suitable soil environments and more C sources for the growth of soil bacteria,and subsequently induced an increase of soil bacterial metabolic activity and diversity.In all the tea plantations,the carboxylic acids were dominantly utilized by soil bacteria,followed by the carbohydrates and amino acids,while the amines,phenolic compounds,and polymers were seldom utilized.Compared with the 23-year-old tea plantation,the bacterial utilization capacity of the carbohydrates,amino acids,carboxylic acids,and amines in the other three tea plantations decreased significantly regardless of aggregate fraction.Differently,continuous increases were observed in phenolic compound and polymer utilization with the increasing age of tea plantations.As shown in redundancy analysis,soil microbial quotient and pH explained the most of changes in the bacterial utilization capacity of different C sources during tea planting.Also,soil environments affected the functional characteristics of soil bacterial communities via altering their structural characteristics.
Keywords/Search Tags:Tea plantation age, Soil aggregates, Microbial biomass, Microbial activity, Microbial community characteristics
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