Ecological Stoichiometry And Soil Microbial Community Characteristics Of Different Grassland Types On The Eastern Tibetan Plateau

Ecological stoichiometry focuses on the ratio relationships of multiple chemical elements in an ecosystem and its changing rule with the environment,and reveals the balance of energy and multiple elements in ecological interactions.The Tibetan Plateau acts as an important ecological barrier of China,and is a hot spot of biodiversity conversation.Alpine meadow,shrub meadow and swamp meadow are widely distributed on its eastern edge,where is the highest production and the most biodiversity in the Tibetan Plateau.Scientific evaluation of the stoichiometric characteristics and interactions among plants,soil and microbes in different alpine grasslands is of great significance for judging the health of the regional ecological environment,which can provide a theoretical basis for the management of alpine grassland ecosystems.At present,most of the studies on ecological stoichiometry in alpine meadows have focused on a single perspective of plants,soil or microbes,or a single grassland type,therefore,we conducted this study on ecological interactions among plants,soil and microbes in three types of grasslands.Using conventional experimental methods and high-throughput sequencing technology,we determined the plant community composition and nutrient elements,soil physicochemical properties,microbial biomass carbon,nitrogen and phosphorus and soil enzyme activities and soil microbial community structure.Based on ecological stoichiometry,the ecological stoichiometric characteristics of plants,soil and microorganisms in three types of grasslands were analyzed,and the composition and diversity of microbial communities and their influencing factors were also analyzed.The main results were:(1)The C/N value of plant leaves was the highest in swamp meadow,and the leaf C/P of the shrub meadow and swamp meadow were significantly higher than that that in the alpine meadow,indicating that the shrub meadow and swamp meadow had higher nutrient utilization efficiency,and leaf N/P value of three grassland types were all less than 14,indicating that plant growth was restricted by N element.(2)Soil C/N was higher in alpine meadow and shrub meadow than in swamp meadow,while soil C/P and N/P were the highest in swamp meadow,indicating that the availability of soil P in swamp meadow was low and was severely restricted by P.The microbial biomass carbon,nitrogen and phosphorus decreased with the increase of the soil layer.The MBC/MBN of the two soil layers was the highest in the swamp meadow,and the MBC/MBP and MBN/MBP of the soil in the 0-20 cm soil layer were significantly highest in the shrub meadow,and the MBC/MBP value in 0-20 cm soil layer showed that shrub meadow > swamp meadow > alpine meadow,indicating that the soil microorganisms in the alpine meadow have a great potential to release P element in the process of mineralizing soil organic matter,and then MBP plays an important role in releasing P elements to supplement the soil available phosphorus pool.(3)Soil C/N was significantly negatively correlated with plant leaf C/N and MBC/MBN in the two soil layers;soil C/P was only significantly positively correlated with leaf C/P and MBC/MBP at 0-20 cm;Soil N/P in all layers was significantly negatively correlated with plant leaf N/P,and was significantly negatively correlated with MBN/MBP only in 20-40 cm soil layer.(4)Soil enzyme activity showed a decreased trend with the increase of soil layer,βG enzyme was significantly highest in alpine meadow,while N-cycle enzyme and Pcycle enzyme were significantly lowest in alpine meadow;enzyme C/N and enzyme C/P is significantly higher in alpine meadow than in shrub meadow and swamp meadow.Enzyme N/P is generally lower in swamp meadow,and the vector angle is the highest,indicating that swamp meadow are restricted by P.(5)Bacterial community diversity,Chao1 index had no significant difference among three grassland types,and Shannon and Simpson indices were the lowest in swamp meadow;for fungal community diversity,Chao1 index,Shannon and Simpson index in 0-20 cm soil layer were the highest in the shrub meadow,while the Chao1 index and the Ace index in 20-40 cm soil layer were the lowest in the swamp meadow.NMDS analysis showed that soil microbial community structure of alpine meadow and shrub meadow had high similarity,while soil microbial community structure of swamp meadow was different from that of other two grassland types.Soil depth had no significant effect on microbial community.(6)The dominant bacteria in bacterial communities of different grassland types were Actinobacteria,Acidobacteria,and Proteobacteria;the dominant fungi in fungal communities are Basidiomycota and Ascomycota,but the relative abundances were different in different grassland types.Mantel analysis showed that soil properties had a greater impact on microbial community structure than plant communities.Results showed that grassland types significantly affected the ecological stoichiometric characteristics of plants,soil and microbes.There were interactive effects on ecological stoichiometry among plants,soil and microbes.Compared to plant community,soil characteristics had a greater role in shaping soil microbial communities.