Study On Carbon And Nitrogen Forms And Soil Enzyme Activities Of Rhizosphere Soil Of Main Tree Species In Northern Daxing'anling Mountains

Rhizosphere soil is the most active area for plant roots to communicate with external materials and energy.It is of great significance to the growth and development of forest trees and soil carbon and nitrogen cycles.The northern part of Daxing'anling is located in the cold temperate zone,rich in forest resources,and the zonal vegetation is a bright coniferous forest dominated by Xing'an larch.In this study,four tree species(Pinus sylvestris var.mongolica,Larix gmelinii Betula platyphylla,and Populus davidiana)in the northern mixed forest of Daxing'anling were used as research objects.The rhizosphere soil samples were collected by shaking root method to explore the growth of carbon and nitrogen nutrients and enzyme activities in rhizosphere soil.Seasonal dynamics,rhizosphere effects and differences,and correlation analysis of their impact factors,in order to further reveal the mechanism and circulation of soil carbon and nitrogen nutrients and provide a basis for forest succession and protection.Research shows:(1)The dynamics of soil organic carbon,light organic carbon and recombinant organic carbon in the four main tree species in the northern Daxing'anling were similar,all of which were higher in May and June,and slightly fluctuated from July to October.They were 17.39?56.13g·kg-1,1.32?15.43g·kg-1,15.68?40.70g·kg-1 respectively.The content of soluble organic carbon was mainly "M" type,and the fluctuation range was 63.47?206.88mg·kg-1;The ratio of organic carbon allocation in the rhizosphere soil light group ranged from 7.5%to 27.5%.Rhizosphere soil organic carbon,light organic carbon and recombinant organic carbon were significantly higher than non-rhizosphere,showing obvious positive rhizosphere effects,indicating that rhizosphere plays an important role in soil carbon pool supplementation.The enrichment rate of organic carbon,light organic carbon,recombinant organic carbon and soluble organic carbon and light organic carbon were the highest in the rhizosphere soil of Betula platyphylla contributes the most to the enrichment and supplementation of soil carbon pools in the study area.(2)The total nitrogen content in the rhizosphere soil of four tree species fluctuated between 1.22 and 5.43 g·kg-1 from May to October,and the maximum value was in May.The ammonium and nitrate nitrogen in the rhizosphere soil fluctuated between 22.41?53.75mg·kg-1 and 0.79?2.06mg·kg-1,respectively,and the contents were lower in July and August.The rhizosphere soils of the four tree species had significant positive rhizosphere effects on nitrogen nutrient content.The coniferous tree species had stronger enrichment ability of inorganic nitrogen than broad-leaved tree species;Larix gmelinii has the strongest rhizosphere effect on nitrogen nutrients.(3)The fluctuation of microbial biomass carbon content in rhizosphere soil was 114.14?451.05mg·kg-1,the fluctuation of microbial biomass nitrogen content in rhizosphere soil was 40.38?185.00mg·kg-1.The soil microbial biomass carbon to nitrogen ratio was 1.42?5.24.The contribution rate of microbial biomass carbon to the rhizosphere soil organic carbon pool of the four tree species was 0.83?0.95%.The contribution rate of microbial biomass nitrogen to the rhizosphere soil organic nitrogen pool of the four tree species was 3.63-5.08%.The microbial biomass carbon and microbial biomass nitrogen content in rhizosphere soil were significantly higher than non-rhizosphere,and the rhizosphere effect was significant,and showed obvious growth season differences.At the end of the growing season,the rhizosphere effect of the coniferous species was It is more obvious than broad-leaved trees;the effect of microbial biomass on the soil structure and function of rhizosphere soil of coniferous trees in cold temperate zone is higher than that of broad-leaved species.(4)The fluctuation of catalase activity in rhizosphere soil was 2.92?3.43 g·min-1 mg-1;the fluctuation of invertase activity in rhizosphere soil was 5.38?11.36 mg·g-1·24h-1;the rhizosphere soil protease activity month The difference was large,the fluctuation was 0.150?0.589 mg·g-1·24h-1;the urease activity of rhizosphere soil fluctuated slightly with the month,ranging from 0.369?0.599 mg·g-1·24h-1.The positive rhizosphere effect of rhizosphere soil enzyme was obvious.Sucrase,protease and urease are affected by both tree species and monthly changes,while catalase is relatively insignificant;rhizosphere soil enzymes can characterize the fertility of rhizosphere soil to some extent.