Study On Soil Aggregates And Their Organic Carbon And Nitrogen In Cold Temperate Forest

Soil aggregates are the basic unit of soil.The distribution characteristics of aggregates have an important influence on the stability of soil structure.The content and distribution law of aggregates combined with organic carbon and nitrogen also affect the interception and retention of soil organic carbon and nitrogen.The northern forest of daxing 'an mountains is the only temperate forest in China with a forest coverage rate of more than 70%.However,the daxing'an mountain area has a thin soil layer and permafrost,This study greater hinggan mountains north of the main forest types(Larix gmelinii,Pinus sylvestris var.mongolica,Betula platyphylla,Populus davidiana)as the research object,the determination of 0?5 cm,5?10 cm,10?20 cm of soil aggregate composition and stability,as well as aggregate in combination with characteristics of organic carbon and nitrogen content and enzyme activity,It provides a theoretical basis for the in-depth study of soil structure and carbon and nitrogen cycle in cold temperate regions of China.Results:(1)The soil aggregates of the four forest communities in cold temperate zone of China all showed that the proportion of large aggregates decreased gradually with the deepening of soil layer,while the proportion of micro aggregates increased.The content of macroaggregate in broad-leaved forest was higher than that in coniferous forest.The macroaggregate in the 0?10 cm soil layer of Pinus sylvestris var.mongolica,Betula platyphylla and Populus davidiana was the absolute dominant,accounting for more than 60%of the total aggregate,while the macroaggregate in the Larix gmelinii was mainly concentrated in the 0?5 cm soil layer,fluctuating between 59.39%and 88.38%.The content of large aggregates in the middle growth season of the four forest communities was higher than that at the beginning and the end of the growth season.(2)Soil MWD and GMD in all soil layers of the four main forest types in the cold temperate zone were higher in the middle of the growing season,and the soil D value was higher in the early and late growing season.As the soil layer decreased,the MWD and GMD values of the soil decreased and the D values of the soil increased.The values of MWD and GMD in broadleaved forests were higher than those in coniferous forests,while the values of D were lower.With the decrease of soil layer,the stability of soil aggregates decreased,and the stability of soil aggregates of the two broad-leaved forest types was better than that of the two coniferous forest types.(3)Soil aggregate organic carbon content of the four main forest types in the cold temperate zone were decreases with soil decreased,and the organic carbon content is higher than that of coniferous forest,broad-leaved forest aggregate increases with the reduction of particle size distribution of organic carbon content is reduced,since some micro aggregate and organic carbon content increasing trend,along with the change in Larix gmelinii aggregate organic carbon content change trend in a fluctuant way,Pinus sylvestris var.mongolica with higher levels of the early stage of the growing season,broad-leaved forest in the middle and later periods of the growing season aggregate organic carbon content is relatively high.The organic carbon contribution rate of the aggregates of the four forest types presented the same rule roughly.The organic carbon contribution rate of the aggregates with a depth of 0?10 cm was higher,and the organic carbon contribution rate of the aggregates decreased with the decrease of the soil layer.(4)The total nitrogen content of soil aggregates in four forest types in cold temperate zone decreased with the decrease of soil layer,along with the decrease of the particle size of aggregate total nitrogen content decreases,Larix gmelinii forest and Betula platyphylla forest soil aggregate along with the change in total nitrogen content showed a trend of fluctuations,Pinus sylvestris var.mongolica forest in the early stage of the growing season the aggregate total nitrogen content is higher,Populus davidiana forest in middle and later periods of the growing season,content is higher.The total nitrogen contribution rate of soil aggregates of the four forest types was the same as that of organic carbon.With the deepening of the soil layer,the total nitrogen contribution rate of the large aggregates decreased,while the total nitrogen contribution rate of the micro aggregates increased.(5)Soil D of four forest types in the cold temperate zone was significantly negatively correlated with>0.5 mm particle size aggregates,total porosity,non-capillary porosity,and organic carbon content.Soil WR0.25,MWD,and GMD aggregated with diameters>0.5 mm.particle size aggregates,total porosity,capillary porosity,non-capillary porosity and organic carbon content have a very significant positive correlation,>1 mm particle size aggregates,organic carbon content and total porosity contribute the most to the stability of soil aggregate.The organic carbon and total nitrogen content of>0.5 mm particle size aggregates has a positive correlation with the corresponding particle size aggregates,and the organic carbon content of>1 mm particle size aggregates has a very significant positive correlation,indicating that>1 mm and 0.5?1 mm particle size aggregates The body is the main carrier of organic carbon and total nitrogen.