| Pinus tabuliformis is widely distributed in China and is one of the main aerial tree species in China.As the largest contiguous forest area in northern China,the aerial seeding forest of Pinus tabuliformis in Danfeng County has played a positive and irreplaceable role in maintaining ecological balance.The soil carbon pool of Pinus tabuliformis aerial seeding forest is an important part of its ecosystem carbon pool.Studying the soil organic carbon density of Pinus tabuliformis aerial seeding forest and its influencing factors plays a very important role in regulating the carbon cycle of Pinus tabuliformis aerial seeding forest ecosystem.Previous studies have mainly explored the single-factor or multi-factor relationship between various factors(such as topography,vegetation,soil physical and chemical properties,etc.)and forest soil carbon.However,the identification of key factors in multiple factors and their interaction mechanisms are still unclear.Therefore,this study used the survey data of 50 standard plots of Pinus tabuliformis in Danfeng County,Shangluo City,Shaanxi Province.The characteristics of trees,shrubs and grasses and soil characteristics were studied,and the structural equation model was used to explore the influencing factors of soil organic carbon density.The above 30 indicators of tree characteristics,shrub and grass characteristics,biomass and soil physical and chemical properties were selected as observation indicators,and the structural equation model of partial least squares method was constructed.It provides a theoretical basis for forest soil carbon stability of Pinus tabuliformis aerial seeding forest in Danfeng County.The main results are as follows:(1)Non-spatial structure of Pinus tabuliformis forest in Danfeng County:The species composition of the stand was expressed by the basal area ratio,and P.tabuliformis was the dominant species in all 50 standard plots.Besides,other tree species in the canopy layer include Quercus variabilis,Quercus serrata,Quercus aliena,Pinus massoniana,Pinus huashanensis,Robinia pseudoacacia,and Platycarya strobilacea.The diameter structure of the whole forest showed an irregular inverse“J”distribution,with the majority of trees in the small and medium diameter classes.The height structure of the whole forest was approximately bimodal,with the tallest trees reaching a height of 10m.The average tree density was 2387.34 plants/hm~2,and the crown width decreased with the increase of tree density.It was found that the species Margalef and Pielou index of the tree layer were low,the dominance of Pinus tabuliformis was large,and there were many rare species in the stand.(2)The spatial structure of Pinus tabuliformis aerial seeding forest in Danfeng County:For the uniform angle index,the distribution pattern of 25 standard plots was random distribution,the distribution pattern of 12 standard plots was uniform distribution,and the distribution pattern of 13 standard plots was aggregated distribution.For the mingling index,67.38%of the trees were in the mixed state of neighborhood comparison,and most of the trees had low spatial isolation.The proportion of trees in the state of advantage,sub-advantage,moderation,disadvantage and absolute disadvantage is about20%,and the overall stand is relatively stable.In the crowding index,80.84%of the trees are in a very dense state,and the trees grow more crowded.(3)The shrub and grass characteristics of Pinus tabuliformis aerial seeding forest in Danfeng County:The diversity index of shrub and grass layer is that the average Margalef index of shrub layer is higher than that of herb layer,and the species richness of shrub layer is higher than that of herb layer.The Pielou index of shrub and grass layer was low,indicating that the number of individuals of most species in shrub layer and herb layer was small and rare.The total biomass of shrubs in 50 standard plots of Pinus tabulaeformis aerial seeding forest was 36.98 t/hm~2,and the average biomass of shrubs in a single standard plot was 0.74 t/hm~2.In addition to biomass,the average height and coverage of shrub layer in each standard plot were also higher than those of herb layer.The coefficient of variation of shrub biomass was 129.73%,and the data of shrub biomass in each standard plot were discrete.(4)The soil physical and chemical properties of Pinus tabuliformis aerial seeding forest in Danfeng County:The average soil organic carbon density in 0-30cm soil layer of Pinus tabuliformis aerial seeding forest is 36.61t/hm~2,the average soil total nitrogen content is 0.48g/kg,the average soil total phosphorus content is 0.26g/kg,the average soil water content is 11.81%,and the average soil bulk density is 1.47g/cm~3.Soil organic carbon density and soil total nitrogen content showed a decreasing trend in the vertical direction.According to the results of one-way analysis of variance,the soil organic carbon density and soil total nitrogen content of the three soil layers were significantly different,the soil total phosphorus content of each soil layer was not significantly different,the soil water content of 0–10 cm soil layer and 20–30 cm soil layer was significantly different,and the soil bulk density of 0–10 cm soil layer and 10–20 cm soil layer and 20–30 cm soil layer was significantly different.(5)The influencing factors of soil organic carbon density of Pinus tabuliformis aerial seeding forest in Danfeng County:The results of SRMR of the structural equation model of the influencing factors of soil organic carbon density in three soil layers were0.093,0.071 and 0.083,respectively.The influence path between the latent variables of each model is consistent.Other soil physical and chemical properties directly positively affect soil organic carbon density.Shrub and grass characteristics directly positively affect other soil physical and chemical properties,and indirectly positively affect soil organic carbon density.Tree characteristics directly negatively affect shrub and grass characteristics,and indirectly negatively affect soil organic carbon density.The observed variables selected by the structural equation model of each soil layer are different,indicating that the main influencing factors of soil organic carbon density in different soil layers are different. |
PDF Full Text Request