| Jiangjiagou is a typical fragile ecological environment in southwest China,mountain disasters,increase the dual role in the harsh natural conditions and human activities,increased soil erosion,water pollution,river siltation and other ecological and environmental problems have become increasingly prominent.At present,the research contents on carbon storage and carbon density of different types of ecosystems in China are continuously enriched,but studies on the distribution of carbon stocks,landslide instability,slope vegetation,and soil carbon stocks,and influencing factors are rarely reported.To understand the distribution of vegetation community characteristics and carbon stocks and the influencing factors on the unstable slope vegetation in frequent landslides,this study selected Jiangjiagou debris flow frequent watershed subtropical dry hot valley(Chajinggougou sunny slope,Da’aozigou shade slope),subtropical and warm temperate semi-humid area(Duozhaogou sunny slope),temperate humid mountain area(Xiaojianfeng sunny slopes and Da’di shady slopes are the study areas,Samples of stable slope stability,instability,and accumulation areas are taken as plots,the vegetation community survey,plant sample collection and soil sampling were conducted from July to August 2017.The plant biomass,plant carbon content and soil physical and chemical properties were measured.The characteristics of the vegetation communities at different parts of the unstable slope in each climate zone,vegetation and Soil carbon stocks and influencing factors.In order to clarify the characteristics of surface vegetation communities and the distribution of ecosystem carbon stocks on unstable slopes in different climatic regions,provide basic data and theoretical reference for the vegetation restoration and instability of soil carbon in the ecologically fragile regions.The study results are reflected in the following aspects:(1)Characteristics of vegetation communities of unstable slope in different climate regionsA total of 49 species of plants have emerged in the subtropical dry-hot valley area,with herbaceous plants accounting for the vast majority of the population.Heteropogon contortus,Eulaliopsis binata,and Arthraxon hispidus are common species in the area.There were 9 species of herbaceous plants,4 species of shrubs,1 species of arbors in the subtropical and warm temperate semi-humid areas,the herbaceous layer was dominated by Caryopteris divaricata and Ser.Abrotanum,the shrub layer was dominated by Coriaria sinica,and the arbor layer was Pinus yunnanensis.There were 87 species of herbaceous plants,7 species of shrubs,and 1 species of arbors in the temperate humid mountainous terrain,the herbaceous layer was mainly composed of Potentilla anserine,Elsholtzia ciliata,Vicia cracca,the shrub layer was Chenopodium ambrosioides and Vaccinium bracteatum.The arbor layer was mainly composed of Pinus yunnanensis.In the subtropical dry hot-hot valley area,the richness index of different parts of the Chajinggou sunny slope is highest in the instability area,and the Simpson index and the ShannonWiener index are highest in the accumulated area,and the Pielou index is the highest in the stable area.Da’aozigou shade slope richness index,Pielou index,Shannon Wiener index are the highest in accumulated area,Simpson index up to unstable area,The richness index,Pielou index,and ShannonWiener index in the temperate humid mountainous area are all highest in the accumulated area,and the Simpson index is the highest in the stable area(0.105).The Margalef index of Xiaojianfeng sunny slope is the highest in the unstable area,and the Simpson index,Pielou index,and ShannonWiener index are all highest in the accumulated area.(2)Distribution of vegetation carbon and biomass carbon on unstable slopes in different climate regionsArbor biomass of Duozhaogou sunny slope is the highest,followed by Da’di shady slope,with that of Xiaojianfeng sunny slope lowest.The litter biomass showed as the Da’di shady slope>Xiaojianfeng sunny slope>Duozhaogou sunny slope,and the biomass of litter on the Da’di shady slope and Xiaojianfeng sunny slope was significantly higher than that of the Duozhaogou sunny slope.In herbaceous layer,total biomass in temperate zone and humid mountain range was between 44.13～221.00 g·m-2,with the highest in accumulated area of the Da’di shady slope,and the lowest in the stable area of the Da’di shady slope.The above-ground biomass is between 21.20 and 165.47 g·m-2.The Da’di shady slope accumulated area shows the highest aboveground biomass,and the stable area show the lowest aboveground biomass.The underground biomass is between 22.93～106.17 g·m-2,with the highest in the accumulated area,and the lowest in the stable area of the Da’di hady slope.The total herb biomass in the subtropical and warm temperate subhumid areas was the highest in the unstable area,followed by the accumulated area,and the lowest in the stable area.The above-ground and below-ground biomass all represented unstable area>accumulated area>stable area.The total herb biomass in the subtropical dry-hot valley region is between 39.19 and 640.25 g·m-2,the highest total herb biomass in stable area of the Da’aozigou shady slope,the lowest in accumulated area,and the above-ground biomass is 31.24～469.05 g·kg-1,with the highest in stable area of Da’aozigou and the lowest is accumulated area of Da’aozigou,the underground biomass was between 9.37 and 171.20 g·kg-1,showing the same trend as the total biomass.The carbon content of aboveground part of herbaceous plants in each climate zone was higher than that in the underground part but the difference was not significant.The carbon content in the aboveground part of the Xiaojianfeng sunny slope was the highest(344.35 g·kg-1),the lowest is unstable area of Xiaojianfeng sunny slope(144.42 g·kg-1).There was a significant difference between the two(P<0.05).The litter carbon content was the highest in stable area of Duozhaogou sunny slope,and the lowest is stable area of Xiaojianfeng sunny slope slope.(3)Distribution of soil organic carbon content in unstable slopes in different climate regionsThe content of soil organic carbon in different parts of the Chajinggou sunny slope in the subtropical dry-hot valley area shows a decrease as the soil depth increases,the soil organic carbon content in the Da’aozigou shady slope stable area shows a trend of decreasing first and then increasing gradually with deeper soil depth.The contents of soil organic carbon in unstable area and accumulated area all decreased with the deepening of soil layers.The content of soil organic carbon in the same soil layers at different sites on the destabilizing slopes of all plots showed stable area>unstable area>accumulated area.The highest content of soil organic carbon in all plots was 0-5 cm soil layer in the Da’aozigou shady slope stable area,and the lowest was 10-20 cm soil layer in the Chajinggou sunny slope accumulated area.In the subtropical and warm temperate semi-humid areas,the content of soil organic carbon in the stable and unstable areas of Duozhaogou sunny slopes decreases with the deepening of soil layers,while the accumulated area shows the tendency of decreasing first and then increasing with the deepening of soil depth,the soil organic carbon content in the 0-5 cm soil layer was in the order of unstable area>stable area>accumulated area,5-10 cm soil layer was unstable area>accumulated area>stable area,10-20 cm soil layer was accumulated area>unstable area>stable area.The content of soil organic carbon showed a decrease as the soil depth increased in different parts of the destabilized slope surface in the temperate humid mountainous area,and the content of soil organic carbon in the same soil layer at different parts of the Da’di shady slope represented unstable area>stable area>accumulated area,while the Xiaojianfeng sunny sharp slope showed stable area>unstable area>accumulated area.(4)Main influencing factors of soil organic carbon on unstable slope in different climate regionsThe correlation analysis showed that there was a significant positive correlation between soil organic carbon and soil organic carbon density and total nitrogen(P<0.01),and there was a significantly negative correlation between soil organic carbon density and soil organic matter density(P<0.01),there was a significant positive correlation with total phosphorus(P<0.05),but no significant correlation with pH.There was a significant negative correlation between soil organic carbon density and soil bulk density and pH(P<0.05).There was a significantly positive correlation between soil organic carbon density and total nitrogen(P<0.01),but there was no significant correlation between soil organic carbon density and total soil phosphorus.In general,soil organic carbon content in the climatic regions of the study area was mainly affected by soil bulk density,nitrogen,and phosphorus.(5)Vegetation carbon stocks and soil carbon stocks distribution trends on unstable slopes in different climatic regionsThe herbaceous carbon reserves in different parts of the subtropical dry-hot valley area were higher in the aboveground part than in the underground parts,and the proportion of the herbaceous layer carbon storage in the parts was higher than 72%.Temperate moist mountainous areas,subtropical and warm-temperate semi-humid areas in three stable plots have arbor communities in the plots.High biomass of trees and litter layers make the ecosystem biomass much higher than the instability and accumulation areas.In addition,the proportion of carbon storage in the vegetation area of the tree in the stable area was higher than 45%,while the proportion of carbon storage in the understory layer was less than 1%.The distribution trend of organic carbon storage in different soil layers at various locations on the destabilized slope in the subtropical dry-hot valley region is as follows:the depth of the soil layer increases and decreases first and then increases,with the proportion of 10-20 cm soil layer being the largest;subtropical and warm temperate zones.The distribution of soil carbon storage in different soil layers in the semi-humid area is similar to that in the subtropical dry and hot valley area,but the ratio of 0-5 cm soil layer is the highest in the stable and destabilizing areas,and the highest is in the 10-20 cm soil layer in the accumulation area;The organic carbon storage in the soil profile of moist mountainous areas shows a trend of decreasing first and then increasing as the soil depth deepens,indicating that organic carbon is more distributed in the surface and deep layers.(6)The distribution trend of carbon storage in unstable slope ecosystems in different climate regionsThe soil carbon storage among the different parts of the slopes of Xiaojianfeng and Chajinggou sunny slope,and Da’aozigou shady slopes was the highest in the stable area,followed by the unstable area,and the accumulated area was the lowest,while the opposite is true of the trend of Duozhao sunny slopes.The soil carbon storage in the shady slope is highest in the unstable area,followed by the stable zone,and the lowest is accumulated area.The proportion of soil carbon storage in different parts of the unstable slope in each climate zone accounts for 48.34 to 99.76%of the carbon storage in the ecosystem.The highest proportion is in the unstable area of the Xiaojianfeng sunny slope(99.76%),and the lowest is in the Duozhao sunny slope,stable area(48.34%).Soil carbon stocks accounted for less than 83%of the sites where trees were distributed,indicating that higher vegetation biomass is beneficial to the storage of carbon,while soil carbon stocks in the herb-dominated parts account for Above 97.92%. |
