| As one of the important circulating substances in karst mountainous areas,calcium is closely related to the dissolution and weathering of parent rock,the formation and evolution of soil and the growth and development of plants in karst mountainous areas.The study of spatial heterogeneity of calcitin in soil and plants in karst mountainous area could provide basis for the restoration of rocky desertification and soil resource management in the area.In this paper,the dominant tree species(Toona sinensis,Cladrastis platycarpa,Koelreuteria paniculata,Broussonetia papyrifera)and soil at different altitude(500 m,700 m,900m,1100 m)in huajiang dry-hot valley mountain area of Guizhou Province are taken as research objects to study the vertical distribution characteristics and influencing factors of calcium content in leaves of tree species and soil in the study area.In order to further explored the adaptation characteristics of dominant tree species to karst rocky desertification areas in different altitude gradients,and to provide scientific basis for rational utilization of soil nutrients and tree species selection in ecological restoration in karst rocky desertification areas.The main research achievements of this paper are as follows:(1)In the study area,the results showed that soil total calcium content ranged from 18.82 to 36.48 g·kg-1,water-soluble calcium content ranged from 0.017 to 0.22 g·kg-1,exchangeable calcium content ranged from 0.96 to 4.95 g·kg-1,acid-soluble calcium ranged from 0.088 to 0.43g·kg-1,and organically bound calcium ranged from 0 to 0.06 g·kg-1.The maximum values of all calcium forms were found at 700 m,and the proportions of calcium forms at all altitude were in the order of exchangeable>acid-soluble>water-soluble>organic.In the soil layer,the contents of soil total calcium,water-soluble calcium,exchangeable calcium and acid-soluble calcium gradually decreased with the increase of soil depth except at 500 m altitude.Among the environmental factors,the changes of rocky desertification degree,vegetation coverage and climatic conditions at different altitude may be the important reasons for the altitude differentiation of calcium content.At 700 m altitude,the moisture and temperature balance and suitable for the living conditions of the microbial activity,make the soil nutrient content at a higher level.The correlation analysis and redundancy analysis showed that p H value,total carbon,organic carbon,total magnesium,total nitrogen and total phosphorus were the main physical and chemical factors affecting soil calcium content(The correlation between the physical and chemical factors and soil total calcium or soil form calcium reached a significant level,and they have a high level of importance).(2)The leaf calcium content of dominant tree species varied at different altitude.The calcium content in leaves of Toona sinensis ranged from 28.49 to 38.99 g·kg-1,which decreased gradually with the increase of altitude,and had the maximum value at 500 m and minimum value at1100 m.The leaf calcium content of Cladrastis platycarpa ranged from27.66 to 41.42 g·kg-1,which increased firstly and then decreased with the increase of altitude,and had the maximum value at 900 m and the minimum value at 700 m.The leaf calcium content of Koelia paniculata ranged from 34.24 to 44.72 g·kg-1,which decreased firstly,then increased and decreased finally with the increase of altitude,and had the maximum value at 1100 m and the minimum value at 700 m.The leaf calcium content of Broussonetia papyrifera ranged from 33.21 to 51.21 g·kg-1,which increased with the increase of altitude,and had the maximum value at 1100 m and the minimum value at 500 m.The order of leaf calcium content of four tree species was as follows:Broussonetia papyrifera>Koelreuteria paniculata>Toona sinensis>Cladrastis platycarpa.Among the soil physical and chemical factors,the increase of soil potassium content could promote the calcium storage capacity of Toona sinensis leaves,and the correlation coefficient was 0.474(P<0.01).The soil environment with sufficient moisture,high p H value and rich carbon content could promote the calcium storage capacity of Broussonetia papyrifera leaves,and the correlation coefficients were 0.552,0.464 and0.591(P<0.01).Among the forms of soil calcium,the water-soluble calcium could promote the calcium storage capacity in leaves of Koelia paniculata and Cladrastis platycarpa,and the correlation coefficients were 0.441 and 0.595(P<0.05).The exchangeable calcium could promote the calcium storage capacity in leaves of Toona sinensis and Broussonetia papyrifera,and the correlation coefficients were 0.421 and0.536(P<0.05).According to the degree of correlation between calcium content in leaves and exchangable calcium content in soil,Toona sinensis and Broussonetia papyrifera were classified as random type plants,while Cladrastis platycarpa and Koelreuteria paniculata were classified as high calcium type plants.(3)The calcium biological absorption coefficients of the four dominant tree species showed two trends with the increase of altitude.One type was Toona sinensis and Cladrastis platycarpa,which increased first and then decreased.The other type was koelreuteria paniculata and Broussonetia papyrifera,which decreased first and then increased.The calcium biological absorption coefficients of Toona sinensis and Cladrastis platycarpa ranged from 1.67 to 2.71 and 0.53 to 1.07,both of which increased firstly and then decreased with the increase of altitude,and had the maximum value at 900 m.The calcium biological absorption coefficients of koelreuteria paniculata and Broussonetia papyrifera ranged from 0.79 to 1.53 and 0.80 to 1.41,both of which decreased firstly and then increased with the increase of altitude,and had the minimum value at 900 m.The order of calcium biological absorption coefficients of the four tree species was Toona sinensis>Koelia paniculata>Broussonetia papyrifera>Cladrastis platycarpa.The climatic conditions at high altitude were more conducive to the absorption and utilization of soil calcium by Toona sinensis and Cladrastis platycarpa,while the climatic conditions at low altitude were more conducive to the absorption and utilization of soil calcium by Koelia paniculata and Broussonetia papyrifera.The increase of soil organic matter content could weaken the calcium absorption efficiency of Koelia paniculata and Broussonetia papyrifera,and the correlation coefficients were 0.366 and 0.44,respectively(P<0.05).The increase of soil potassium and natriuretic contents could enhance the calcium absorption efficiency of Toona sinensis(the correlation coefficients were0.359 and 0.413(P<0.05)),but weaken the calcium absorption efficiency of Koelia paniculata(the correlation coefficients were 0.469 and 0.464(P<0.05)).The increase of human disturbance could enhance the calcium absorption efficiency of Koelia paniculata and Broussonetia papyrifera,but weaken the calcium absorption capacity of Toona sinensis and Cladrastis platycarpa.There was a strong correlation between the calcium absorption efficiency of four tree species and total soil calcium content(P<0.01),but a weak correlation with soil calcium form.On the basis of fully exploiting the utilization efficiency of soil nutrients by plants in the ecological restoration and reconstruction of rocky desertification area in southwest China,Toona sinensis and Cladrastis platycarpa should be selected as the pioneer species for vegetation restoration at middle and high altitude,while Koelia paniculata and Broussonetia papyrifera should be selected as the pioneer species for vegetation restoration at low altitude. |
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