Features And Distribution Of Soil Humus With Vegetation Restoration In The Karst Areas

Karst ecosystem is a kind of fragile ecosystem.soil organic carbon(SOC) is essentially a driving force in karstification,moreover,SOC transfer is also the main pathway of carbon circulation in karst ecosystem.Karst area in China ranks first in the world,is also the most extensive range of distribution.The vulnerability of karst ecosystem and unreasonable human activities result in rocky desertification landscape which is marked by vegetation degradation,decline in soil quality and soil erosion.The natural vegetation succession is a major means of ecological rehabilitation in karst area,moreover,it also a pressing need for agricultural production improvement,regional economic development and shaking off poverty.As an important component of organic matter,soil humus have an important influence on the formation of soil structure,retention and supply of soil moisture and soil nutrient,moreover,as the most stable component of soil organic matter,soil humus play an important role on carbon sequestration in soil. Within the background of global warming,a research on combined forms and components of soil humus with vegetation restoration is of great significance.Taking soil of JiGong mountain in ChongQing as an example,trends and vertical distribution of soil physiochemical properties,combined forms and components of soil humus with vegetation restoration were discussed in this paper.The main conclusions were as follows:(1)Soil pH values in study area ranged from 5.15-7.24,which was acid or neutral. The vertical distribution of soil pH values increased with soil depth; the CEC increased with both vegetation restoration and soil depth;the physical clay content varied from 26.23% to 43.98%,which belong to clay soil.and the physical clay content distributed uniformly at the depth; total soil organic carbon(TOC),total nitrogen(TN) and available nitrogen(AN) contents both increased with vegetation restoration while total phosphorus(TP) and available phosphorus(AP) to the contrary. The soil nutrients decreased with soil depth.(2)Profile TOC in average respectively was:the arbor stage(17.45g.kg)> the shrub-arbor stage(17.16g.kg)>the scrub-shrub stage(15.54g/kg)>the herbaceous stage(12.90g.kg)> the bare land stage(11.63g.kg),increasing with the process of vegetation restoration. TOC of layer A increased significantly with vegetation restoration while TOC of layer AB increased in early succession then remained stable in middle and later succession.TOC of layer B first increased and then decreased.Profile TOC in different stages of vegetation restoration decreased with soil depth,i.e. layer A>layer AB>layer B.(3)Along with vegetation restoration,profile humus carbon in average respectively was:the arbor stage(7.08g/kg)> the shrub-arbor stage(6.45g/kg)>the scrub-shrub stage(5.70g/kg)>the herbaceous stage(5.69g/kg)> the bare land stage(5.27g/kg).Humus carbon of layer A had a slightly increase in early succession and then improved significantly in the arbor stage. Humus carbon of layer AB decreased slightly from the bare land stage to the herbaceous stage and then increased till the shrub-arbor stage while decreased again in the arbor stage.Humus carbon of layer B generally increase with vegetation restoration.Humus carbon in different stages of vegetation restoration decreased with soil depth,i.e. layer A>layer AB>layer B.(4)Along with vegetation restoration,profile humic acid carbon(HAc) in average respectively was:the arbor stage(3.09g/kg)>the scrub-shrub stage(2.06g/kg)>the shrub-arbor stage(1.82g/kg)>the herbaceous stage(1.78g/kg)>the bare land stage(0.91g/kg).HAc of layer A increased first with vegetation restoration and then decreased in the the shrub-arbor stage.HAc of layer AB increase generally with vegetation restoration.HAc of layer B first increased and then decreased.Profile fulvic acid carbon(FAc) in average from high to low were:the shrub-arbor stage(4.63g/kg)> the bare land stage(4.36g/kg)>the arbor stage(3.99g/kg)>the herbaceous stage(3.92g/kg)> the scrub-shrub stage(3.64g/kg).Trend of FAc with vegetation restoration were not obvious owning to its activity and migration.FAc of layer A decreased from the bare land stage to the herbaceous stage and the increased to top in the shrub-arbor stage while decreased again in the arbor stage.FAc of layer AB generally decreased with vegetation restoration while layer AB increased.FAc in different stages of vegetation restoration decreased with soil depth,i.e. layer A>layer AB>layer B.(5)Profile heavy fraction organic carbon(HFOC) in average from high to low was:the arbor stage(12.78g/kg)> the shrub-arbor stage(12.23g/kg)>the scrub-shrub stage(11.52g/kg)>the herbaceous stage(10.10g/kg)> the bare land stage(8.82g/kg),increasing with the process of vegetation restoration.HFOC in different stages of vegetation restoration decreased with soil depth,i.e. layer A>layer AB>layer B.HFOC of layer A increased from the bare land stage to the shrub-arbor stage and then remained stable in the arbor stage.HFOC of layer AB increased generally with vegetation restoration while layer B first decreased and then increased.(6)Along with vegetation restoration,profile loosely combined humus carbon increased.Stably combined humus carbon showed the following trend:the arbor stage>the shrub-arbor stage＞the bare land stage>the scrub-shrub stage>the herbaceous stage.Tightly combined humus carbon from high to low was:the shrub-arbor stage＞the scrub-shrub stage>the herbaceous stage＞the arbor stage＞the bare land stage.combined forms of humus carbon in different stages of vegetation restoration decreased with soil depth.rends of Combined forms of humus carbon with vegetation restoration in the same layer varies.