Soil Organic Carbon Under Different Land Use Types At Mountain Forest-drought Valley Ecotone In The Upper Reaches Of Minjiang River

Ecotone is a sensitive region for global climate change, and study on soil organic carbon under different land use types at ecotone could provide basal data for land management.The mountain forest-drought valley ecotone in the upper reaches of Minjiang River is a typical tension zone,It can inhibit the extension of the drought valley and extension the function of subalpine forest ecosystem.This paper usethe method of sampling by the typical, research on soil organic carbon,microbial biomass carbon,water-soluble organic carbon,readily oxidation carbon,soil water physical property and the relationship between them at mountain forest-drought valley ecotone in the upper reaches of Minjiang River. the results show that:(1) Soil organic carbon content under Six kinds of land use lies between 8.86±3.99 gC·kg-1-17.52±7.77gC·kg-1,Soil organic carbon storage lies between 56.56±7.21 tC·hm-2-104.15±4.84 tC·hm-2,soil organic carbon content and storage were decreased with the soil depth increment.Soil organic content and storage followed the order of Quercus semicarpifolia secondary forest>shrubbery > shrub> economic forest> Robinia pseudoacacia plantation> farmland.Among them, the Soil organic carbon storage under Quercus semicarpifolia secondary forest higher than the other five kinds of land use(p<0.05); show that the forest Soil is the largest carbon storage under different land use types at mountain forest-drought valley ecotone in the upper reaches of Minjiang River. However, because of the Jamming and frangibility of ecotone, soil organic carbon of mountain forest-drought valley ecotone in the upper reaches of Minjiang River under six kinds of land use was lower than the same area(Miyaluo forest area in the upper reaches of Minjiang River).(2) Soil microbial biomass carbon content under six kinds of land use lies between 145.34±64.70mgc·kg-1-411.55±102.12 mgc·kg-1,they followed the order of Quercus semicarpifolia secondary forest> shrubbery> shrub> Robinia pseudoacacia plantation >economic forest> farmland .Soil microbial biomass carbon content of Quercus semicarpifolia secondary forest higher than the shrubbery, it were much higher than the other four types of land use(p<0.05).The extent of reduction were significantly in the 0-40cm soil layer under Six kinds of land use,it were decreases gradually with the soil depth increment.The percentage was lower which of Soil microbial biomass carbon to soil organic carbon under Six kinds of land use lies between 1.36%-2.35%, show that the Soil organic carbon have downward trend at ecotone.(3) water-soluble organic carbon content of soil profile under six kinds of land use lies between 84.41±16.09mgc·kg-1-198.27±17.75mgc·kg-1,they followed the order of Quercus semicarpifolia secondary forest>Robinia pseudoacacia plantation>shrubbery>shrub>economic forest> farmland,water-soluble organic carbon were decreased with the soil depth increment.water-soluble organic carbon content of Quercus semicarpifolia secondary forest were much higher than the other five types of land use(p<0.05);The percentage of soil water-soluble organic carbon to Soil organic carbon under Six kinds of land use lies between 0.82%-1.34%,the robinia pseudoacacia plantation presents a maximum conductivity and a minimum shrubbery.Effect of specific distribution of soil moisture at the ecotone,the percentage were higher in the 20-40cm soil layer which of water-soluble organic carbon to soil organic carbon under six kinds of land use.(4)Readily oxidation carbon content under six kinds of land use lies between0.90±0.26gc·kg-1-1.84±0.25 gc·kg-1,they followed the order of Quercus semicarpifolia secondary forest>shrubbery>shrub>Robinia pseudoacacia plantation>economic forest> farmland; Readily oxidation carbon content of Quercus semicarpifolia secondary forest higher than the shrubbery, it were much higher than the other four types of land use(p<0.05); soil readily oxidation carbon content were decreased with the soil depth increment under all kinds of land use types.The percentage was higher which of Soil readily oxidation carbon to soil organic carbon under Six kinds of land use lies between 7.77%-10.50%, show that the Soil organic carbon have high reactivity and easy conversion at ecotone.(5)soil organic carbon,microbial biomass carbon,water-soluble organic carbon and readily oxidation carbon under six kinds of land use showed a significant negative correlation with Soil bulk density (p<0.01);Soil organic carbon and soil active organic carbon of six kinds of land use have different correlation with soil water content under the double influence which natural conditions of ecotone and human disturbance.Soil organic carbon and soil active organic carbon of Six kinds of land use have negative correlation with soil PH and they had a great closely correlation.The ecotone of the soil PH is too high but go against accumulation in soil organic carbon and soil active organic carbon at a certain extent.(6)Arter farmland transformed into robinia pseudoacacia plantation and economic forest ,Soil organic carbon content increased by36.73% and 21.93%, Soil organic carbon storage increased by 50.56% and 25.13%, readily oxidation carbon content increased by 4.58% and 7.53%, microbial biomass carbon content increased by 13.16% and 23.31%, there was a big rate of increase amplitude of the water-soluble organic carbon,increased by 27.28% and 71.06%.It shows that the soil organic carbon and soil active organic carbon is increased after conversion of cropland to forest, but the degree of this increase is related to vegetation types.The water-soluble organic carbon is more sensitive to land use change at mountain forest-drought valley ecotone.