Distribution Of Soil Carbon And Estimation Of Carbon Sequestration Potential In The Taklimakan Desert Highway Shelterbelt

The Taklimakan Desert is located in hinterland of the Eurasian continent which belongs to a warm temperate arid climate zone.The climate is extremely dry,the surface water resources are scarce,the groundwater resources are abundant but the salinitiesarehigh,the highest value is close to 30 g/L,sothe high salinity water is a major factor limiting vegetation growth in this region.The Taklimakan Desert Highway Shelterbel thaving a length of 522 km was built more than 15 years ago,it is drip-irrigated by pumping local saline ground water.At present,the shelterbelt plants grow well and completely eradicate the sand damage to the highway,and greatly improve the landscape along it.The construction of shelterbelt has a great impact on the soil and environment at this region.Study on the soil carbon storage and distribution characteristics in the shelterbelt can provide support for the assessment of the service function of desert artificial ecosystem.We selected 8 sections of shelterbelt with different planting years(23a,21a,19a,17a)and different salinities of the irrigation water(28.40 g/L,18.36 g/L,10.00 g/L,4.82 g/L).The species of the shelterbelt are mainly composed by Calligonum mongolicum,Tamarix chinensis and Haloxylon ammodendron,and the shifting sandy land was taken as the control(CK).Through field sampling and indoor analysis,the distribution characteristics and influencing factors of soil carbon in shelterbelt were studied,and the carbon sequestration potential estimated.We aim to provide theoretical basis for sustainable management of the shelterbelt.The main conclusions are as follow:(1)The soil organic carbon content(SOC)of different forest age shelterbelt increased first and then decreased with the soil depth,and slowly declined below 60 cm and eventually stabilized.Soil inorganic carbon content(SIC)in shelterbelt planted for 23a,19a and 17a decreased firstly and then increased with the soil depth,but shelterbelt planted for 21a showed a trend of“down-up-down”with the increasing soil depth.The average SOC content in the surface layer(0~40 cm)showed as 23a>21a>19a>17a>CK,which increased with the shelterbelt age.The average SIC content sowed as 17a>19a>21a>23a>CK,decreased with the shelterbelt age,but all were higher than shifting sandy land.The soil carbon density in the 0~5 m profile was shown as 19a(162.06 kgC/m~2)>23a(156.39 kgC/m~2)>17a(144.53kgC/m~2)>21a(142.27 kgC/m~2)>CK(133.93 kgC/m~2).The inorganic carbon density(SICD)is 15.14~16.35 times of the organic carbon density(SOCD).The shelterbelt soil has a high carbon sequestration potential,and itstotal carbon sequestration potential is 7.58 Tg,and the inorganic and organic carbon sequestration potentials are 7.31 Tg and 0.27 Tg,respectively.(2)SOC content in shelterbelt irrigated with different salinity water showed a“decrease-increase-decrease”trend with the soil depth and gradually stabilized below 2 m,and the SIC increased firstly and then decreased,finally rised slowly and stabilized below 3m.SOC of shifting sandy land increased with soil depth,and SIC increased firstly and then decreased slowly with soil depth.The average SOC content of0~5 m profile showed as28.40 g/L>18.36 g/L>10.00 g/L>4.82 g/L>CK,and the average SIC content showed as28.40 g/L>10.00 g/L>18.36 g/L>4.82 g/L>CK,both showed an increasing trend with irrigation water salinity.Soil carbon storage in the 0~5 m showed as 28.40 g/L(173.83kgC/m~2)>10.00 g/L(153.66 kgC/m~2)>18.36 g/L(151.84 kgC/m~2)>4.82 g/L(144.95kgC/m~2)>CK(133.87 kgC/m~2),of which SICD was 11.01~15.57 times of SOCD.(3)The overall grain size distribution of each treatment showed as fine sand(0.1~0.05mm)>coarse sand(>0.1 mm)>silt-clay(<0.05 mm).The content of silt-clay in shelterbelts decreased firstly and then increased with the increasing soil depth,and the content of sand was much higher than silt-clay.Silt-clay had a higher content in the surface layer(0~0.4 m),and the average content is 7%~13%,which was much higher than shifting sandy land(2.63%).The content of silt-clay in CK was relatively stable(about 2.5%).The content of coarse sand increased,and fine sand decreased firstly and then increased with the soil depth.Under the same shelterbelt age,the SOC of coarse sand and fine sand increased with the irrigation water salinity.The SIC content of coarse sand wasthe lowest,the SIC content of fine clay and fine sand were small,and the SIC content of coarse sand increased and the SIC content of the silt-clay decreased with the increasing irrigation water salinity.SOC and SIC contents of different shelterbelt age were all higher than shifting sandy land,and SOC of silt-clay increased the most.SIC content of silt-clay increased with the shlterbelt age.SIC content of coarse sand and fine sand decreased as the shelterbelt age increased.SOC and SIC contents of the CK were all showed as silt-clay>fine sand>coarse sand.However,the carbon contribution rate of each particle size was mainly affected by the particle content,and overall showed as fine sand>coarse sand>silt-clay.