Carbon Sequestration Of The Artificial Shelterbelt Salix Cheilophila Plantation With Different Stand Age In High-cold Sandy Land

Revegetation and restoration is the effective measure to prevent and control desertification.Moreover, the sand-fixing vegetaions have multiple ecosystem services and the carbonsequestration is one of the most important ecosystem service. In this research, the typicalhigh-cold sandland ecosystem in the Gonghe Basin, Qinghai Province was used to study thesoil physical and chemical properties, the characteristics of root distribution, the plantationbiomass and productivity, the carbon storage of ecosystem. The aim of this study is to researchthe characteristic of carbon sequestration and its effect factor about the Salix cheilophila shelterbelt, and providing a scientific basis for a comprehensive evaluation of the carbonsequestration in high-cold sand land ecosystem. Besides, it could also be benefits to providereference for the vegetation restoration and protection, revegetation in degraded ecosystem andthe assessment of ecosystem services in sandy land in arid and semi-arid ecosystems in thefuture. The main results are as follows:（1） Soil chemical and physical properties of Salix cheilophila plantation with different ageThe contents of soil organic matter （SOM） showed significantly increment with theextension of restoration time of S. cheilophila plantations （P<0.05）. Soil organic matter contentwas affected significantly by restoration time and soil depths （P<0.05）. The contents of totalnitrogen （TN） showed significantly increment with the extension of restoration time, thespecific data is21a>16a>11a>6a>ck. SOM and TN changed not only in the subsoil but also inthe deep soil layer. The content of the soil NO3-N, NH4-N, AP （available phosphorus） and AK（available potassium） showed significant differences in different ages of S.cheilophilaplantation （P<0.05）. In the same stand age, soil nutrients contents of the upper soil layer（depth<100cm） were higher than deeper soil. The content of AP and AK increased, and soil pHvalues decreased gradually with restoration time. The soil chemical properties and soil fertilitylevels were improved gradually after the establishment of S. cheilophila plantation.The soil water content exhibited significant difference （P<0.05） among different stand ages in general, and marked differences were also found among different soil depth. The soilwater content in10²0cm and20³0cm were superior to the surface （0¹0cm）. The soilwater condition was the best in21-years old. S. cheilophila plantation, which showed higherSOM and soil porosity relatively, with better water holding capacity. With longer restorationtime, the soil bulk density decreased gradually; on the contrary, the soil porosity, soil capillaryporosity, soil capillary holding capacity and maximum water holding capacity increased. Thesoil structure and porosity properties of S.cheilophila were improved effectively. Theinteractions between root and soil led to the change of soil bulk density, which caused thechange of soil organic carbon storage.（2） The biomass and productivity of Salix cheilophila plantation with different agesThe biomass of the S. cheilophila plantation increased gradually with ages. Biomass of6,11,16,21-years-old plantation were10.58,19.49,28.90and41.27t hm^-2respectively. Thebiomass allocation of each component was different. On the numerical side, it could beexpressed as: the trunk> root> branches> leaves> bark. The Single-Equation Model was areasonable way to evaluate the biomass and the basal diameter （B） was used as the independentvariable.The root system of S. cheilophila with different plantation ages was mainly consist of fineroots and middle roots with diameter less than5.0mm, among which more than50%were fineroots with diameter less than2.0mm. The root system of S.cheilophila plantation wasconcentratedly distributed in soil depth of0⁵0cm. The root system of6-years-old wasdistributed in0¹30cm, and the vertical distribution of21-years-old could reach200cm. Theroot biomass increased gradually with revegetation time. Besides, root specific length and rootlength density also showed significant increment （P<0.05）. The root extinction coefficientgradually increased with stand age. S. cheilophila showed the characteristics of deep-root,which reflected excellent ecological plasticity. Revegetation also showed significant influenceto the change of SOM. The increment of root specific length and root length density lead tochange of soil bulk density. There was highly significant correlation between soil organicmatter and root distribution. The net ecosystem productivity of the S. cheilophila of6,11,16, 21years old plantation were1.76,1.78,1.81and1.97t hm^-2 a^-1respectively. The proportion ofbiomass in the herb layer was gradually reduced in the entire ecosystem. And the productivityof each component could be arranged in numerical size, as the trunk> root> branches>foliage> bark.（3） The carbon density and carbon storage of Salix cheilophila plantation with different agesThere is no significant difference of carbon density variation between each componentwith the increment of restoration time （P>0.05）. The carbon density of root did not reach asignificant level in any age of plantation. The range of variation in carbon density in differentorgans was0.4105⁰.5087gC g^-1for6-years-old plantation,0.4523⁰.5342gC g^-1for11-years-old plantation,0.4514⁰.5485gC g^-1for16-years-old plantation, and0.4704⁰.5992gC g^-1for21-years-old plantation. The variation of carbon density in the coarse root, middleroot and fine root was different in different stand ages. The carbon storage of6,11,16, and21-years-old was10.58,19.49,28.90and41.27t hm^-2respectively. The proportion of carbonpools of different components differed in different stand ages. The carbon storage in the trunktook up the highest percentage in all components.The soil organic carbon pools showed significant difference in the same depth of differentages （P<0.05）. The soil carbon pools increased with the restoration time, the soil carbon poolsof11-year-old plantation increased26.78%compared to the6-years-old, the16-years-oldplantation increased24.16%compared to the11-years, and the21-year increased9.82%compared to the16-years-old. The contents of soil organic carbon and soil bulk density showedhighly significant negative correlation （P<0.01）. On the contrary, positive correlation showedbetween the contents of soil organic carbon and the contents of TN. Take soil organic carbon asdependent variables, the three-dimensional model and linear equation were set up to simulatethe changes among the soil organic carbon, soil bulk density, soil depth and total nitrogen withthe extension of the restoration time, respectively. Regression models showed that the soil bulkdensity, soil total nitrogen significantly effect on the soil organic carbon （P<0.01）, whichprovided thoughts for the modeling of soil carbon pool in the vegetation restoration area on theregional and even large-scale. The ecosystem carbon pools of the S.cheilophila of6,11,16and21-years-old were14.76,23.25,32.18and41.48t hm^-2respectively. And the soil carbon pools were9.54,13.03,17.18,19.05t hm^-2. The carbon pools increased57.05%、36.52%、27.75%and22.42%compared toCK, respectively. The total area of the Salix cheilophila in the restoration area is223.2hm^-2,calculated with the average of the carbon storage (12.795t hm^-2), the carbon sequestration ofthe S. cheilophila in the restoration area reached2855.844Mg C. The establishment ofregression equation of biomass and carbon storage of each component provided basis tomeasure the carbon storage according to biomass in the future. The net primary productivity ofthe S. cheilophila plantation of6,11,16,21-years-old was1.76,1.78,1.81and1.97t hm^-2, theaverage annual carbon sequestration of each stand was0.83,0.90,0.92and1.05t hm^-2 a^-1. Thetrunk has the highest carbon sequestration. The net carbon storage increased with therestoration time. The artificial shelterbelt of S. cheilophila plantation could be considered as a“carbon sink”.