Effects Of Thinning On Soil Carbon Input Of Caragana Korshinskii Plantation On The Loess Plateau

The Loess Plateau of China is the core area of “Grain for Green Programme”.Planting Caragana korshinskii is one of the main measures for vegetation restoration in this area.C.korshinskii plantation can controll soil erosion and improve soil carbon restoration.However,long-term plantations showed signs of degradation such as dieback and soil dried layers.Therefore,observing the characteristic of soil carbon sequestration and their main driving factors is important for exploring sustainable management.Here,we used the method of “space for time”and selected three C.korshinskii plantations with different ages(10,20,and 30 years)on the Loess Plateau to evaluate soil origin carbon(SOC),soil total nitrogen(STN),and soil water content(SWC).Meanwhile,we analyzed effects of different thinning intensity(all removed,1/3 thinning,2/3 thinning,no thinning)on soil carbon input of C.korshinskii plantations.The main results as follows:(1)Compared with a natural restored grassland,C.korshinskii platations improved soil carbon,soil nitrogen,and soil water stock in short term(10 years),but these benefits were depleted in long term(>20 years).The results showed that SOC,STN,and soil water stocks(0-100 cm)were significantly decreased by 23.9%,19.9%,and 29.2% from 10 to 30 years,respectively.(2)Thinning exacerbated soil surface water consumption,while replenished depper soil water.The SWC(0-100cm)was gradually decreased with the increase of the thinning intensities.Compared with 1/3 thinning,2/3 thinning,and no thinning,the soil water storage of all removed was reduced by 3.41mm?6.68mm?8.15 mm,respectively.In 100-200 cm soil depth,all removed treatmenet reduced SWC by 5.49 mm and 5.56 mm than no thinning and 1/3 thinning.However,1/3 thinning improved SWC by 3.43 mm than no thining in 200-300 cm soil depth.Additonally,thinning stimulated soil nutrient availability.Compared with original shrub,soil available phosphorus(SAP)and soil available nitrogen(SAN)under regenerated ones was increased 7.48 and 8.05%,respectively.(3)Thinning reduced shrub layer's biomass.The herbaceous biomass and above-ground net primary productivity was increased by 2/3 intensity thinning.SWC(R2=0.23,P=0.0001),STN(R2=0.17,P=0.0001),SAP(R2=0.11,P=0.0001)was positivly correlation with herbaceous biomass.Herbaceous biomass was increased with soil moisture and nutrient.(4)Soil carbon input(1.09±0.34 Mg C ha-1yr-1)was the highest under the 2/3 thinning intensity.Soil carbon input of herbaceous was 0.92±0.32 Mg C ha-1yr-1,soil carbon input of C.korshinskii was 0.17±0.01 Mg C ha-1yr-1.Therefore,soil carbon input was mainly from herbaceous layer(84%).The decline of soil carbon sequestration capacity in long-term C.korshinskii plantations could be improved by 2/3 thinning intensity.