The Soil Water And Carbon Sequestration Of Pinus Sylvestris Forest In Different Afforestation Ages In Mu Us Desert

Desertification is one of the serious ecological problems in semiarid areas.Vegetation construction is an important tool for improving soil environment.Artificial forest planting generally increases soil carbon storage but its continuous growth is limiting by soil water content.Exploring the variation of water and carbon pools at chronosequences of artificial forest ecosystem in the semiarid sandy land contributes to further reveal the effects of vegetation on sandy soil conditions,which is of great significance to vegetation construction and sustainable development.This study was conducted in the Mu Us Desert.Pinus sylvestris with different afforestation ages(20-,30-,40-,50-,and 60-year-old)were selected,and the bare land was used as a control(referred as plantation age of 0).The combination of field survey and indoor analysis was used to explore the soil moisture(0-10 m),carbon stocks(arbor layer carbon pool,litter layer carbon pool,soil layer carbon pool)and carbon sequestration rate along different afforestation ages,and the relationship between soil moisture and soil carbon storage at 0-4 m soil layer was also analyzed.The main results were as follows:(1)The afforestation ages of P.sylvestris artificial forest significantly affect soil water content in semiarid sandy land.The 20-years forests mainly consumed soil water at the depth of 0-2 m soil profile,with the highest net soil water consumption of 172.29 mm.The 30-years and 40-years forests mainly consumed soil water at the depth of 0-4 m,with the highest net soil water consumption of 176.48 mm.The 50-60-years forests mainly consumed soil water of the deepest soil profile(0-10 m),and the highest net soil water consumption(330.71 mm)occurred on 8-10 m.The soil water content at 8-10 m soil depth was higher than that at 0-8 m,and it decreased with the increasing stand age.(2)The afforestation ages had significant impacts on forest carbon sequestration(arbor layer carbon pool,litter layer carbon pool and soil layer carbon pool).The carbon storage of arbor layer initially increased and then decreased along the afforestation ages(20-60 years),and it reached maximun in 30 years.The carbon storage of surface litter continuously accumulated during vegetation restoration,and it reached maximun in 60 years.In the soil layer(0-4 m),the carbon storage significantly decreased after afforestation and then returned to the original level,and the highest carbon storage occurred in 30-40 years.(3)The distribution of each C cool showed the same trend with different planting years: the carbon storage of arbor layer>the carbon storage of soil layer>the carbon storage of surface litter layer.Compared to the soil layer and surface litter layer,the carbon storage of arbor layer had a largest proportion in the total carbon pool,with 78.73% in 30 years,72.19% in 40 years,79.61% in 50 years,and 67.79% in 60 years,respectively.(4)The carbon sequestration rate of soil layer,litter layer and arbor layer showed the highest values during 20-30 years,with 20.793 Mg C hm-2 yr-1 in arbor layer,0.127 Mg C hm-2 yr-1 in surface litter layer and 2.552 Mg C hm-2 yr-1 in soil layer,respectively.(5)In the soil layer(0-4 m),the soil carbon storage initially increased and then decreased with the increasing planting ages,while the soil water storage initially decreased and then increased.There was a significantly negative correlation between soil carbon storage and soil water storage(P<0.01).And there was a significantly negative correlation between soil carbon storage and soil water storage in the soil layer of 1-2 m and 2-3 m and 3-4 m(R2 =0.46,P<0.01;R2 =0.64,P<0.01;R2=0.62,P<0.05).Afforestation age affected the soil water and sol carbon sequestration in the sandy ecosystem,which resulting in an unbalance distribution of soil water and carbon storage to a certain extent.Young forest consumed the shallow soil water and had high carbon sequestration rate in the C pools(arbor layer,soil layer and surface litter layer).With the increasing of planting ages,mature forest gradually consumed the water resources in deep soil depth,and its soil carbon sequestration rate also decreased.In summary,from the perspective of keeping low soil water consumption and high carbon sequestration rate,optimal management should be considered to promote the sustainability of artificial forest.These results can provide theoretical basis for the forest construction and management in semiarid sandy land.