Dynamic Changes of Carbon Sink of Picea schrenkiana Plantation with Forest Age in Middle Section of Northern Slope of Tianshan Mountains

Artificial forest is an important component of forest carbon sequestration and sink enhancement, and its carbon dynamics are quite different with the increase of forest age. Taking Picea schrenkiana, a single plantation widely distributed in Tianshan forest area, as the research object, the untended plantation sample plots of different ages and no forest land as the control were selected. Through the investigation and sampling of sample plots, the carbon density of vegetation above ground, vegetation under ground, litter and soil were calculated, and the variation law of carbon sink and carbon sequestration after afforestation with forest age were quantified by using the method of replacing time with space. The results showed that: 1) The above ground carbon density of different age groups was 1.82~119.34 t·hm⁻² and the under ground carbon density was 1.26~27.77 t·hm⁻². The trunk accumulated 46.4%~62.0% of the vegetation carbon. The carbon density (carbon sequestration) increased at different speeds with the increase of forest age, while the carbon sink increased at first and then decreased. 2) The carbon density of litter ranged from 0.42 t·hm⁻² to 1.74 t·hm⁻², and the carbon sequestration of litter played a role of 0.23 t·hm⁻²·10 a to 0.42 t·hm⁻²·10 a. 3) In the early stage of afforestation, the carbon density in deep soil was significantly higher; At the later stage of afforestation, the carbon in topsoil gradually accumulated under the action of litter decomposition input, which was significantly greater than 10~60 cm; Afforestation can effectively improve soil carbon sink, the average amount of carbon sink reached 51.66 t·hm⁻²·10 a; Compared with no forest land, the amount of carbon sequestration increased obviously after afforestation, and reached the maximum value of 101.83 t·hm⁻² at 21~30 a of forest age, and the amount of carbon sequestration increased first and then decreased binomial with forest age. 4) The total carbon sequestration of plantation showed a non-uniform growth trend, in which the carbon sequestration potential of 60 a plantation was high, and the total carbon sequestration accumulation could reach 488.60 t·hm⁻², the proportion of above ground and under ground carbon sinks in the total carbon sinks of the ecosystem of plantation increased from 4.6% in 10~20 a to 67.7% in 51~60 a, while the proportion of soil carbon sinks in the total carbon sinks of the ecosystem decreased continuously.