Objective This study aimed to reveal the influencing laws and mechanisms of forest types and stand age on the carbon storage of sand fixation plantation ecosystem in the Nenjiang River Basin of northeastern China in temperate semi-arid regions, and to provide a scientific basis for the practice of carbon sink management in sandy plantations.
Method Relative growth equations, carbon and nitrogen analyzer were used to simultaneously estimate the ecosystem carbon stocks (vegetation and soil), annual net carbon sequestration of vegetation and related environmental factors (soil moisture content, organic matter, total nitrogen, and so on) in two kinds of plantations with a chronosequences of young forests, middle-aged forests, and mature forests of 11, 30 and 45 years old Mongolian pine (Pinus sylvestris var. mongolica) plantation (Ps); 6, 15 and 26 years old Populus × xiaohei plantation (Px) and 28 years old natural Siberian elm (Ulmus pumila) forest (Up) at sand dune sites, and to determine the influencing law and mechanism of forest types and ages on the ecosystem carbon storage.
Result (1) The vegetation carbon storage of Ps and Px increased significantly than Up, which of Ps was the highest among three forest types. Moreover, the vegetation carbon storage of Ps and Px increased with the forest age, but the changing trends of annual net carbon sequestration (ANCS) of vegetation with forest age were different between Ps and Px, the former is young forests > mid-aged forests = mature forests; the latter increased with forest age. (2) In terms of soil carbon sequestration, Px was better than Up, while Ps was less than Up; moreover, the changing law of soil carbon storage with forest age in Ps and Px was also different, increasing first and then stabilizing and increasing, respectively. And both forest types all changed the spatial distribution pattern of soil carbon storage. In the horizontal space, Ps reduced the carbon storage in the upper and lower soil layers, and its soil carbon storage increased with the forest age in the upper soil layer; while Px increased the soil carbon storage in the middle and upper soil layer, and its carbon storage increased with the forest age in the bottom soil layer. In the vertical space, the vertical stratification of soil carbon storage in young forests was evident and tended to weaken in mature forest stage. (3) In terms of ecosystem carbon sequestration, Ps and Px were similar and higher than Up. The ecosystem carbon storage of both Ps and Px increased with stand age. However, the distribution patterns of ecosystem carbon stocks for Ps and Px were mostly dominated by vegetation, which was clearly different from that of Up dominated by soil. (4) The ecosystem carbon storage and ANCS of Ps were mainly controlled by soil total nitrogen. The ecosystem carbon storage and ANCS of Px were mainly controlled by soil organic matter.
Conclusion Therefore, the establishment of Ps and Px could not only fix sand, but also significantly increase forest carbon sink in the temperate Nenjiang Sandy Land, which is dominated by vegetation carbon sequestration. Therefore, in the management of carbon sinks in sandy plantations, it is necessary to strengthen the maintenance of the vegetation carbon pool as well as to focus on the long-term carbon sequestration potential of the soil.