Dynamics of soil and root C stocks following afforestation of croplands with poplars in a semi-arid region in northeast China.

摘要

Background and aims: Afforestation on croplands can help sequester atmospheric CO₂ through increased carbon (C) storage in the soil and vegetation. However, the dynamics of soil organic C (SOC) and root C stocks, particularly those in the deeper soil layers, following afforestation are not well documented for semi-arid regions. The aim of this study was to investigate the dynamics of soil and root C stocks to 1 m depth following afforestation with poplar (Populus x xiaozhuanica W. Y. Hsu & Liang) on croplands at the Keerqin Sandy Lands in northeast China. Methods: Forest floor, root and mineral soil samples were collected from 23 paired plots of poplar plantations with different stand basal areas (SBA, ranging from 0.2 m2ha-1 to 32.6 m2ha-1) and reference croplands using a paired-site design. Changes of SOC concentration and content, and root C content were analyzed using paired t tests, and the relationships between forest floor C content, soil and root Delta _C( Delta _C refers to the difference in C stocks between a poplar plantation and the paired cropland) and SBA were tested with a polynomial regression analysis. Results: Afforestation resulted in linear increases of Delta _Cin the forest floor and 0-10 cm mineral soil with SBA (R2=0.67, p<0.001 and R2=0.34, p=0.003, respectively), but there were no clear relationships between SOC stocks in the soil deeper than 10 cm and SBA. The fine root C stock increased by afforestation across all the soil layers (p<0.05), and root Delta _C had a quadratic curve (the first two mineral soil layers) or linear (the other mineral soil layers) relationship with SBA. About 73% of the variance of Delta _Cin the top soil was explained by changes in the forest floor C stock, but changes in plant derived C stocks did not explain the variance of soil Delta _C in the deeper layers very well. Conclusions: Our study suggest that afforestation increased C sequestration in the forest floor and surface mineral soil, and C stocks in the forest floor and surface mineral soil and roots were strongly controlled by the SBA, which changes with stand development, in the studied semiarid region in northeast China.