青海乐都县30a来农田表层土壤有机碳储量变化特征

青海省地处高寒区,近几十年来针对这一区域农田生态系统中土壤有机碳(SOC)库变化及其影响因素的研究较少.研究利用第二次土壤普查数据(1982 年),结合近期(2011 年)重复采集的田间土壤样品,以土壤类型为单元,对县域尺度(青海乐都县)农田表层(0~20 cm)SOC库的时空变化特征进行分析.结果表明:① 乐都县1982 年表层有机碳密度(SOCD)为3.8kg·m^-2,2011 年降低至2.8 kg·m^-2,30 a 间降幅达26%,且呈东北部和南部降低、西北地区增加的趋势;② 乐都县1982 年表层SOC储量1.8×10⁶ t,2011 年1.4×10⁶ t,30 a 间降幅达24%;③ 土壤类型中,草甸土、栗钙土和黑钙土表现为丢碳,速率分别为-137.3、-35.0、-91.0 g C·m^-2·a^-1,潮土和灰钙土表现为固碳,速率分别为9.7、7.3 g C·m^-2·a^-1,且30 a 来各土类SOCD变化率与1982 年SOCD呈负线性相关(y=0.35-0.13x).

Changing Characteristics of Soil Organic Carbon Storage in Cropland in Ledu of Qinghai in Recent 30 Years

The change of soil organic carbon (SOC) pool in cropland ecosystem and its effecting factors were little investigated in the alpine area of Qinghai Province in recent decades. Using soil type as the unit, combining the second soil survey data (1982) and the recent (2011) repeatedly collected soil samplings, the spatio-temporal distribution characteristics of SOC pool at the surface layer (0-20 cm) of cropland ecosystem were studied at a county scale in Qinghai Province. The results clearly showed that, in Ledu County, the SOC density (SOCD) at the surface layer of cropland was 3.8 and 2.8 kg ·m- 2 in 1982 and 2011 respectively. At a county scale, SOCD decreased by 26% during the period from 1982 to 2011, however it only decreased in the northeast and south of the county while increased in the northwest of the county. The SOC storage at surface layer of cropland was 1.8×10⁶ t in 1982 and 1.4×10⁶ t in 2011, decreasing by 24% in recent 30 years. In all soil types, meadow soil, chestnut soil and chernozem soil showed carbon losing at the rates of -137.3, -35.0 and -91.0 g C·m^-2·a^-1 respectively, while fluvo-aquic soil and sierozem soil showed carbon sequestration at the rates of 9.7 and 7.3 g C ·m^-2 ·a^-1 respectively. Furthermore, the changing rates of SOCD in recent 30 years had a negative linear correlation with the SOCD in 1982 (y=0.35-0.13x).