State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China; University of Chinese Academy of Sciences, Beijing 100049, China.
State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
Sci Total Environ. 2018 May 15;624:1478-1487. doi: 10.1016/j.scitotenv.2017.12.254. Epub 2017 Dec 27.
The grasslands of northern China store a large amount of soil organic carbon (SOC), and the small changes in SOC stock could significantly affect the regional C cycle. However, recent estimates of SOC changes in this region are highly controversial. In this study, we examined the changes in the SOC density (SOCD) in the upper 30cm of the grasslands of northern China between the 1980s and 2000s, using an improved approach that integrates field-based measurements into machine learning algorithms (artificial neural network (ANN) and random forest (RF)). The RF-generated SOCD averaged 5.55kgCm in the 1980s and 5.53kgCm in the 2000s, and the change ranged from -0.17 to 0.22kgCm at the 95% confidence level, suggesting that the overall SOCD did not vary significantly during the study period. However, the change in SOCD exhibited large regional variability; the topsoil of the Inner Mongolian grasslands experienced significant C loss (4.86 vs. 4.33kgCm), while that of the Xinjiang grasslands exhibited an accumulation of C (5.55 vs. 6.46kgCm). Furthermore, the topsoil C in the Tibetan alpine grasslands remained relatively stable (6.12 vs. 6.06kgCm). A comparison of the different grassland types indicated that SOCD significantly decreased in typical steppe, whereas it increased in mountain meadow, and remained stable in the other grasslands (alpine meadow, alpine steppe, mountain steppe and desert steppe). Climate change could partly explain the changes in the SOCD of the different grassland types. Increases in precipitation could lead to SOC accumulation in temperate grasslands and SOC loss in alpine grasslands, while climate warming is likely to cause SOC loss in temperate grasslands. Overall, our study suggests that the grasslands of northern China remained a neutral SOC sink between the 1980s and 2000s.
中国北方草原储存了大量的土壤有机碳（SOC），SOC 储量的微小变化可能会显著影响区域碳循环。然而，该地区 SOC 变化的最新估计存在很大争议。在本研究中，我们使用一种将基于实地测量的方法集成到机器学习算法（人工神经网络（ANN）和随机森林（RF））中的改进方法，研究了中国北方草原上 30cm 土层中 SOC 密度（SOCD）在 20 世纪 80 年代至 2000 年代之间的变化。RF 生成的 SOCD 在 20 世纪 80 年代的平均值为 5.55kgCm，在 2000 年代的平均值为 5.53kgCm，在 95%置信水平下的变化范围为-0.17 至 0.22kgCm，表明研究期间 SOCD 总体没有显著变化。然而，SOCD 的变化表现出很大的区域变异性；内蒙古草原的表土经历了显著的 C 损失（4.86 与 4.33kgCm），而新疆草原的 C 则有所积累（5.55 与 6.46kgCm）。此外，青藏高原草原的表土 C 相对稳定（6.12 与 6.06kgCm）。不同草原类型的比较表明，典型草原的 SOCD 显著下降，而山地草甸的 SOCD 增加，其他草原（高山草甸、高山草原、山地草原和荒漠草原）的 SOCD 保持稳定。气候变化可以部分解释不同草原类型 SOCD 的变化。降水增加可能导致温带草原 SOC 积累和高山草原 SOC 损失，而气候变暖可能导致温带草原 SOC 损失。总体而言，我们的研究表明，中国北方草原在 20 世纪 80 年代至 2000 年代期间仍然是一个中性 SOC 汇。
