Abstract Accurate assessments of soil organic carbon (SOC) stocks are needed at multiple scales given their importance to both local soil health and global C cycles. Rangelands cover 54% of California, representing a large stock of SOC, but existing SOC estimates are uncertain. To improve understanding of fine-resolution SOC stocks in complex terrain and provide guidance to rangeland SOC inventories, we grid-sampled 105 locations (21-m grid cells) at two depths (0–10 and 10–30 cm) in a 10-ha annual grassland catchment in California’s Central Coast Range. Soils were analyzed for bulk density, coarse fragments, SOC and texture. Monthly aerial imagery was acquired by an unmanned aerial vehicle to compare surface reflectance during two contrasting years (wet vs. dry) to SOC stocks. We found that the 0–30 cm soil thickness held 3.64 ± 0.71 kg SOC m−2 (mean ± SD) with a range of 1.97–5.49 kg SOC m−2. The 0–10 cm soil thickness stored 47% of the 0–30 cm SOC stock with SOC concentrations twice as high in the 0–10 cm layer (1.40 ± 0.38%) as in the 10–30 cm layer (0.71 ± 0.15% SOC). Multiple linear regression (MLR) models explained 50–57% of SOC variability at 0–30 and 10–30 cm, but only 25% of variability at 0–10 cm. Based on cross-validation tests, MLR outperformed spatial interpolation methods and Random Forest models, best explaining SOC stocks with five environmental covariates: wet-year greenness, mean curvature, elevation, insolation, and slope. Lower hillslope positions, concave landforms, and enhanced wet-year greenness were associated with more SOC, and explained 11%, 24%, and 31% of variability in 0–30 cm SOC stocks, respectively. This study demonstrates that the accuracy of regional-scale SOC mapping of California rangelands benefits from considering microclimatic and topographic controls at the catchment-scale, in addition to broader scale mineralogical and macroclimatic controls identified in previous SOC studies.

中文翻译：

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地形属性和牧草生产力预测流域规模的土壤有机碳储量

摘要 鉴于土壤有机碳 (SOC) 储量对当地土壤健康和全球碳循环的重要性，需要在多个尺度上对其进行准确评估。牧场覆盖了加利福尼亚州的 54%，代表了大量的 SOC 存量，但现有的 SOC 估计值不确定。为了提高对复杂地形中精细分辨率 SOC 储量的理解并为牧场 SOC 清单提供指导，我们在 10-2 米的两个深度（0-10 和 10-30 厘米）对 105 个位置（21 米网格单元）进行网格采样。加利福尼亚州中央海岸山脉一年一度的草原集水区。对土壤的容重、粗碎片、SOC 和质地进行了分析。无人机每月获取航拍图像，以比较两个对比年份（湿与干）的表面反射率与 SOC 储量。我们发现 0-30 厘米的土壤厚度保持在 3.64 ± 0。71 kg SOC m-2（平均值 ± SD），范围为 1.97–5.49 kg SOC m-2。0-10 厘米土壤厚度储存了 47% 的 0-30 厘米 SOC 储量，其中 0-10 厘米层 (1.40 ± 0.38%) 的 SOC 浓度是 10-30 厘米层 (0.71 ± 0.15%) 的两倍SOC)。多元线性回归 (MLR) 模型解释了 0-30 和 10-30 厘米处 50-57% 的 SOC 变异性，但仅解释了 0-10 厘米处 25% 的变异性。基于交叉验证测试，MLR 优于空间插值方法和随机森林模型，最好用五个环境协变量解释 SOC 储量：湿年绿度、平均曲率、海拔、日照和坡度。较低的山坡位置、凹形地貌和湿润年绿度增强与更多的 SOC 相关，并分别解释了 0-30 cm SOC 储量的 11%、24% 和 31%。