Soil organic carbon (SOC) stocks and nutrient availability are key indicators of soil quality, and both can be influenced by land‐use change. However, it is still unclear whether the impact of land‐use change on SOC and nutrient stocks differs between ecoregions. Grasslands near the northeast border of the Qinghai‐Tibetan Plateau (QTP) occur across several ecoregions that have recently been subjected to substantial land‐use change. Based on long‐term land‐use history, we conducted a field investigation comparing soil C and nutrient stocks between natural grassland (NGL) and three types of converted grassland (agricultural grassland, AGL; farmland, FL; and abandoned farmland, AFL) in three ecoregions along a climate gradient: alpine meadow, temperate steppe and temperate desert. Compared with NGL, soil C stocks in converted grasslands were 22%–30% lower in the alpine meadow, but 60–82% higher in the temperate steppe and 6%–76% higher in the temperate desert. Converted grasslands also contained higher stocks of available nitrogen and phosphorus than NGL in the temperate steppe and desert. Soils (0–40 cm) in NGL contained 14.8 ± 0.1 kg C m⁻² in alpine meadow, 6.7 ± 0.6 kg C m⁻² in temperate steppe and 1.7 ± 0.3 kg C m⁻² in temperate desert. Together, our results indicate that the responses of soil C and nutrients to grassland conversion differed between ecoregions. Thus, to optimize soil C sequestration rates and overall soil quality, we suggest that land‐use policies in this area should take into account local environmental conditions.

中文翻译：

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西北地区气候梯度下的草地转化：对土壤碳和养分的影响

土壤有机碳（SOC）储量和养分有效性是土壤质量的关键指标，两者都可能受到土地利用变化的影响。但是，目前尚不清楚，不同生态区域之间土地利用变化对有机碳和养分储量的影响是否有所不同。青藏高原（QTP）东北边界附近的草地遍布多个生态区域，这些区域最近发生了土地用途的重大变化。根据长期的土地使用历史，我们在田间进行了田间调查，比较了天然草地（NGL）和三种类型的转化草地（农业草地，AGL；农田，FL；废弃土地，AFL）之间的土壤碳和养分储量沿气候梯度分布的三个生态区域：高山草甸，温带草原和温带沙漠。与NGL相比，高寒草地上转化草地的土壤碳储量降低了22％–30％，而温带草原的土壤碳储量则高60–82％，而温带沙漠的土壤碳储量则高6％–76％。与温带草原和沙漠中的NGL相比，转化后的草原还含有更多的可用氮和磷。NGL中的土壤（0–40 cm）含有14.8±0.1 kg C m^-2在高山草甸，6.7±0.6千克碳米^-2在温带草原和1.7±0.3千克碳米^-2在温带沙漠。总之，我们的结果表明，土壤碳和养分对草地转化的响应在不同的生态区域之间是不同的。因此，为了优化固碳速度和土壤整体质量，我们建议该地区的土地使用政策应考虑当地的环境条件。