Soil organic carbon sequestration potential and constraints in arid farmland under climate change: Evaluation based...

Agricultural soils are major global carbon repositories and exhibit considerable potential for soil organic carbon (SOC) sequestration. However, slight climatic variations in these soils can induce significant greenhouse gas emissions. Arid and semi-arid farmlands are especially prone to such impacts within agricultural landscapes due to extreme climatic conditions and minimal organic matter contributions. Nevertheless, the dynamics of SOC reserves and their potential for sequestration under shifting climatic regimes in these drylands remains insufficiently elucidated. In this study, the RothC carbon turnover model was calibrated to simulate the spatiotemporal trajectories of SOC stocks from 2000 to 2020 under farmland expansion conditions. The analysis further assessed the potential for SOC sequestration potential under three climate change scenarios and sustainable soil-management (SSM) practices. Key constraints to SOC sequestration potential were identified, and the practical challenges confronting agricultural production in China's arid regions were examined in the context of achieving national carbon neutrality goals by 2060. The analysis reveals the mean SOC decreased from 24.14 Mg C/ha in 2000 to 22.70 Mg C/ha in 2020. The overall SOC stock increased by merely 0.49 Tg despite the cropland expansion of 2,541,900 ha. Under the combined influences of the SSP5-5.8 climate scenario and SSM practices, the projected SOC sequestration potential during 2021-2060, relative to 2020, averaged -0.263, -0.2617, -0.2601, and -0.2569 Mg C/ha/yr, corresponding to scenarios of carbon input being Business-as-usual (BAU) and 5%, 10%, and 20% increases, respectively. Under the SSP1-1.9 and SSP2-4.5 climate scenarios, the potential for SOC sequestration increased. However, this did not translate into net SOC sequestration potential under the assumed 20% carbon input scenario. This finding suggests that in arid agricultural areas, the role of soil organic carbon management may be more about mitigating carbon loss than achieving net carbon gains. Nevertheless, agricultural soils in Xinjiang retain significant sequestration capacity, with SOC saturation ratios remaining below 0.5 across the region and displaying pronounced spatial patterns. By 2060, under the SSP5-5.8 scenario, maintaining a "4‰" (4 per 1000) SOC stock level will require 60% carbon input. Even under the SSP1-1.9 scenario, 25% input will still be necessary. Temperature and precipitation are the primary drivers of this outcome. On average, temperature, precipitation, and carbon input contribute 49%, 37%, and 14% respectively to SOC sequestration potential. In localized areas, the contribution of the carbon input factor increases. These findings significantly enhance the understanding of SOC dynamics and sequestration potential in arid and semi-arid agroecosystems under prospective climate scenarios and offer empirical evidence to inform regional policy formulation.