Composted manure and green waste amendments have been shown to increase net carbon (C) sequestration in rangeland soils and have been proposed as a means to help lower atmospheric CO₂ concentrations. However, the effect of climate change on soil organic C (SOC) stocks and greenhouse gas emissions in rangelands is not well understood, and the viability of climate change mitigation strategies under future conditions is even less certain. We used a process-based biogeochemical model (DayCent) at a daily time step to explore the long-term effects of potential future climate changes on C and greenhouse gas dynamics in annual grassland ecosystems. We then used the model to explore how the same ecosystems might respond to climate change following compost amendments to soils and determined the long-term viability of net SOC sequestration under changing climates. We simulated net primary productivity (NPP), SOC, and greenhouse gas fluxes across seven California annual grasslands with and without compost amendments. We drove the DayCent simulations with field data and with site-specific daily climate data from two Earth system models (CanESM2 and HadGEM-ES) and two representative concentration pathways (RCP4.5 and RCP8.5) through 2100. NPP and SOC stocks in unamended and amended ecosystems were surprisingly insensitive to projected climate changes. A one-time amendment of compost to rangeland acted as a slow-release organic fertilizer and increased NPP by up to 390–814 kg C ha⁻¹ year⁻¹ across sites. The amendment effect on NPP was not sensitive to Earth system model or emissions scenario and endured through the end of the century. Net SOC sequestration amounted to 1.96 ± 0.02 Mg C ha⁻¹ relative to unamended soils at the maximum amendment effect. Averaged across sites and scenarios, SOC sequestration peaked 22 ± 1 years after amendment and declined but remained positive throughout the century. Though compost stimulated nitrous oxide (N₂O) emissions, the cumulative net emissions (in CO₂ equivalents) due to compost were far less than the amount of SOC sequestered. Compost amendments resulted in a net climate benefit of 69.6 ± 0.5 Tg CO₂e 20 ± 1 years after amendment if applied to similar ecosystems across the state, amounting to 39% of California's rangeland. These results suggest that the biogeochemical benefits of a single amendment of compost to rangelands in California are insensitive to climate change and could contribute to decadal-scale climate change mitigation goals alongside emissions reductions.

中文翻译：

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未来气候下一年生草地的气候变化减缓潜力

堆肥肥料和绿色废物改良剂已被证明可以增加牧场土壤中的净碳 (C) 封存，并已被提议作为帮助降低大气中 CO _{2的一种手段}浓度。然而，气候变化对牧场土壤有机碳 (SOC) 储量和温室气体排放的影响尚不清楚，气候变化减缓策略在未来条件下的可行性更不确定。我们在每天的时间步长中使用基于过程的生物地球化学模型 (DayCent) 来探索未来潜在气候变化对年度草地生态系统中 C 和温室气体动态的长期影响。然后，我们使用该模型探索相同的生态系统在对土壤进行堆肥改良后如何应对气候变化，并确定了在不断变化的气候下净 SOC 封存的长期可行性。我们模拟了加州七个一年生草地的净初级生产力 (NPP)、SOC 和温室气体通量，其中有和没有堆肥改良。我们使用来自两个地球系统模型（CanESM2 和 HadGEM-ES）和两个代表性浓度路径（RCP4.5 和 RCP8.5）的实地数据和特定地点的每日气候数据来驱动 DayCent 模拟到 2100 年。NPP 和 SOC 库存未经修正和修正的生态系统对预计的气候变化出奇地不敏感。一次性改良牧场堆肥作为缓释有机肥，使 NPP 增加高达 390–814 kg C ha⁻¹ 年⁻¹跨站点。修正案对 NPP 的影响对地球系统模型或排放情景不敏感，并持续到本世纪末。在最大改良效果下，相对于未改良土壤，净 SOC 封存量为 1.96 ± 0.02 Mg C ha ^{-1 。}对不同地点和情景进行平均，SOC 封存在修正后 22 ± 1 年达到峰值，然后下降，但在整个世纪保持正值。尽管堆肥刺激了一氧化二氮 (N ₂ O) 排放，但由于堆肥造成的累积净排放量（以 CO ₂当量计）远低于隔离的 SOC 量。堆肥改良带来的净气候效益为 69.6 ± 0.5 Tg CO ₂e 如果适用于全州类似的生态系统，修正后 20 ± 1 年，相当于加州牧场的 39%。这些结果表明，对加利福尼亚州牧场进行单一堆肥改良的生物地球化学效益对气候变化不敏感，并且可能有助于实现年代际尺度的气候变化减缓目标以及减排目标。