Due to the geographical expanse of grasslands with depleted organic matter stocks, there has been growing interest in the management of these ecosystems for C sequestration to help mitigate climate change. It is generally accepted that management practices intending to increase forage production (e.g. decreasing grazing density) result in increased soil C stocks by increasing the return of biomass inputs to the soil organic carbon (SOC) pool. However, the contribution of C inputs to stable SOC versus GHG losses, and how this is affected by soil properties, remains largely unknown, particularly within subtropical biomes. To investigate the role of soil texture and mineralogy on SOC stabilisation, we identified three different soil types with varying physical properties in close proximity (< 2 km 2 ) to each other. We used isotopically labelled plant material ( 13 C), placed on the soil surface versus incorporated within the mineral soil, to trace the fate of fresh residue inputs into SOM fractions that differed in their degree of protection and mechanistic interactions with the soil matrix. Weekly GHG measurements (CO 2 , N 2 O and CH 4 ) were taken to understand the overall GHG balance resulting from C inputs (i.e. SOC accrual versus GHG losses in CO 2 equivalents). In finer textured soils with a greater smectite content, SOC accrual was greater but was significantly outweighed by GHG losses, primarily from native SOC priming. The incorporation of residue within the soil increased residue-derived SOC accrual by 4- to 5-fold, whilst also suppressing the priming of native SOC. This improved understanding of how soil texture and residue placement affect the global warming mitigation potential of subtropical grassland soils will be important in determining identifiable regions that should be targeted for SOC restoration efforts by increasing C inputs.

中文翻译：

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来自地上输入的“新”SOC 稳定与由土壤类型和残留物放置决定的天然碳启动之间的权衡

由于草原地域辽阔，有机质储备枯竭，人们对管理这些生态系统以固碳来帮助缓解气候变化越来越感兴趣。人们普遍认为，旨在增加牧草产量（例如降低放牧密度）的管理做法会通过增加生物量输入到土壤有机碳 (SOC) 库的回报来增加土壤碳储量。然而，碳输入对稳定 SOC 与 GHG 损失的贡献，以及这如何受土壤性质的影响，在很大程度上仍然未知，尤其是在亚热带生物群落中。为了研究土壤质地和矿物学对 SOC 稳定的作用，我们确定了三种不同的土壤类型，它们彼此靠近（< 2 km 2 ）具有不同的物理特性。我们使用同位素标记的植物材料 ( 13 C) ，放置在土壤表面而不是掺入矿质土壤中，以追踪新鲜残留物输入到 SOM 部分的命运，这些部分的保护程度和与土壤基质的机械相互作用不同。每周进行一次 GHG 测量（CO 2 、N 2 O 和 CH 4 ）以了解 C 输入导致的总体 GHG 平衡（即 SOC 应计与 CO 2 当量中的温室气体损失）。在具有更高蒙脱石含量的质地更细的土壤中，SOC 增加量更大，但被温室气体损失显着超过，主要来自天然 SOC 引发。土壤中残留物的加入使残留物衍生的 SOC 增加了 4 到 5 倍，同时也抑制了天然 SOC 的启动。