Abstract. A substantial carbon (C) debt has been accrued due to long-term cropping for global food production emitting carbon dioxide from soil. However, the factors regulating the persistence of soil organic C (SOC) remain unclear, with this hindering our ability to develop effective land management strategies to sequester organic C in soil. Using a Ferralsol from semi-arid subtropical Australia, alteration of bulk C contents and fractions due to long-term land use change (up to 72 years) was examined with a focus on understanding whether SOC lost due to cropping could be restored by subsequent conversion back to pasture or plantation. It was found that use of soil from cropping for 72 years resulted in the loss of >70 % of both C and N contents. Although conversion of cropped soil to pasture or plantation for up to 39 years resulted in an increase in both C and N, the C contents of all soil fractions were not restored to the original values observed under remnant vegetation. The loss of C with cropping was most pronounced from the particulate organic matter fraction, whilst in contrast, the portion of the C that bound strongly to the soil mineral particles (i.e. the mineral-associated fraction) was most resilient. Indeed, aliphatic C was enriched in the fine fraction of mineral-associated organic matter (<53 µm). Our findings were further confirmed using Synchrotron-based micro-spectroscopic analyses of intact microaggregates, which highlighted that binding of C to soil mineral particles is critical to SOC persistence in disturbed soil. The results of the present study extend our conceptual understanding of C dynamics and behaviour at the fine scale where C is stabilized and accrued, but it is clear that restoring C in soils in semi-arid landscapes of subtropical regions poses a challenge.

中文翻译：

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土地利用和管理对亚热带铁拉索尔土壤有机碳行为和持久性的影响


摘要。由于全球粮食生产的长期种植从土壤中排放二氧化碳，积累了大量碳（C）债务。然而，调节土壤有机碳（SOC）持久性的因素仍不清楚，这阻碍了我们制定有效的土地管理策略以封存土壤中有机碳的能力。使用来自半干旱亚热带澳大利亚的铁拉尔索尔，检查了由于长期土地利用变化（长达 72 年）引起的大量碳含量和分数的变化，重点是了解因种植而造成的 SOC 损失是否可以通过后续转换来恢复回到牧场或种植园。研究发现，使用耕作土壤 72 年导致碳和氮含量损失超过 70%。尽管耕作土壤转变为牧场或种植园长达 39 年导致碳和氮含量增加，但所有土壤部分的碳含量并未恢复到残余植被下观察到的原始值。耕作过程中碳的损失最明显的是颗粒有机物部分，而相比之下，与土壤矿物颗粒（即矿物相关部分）牢固结合的碳部分最具弹性。事实上，脂肪族碳富含于与矿物相关的有机质的细小部分（<53μm）中。我们的研究结果通过对完整微团聚体进行基于同步加速器的微光谱分析得到了进一步证实，这强调了 C 与土壤矿物颗粒的结合对于扰动土壤中 SOC 的持久性至关重要。 本研究的结果扩展了我们对碳稳定和累积的精细尺度上碳动态和行为的概念理解，但很明显，恢复亚热带地区半干旱景观土壤中的碳提出了挑战。