SOIL ORGANIC C IN LATOSSOLOS_RS_BRAZIL

Approximately 5% of the total Brazilian GHG emissions (0.11 Gt CO₂ and GWP-AR5) originate in the<i> Planalto </i>of Rio Grande do Sul state (RS), a representative agricultural region in Southern Brazil. This study aimed to assess SOCS (soil organic C stocks) in Oxisols (Latossolos) of the Planalto, with up-to-date data obtained from recent field campaigns and legacy data, and relate these SOC stocks to environmental variables. A literature search identified 195 documents with SOCS in layers 0-30 cm and 0-100 cm. The mean SOCS (0-30 cm) in the Latossolos was significantly higher (73,6 Mg ha^-1) than the suggested IPCC default (55 Mg ha^-1). The highest stocks (237 ±39 Mg ha^-1) were measured in uncultivated Latossolos Brunos in the 0-100 cm layer. The most frequently occurring soil Latossolo Vermelho distroférrico-LVdf (25% of the Planalto), also had high SOCS. Surprisingly Latossolos Vermelho Distrófico (LVd) also had high SOCS, in spite of the coarser texture. The estimated SOCS in Latosoolos of the Planalto is 419,9 Tg C, 36% larger than reported previous studies. We concluded that, despite significant land use changes, soils of this region maintain large SOCS which had been underestimated in previous studies.巴西总温室气体（Greenhouse Gas, GHG）排放中约5%（合0.11十亿吨二氧化碳，采用第五次评估报告全球变暖潜势（GWP-AR5）核算）源自南里奥格兰德州（简称RS）的高原地带（Planalto），该区域是巴西南部极具代表性的农业产区。本研究旨在评估该高原地带老成土（Oxisols，又称Latossolos）的土壤有机碳储量（soil organic C stocks, SOCS），所用数据涵盖近期野外调查获取的最新实测资料与历史留存数据，并将上述土壤有机碳储量与各类环境变量进行关联分析。通过系统文献检索，共筛选出195篇涉及0-30 cm及0-100 cm土层土壤有机碳储量的研究文献。该区域老成土0-30 cm土层的平均土壤有机碳储量为73.6 Mg ha⁻¹，显著高于政府间气候变化专门委员会（Intergovernmental Panel on Climate Change, IPCC）推荐的默认值（55 Mg ha⁻¹）。在0-100 cm土层中，未耕作的暗棕色老成土（Latossolos Brunos）的碳储量最高，达237±39 Mg ha⁻¹。分布占比最高的暗红铁质老成土（Latossolo Vermelho distroférrico-LVdf，占高原地带总面积的25%）同样拥有较高的土壤有机碳储量。令人意外的是，尽管 dystric 红色老成土（Latossolos Vermelho Distrófico, LVd）质地偏粗，其土壤有机碳储量依然处于较高水平。经估算，该高原地带老成土的总土壤有机碳储量为419.9 Tg C，较此前已有研究的报道结果高出36%。本研究最终得出结论：尽管该区域土地利用方式发生了显著变化，其土壤仍保有大量土壤有机碳储量，而这一情况在既往研究中被低估了。