Redmile-Gordon M, Gregory A S, White R P, Watts C W
Environmental Horticulture Department, Royal Horticultural Society, Wisley, GU23 6QB, United Kingdom.
Sustainable Agriculture Sciences Department, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, United Kingdom.
Geoderma. 2020 Apr 1;363:114143. doi: 10.1016/j.geoderma.2019.114143.
While soil microbial ecology, soil organic carbon (SOC) and soil physical quality are widely understood to be interrelated - the underlying drivers of emergent properties, from land management to biochemistry, are hotly debated. Biological binding agents, microbial exudates, or 'extracellular polymeric substances' (EPS) in soil are now receiving increased attention due to several of the existing methodological challenges having been overcome. We applied a recently developed approach to quantify soil EPS, as extracellular protein and extracellular polysaccharide, on the well-characterised soils of the Highfield Experiment, Rothamsted Research, UK. Our aim was to investigate the links between agricultural land use, SOC, transient binding agents known as EPS, and their impacts on soil physical quality (given by mean weight diameter of water stable aggregates; MWD). We compared the legacy effects from long-term previous land-uses (unfertilised grassland, fertilised arable, and fallow) which were established > 50 years prior to investigation, crossed with the same current land-uses established for a duration of only 2.5 years prior to sampling. Continuously fallow and grassland soils represented the poorest and greatest states of structural integrity, respectively. Total SOC and N were found to be affected by both previous and current land-uses, while extractable EPS and MWD were driven primarily by the current land-use. Land-use change between these two extremes (fallow → grass; grass → fallow) resulted in smaller SOC differences (64% increase or 37% loss) compared to MWD (125% increase or 78% loss). SOC concentration correlated well to MWD (adjusted = 0.72) but the greater SOC content from previous grassland was not found to contribute directly to the current stability (p < 0.05). Our work thus supports the view that certain distinct components of SOC, rather than the total pool, have disproportionately important effects on a soil's structural stability. EPS-protein was more closely related to aggregate stability than EPS-polysaccharide ( values of 0.002 and 0.027, respectively), and ranking soils with the 5 greatest concentrations of EPS-protein to their corresponding orders of stability (MWD) resulted in a perfect match. We confirmed that both EPS-protein and EPS-polysaccharide were transient fractions: supporting the founding models for aggregate formation. We suggest that management of transient binding agents such as EPS -as opposed to simply increasing the total SOC content- may be a more feasible strategy to improve soil structural integrity and help achieve environmental objectives.
虽然土壤微生物生态学、土壤有机碳（SOC）和土壤物理质量之间的相互关系已广为人知，但从土地管理到生物化学等新兴特性的潜在驱动因素仍存在激烈争论。由于克服了一些现有的方法学挑战，土壤中的生物粘合剂、微生物分泌物或“细胞外聚合物物质”（EPS）现在受到越来越多的关注。我们采用了一种最近开发的方法，对英国洛桑试验站高田实验中特征明确的土壤中的细胞外蛋白质和细胞外多糖形式的土壤EPS进行了量化。我们的目的是研究农业土地利用、SOC、被称为EPS的瞬时粘合剂之间的联系，以及它们对土壤物理质量的影响（以水稳性团聚体的平均重量直径；MWD表示）。我们比较了调查前50多年建立的长期先前土地利用（未施肥草地、施肥耕地和休耕地）的遗留效应，并与采样前仅2.5年建立的相同当前土地利用进行了交叉比较。连续休耕地和草地土壤分别代表了结构完整性最差和最好的状态。发现总SOC和N受到先前和当前土地利用的影响，而可提取的EPS和MWD主要受当前土地利用的驱动。与MWD（增加125%或减少78%）相比，这两个极端之间的土地利用变化（休耕→草地；草地→休耕）导致SOC差异较小（增加64%或减少37%）。SOC浓度与MWD相关性良好（调整后 = 0.72），但未发现先前草地中较高的SOC含量对当前稳定性有直接贡献（p < 0.05）。因此，我们的工作支持这样一种观点，即SOC的某些特定成分而非总量对土壤结构稳定性具有不成比例的重要影响。EPS - 蛋白质与团聚体稳定性的关系比EPS - 多糖更密切（分别为0.002和0.027），将EPS - 蛋白质浓度最高的5种土壤按其相应的稳定性顺序（MWD）排序，结果完全匹配。我们证实EPS - 蛋白质和EPS - 多糖都是瞬时组分：支持团聚体形成的基础模型。我们建议，管理诸如EPS这样的瞬时粘合剂——而不是简单地增加总SOC含量——可能是改善土壤结构完整性并帮助实现环境目标的更可行策略。
