Soils form the skin of the Earth’s surface, regulating water and biogeochemical cycles and generating production of food, timber, and textiles around the world. Changes in soil and its ability to perform a range of processes have important implications for Earth system function, especially in the critical zone (CZ)—the area that extends from the top of the canopy to the bottom of groundwater and that harbors most of Earth’s biosphere. A key aspect of the way soil functions results from its structure, defined as the size, shape, and arrangement of soil particles and pores. The network of pores provides storage space for at least a quarter of Earth’s biodiversity, while the abundance, size and connectivity of the pore space regulates fluxes of heat, water, nutrients and gases that define the physical and chemical environment. Here we review the nature of soil structure, focusing on its co-evolution with the plants and microbes that live within the soil, and the degree to which these processes have been incorporated into flow and transport models. Though it is well known that soil structure can change with wetting and drying events, often oscillating seasonally, the dynamic nature of soil structure that we discuss is a systematic shift that results in changes in its hydro-bio-geochemical function over decades to centuries, timescales over which major changes in carbon and nutrient cycles have been observed in the Anthropocene. We argue that the variable nature of soil structure, and its dynamics, need to be better understood and captured by land surface and ecosystem models, which currently describe soil structure as static. We further argue that modelers and empiricists both are well-poised to quantify and incorporate these dynamics into their studies. From these efforts, four fundamental questions emerge: 1) How do rates of soil aggregate formation and collapse, and their overall arrangements, interact in the Anthropocene to regulate CZ functioning from soil particle to continental scales? 2) How do alterations in rooting-depth distributions in the Anthropocene influence pore structure to control hydrological partitioning, biogeochemical transformations and fluxes, exchanges of energy and carbon with the atmosphere and climate, regolith weathering, and thus regulation of CZ functioning? 3) How does changing microbial functioning in a high CO₂, warmer world with shifting precipitation patterns influence soil organic carbon dynamics and void-aggregate profile dynamics? 4) How deeply does human influence in the Anthropocene propagate into the subsurface, how does this depth relate to profile structure, and how does this alter the rate at which the CZ develops? The United Nations has recently recognized that 33% of the Earth's soils are already degraded and over 90% could become degraded by 2050. This recognition highlights the importance of addressing these proposed questions, which will promote a predictive understanding of soil structure.

土壤形成地球表面的表皮，调节水和生物地球化学循环，并在世界各地生产食物、木材和纺织品。土壤的变化及其执行一系列过程的能力对地球系统功能具有重要意义，尤其是在临界区 (CZ)——从冠层顶部延伸到地下水底部并容纳地球大部分生物圈. 土壤功能的一个关键方面来自其结构，定义为土壤颗粒和孔隙的大小、形状和排列。孔隙网络为地球上至少四分之一的生物多样性提供了存储空间，而孔隙空间的丰度、大小和连通性调节了定义物理和化学环境的热量、水、营养物质和气体的通量。在这里，我们回顾了土壤结构的性质，重点是它与植物和微生物的共同进化。生活在土壤中的物质，以及这些过程被纳入流动和运输模型的程度。虽然众所周知，土壤结构会随着干湿事件发生变化，通常会随季节发生波动，但我们讨论的土壤结构的动态性质是一种系统性转变，导致其水生生物地球化学功能在数十年到数百年间发生变化，在人类世中观察到碳和养分循环发生重大变化的时间尺度。我们认为，目前将土壤结构描述为静态的地表和生态系统模型需要更好地理解和捕捉土壤结构的可变性质及其动态。我们进一步认为，建模者和经验主义者都准备好量化这些动态并将其纳入他们的研究中。1)在人类世中，土壤团聚体形成和坍塌的速度及其总体安排如何相互作用，以调节从土壤颗粒到大陆尺度的 CZ 功能？2) 人类世生根深度分布的改变如何影响孔隙结构以控制水文分区、生物地球化学转化和通量、能量和碳与大气和气候的交换、风化层风化，从而调节 CZ 功能？3) 在高 CO ₂ 、气候变暖、降水模式不断变化的世界中，微生物功能的变化如何影响土壤有机碳动态和空隙聚合剖面动态？4) 人类对人类世的影响传播到地下有多深，这个深度与剖面结构有什么关系，这如何改变 CZ 的发展速度？联合国最近认识到，地球上 33% 的土壤已经退化，到 2050 年超过 90% 可能会退化。这一认识凸显了解决这些拟议问题的重要性，这将促进对土壤结构的预测性理解。