Biotically-mediated weathering helps to shape Earth’s surface. For example, plants expend carbon (C) to mobilize nutrients in forms whose relative abundances vary with depth. It thus is likely that trees’ nutrient acquisition strategies—their investment in rooting systems and exudates—may function differently following disturbance-induced changes in depth of rooting zones and soil nutrient stocks. These changes may persist across centuries. We test the hypothesis that plant C allocation for nutrient acquisition is depth dependent as a function of rooting system development and relative abundances of organic vs. mineral nutrient stocks. We further posit that patterns of belowground C allocation to nutrient acquisition reveal anthropogenic signatures through many decades of forest regeneration. To test this idea, we examined fine root abundances and rooting system C in organic acid exudates and exo-enzymes in tandem with depth distributions of organically- and mineral-bound P stocks. Our design permitted us to estimate C tradeoffs between organic vs. mineral nutrient benefits in paired forests with many similar aboveground traits but different ages: post-agricultural mixed-pine forests and older reference hardwoods. Fine roots were more abundant throughout the upper 2 m in reference forest soils than in regenerating stands. Rooting systems in all forests exhibited depth-dependent C allocations to nutrient acquisition reflecting relative abundances of organic vs. mineral bound P stocks. Further, organic vs. mineral stocks underwent redistribution with historic land use, producing distinct ecosystem nutritional economies. In reference forests, rooting systems are allocating C to relatively deep fine roots and low-C exudation strategies that can increase mobility of mineral-bound P stocks. Regenerating forests exhibit relatively shallower fine root distributions and more diverse exudation strategies reflecting more variable nutrient stocks. We observed these disparities in rooting systems’ depth and nutritional mechanisms even though the regenerating forests have attained aboveground biomass stocks similar to those in reference hardwood forests. These distinctions offer plausible belowground mechanisms for observations of continued C sink strength in relatively old forests, and have implications for soil C fates and soil development on timescales relevant to human lifetimes. As such, depth-dependent nutrient returns on plant C investments represent a subtle but consequential signal of the Anthropocene.

中文翻译：

---

再生根系及其功能的持久人为遗产结构深度依赖性

生物介导的风化作用有助于塑造地球表面。例如，植物消耗碳 (C) 以调动相对丰度随深度变化的形式的养分。因此，树木的养分获取策略——它们对生根系统和渗出物的投资——可能会随着干扰引起的生根区深度和土壤养分储量的变化而发挥不同的作用。这些变化可能会持续几个世纪。我们检验了以下假设：用于养分获取的植物 C 分配是深度依赖的，它是根系发育和有机与矿物营养库相对丰度的函数。我们进一步假设，通过数十年的森林更新，地下碳分配到养分获取的模式揭示了人为特征。为了测试这个想法，我们检查了有机酸分泌物和外酶中的细根丰度和生根系统 C，以及有机和矿物结合的 P 库的深度分布。我们的设计使我们能够估计具有许多相似地上特征但不同年龄的成对森林中有机与矿物营养益处之间的 C 权衡：后农业混合松林和较老的参考硬木。与再生林相比，参考森林土壤上层 2 m 处的细根更丰富。所有森林中的生根系统都表现出与深度相关的 C 分配到养分获取，反映了有机与矿物结合 P 库的相对丰度。此外，有机与矿物资源随着历史土地利用进行了重新分配，产生了不同的生态系统营养经济。在参考森林中，生根系统正在将 C 分配到相对较深的细根和低 C 渗出策略，这些策略可以增加矿物结合 P 库的流动性。再生林表现出相对较浅的细根分布和更多样化的渗出策略，反映了更多可变的营养储备。我们观察到这些在生根系统深度和营养机制方面的差异，即使再生林的地上生物量储量与参考阔叶林相似。这些区别为观察相对古老的森林中持续的碳汇强度提供了合理的地下机制，并对与人类寿命相关的时间尺度上的土壤碳命运和土壤发展产生影响。因此，