Evolutionary rise of deep-rooting forests and enhanced chemical weathering: Quantitative investigations into the current paradigm

树木和深根系统的共同进化和地理分布被广泛认为是全球变化的“泥盆纪引擎”，推动了土壤矿物的风化和元素的地球化学循环，对地球大气中的CO2历史产生了重大影响。如果正确的话，这种范式表明，在泥盆纪（4.18 - 3.6亿年前），森林生态系统的进化外观构成了地球化学碳循环的单一最重要的生物反馈，在整个5.4亿年的时间里出现的浮世绘。至关重要的是，树木的进化进程与其对古土壤的地球化学影响之间尚未建立联系。其中一个影响另一个的直接证据仍在等待，主要是因为迄今为止缺乏跨学科的调查。我们的建议解决了这个高层次的“地球系统科学”的挑战。其总体目标是提供一个机制的理解，如何进化的深腐森林的崛起加剧风化和成土作用，构成了长期的C-周期的主要生物反馈。我们的中心假设是，树木的进化进步留下的地球化学效应在古土壤中检测到的森林生态系统的数量和深度的化学能量通过根，菌根真菌和凋落物输送到土壤中。这加剧了土壤酸化，增加了同位素和元素富集的强度在表层土壤层，增强了风化的钙硅和钙磷矿物，和成壤粘土的形成，导致长期封存大气中的二氧化碳通过形成海洋碳酸盐与释放的陆地钙。我们将调查这一研究假设，通过获得和分析保存完好的古土壤剖面从时间序列的地方在北美东部通过关键的志留-泥盆纪间隔，代表地球的过渡到一个森林覆盖的星球。这些古土壤序列将进行有针对性的地球化学，粘土矿物学和古生物学分析。这将允许，第一次，生根结构的混合和单种中泥盆世森林直接链接到古土壤风化剖面通过钻孔复制未风化的配置文件。这些森林的风化将与“对照情况”进行比较-前林风化，早期维管陆地植物与小型/浅生根系统志留纪和下泥盆世的地方。这些网站为我们提供了以前未开发的能力，在关键的志留-泥盆纪间隔的植物-根-土壤关系的演变特征，同时控制古地理和古土壤发育的影响。针对元素和同位素进行地球化学分析，这些元素和同位素被树木强烈地集中在当代土壤的表面，并通过森林下的矿物风化而显示出丰度的重大变化，这为解决和重建森林生态系统演变的不同阶段的风化和成土作用的强度和深度提供了一个强有力的新战略。该项目的重点是“提高当前对生命进化与地球相互作用的认识”，这是NERC地球系统科学主题中的三大高层次挑战之一。

The co-evolution and geographical spread of trees and deep-rooting systems is widely proposed to represent the 'Devonian engine' of global change that drove the weathering of soil minerals and biogeochemical cycling of elements to exert a major influence on the Earth's atmospheric CO2 history. If correct, this paradigm suggests the evolutionary appearance of forested ecosystems through the Devonian (418-360 Myr ago) constitutes the single most important biotic feedback on the geochemical carbon cycle to emerge during the entire 540 Myr duration of the Phanaerozoic. Crucially, no link has yet been established between the evolutionary advance of trees and their geochemical impacts on palaeosols. Direct evidence that one has affected the other is still awaited, largely because of the lack of cross-disciplinary investigations to date.Our proposal addresses this high level 'earth system science' challenge. The overarching objective is to provide a mechanistic understanding of how the evolutionary rise of deep-rotting forests intensified weathering and pedogenesis that constitute the primary biotic feedbacks on the long-term C-cycle. Our central hypothesis is that the evolutionary advance of trees left geochemical effects detectable in palaeosols as forested ecosystems increased the quantity and depth of chemical energy transported into the soil through roots, mycorrhizal fungi and litter. This intensified soil acidification, increased the strength of isotopic and elemental enrichment in surface soil horizons, enhanced the weathering of Ca-Si and Ca-P minerals, and the formation of pedogenic clays, leading to long-term sequestration of atmospheric CO2 through the formation of marine carbonates with the liberated terrestrial Ca. We will investigate this research hypothesis by obtaining and analysing well-preserved palaeosol profiles from a time sequence of localities in the eastern North America through the critical Silurian-Devonian interval that represents Earth's transition to a forested planet. These palaeosol sequences will then be subjected to targeted geochemical, clay mineralogical and palaeontological analyses. This will allow, for the first time, the rooting structures of mixed and monospecific Mid-Devonian forests to be directly linked to palaeosol weathering profiles obtained by drilling replicate unweathered profiles. Weathering by these forests will be compared with the 'control case' - weathering by pre-forest, early vascular land plants with diminutive/shallow rooting systems from Silurian and lower Devonian localities. These sites afford us the previously unexploited ability to characterize the evolution of plant-root-soil relationships during the critical Silurian-Devonian interval, whilst at the same time controlling for the effects of palaeogeography and provenance on palaeosol development. Applying geochemical analyses targeted at elements and isotopes that are strongly concentrated by trees at the surface of contemporary soils, and which show major changes in abundance through mineral weathering under forests, provides a powerful new strategy to resolve and reconstruct the intensity and depth of weathering and pedogenesis at different stages in the evolution of forested ecosystems. The project is tightly focused on "improving current knowledge of the interaction between the evolution of life and the Earth", which represents one of the three high level challenges within NERC's Earth System Science Theme.