On geological timescales, phosphorus is considered to be the ultimate limiting nutrient to primary productivity (Tyrrell, 1999), which is intrinsically linked to organic carbon production and burial, and therefore atmospheric oxygen content (Canfield et al., 2020). Knowing the sources, abundances, and transformations of phosphorus on the early Earth is critical to our understanding of the coevolution of life and its environment.Our knowledge of ancient marine phosphate concentrations (dissolved inorganic phosphate; DIP) principally relies on indirect measurements (e.g., total rock phosphorus abundance, or biomineralization). Marine DIP levels through time are qualitatively recorded by: (a) phosphorites, marine sediments that contain up to 20 wt % P 2 O 5 that require specific redox conditions to form (Kipp et al., 2020;Stüeken et al., 2021), occur infrequently with a record that only extends to ∼2.1 Ga (Planavsky, 2014); (b) biomineralizing organisms that produced their shells from apatite with the first appearance in the rock record at ∼810 Ma (Cohen et al., 2017); (c) P/Fe ratios and phosphate nanoparticles in banded iron formations which punctuate the rock record from ∼3.2 to 1.8 Ga (Bjerrum & Canfield, 2002;Rasmussen et al., 2021) and (d) rare traces of phosphite recorded in Eoarchean carbonate rocks (Pasek et al., 2013). To overcome the temporal limitations of these records, recent research has focused on the bulk phosphorus content of ancient marine mudstones, which are generally ubiquitous in the geologic record. Bulk phosphorus is measured in mudstone as homogenized fluorapatite, iron oxide-sorbed phosphorus

The early‐middle Neoproterozoic is thought to have witnessed significant perturbations to marine P cycling, in turn facilitating the rise of eukaryote‐dominated primary production. However, with few robust constraints on aqueous P concentrations, current understanding of Neoproterozoic P cycling is generally model‐dependent. To provide new geochemical constraints, we combined microanalytical data sets with solid‐state Nuclear Magnetic Resonance, synchrotron‐based X‐ray Absorption Near Edge Structure spectroscopy, and micro‐X‐ray Fluorescence imaging to characterize the speciation and distribution of P in Tonian shallow‐water carbonate rocks. These data reflect shallow water phosphate concentrations 10–100× higher than modern systems, supporting the hypothesis that tectonically‐driven influxes in P periodically initiated kinetically‐controlled CaCO3 deposition, in turn destabilizing marine carbonate chemistry, climate, and nutrient inventories. Alongside these observations, a new compilation and statistical analysis of mudstone geochemistry data indicates that, in parallel, Corg and P burial increased across later Tonian continental margins until becoming decoupled at the close of the Tonian, implicating widespread N‐limitation triggered by increasing atmospheric O2.

Plants rely on potassium for many critical biological processes, but most soils are potassium limited. Moving potassium from the inaccessible, mineral-bound pool to a more bioavailable form is crucial for sustainably increasing local potassium concentrations for plant growth and health. Here, we use a synthetic soil habitat (mineral doped micromodels) to study and directly visualize how the saprotrophic fungus, Fusarium sp. DS 682, weathers K-rich soil minerals. After 30 days of fungal growth, both montmorillonite and illite (secondary clays) had formed as surface coatings on primary K-feldspar, biotite, and kaolinite grains. The distribution of montmorillonite differed depending on the proximity to a carbon source, where montmorillonite was found to be associated with K-feldspar closer to the carbon (C) source, which the fungus was inoculated on, but associated with biotite at greater distances from the C source. The distribution of secondary clays is likely due to a change in the type of fungal exuded organic acids; from citric to tartaric acid dominated production with increasing distance from the C source. Thus, the main control on the ability of Fusarium sp. DS 682 to weather K-feldspar is proximity to a C source to produce citric acid via the TCA cycle.