Biological enhancement of mineral weathering by <i>Pinus sylvestris</i> seedlings – effects of plants, ectomycorrhizal fungi, and elevated CO<sub>2</sub>

Abstract

<p><strong>Abstract.</strong> Better understanding and quantifying the relative influence of plants, associated mycorrhizal fungi, and abiotic factors such as elevated CO<sub>2</sub> on biotic weathering is essential to constraining weathering estimates. We employed a column microcosm system to examine the effects of elevated CO<sub>2</sub> and <i>Pinus sylvestris</i> seedlings, with or without the ectomycorrhizal fungi <i>Piloderma fallax</i> and <i>Suillus variegatus</i>, on rhizosphere soil solution concentrations of low molecular weight organic acids (LMWOA) and weathering of primary minerals. Seedlings significantly increased mineral weathering, as estimated from elemental budgets of Ca, K, Mg, and Si. Elevated CO<sub>2</sub> increased plant growth and LMWOA concentrations, but had no effect on weathering. Colonization by ectomycorrhizal fungi, particularly <i>P. fallax</i>, showed some tendency to increase weathering. LMWOA concentrations correlated with seedling biomass across both CO<sub>2</sub> and mycorrhizal treatments, but not with total weathering. We conclude that nutrient uptake, which reduces transport limitation to weathering, is the primary mechanism by which plants enhanced weathering in this system. While the experimental system used departs from conditions in forest soils in a number of ways, these results are in line with weathering studies performed at the ecosystem, macrocosm, and microcosm scale, indicating that nutrient uptake by plants and microbes is an important biological mechanism by which mineral weathering is enhanced.</p>

Nano- to Global-Scale Uncertainties in Terrestrial Enhanced Weathering

“…Evidence of "active" weathering by most biological components of soil systems (which is particularly relevant to EW), including vascular plants, 80 fungi, 81,82 bacteria, 83 and some animals, 84 is well established (see e.g. Rosenstock et al 85 for a review), in particular for EW-relevant minerals. 86−90 More work, however, is needed to precisely understand and quantify these processes.…”

“…Evidence of “active” weathering by most biological components of soil systems (which is particularly relevant to EW), including vascular plants, fungi, , bacteria, and some animals, is well established (see e.g. Rosenstock et al for a review), in particular for EW-relevant minerals. − More work, however, is needed to precisely understand and quantify these processes. For instance, whether this weathering-enhancing trend can be generalized is not clear. , Additionally, while both plants and microorganisms can independently affect mineral dissolution rates, they can also cooperate in the rhizosphere, where plants can retribute microbial communities (mostly mycorrhizal symbiotic fungal partners and possibly associated mycorrhizal helper bacteria) with compounds derived from photosynthesis in exchange for enhanced water and nutrient acquisition in the soil microenvironments. − These complex interactions are not fully understood and remain challenging to model.…”

The advancing mycelial frontier of ectomycorrhizal fungi

“…Over the past decade our ability to characterize soil fungal communities has dramatically increased with the development and widespread implementation of metabarcoding approaches with high‐throughput sequencing (Lindahl et al ., 2013; Nguyen et al ., 2015). While this approach is regularly applied to soil and root systems to characterize ectomycorrhizal fungal communities, it has less commonly been applied to in‐growth bags to understand the contribution of individual taxa to EMM dynamics (Wallander et al ., 2010; Phillips, et al ., 2014; Hagenbo et al ., 2018; Rosenstock et al ., 2019). Furthermore, most studies use fungal biomarkers (e.g.…”