Decoupling silicate weathering from primary productivity – how ecosystems regulate nutrient uptake along a climate and vegetation gradient

Abstract

In addition to the supply of primary minerals and water flow the presence and growth rate of land plants are thought to drive rock weathering. While doubtlessly plants and their associated below-ground microbiota possess the tools for considerable weathering work, the quantitative evaluation of their impact relative to the common abiogenic weathering 10 processes remains poorly known. Here we report on a strategy to decipher the relative impact of these two drivers. We did so by quantifying weathering rates and nutrient uptake along the "EarthShape" transect in the Chilean Coastal Cordillera where landscapes are subjected to a substantial north to south gradient in precipitation and vegetation growth, whereas rock type is granitoid throughout and tectonic process rates do not differ much along the gradient. We quantified the bio-available fraction of nutritive elements in regolith and we measured 87 Sr/ 86 Sr isotope ratios in the different compartments of the Earth's Critical 15 Zone (bedrock, regolith, bio-available fraction in saprolite and soil, and vegetation) to identify the sources of mineral nutrients to plants. We thereby budgeted inventories, gains, and losses of nutritive elements in and out of these ecosystems, and quantified mineral nutrient recycling. We found that the weathering rates do not increase with precipitation from north to south along the climate gradient. Instead, the simultaneous increase in biomass growth rate is accommodated by faster nutrient recycling. The absence of an increase in weathering rate in spite of a five-fold increase in precipitation leads us to hypothesize 20 that the presence of plants can negatively impact weathering through inducing secondary-mineral formation and by fostering a microbial community that is adapted for nutrient-recycling rather than nutrient-acquisition through weathering.

Plant nutrient mobilization and acquisition strategies: adaptation to water and nutrient availability

“…This is supported by a study of Oeser and Blanckenburg (2020), who examined the same study sites, and found no increase in weathering depths with increasing precipitation. At the same time, net primary productivity, and thus, P demand along the same ecosequence increased strongly from arid to humid ecosystems (Werner et al, 2018).…”