Impact of Enhanced Rock Weathering on Soil Organic Carbon Dynamics through Microbial Activity

Abstract

Enhanced Rock Weathering (ERW) is a method for capturing carbon dioxide from the atmosphere and turning it into inorganic carbon, which is then stored in soil or oceans. While ERW is typically acclaimed for its influence on inorganic carbon cycling, its interactions with soil organic carbon (SOC) - mainly formed through biological processes like plant and microbial activity - are less explored. This study aims to investigate the impact of ERW application on SOC dynamics, particularly through modifications in microbial activity. We tested two hypotheses: (1) The change in soil pH and micro-nutrient levels by ERW amendments could boost soil microbial activity, which then accelerate breakdown of easily decomposable SOC, and 2) Higher labile SOC content could increase SOC stabilization within soil aggregates or bound to minerals, which further contribute to an increase in long lasting SOC stock by ERW. In this study, to analyze SOC dynamics under the influence of ERW, we applied olivine, a common ERW material, to soil and conducted a four-month pot experiment with alfalfa. After experiment, soil samples from each pot were analyzed using size and density fractionation to distinguish SOC into four forms: light fraction carbon (LFC), particulate organic carbon in macroaggregates (Macro_oPOC), particulate organic carbon in microaggregates (Micro_oPOC), and mineral-associated organic carbon (MAOC). Additionally, to assess microbial activity, we measured microbial biomass carbon (MBC), extracellular enzyme activities (three hydrolases and two oxidases) associated with C decomposition, and glomalin-related soil protein (GRSP), thus providing insights into microbial processes influenced by ERW. As a result, the increased soil pH and supply of minerals from ERW are expected to boost microbial activities, potentially leading to a higher rate of labile SOC decomposition. This could result in decreases in LFC and Macro_oPOC and increases in both Micro_oPOC and MAOC. This research underscores the multifaceted role of ERW in carbon management strategies, demonstrating its potential not only in mitigating climate change through inorganic carbon sequestration but also in influencing SOC sequestration.