The role of forest trees and their mycorrhizal fungi in carbonate weathering and phosphorus biogeochemical cycling

• Main Author: Thorley, Rachel Marianne Sarah
• Format: Thesis
• Language: English
• Published: University of Sheffield 2017
• Subjects: Ocean acidification
• Online Access: https://etheses.whiterose.ac.uk/15945/; https://etheses.whiterose.ac.uk/15945/1/Rachel%20Thorley%20-%20Thesis.pdf

Over millions of years, atmospheric CO2 concentrations, and Earth’s climate, are regulated by continental silicate weathering and associated marine carbonate deposition. On this geological timescale, carbonate weathering has no net effect on CO2 drawdown. However, over the coming decades-to-centuries, accelerated weathering of carbonate rocks may provide a sink for anthropogenic CO2 emissions and increase alkalinity flux to the oceans to counteract ocean acidification. Recent experimental evidence strongly supports trees and their associated mycorrhizal fungi as key drivers of silicate mineral weathering; however, their role in the context of carbonate weathering is largely unknown. Carbonate lithology is abundant globally and underlies many boreal and temperate forest ecosystems in the northern hemisphere. If biological enhancement of carbonate weathering by forests occurs, this might presents a new opportunity for CO2 sequestration. This thesis presents results from a 14-month field experiment at the UK's national pinetum investigating carbonate rock weathering under a common climate. Overall, I find original evidence for biotic enhancement of calcite- and dolomite weathering by an evolutionary diverse range of trees that host either arbuscular (AM) or ectomycorrhizal (EM) root-associating fungal symbionts. Recent soil analyses are integrated with a re-interpretation of historic data to provide an 85-year record of in-situ soil development under different forestry species. This study challenges the classic dogma that divergence of properties is driven by the major tree functional groups, angiosperms and gymnosperms. Instead, we find that over decades, mycorrhizal functional type plays a dominant role in determining soil physico- chemical characteristics, and conditions generated by EM fungi are likely to enhance mineral weathering. Field trials next investigated the impact of tree-mycorrhizal functional group on weathering of the four main carbonate rock types (chalk, limestone, marble and dolomite) and a ...