The role of the Earth’s mycelial community and enzyme activity on global atmospheric CO2 and COS budgets

The recent activity of humans has had such a profound impact on the chemistry of the Earth’s atmosphere that ecosystems and societies face a ‘human-induced’ climate crisis.

Given the key role of the biosphere in climate change feedbacks, the Paris Agreement emphasised every effort should now be taken to ensure ecosystems are managed to reduce the growth rate of atmospheric CO2 without altering climate.

However, Land Surface Models (LSM) still lack consensus on critical processes driving the exchange of CO2 between ecosystems and the atmosphere.

Variations in atmospheric carbonyl sulphide (COS) could provide independent constraints on LSM performance at large scales and evidence for the recent ‘CO2 fertilisation’ effect on the biosphere.

Free-Air CO2 Enrichment (FACE) studies also reveal that, as CO2 rises, trees forming symbiotic relationships with ectomycorrhizal (EM) fungi may accumulate biomass more readily than trees in symbiosis with arbuscular mycorrhizal (AM) fungi, especially in nutrient-poor soils. So far, incorporating EM and AM functional traits into LSMs remains a challenge.

Representing key differences in AM and EM plant root and fungal processes in LSMs such as the secretion of acids and enzymes into the soil will be necessary, as they augment organic matter mineralisation and soil weathering, impacting atmospheric CO2, and potentially COS budgets.

Because EM plants tend to grow on acidic soils, EM fungi should express more carbonic anhydrase (CA) an enzyme that helps regulate their internal pH, with repercussions on COS fluxes.

As nitrogen availability inhibits CA activity this may help explain why the growth of EM plants is reduced in acid environments.

COSMYCA will quantify EM and AM fungal CA activity for the first time and characterise mechanistically how CO2 levels and nutrients drive changes in fungal enzyme activity, weathering rates and SOM mineralisation, and their large-scale consequences on the COS and CO2 budgets over the last century.