Moisture Fluctuations Modulate Abiotic and Biotic Limitations of H-2 Soil Uptake

Soil uptake by H-2-oxidizing bacteria is the main sink of the global hydrogen cycle, accounting for nearly 80% of the atmospheric H-2 consumption. Although the H-2 uptake is strongly influenced by soil moisture, little attention has been paid to coherently couple the water and hydrogen dynamics in soils. Toward this goal, we improve the mechanistic representation of the H-2 uptake as a function of soil moisture and highlight the role of the moisture temporal fluctuations on the biotic consumption of H-2. The results show that, due to the strongly nonlinear relationship between soil moisture and H-2 uptake, addressing the dry-wet sequences is necessary to characterize the H-2 uptake in semi-arid regions correctly. From novel analytical relationships validated with field data, we also infer the biotic and abiotic limitations in the global soil H-2 uptake. It is shown that, diffusion generally limits the uptake in humid temperate and tropical regions, while biotic limitations tend to occur in very arid or cold soils. Finally, we discuss the implications that climate change may have on the H-2 soil sink.