Bioenergetic control of soil carbon dynamics across depth

Area of Science:

• Soil Science
• Biogeochemistry
• Ecology

Background:

• Soil carbon dynamics exhibit a strong depth dependency globally, with slower processes at greater depths.
• The underlying mechanisms controlling this depth-related slowdown are debated, hindering accurate predictions of carbon cycle-climate feedbacks.

Purpose of the Study:

• To elucidate the mechanistic basis for the depth-dependent regulation of soil carbon dynamics.
• To investigate the role of decomposer bioenergetics and root activity in subsoil carbon persistence.

Main Methods:

• Utilized radiocarbon and thermal analyses.
• Conducted long-term soil incubations with 13C/14C-labeled plants.
• Assessed decomposition rates in the presence and absence of root activity.

Main Results:

• Decomposer bioenergetic constraints (low energy density and high activation energy) consistently explain the depth-dependency of soil carbon dynamics.
• Subsoil carbon decomposition is significantly accelerated by root activity (rhizosphere priming), overcoming energy limitations.
• Subsoil carbon persistence is attributed to its low energy quality and limited root-derived energy supply at depth.

Conclusions:

• Decomposer bioenergetics are a primary driver of soil carbon depth-dependency.
• Root exudates can overcome energy limitations, enhancing the decomposition of recalcitrant subsoil carbon.
• Understanding these energy dynamics is crucial for predicting soil carbon storage and climate feedbacks.