Functional differentiation of glomalin-related soil protein fractions reveals dual pathways for carbon storage in...

Contradictory findings in glomalin-related soil protein (GRSP) research have obscured its contribution to soil carbon storage due to treating easily extractable GRSP (EEG) and totally extractable GRSP (TEG) as functionally equivalent. This study resolves this functional ambiguity by investigating differential pathways of GRSP fractions across organic farming durations using structural equation modeling. Results demonstrate that EEG and TEG operate through distinct but complementary mechanisms: EEG primarily facilitates soil aggregation processes that indirectly protect organic carbon, while TEG directly contributes to stable carbon pools as a recalcitrant biochemical reservoir. Prolonged organic farming shifted toward TEG dominance, with EEG/TEG ratios decreasing from 0.26 ± 0.1 to 0.11 ± 0.0 and TEG/SOC ratios doubling from 0.08 ± 0.0 to 0.16 ± 0.0. TEG exhibited exceptionally strong correlation with soil organic carbon (rho = 0.96) compared to EEG (rho = 0.63). Structural equation modeling identified TEG as the strongest predictor of SOC (β = 0.96), while organic farming duration independently promoted EEG production through fungal activity (β = 0.74) and microaggregate formation (β = 0.69). This functional differentiation establishes TEG as a quantitatively significant component comprising up to 16% of soil organic carbon in long-term organic systems, providing a new theoretical framework for optimizing soil carbon sequestration through targeted GRSP management.