Simulated climate extremes alter dynamics of mineral-organic associations in the rhizosphere

Mineral-organic associations are central to soil carbon persistence and nutrient cycling, yet their vulnerability to climate change remains uncertain. In particular, the mechanisms underlying their formation and disruption in the rhizosphere are insufficiently resolved. Here we examined how anticipated shifts in precipitation influence the disruption and (neo)formation of mineral-organic associations in the wheat rhizosphere, and how mineral crystallinity influences this processes. To investigate this, we conducted a 12‑week pot experiment with winter wheat (Triticum aestivum L.), using agricultural soil amended with mineral-organic associations formed by ¹³C‑labeled microbial necromass adsorbed onto ⁵⁷Fe‑labeled iron oxides of contrasting crystallinity (ferrihydrite vs. goethite). Plants were exposed to three precipitation regimes reflecting projected Central European climate patterns: optimal irrigation compared to intermittent droughts or floodings. Precipitation exerted notable and opposing effects on necromass-ferrihydrite associations: disruption (and subsequent ¹³C mineralization) was reduced under intermittent drought (0.8x), but intensified under intermittent flooding (1.4x) compared with optimal precipitation. Necromass-goethite associations, by contrast, were largely stable across precipitation regimes. ⁵⁷Fe Mössbauer spectroscopy and nanoSIMS imaging revealed Fe mineral transformations, especially under intermittent flooding conditions, and preliminary nanoSIMS data indicate rapid (neo)formation of mineral-organic associations. Together, these findings show that root-driven transformations of mineral-organic associations, particularly those comprised of poorly crystalline mineral phases, are sensitive to changing precipitation patterns, suggesting enhanced vulnerability of this carbon pool under future climate scenarios.