Zea mays rhizosphere respiration, but not soil organic matter decomposition was stable across a temperature gradient

In a greenhouse experiment, we grew maize plants at different densities. We added fertilizer to half of the pots and created a temperature gradient. After 10 weeks of plant growth, we measured soil CO2 efflux (SCE) and determined rhizosphere respiration (Rrhizo) and the decomposition rate of soil organic matter (RSOM) using the different δ13C of the C3 soil and C4 plants. Whereas Rrhizo remained stable across the temperature gradient, RSOM significantly increased with growth temperature. Neither plant density, nor the fertilizer treatment affected the relation between Rrhizo or RSOM and growth temperature. Although Rrhizo might still increase with temperature in the short term, long term exposure to higher temperatures revealed full thermal acclimation of Rrhizo, but not of RSOM.