Temperature sensitivity of soil organic carbon decomposition responses to warming and elevated CO2 in the tidal marsh ecosystem

Tidal marsh is a large reservoir of soil organic carbon (SOC), considered one of the most efficient natural carbon sinks. However, the future carbon pool of this ecosystem has large variability and uncertainty due to climate change such as temperature rise and elevated atmospheric CO₂ concentration. Microbial-mediated SOC decomposition is a key process that regulates the carbon cycle of tidal marsh. This process is largely temperature-dependent, thus understanding the response of temperature sensitivity (Q10) of SOC decomposition to climate change is critical to improving our prediction capability of the tidal marsh carbon cycle and the climate feedback. However, the response of Q10 of SOC decomposition on climate change in tidal marsh ecosystem is yet to be revealed, hampering our prediction capability of the future tidal marsh carbon cycle. Here, we elucidate the effect of warming and elevated CO₂ concentration on the Q10 of SOC decomposition at a Salt Marsh Accretion Response to Temperature eXperiment (SMARTX). Surface sediments were collected in 2022 (6 years after manipulation started) from ambient, +5.1℃ (W), elevated CO₂ (750ppm, eCO₂), and +5.1℃+elevated CO₂ (W+eCO₂) plots and the Q10 of SOC decomposition was determined. W significantly decreased aerobic SOC decomposition rate most likely due to the labile carbon depletion and thermal adaptation, whereas eCO₂ and W+eCO₂ increased the aerobic decomposition rate at high temperatures (25 and 30℃). Anaerobic SOC decomposition rate was not affected by W whereas eCO₂ and W+eCO₂ significantly increased anaerobic decomposition rate at all temperatures. Q10 of aerobic SOC decomposition was not affected by W whereas eCO₂ and W+eCO₂ significantly increased. Q10 of anaerobic SOC decomposition was not affected by climate change. Overall, our finding demonstrates that elevated CO₂ concentration increases the vulnerability of soil carbon stock to warming in tidal marshes, with implications for modeling the future carbon cycle of the ecosystem.