Response of mangrove soil respiration to climate change

Mangroves are among the world's most carbon-rich ecosystems. However, the vulnerability of mangrove soil carbon to climate change—whether mangrove carbon stock in the soil will be released into the atmosphere or remained stored in the soil under future climatic conditions—remains unknown.

We conducted an incubation experiment with a fully multifactorial design to improve our understanding of how mangrove soil carbon will respond to climate change drivers. We evaluated how soil respiration responds to i) an extended inundation gradient (0, 2, 6 hours/day) simulating sea level rise and drop and to ii) a temperature increase (27.0°C vs 31.4°C).

The soil CO₂ emission generally increased with a rise in temperature. However, the impact of temperature was variable according to the inundation duration. When the soil was never inundated, the soil CO₂ emission increased by 40% with the rise of temperature , but when the soil was inundated for 2 hours, the emission rose only by 15%, and when inundated for 6 hours, the soil did not emit more CO₂ under warmer temperature. Conversely, the increase of inundation alone did not linearly decrease the soil CO₂ emission. Instead, there was a dichotomy in CO₂ emission between inundated and not-inundated soil—we noted strong CO₂ emission when the soil was not inundated, but no increase with a reduced duration of inundation (2h vs 6h).

These findings show that mangrove soil carbon is likely to be retained in the soil despite the cumulative impacts of sea level rise and temperature increase. However, in case of sea level drop and temperature increase, the carbon stored in the soil is likely to be emitted relatively fast into the atmosphere. Climate change mitigation measures to preserve the soil carbon stock of mangroves should therefore consider regional impact of climate change.