Will elevated CO2 enhance mineral bioavailability in wetland ecosystems? Evidence from a rice ecosystem

Mineral cycling plays a critical role in wetland ecosystem functions and can be affected by environmental changes, such as CO2 enrichment. Learning the responses of mineral bioavailability in wetlands to elevated CO2 under field conditions will provide enormous benefits to the assessment of climate change impacts on wetland ecosystems. A free-air CO2 enrichment (FACE) experiment was conducted in a rice ecosystem in Jiangsu, China, with two nitrogen (N) application levels. Responses of K, Ca, Mg, Fe, Mn, Zn, and Si in this ecosystem were investigated in situ. CO2 enrichment increased rice biomass Ca, Mg, Fe, Mn, Zn, and Si regardless of N application levels. Dissolved mineral contents in surface water and available mineral contents in the 0-15 cm soil layer were higher in the FACE plots than in the ambient under both N levels. Elevated CO2 reduced the pH values of the 0-15 cm soil layer and surface water, but increased the cation exchange capacity of the soil layer. The effects of N treatment and its interaction with CO2 enrichment were mostly insignificant on the above parameters. Our results indicate that CO2 enrichment can enhance mineral bioavailability in a rice ecosystem through accelerating mineral transformation from the bio-inactive reservoirs to the bioactive ones.