Effect of azolla on CH₄ and N₂O emissions in Fuzhou Plain paddy fields

Azolla is a common aquatic fern that floats in paddy fields. It grows rapidly and has the ability to fix N₂ into the soil. However, the effects of azolla growth on emissions of greenhouse gases are yet uncertain. This study measured CH₄ and N₂O emissions in two paddy fields in Fuzhou Plain, one with floating azolla and the other with non-floating azolla. The purpose of the study was to draw on the benefits of scientific evaluation of emissions of greenhouse gases in China’s paddy fields. The results showed that CH₄ emissions were in the range of 0.19~26.50 mg?m^-2·h^-1 and 1.02~28.02 mg?m^-2·h^-1 and with average values of 9.28 mg?m^-2·h^-1 and 11.66 mg?m^-2·h^-1 in the azolla treatment and non-azolla treatment, respectively. CH₄ emission in azolla plots was significantly lower than that in non-azolla plots at P < 0.01. Peak CH₄ emission in azolla plots was early by about one week compared with non-azolla plots, after which period it decreased rapidly. N₂O emissions were in the range of ?50.11~201.82 μg?m^-2·h^-1 and ?28.93~54.42 μg?m^-2·h^-1 with average values of 40.29 μg?m^-2·h^-1 and 11.93 μg?m^-2·h^-1 in azolla plots and non-azolla plots, respectively. N₂O emission in azolla plots was significantly higher than that in non-azolla plots at P < 0.05. N₂O emission increased rapidly after paddy fields drainage and both plots followed similar trends. Different driving factors of CH₄ and N₂O emissions were noted in azolla and non-azolla plots. A comprehensive consideration of CH₄ and N₂O greenhouse gases showed that CH₄ was the key contributor to greenhouse effects in paddy fields. Azolla reduced integrated greenhouse effects by 17.3% in the humid sub-tropical Fuzhou Plain region.