Effects of frequency and intensity of drying-rewetting cycles on Hydrocotyle vulgaris growth and greenhouse gas emissions from wetland microcosms

Drying-rewetting cycles can affect ecosystem functioning, but little is known about how the interaction between frequency and intensity of drying-rewetting cycles affects greenhouse gas emissions from plant-soil systems. We assembled microcosms initially each having two vegetative individuals (ramets) of a clonal, wetland plant Hydrocotyle vulgaris, and subjected them to three frequencies (6, 9 and 18 cycles with 9, 6 and 3 days per cycle) crossed with three intensities (adding 200, 400 and 600 ml water per cycle) of drying-rewetting cycles for 54 days. Increasing frequency of drying-rewetting cycles significantly increased growth and net photosynthesis rate of H. vulgaris under the lowest intensity of drying-rewetting cycles, but decreased them or had no effect under the two higher intensities. Increasing drying-rewetting frequency significantly increased CO2 emission under the lowest intensity and decreased it under the highest intensity, whereas no effect was found under the intermediate intensity. CO2 emission was positively related to growth of H. vulgaris. Under the lowest intensity CH4 emission was not significantly affected by frequency, but under the two higher intensities it was the highest in the highest frequency. Under the lowest intensity N2O emission was the highest in the highest frequency, but it was not affected by frequency under the two higher intensities. Therefore, frequency and intensity of drying-rewetting cycles can interact to affect greenhouse gas emissions from plant-soil systems. Prolonged drought (low frequency of precipitation) can decrease CO2 emission under a lower amount of precipitation, but promote it under a higher amount of precipitation.