互花米草入侵盐沼湿地CH4和N2O排放日变化特征研究

甲烷（CH4）和氧化亚氮（N2O）是导致全球气候变暖的2种重要温室气体，探索其源汇及地域排放特征一直是全球变化研究领域的核心内容。CH4和N2O通量的日变化研究是正确估算大时间尺度下CH4和N2O排放量的基础。利用静态箱法原位观测了江苏沿海芦苇（Phragmites australis）、盐蒿（Suada salsa）、光滩、水面以及互花米草（Spartina alterniflora）入侵湿地CH4和N2O排放的日变化特征。结果表明，1）互花米草湿地地上部生物量为1.70 kg·m^-2，土壤有机碳质量分数为13.55 g·kg^-1；分别是芦苇和盐蒿湿地的2.50-3.43和2.15-4.15倍。2）互花米草和芦苇湿地土壤10 cm处氧化还原电位（Eh）有明显日变化，最低值出现在3：00，最高值出现在12：00；光滩和盐蒿湿地没有明显的日变化。3）互花米草湿地 CH4日平均排放通量为0.52 mg·m^-2·h^-1，是其他湿地的2.12-6.40倍；N2O日平均通量为-3.24μg·m^-2·h^-1，显著低于盐蒿湿地、光滩和水面（P＜0.05）。互花米草和芦苇湿地CH4排放通量最高值（0.73 mg·m^-2·h^-1和0.30 mg·m^-2·h^-1）出现在15：00，最低值（0.37 mg·m^-2·h^-1和0.17 mg·m^-2·h^-1）出现在3：00，均与土壤孔隙水中CH4浓度呈显著负相关（P＜0.05）。互花米草湿地CH4排放通量与10 cm土温、Eh和生态系统CO2净交换量（NEE）显著正相关（P＜0.05）。互花米草和芦苇湿地N2O通量9：00-18：00为负值，21：00—6：00为正值，均与NEE呈显著负相关（P＜0.05）。盐蒿湿地、光滩和水面CH4和N2O排放通量没有明显日变化特征。互花米草入侵提高了沿海湿地CH4排放，但降低了N2O排放，植物对CH4传输作用以及向根际传输O2和易分解有机物是导致互花米草和芦苇湿地CH4和N2O排放表现出日变化特征的原因。

Diel Variation of CH4 and N2O Emissions in the Salt Marsh with Spartina alterniflora Invasion

Atmospheric CH4 and N2O are two most potent long-lived greenhouse gases that contribution to global warming. Sources and sinks of CH4 and N2O and the processes driving their spatio-temporal heterogeneity are critically important to global change. Understanding the diel variation in CH4 and N2O emissions is of importance to estimating CH4 and N2O budgets in large spatial and time scales. In this study, diel variations of CH4 and N2O fluxes in coastal salt marsh that invaded by Spartina alterniflora and vegetated with or without native Phragmites australis and Suaeda salsa were measured in site by using static chamber technique. Our results showed that aboveground biomass in S. alterniflora marsh was 1.70 kg·m^-2 and SOC concentration was 13.55 g·kg^-1, which were 2.50-3.43 and 2.15-4.15 times, respectively, those of P. australis and S. salsa marshes. Soil radox potential at 10-cm depth showed apparent diel variations in S. alterniflora and P. australis marshes, which were both highest at 12：00 am and lowest at 3：00 am. However, no significant diel variations of radox potential were found in S. salsa marsh, bare tidal flat and open water. Mean CH4 flux was 0.52 mg·m^-2·h^-1 in S. alterniflora marsh, which was 2.14-6.40 times those in other sites. Mean N2O flux was-3.24 μg·m^-2·h^-1 in S. alterniflora marsh and was significantly lower than those in S. salsa marsh, tidal flat and open water. CH4 fluxes peaked at 0.73 and 0.30 mg·m^-2·h^-1 at 15：00 and showed the lowest of 0.37 and 0.17 mg·m^-2·h^-1 at 3：00 in S. alterniflora and P. australis marshes, respectively. CH4 fluxes were negatively （P〈0.05） correlated with porewater CH4 concentrations in S. alterniflora and P. australis marshes and it was positively （P〈0.05） correlated with soil temperature and redox potential at 10 cm and net ecosystem CO2 exchange （NEE） in S. alterniflora marsh. N2O fluxes were negative at 9：00-18：00 and positive at 21：00~6：00 and were negatively correlated with NEE in S. alterniflora and P. austr