闽江河口湿地土壤CH_4产生与氧化速率对外源氮、硫添加的响应

Effects of nitrogen and sulfate additions on methane production and oxidation in the Min River estuarine marsh

通过室内培养实验,研究了外源氮、硫添加对闽江河口湿地土壤CH_4产生/氧化速率以及土壤理化性质的短期影响。NH_4Cl(N1)和NH_4NO_3(N3)处理在各培养阶段均显著促进土壤CH_4产生速率(P<0.05),较对照分别提高136.70%和136.55%;NH_4Cl+K_2SO_4(NS1)和NH_4NO_3+K_2SO_4(NS3)处理在培养第3、6、12、15和18天均显著促进了CH_4产生速率(P<0.05)。KNO_3(N2)、K_2SO_4(S)处理在不同培养时间对CH_4产生速率影响均不显著(P>0.05);KNO_3+K_2SO_4(NS2)处理除在第21天外(P<0.05),其他时间影响均不显著(P>0.05)。N2、N3、NS2和NS3处理均显著促进了土壤CH_4氧化速率(P<0.05),平均CH4氧化速率较CK分别提高了145.30%、142.93%、139.48%和112.68%。整体而言,不同添加处理并没有显著改变湿地土壤CH_4产生/氧化速率的时间变化规律,各处理均表现为随培养时间先增加而后逐渐降低。短期培养结束后,土壤可溶性有机碳(DOC)、电导率、p H值在不同处理间均不存在显著差异(P>0.05);土壤NH+4-N含量在N1、N3、NS1和NS3处理下,NO_3^--N含量在N2、N3、NS2和NS3处理下,SO_4^(2-)含量在S、NS1、NS2和NS3处理下均显著高于对照处理(P<0.05)。相关分析显示,DOC、铵态氮(NH+4-N)和硝态氮(NO_3^--N)是氮、硫添加处理下影响闽江河口湿地土壤CH_4产生/氧化速率短期变化的主要控制因素。

Methane （CH4） is a major greenhouse gas （GHG）, accounting for approximately 17% of global warming, with a relative global warming potential 34 times more powerful than carbon dioxide （CO2） on a mass basis. Wetland systems are considered to be the largest natural source of CH4 emitted to the atmosphere, with CH4 fluxes determined through analysis the balance of CH4 production by methanogens under anoxic conditions, and CH4 oxidation by methanotrophs under aerobic conditions. Human activities, such as fossil-fuel combustion and nitrogen fertilizer application, have resulted in much higher nitrogen and sulfate loads in wetlands. Although estuarine tidal marshes are important contributors to GHG emissions, the relationships between CH4 production, oxidation, and nitrogen and sulfate enrichment have not been thoroughly investigated in these environments. Using laboratory incubation techniques, the short-term effects of nitrogen and sulfate addition on soil CH4 production and oxidation of the tidal Cyperus malaccensis wetlands of the Min River estuary were measured in July 2015, and the soil physical and chemical properties were examined following nitrogen and sulfate treatments. Under anoxic conditions, CH4 production rates in the NH4Cl （N1） and NH4NO3 （N3） treatments at different stages increased by 136.70% and 136.55%, respectively, which were significantly higher than in the control treatment （P 〈 0.05）. CH4 production rates in soils under the NH4Cl＋K2SO4 （NS1） and NH4NO3＋K2SO4 （NS1） treatments increased after the 3rd, 6th, 12th, 15th, and 18th days following incubation. However, there were no significant differences in the KNO3 （N2）, K2SO4 （S）, and KNO3＋K2SO4 （NS2） treatments compared with the control. Under aerobic conditions, CH4 oxidation rates in the N2, N3, NS2, and NS3 treatments increased by 145.30%, 142.93%, 139.48%, and 112.68%,respectively, compared with the control, whereas CH4 oxidation rates in the N1 and S treatments decreased by 16.54% and 20.99%, respectively, compared to the control treatment, although no significant differences were observed across the treatments. During the incubation period, daily CH4 production and oxidation initially increased with incubation time but then decreased in different nitrogen and sulfate treatments, with the magnitudes of both CH4 production and oxidation exhibiting similar temporal patterns across treatments. There were no significant differences in soil dissolved organic carbon （DOC）, electrical conductivity, and pH among the different treatments （P 〈 0.05） following short-term incubation; however, ammonium nitrogen （NH4＋-N） concentrations increased significantly in the N1, N3, NS1, and NS3 treatments （P 〈 0.05）; nitrate nitrogen （NO3--N） concentrations increased significantly in soils under the N2, N3, NS2, and NS3 （P 〈 0.05）; and sulfate （SO42-） concentrations increased significantly in soils under the S, NS1, NS2, and NS3 treatments （P 〈 0.05）. Correlation analyses indicated that DOC, NH4＋-N, and NO3--N were the main driving factors influencing the production and oxidation of CH4 in the Min River estuary tidal wetlands.