| Global warming, one of the most important environmental issues, greenhouse gases emission is related with this problem. In recent years, methane as one of the main greenhouse gas its research become a hot topic. In this study, soil methane fluxes were measured by static chamber-gas chromatograph technique from January 2015 to December 2015 in subtropical three forest types （Cunninghamia lanceolata（CL）, Cyclobalanopsis glauca-Lithocarpus glaber（CG） and Pinus massoniana-Lithocarpus glaber（PM））. Related environmental factors were recorded including soil temperature, soil moisture, soil total organic carbon and total nitrogen, soil microbial biomass carbon and nitrogen. Aimed to understand the diurnal and seasonal variations of soil CH4 fluxes in three forest types.Results showed that the soil methane fluxes of three subtropical forest types presented a similar trend in seasonal dynamics and soil sink of CH4 with the highest in summer （July and August） and lower in winter （January-February）. The annual of CH4 fluxes were CL> CG> PM, the average methane flux was -2.01μg/m2·h,-6.45μg/m2·h and -8.59μg/m2·h.These indicated the forests were the sink of methane.Soil methane fluxes in three forest types were significant correlated with soil temperature （soil surface temperature,5cm and 10cm depth soil temperature） （p< 0.01）. Soil methane flux was significant correlated with soil moisture at 5cm depth in CL and PM stands （p<0.05）, with soil moisture at 5cm and 10cm depths in CG. Soil organic carbon and total nitrogen to the three forest types were negatively correlated, with TN in CL （p<0.05）, and with SOC and C/N in CG （p<0.01）, with SOC and soil total nitrogen in PM （p<0.01） were significantly correlated.In the CL the methane daily flux showed:summer<autumn<spring<winter, average of CH4 daily flux was -12.16μg/m2·h,-11.82μg/m2·h,-3.26μg/m2·h, 0.43μg/m2·h, except for winter showed soil methane sinks. The CL forest Soil methane which high fluxes appear in the nighttime and low appear fluxe in daytime in winter and spring, but on the contrary in summer.The law of the autumn is not obvious. In the CG the methane daily flux showe:autumn<summer<spring <winter, average of CH4 daily flux was -20.51μg/m2—h,-12.74μg/m2·h,-7.42μg/m2·h,-0.81μg/m2·h, all for soil methane sinks. Winter and summer diurnal variation exhibits multimodal, no significant changes in the law. In spring and autumn is unimodal or single-valley. In the PM, soil CH4 daily flux showed: autumn<summer<spring<winter, average of CH4 daily flux was-13.97μg/m2·h,-10.27μg/m2·h,-4.86μg/m2·h,-0.46μg/m2·h. In the PM, soil CH4 flux diurnal variation the seasons are roughly unimodal or single-valley. In three forest types daily average of methane flux was less affected by time of day in the forest, while about 10:00 and 24:00 may be the best time for measurement in forest.Soil temperature on CH4 flux diurnal variation showed that:CH4 flux diurnal variation of CL in winter and spring are negatively correlated with temperature, and surface temperature and air temperature in winter was significantly correlated （p <0.05）, in spring the highest correlation with surface temperature （p<0.05）. In the summer, CH4 flux and soil temperature was significantly correlated positively correlated, and the better with 5cm soil temperature（p<0.01）. In the autumn, CH4 flux and soil temperature was significantly correlated negatively,5cm soil temperature and air temperature were the best correlation （p<0.01）. There were no significant for the correlation between CG soil CH4 flux diurnal variation and soil temperature. PM soil CH4 flux diurnal variation similarity between CL in winter, summer and autumn, but soil CH4 flux and surface temperature was positively correlated in spring （p<0.05）.The significant correlation were found between CL with 5cm,10cm soil moisture and soil microbial biomass nitrogen （p<0.05）. CG with 5cm,10cm soil moisture and microbial biomass carbon and nitrogen contents were significantly correlated （p <0.01）. PM with 5cm,10cm soil moisture and soil microbial biomass nitrogen contents were also significantly correlated （p<0.05）.In summary, the temporal and spatial variation of soil CH4 flux of three forest types was due to the integral effects by environmental factors in in subtropical forests Therefore, future research needs to increase observation density, and in combination with other environmental factors influence, enrich and improve the dynamic mechanism of temporal flux of methane in the region. |
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