| In this paper, eddy covariance method was used to monitor carbon flux in north subtropical secondary oak forest of Yangtze River Delta Urban Forest Ecosystem Research Station, which is located in Xiashu forest farm, Jiangsu Province. The carbon flux data and daily meteorological data was collected from January,2010 to December,2010 in this area. After meticulous processing and analysis, the results were showed as bellow:(1) The average CO2 flux above crown canopy in January and February were 0.004622mg/(m2-s) and 0.079421mg/(m2·s). And the average CO2 flux from March to December were between-0.21388mg/(m2·s) and -0.03458 mg/(m2·s). The oak forest became the strongest carbon sink in July, while it came to weak gradually. The tendency of CO2 flux monthly variations were affected by CO2 flux in the daytime, while its CO2 flux was bigger in the daytime than in the evening. Monthly variations of Le in experimental plot were like a single-peak curve. The max Le of February was 385.4087W/m2, while it was the lowest in the year. Le was steady duaring March to June, and it became the highest in August, while the Le was 804.1308 W/m2. And then, Le was reducing gradually. H showed the tend of raising in the first and falling at the last. The average H of June and July were 525.2621W/m2 and 510.3394W/m2. The monthly variation of SHFLUX showed a trough-prak curve. The amplitude range of autumn and winter was between-20W/m2 and 30W/m2, while it ranged from-10W/m2 to 10W/m2 from March to August.(2)T The daily variation of PAR above the crown canopy of the oak forest showed a single unimodal curve. PAR reached the largest value in August 1098.94μmol/(m2·s). However it was below 7μmol/(m2·s) in the morning and evening. The average daily range of Tair above the crown canopy was from 3.99℃to 5.81℃. While the average daily range of Ts basic maintenanced at 1℃. The precipitation days of 2010 were 88d, and the forest rainfall of the year reached 650.9mm, while summer accounted for 42% and 63.0%. VPD raised from January, and it reached peak value 27.72hPa, and then it fell. Hs raised from January, and it reached peak value 22.36%, and then it fell. Wind speed of oak forest was greater in winter than in other seasons. Wind speed became greater in the daytime, and became weak in the evening. In the first half of the evening, wind speed was weaker than the other time in the evening. Leading wind direction of spring and summer was SSE. However, it changed to NNE in autumn and winter.(3) The response equation of Fc and PAR was that, Fc=-0.2985Ln(PAR)+1.5429, very significant. The correlationship of daily carbon fluxes and PAR is significant. Fc and Tair were linear correlation, and the response equation was Fc=-0.0083Tair+0.0375, very significant. Fc and Ts were logarithmic correlation, and the response equation was Fc=-0.097Ln(Ts)+0.1408, very significant. The correlationship of Fc and SHFLUX was Fc=-0.097Ln(Ts)+0.1408, more significant. The variation of Fc with Hs was not obvious. Fc and Ts were logarithmic correlation, but they were poor fit. In the whole, PAR and Tair were the leading factors affecting Fc above the crown canopy of north subtropical secondary oak forest. |
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