CO2 flux of alfalfa pasture with different ages

Alfalfa pasture with 1, 2, 3, and 5 years was used to determine the effect of ages on CO2 flux of alfalfa pastures by measuring photosynthetic characteristics, soil respiration and net flux of soil organic carbon in the agropastoral ecotone of Northern China. This study indicated that the photosynthetic rate of alfalfa with different ages presented a single peaked curve, and the maximum of which was observed at the flowing stage in the first and the fifth year with the value of 50 and 69 mol/（m2s）, respectively, while it was observed at the podding stage in the second and the third year with the value of 60 and 72 mol/（m2s）, respectively. The photosynthetic rate had no significant correlation to chlorophyll a and chlorophyll b. The soil respiration of alfalfa pasture showed a irregular peak curve, with the minimum value at June and the maximum at July, and followed the pattern with the fifththe thirdthe secondthe first year. The soil respiration of alfalfa pasture was not significantly correlated to soil temperature; however, was significantly correlated the soil moisture (P0.05) except the first year. The net fluxes of soil organic carbon of alfalfa pasture were 3.71, -1.71, 12.17 and 12.53 g/kg in the first, the second, the third, and the fifth year.