Effect Of Harvesting On The Emssion Of N₂O In Temperate Forest Of Northeast China

Nitrous oxide(N₂O) is one of the most important greenhouse gases and forest soil is major source of atmospheric N₂O emission.Harvesting is one of the main modes in forest management.In order to find out the law of N₂O emission in different harvesting methods by the method of static chamber-gas chromatography,the nitrous oxide flux of four different harvesting methods(cropland:farming after clear cutting;afforestation:forestation after clear cutting;50%harvesting;25%harvesting;uncut) was measured in Maoershan of Heilongjiang Province from May to October,2008.The results showed that:Among the growing season,soil N₂O flux showed mulpi-peek volatile in different treatments,the average of N₂O flux in growing season showed:afforestation(12.740μgN·m^-2 h^-1)＞cropland(10.877μgN·m^-2h^-1)＞50%harvesting(4.096μgN·m^-2h^-1)＞25%Harvesting (2.331μg N·m^-2h^-1)＞control(-0.002μgN·m^-2h^-1).There were significant differences among different treatments,the soil N₂O flux was significant effected by different harvesting methods in temperate forest.Among the growing season,there were different dynamic variation of net N mineralazition rates in different treatments.The average of net N mineralazition rate and net nitration rate ranged as follow:afforestation＞cropland＞50%harvesting＞25%Harvesting＞uncut.There were significant differences among different treatments of nitrate nitrogen concentration,but there were no significant differences in ammonium nitrogen concentration. Net N mineralazition rate,net nitration rate,nitrate nitrogen concentration had a significant effect on soil N₂O flux,with a linear relationship between them.Ammonium nitrogen concentration and soil temperature(surface,5cm,10cm and 15cm) all had a little effect on soil N₂O flux,and there were non-linear relationship among them.Soil water rate(0～7.5cm,0～12cm,0～20cm) had a significant effect on soil N₂O flux,with a linear relationship between them.It seemed that soil water rate and soil N₂O flux had a close relationship in the 0～7.5cm soil horizon.It suggests that soil N₂O flux would increased greatly after clear cutting, compared with few emission of secondary forest.Selection cutting with some strength is a better forest cutting method to decrease N₂O emissions.