Effects Of Different Intensity Of Harvesting On Soil Nitrogen Mineralization In The Temperate Secondary Forest Of Northeast China

Soil nitrogen mineralization is an important process of the forest ecosystem nitrogen cycle.It is important to research the dynamics of soil nitrogen mineralization rate and inorganic nitrogen for understanding forest ecosystem nutrient cycling and productivity.Harvesting is one of the main forest management measures.Different harvesting methods and intensities would have effects on soil nitrogen mineralization progress.In order to understand the effect of harvesting on soil nitrogen mineralization rate,the study employed the resin-core technique,investigated the nitrogen mineralization rate and factors of top soil layer(0-10 cm)after different harvesting densities(afforestation after clear cutting,50%of the stand volume removed,25%of the stand volume removed,control)8 years in secondary forest.Results showed that:1.Harvesting had a significant impact on soil inorganic nitrogen,ammonium nitrogen and nitrate nitrogen concentration.Seasonal average inorganic nitrogen concentration range as follow:25%of the stand volume removed>50%of the stand volume removed>aFForestation after clear cutting>control.Except 25%of the stand volume removed was higher than control significantly(P<0.05),there was no significant difference between the rest harvesting treatments.Seasonal average nitrate nitrogen concentration range as follow:25%of the stand volume removed>afforestation after clear cutting>50%of the stand volume removed>control.Soil nitrate nitrogen concentration of 25%of the stand volume removed and afforestation after clear cutting were higher than control significantly(P<0.05),there was no significant difference between 50%of the stand volume removed and control.Seasonal average ammonium nitrogen concentration range as follow:50%of the stand volume removed>control>25%of the stand volume removed>afforestation after clear cutting.Afforestation after clear cutting was lower than control significantly(P<0.01).There was no significant difference between the rest harvesting treatments.In growing season,the proportion of soil nitrate nitrogen in inorganic nitrogen was ranged from 49.25?81.52%.The proportion of soil nitrate nitrogen in inorganic nitrogen of afforestation after clear cutting was higher than the rest treatments.2.Harvesting have a significant impact on soil net ammonification rate,but not significant on soil net nitrogen mineralization rate and net nitrification rate.Seasonal average soil net ammonification rate range as follow:25%of the stand volume removed>50%of the stand volume removed>control>afforestation after clear cutting.There was no significant difference between each harvesting treatments and control(P>0.05),but afforestation after clear cutting lower than 25%of the stand volume removed significantly(P<0.05).Seasonal average soil net nitrogen mineralization rates range as follow:25%of the stand volume removed>50%of the stand volume removed>afforestation after clear cutting>control.Each harvesting treatments and control were not significantly different(P>0.05).Seasonal average soil net nitrification rates range as follow:afforestation after clear cutting>25%of the stand volume removed>50%of the stand volume removed>control.There was no significant difference between each harvesting treatments and control(P>0.05).3.Soil organic carbon,total nitrogen,water-soluble organic carbon and nitrogen,microbial biomass carbon and nitrogen concentrations of each harvesting treaments were not significantly different compare with control(P>0.05).Soil water-soluble organic carbon was significantly correlated with soil net nitrogen mineralization rates and net nitrification rates(P<0.05),indicating that soil water-soluble organic carbon were important factors for soil nitrogen mineralization progress.Except soil organic carbon and total nitrogen,the indicators of others showed clear seasonal dynamic.4.Harvesting had significant effect on soil water content,but not significant on soil temperature.Seasonal average soil water content range as follow:25%of the stand volume removed>50%of the stand volume removed>afforestation after clear cutting>control.Soil water content of 25%of the stand volume removed was significantly higher than control(P<0.05),but others harvesting treatments did not.Soil water content and temperature were significantly correlated with net nitrogen mineralization rates(P<0.01),indicating that they were important factors for soil nitrogen mineralization rates.