Response Of Natural Abundance Of ¹⁵N In Natural Secondary Forest Dominant Species Aspen And Birch To Nitrogen Addition In Changbai Mountain

Plant and soil nitrogen isotopes can help understand the impact of nitrogen input on ecosystem nitrogen cycle,and the study on the difference of response of different tree species to N addition can help better understand the preference of tree species to N.This study was conducted under the condition of eliminating environmental differences and nitrogen source differences,and the differences between Betula Platyphylline and Populus Davidian,the dominant species in the natural secondary forest of Changbai Mountain,were analyzed in response to N addition.Here are the main results:(1)Under different N supplemental treatments,the?¹⁵N values of poplar leave increased with the increase of N supplemental concentration,and the?¹⁵N values of Betula platyphylline leaves under low N treatment were significantly lower than those under high N treatment(P<0.01).There was no significant difference in the?¹⁵N of poplar core(P>0.05),but the?¹⁵N of Birch core was significantly decreased under low N and high N treatments(P<0.01),and the?¹⁵N of fine roots of poplar was significantly higher under high N treatments than that under low N treatments(P<0.01),but there was no significant difference between the two treatments(P>0.05).?¹⁵N in fine roots of Betula platyphylline increased with N application(P<0.01).(2)There were no significant differences among soil indexes in different soil layers under the same N concentration treatment(P>0.05);The N content in the upper layer(0-10 cm)and the lower layer(10-20 cm)showed a significant decreasing trend(P<0.01),and the?¹⁵N in the upper layer(0-10cm)was significantly lower than that in the lower layer(10-20 cm)(P<0.01).(3)Through the analysis of plant and soil?¹⁵N and enrichment factor,it can be concluded that the plot has not reached nitrogen saturation state.According to the experiment results,different plant tissues may have different degrees of fractionation when they absorb and utilize nitrogen from the soil,resulting in the change of?¹⁵N.It is also affected by plant preference for nitrogen source types.In this study,Betula platyphylline was more likely to absorb ammonium nitrogen,while Populus Himalayan was more likely to absorb nitrate nitrogen.Therefore,the?¹⁵N and N contents of the two species showed significant differences under the same N addiction treatment.