Effects Of Nitrogen Deposition And Phosphorus Addition On Photosynthesis Of Chinese Fir

In this paper,10-year-old Chinese fir was used to study the effects of simulated nitrogen（N）deposition and phosphorus（P）addition on ecological stoichiometry and Non-structure carbohydrate（NSC）.We designed nine different treatments,including low N treatment(N30:30kg·hm^-2·a^-1),high N treatment(N60:60 kg·hm^-2·a^-1),low P treatment(P20:20 mg·kg^-1),high P treatment(P40:40 mg·kg^-1),and four combination treatments（N30+P20,N30+P40,N60+P20,and N60+P40）and a control（CK）.Our results showed:（1）P addition alone had no effect on leaf carbon（C）,N,P concentrations and the ratio of C:N,C:P,and N:P in summer.Leaf N concentration and N:P significantly increased after N addition（P<0.05）,but leaf C and P concentrations did not significantly change（P>0.05）.（2）In autumn,leaf N and P concentrations and the ratio of N:P increased first and then decreased with the increase of P addition alone（P<0.05）,while leaf C concentration and the ratios of C:N and C:P exhibited opposite trend（P<0.05）.Nitrogen addition significantly increased leaf N and P concentrations but decreased leaf C concentration and ratios of N:P and C:P（P<0.05）indicating that N deposition decreased the nutrient utilization efficiency of Chinese fir under P stress.（3）In winter,leaf N and P concentrations decreased and the ratio of C:P increased with the increase of P addition alone（P<0.05）.However,under the simulated nitrogen deposition,the leaf P concentration and C:P increased significantly with P addition.（4）In spring,leaf N and P concentrations increased and the ratio of C:P decreased with the increase of P addition alone（P<0.05）.Nitrogen addition significantly increased ratios of C:P with P addition（P<0.05）.（5）In autumn and winter,The effect of low phosphorus stress was more severely than nitrogen stress with the growth of Chinese fir,while the spring and summer exhibited opposite.（6）P addition alone had positive effect on leaf starch concentrations in spring.Nitrogen addition significantly increased leaf starch concentrations with P addition（P<0.05）.The leaf starch concentrations in spring and autumn was higher than starch concentrations in summer and winter.（7）Nitrogen addition significantly decreased leaf soluble sugar concentrations in autumn（P<0.05）,but nitrogen addition significantly increased leaf soluble sugar concentrations with P addition（P<0.05）.（8）Nitrogen addition significantly decreased leaf non-structure carbohydrate（NSC）concentrations in autumn（P<0.05）,but nitrogen addition significantly increased leaf NSC concentrations with P addition（P<0.05）.Leaf NSC concentrations in summer was the minimum value all the year round.The interactive effects of N deposition and P addition on C,N,P concentrations and ratios of C:P,C:N,N:P in Chinese fir leaves changed with treatment time.According to our study,the nutrient limitation of young Chinese fir varies with season,which provides a scientific basis for the precision fertilization of Chinese fir.The leaf NSC concentration responded to simulated nitrogen deposition more than phosphorus addition.The level of leaf NSC concentrations was generally stable.In summer,increased precipitation led to decreased leaf NSC concentrations.