| Due to the induction of global warming and population growth,nitrogen deposition has become one of the major global problems,so it will have a significant impact on the composition and operation of ecosystems and will also bring environmental pressures on forest ecosystems.This paper selects five main forest plants in two forest types（evergreen broad-leaved forest and bamboo and broad-leaved mixed forest）in Yangjifeng National Nature Reserve in Jiangxi Province,Castanopsis eyrei（Ce.）,Quercus glauca（Qg.）,Schima superba（Ss.）,Albizzia julibrissin（Aj.）and Eurya muricate（Em.）were used as research objects,three N treatment gradients were set:control treatment(CK:0 kg?hm-2?a-1),low nitrogen treatment(LN:50kg?hm-2?a-1),high nitrogen treatment(GN:100 kg?hm-2?a-1).Taking the effect of N addition on the phenotypic characteristics and nutrient characteristics of leaves of 5 major forest plants as the starting point,the effects of N on the photosynthetic characteristics and anatomical structure of plant leaves were studied,and the leaf morphology and physiological and ecological characteristics of the main forest plants on different N addition processing response mechanism.This study helps us understand the feedback mechanisms of dominant species in subtropical regions on future environmental changes,and provides theoretical support for the study of regional scientific forestry and ecological construction.The main conclusions are as follows:（1）N addition had significant effects on leaf area（LA）,specific leaf area（SLA）,and leaf relative water content（LRWC）of the phenotypic traits of major forest plants（P<0.05）,but had no significant effect on leaf dry matter content（LDMC）（P>0.05）.Significant differences in LA,SLA and LDMC of major forest plants among tree species（P<0.05）.In evergreen broad-leaved forests,the LA of five tree species was significantly reduced after N addition（P<0.05）;the changes in SLA of Ss.,Aj.,and Em.were consistent,all reaching the maximum at LN and then at GN decreased;LRWC of Ce.,Ss.and Em.decreased significantly after N addition（P<0.05）.In the bamboo and broad-leaved mixed forest,the LA of Ce.and Ss.significantly decreased under GN treatment（P<0.05）;the SLA of Ce.,Qg.and Aj.increased significantly under LN treatment（P<0.05）;the LRWC of Ce.,Aj.and Em.was significantly reduced in GN treatment（P<0.05）.It shows that the response of five plants to N addition varies with species,and there is not consistent regularity.（2）The N addition had significant effects on the nutrient and stoichiometric indicators of the main forest plants except for the C:P ratio（C/P）（P<0.05）.The differences in nutrient and stoichiometric indicators of the main forest plants were significant differences among tree species（P<0.05）.In evergreen broad-leaved forests,the leaf nitrogen content（LNC）of Ce.,Ss.,Aj.,and Em.was significantly reduced during GN treatment（P<0.05）;C:N ratio（C/N）of Ce.and Aj.significantly increased under GN treatment（P<0.05）,C/N of Ss.and Em.decreased significantly under LN treatment（P<0.05）;N:P ratio（N/P）of Ce.,Ss.and Em.was significantly increased in the N addition（P<0.05）.In bamboo and broad-leaved mixed forest,the LNC of Ce.,Ss.and Aj.were significantly reduced after N addition（P<0.05）;the C/N of Ce.,Ss.and Em.decreased significantly under GN treatment（P<0.05）;N/P of Ce.,Qg.,Ss.and Em.significantly increased after N addition（P<0.05）.The five plants in this study adopted different leaf nutrient strategies to deal with the effects of N addition on plant leaves.（3）The N addition significantly affected the photosynthetic characteristics of the main forest plants（P<0.05）.The photosynthetic characteristics of the main forest plants had significant differences among tree species（P<0.05）.In evergreen broad-leaved forests,the photosynthetic rate（Pn）of Ce.and Ss.significantly increased under LN treatment（P<0.05）;the transpiration rates（Tr）of Ss.and Aj.significantly increased after N addition（P<0.05）;the stomatal conductance（Gs）of Ce.,Qg.and Ss.increased significantly after N addition（P<0.05）;the intercellular CO2 concentration（Ci）of Qg.,Aj.and Em.increased significantly after N addition（P<0.05）;the water use efficiency（WUE）of Ce.,Aj.and Em.was significantly reduced under GN treatment.In bamboo and broad-leaved mixed forest,the Pn of Ss.and Em.significantly increased when nitrogen was applied（P<0.05）;the Tr of Ss.,Aj.and Em.increased significantly after N addition（P<0.05）;Gs of Ce.and Ss.increased significantly after N addition;Ci of Qg.and Aj.significantly increased after N addition（P<0.05）;WUE of Qg.,Ss.and Aj.decreased significantly after N addition（P<0.05）.It shows that the appropriate amount of N addition is beneficial to enhance the Pn,Tr,Gs and Ci of the main forest plant leaves,but it will reduce the WUE of the plant leaves.（4）The N addition significantly affected the lower epidermis thickness（LET）,palisade tissue thickness（Pt）,spongy tissue thickness（St）,and leaf thickness（LT）of the anatomical structure of the leaves of major forest plants（P<0.05）,not significant effect on upper epidermis thickness（UET）（P>0.05）.The indexes of main forest plant leaf anatomical structure were significantly different among tree species（P<0.05）.In the evergreen broad-leaved forest,the LET of Qg.increased significantly during N addition treatment,while the LET of Aj.and Em.decreased significantly（P<0.05）;Pt of Qg.and Em.increased significantly after N addition,the Pt of Ce.and Ss.significantly decreased during GN treatment（P<0.05）;the St of Ce.,Qg.,and Em.increased significantly after N addition（P<0.05）;the LT of five tree species increased significantly after N addition（P<0.05）.In bamboo and broad-leaved mixed forest,the LET of Ss.and Aj.increased significantly after N addition（P<0.05）;the Pt of Ss.,Aj.,and Em.reached their maximum values after LN treatment and then GN treatment decreased（P<0.05）;St of Ce.,Ss.,Aj.,and Em.significantly increased after N addition（P<0.05）;LT in Qg.and Em.were significantly increased when treated with GN decrease（P<0.05）.It shows that the addition of N promoted the change of the internal structure of the main forest plants.In summary,the five forest plants mainly respond to the effects of N addition by changing their photosynthetic characteristics and anatomical structure.The appropriate amount of N addition will increase the photosynthetic efficiency of forest plants and change their anatomical structure,thereby promoting plant growth.In future studies,a large-scale internal response mechanism of leaf traits of major forest plants to N addition should be constructed. |
