Effects of nitrogen addition on foliar traits of the dominant tree species in two subtropical evergreen forests in eastern China
Authors: Zhao Changti , Lin Quanhong , Tian Di 
Published: March 2022

&lt;p&gt;As important components of leaf economic spectrum&amp;#160;(LES), specific leaf area (SLA), chlorophyll (Chl) content, and foliar nutrient content&amp;#160;are crucial plant functional traits (PFT) and essential parameters in most earth system models. Among those, SLA, Chl, foliar carbon (C), nitrogen (N), phosphorus (P) content&amp;#160;and their stoichiometry are key indicators&amp;#160;which are frequently focused on due to their application in predicting vegetation dynamics and ecosystem productivity in response to anthropogenic perturbations, especially atmospheric N deposition increase. With the hotspot of global N deposition transferred to subtropical and tropical regions, how forest ecosystem changes in these ecoregions response to N deposition has attracted great attention during the past decades. Hence, we established a network of nutrient enrichment experiments in eastern China's forests (NEECF) for exploring the effects of N deposition in 2010.&lt;/p&gt;&lt;p&gt;To evaluate the effect of long-term N&amp;#160;addition&amp;#160;on foliar&amp;#160;traits, we conducted field sampling of the dominant tree species (i.e., &lt;em&gt;Castanopsis eyrie &lt;/em&gt;and&lt;em&gt;&amp;#160;Castanopsis sclerophylla&lt;/em&gt;) in two subtropical forests on the platform of NEECF in August, 2020. 100 kg N ha&lt;sup&gt;-1&lt;/sup&gt;&amp;#160;yr&lt;sup&gt;-1&lt;/sup&gt;&amp;#160;were&lt;sup&gt;&amp;#160;&lt;/sup&gt;applied in each forest with 3 replications of plots, respectively.&amp;#160;The adults and seedlings of the two dominant species were sampled to make a contrast. Through the subsequent detection and analysis, we found that: (1)&amp;#160;leaf-trait syndrome of the dominant&amp;#160;species in two subtropical forests&amp;#160;followed the predictions of global LES, and the growth strategy of the old-aged&lt;em&gt;&amp;#160;C&lt;/em&gt;&lt;em&gt;.&lt;/em&gt;&lt;em&gt;eyrie&lt;/em&gt;&amp;#160;forest was&amp;#160;more conservative than the middle-aged C.&lt;em&gt;sclerophylla&lt;/em&gt;&lt;em&gt;&amp;#160;&lt;/em&gt;forest; (2) N addition had no significant effect on leaf N contents&amp;#160;and C:N ratios of both species, but significantly reduced SLA and Chl content of &lt;em&gt;C. eyrie&lt;/em&gt;&amp;#160;adults and increased C content of &lt;em&gt;C. sclerophylla&lt;/em&gt;&amp;#160;seedlings.&amp;#160;Moreover,&amp;#160;both species showed a more consistent trend of decreasing P content and a corresponding increase&amp;#160;of C:P and N:P ratios. (3) N addition shifted the&amp;#160;C~P scaling relationship of both species and SLA~P scaling relationship of &lt;em&gt;C. sclerophylla&lt;/em&gt;.&lt;/p&gt;&lt;p&gt;Our results verified&amp;#160;the existence of LES patterns among closely related species at the local scale. Moreover, we found that N addition showed&amp;#160;varied effects&amp;#160;on different leaf traits and trait-pairs relationship of subtropical evergreen plants. 10 years&amp;#8217; N addition of high dosage significantly aggravated P limitation in subtropical evergreen forests, which led to a more conservative growth strategy, especially in middle-aged C.&lt;em&gt;sclerophylla&lt;/em&gt;&amp;#160;forest. Our&amp;#160;work&amp;#160;through&amp;#160;site-level case study provided data support&amp;#160;for connecting foliar&amp;#160;functional traits with earth system&amp;#160;models, which will&amp;#160;contribute to enhance&amp;#160;the predictions of ecosystem function and vegetation dynamics&amp;#160;in the context of increasing global N deposition.&lt;/p&gt;