AUTHOR=Zhang Zhenzhen , Zhao Yamin , Zhang Xiaoyan , Tao Sichen , Fang Xiong , Lin Xingwen , Chi Yonggang , Zhou Lei , Wu Chaofan 

TITLE=The Accumulated Response of Deciduous Liquidambar formosana Hance and Evergreen Cyclobalanopsis glauca Thunb. Seedlings to Simulated Nitrogen Additions

JOURNAL=Frontiers in Plant Science

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.01596

DOI=10.3389/fpls.2019.01596

ISSN=1664-462X

ABSTRACT=<p>Nitrogen depositions in the Yangtze River Delta have is thought to shift the coexistence of mixed evergreen and deciduous species. In this study, the seedlings of the dominant evergreen species <italic>Cyclobalanopsis glauca</italic> Thunb. and the deciduous species <italic>Liquidambar formosana</italic> Hance from the Yangtze River Delta were chosen to test their responses to simulated N additions using an ecophysiological approach. N was added to the tree canopy at rates of 0 (CK), 25 kg N ha<sup>−1</sup> year<sup>−1</sup> (N25), and 50 kg N ha<sup>−1</sup> year<sup>−1</sup> (N50). The leaf N content per mass (<italic>N</italic><sub>m</sub>, by 44.03 and 49.46%) and total leaf chlorophyll content (<italic>Chl</italic>, by 72.15 and 63.63%) were enhanced for both species, and <italic>C. glauca</italic> but not <italic>L. formosana</italic> tended to allocate more N to <italic>Chl</italic> per leaf area (with a higher slope). The enhanced N availability and <italic>Chl</italic> promoted the apparent quantum yield (<italic>AQY</italic>) significantly by 15.38 and 43.90% for <italic>L. formosana</italic> and <italic>C. glauca</italic>, respectively. Hydraulically, the increase in sapwood density (<italic>ρ</italic>) for <italic>L. formosana</italic> was almost double that of <italic>C. glauca</italic>. Synchronous improved sapwood specific hydraulic conductivity (<italic>K</italic><sub>S</sub>, by 37.5%) for <italic>C. glauca</italic> induced a significant reduction in stomatal conductance (<italic>g</italic><sub>s</sub>) (<italic>p</italic> &lt; 0.05) in the N50 treatments, which is in contrast to the weak varied <italic>g</italic><sub>s</sub> accompanied by a 59.49% increase in <italic>K</italic><sub>S</sub> for <italic>L. formosana</italic>. As a result, the elevated maximum photosynthesis (<italic>A</italic><sub>max</sub>) of 12.19% for <italic>L. formosana</italic> in combination with the increase in the total leaf area (indicated by a 37.82% increase in the leaf area ratio-leaf area divided by total aboveground biomass) ultimately yielded a 34.34% enhancement of total biomass. In contrast, the <italic>A</italic><sub>max</sub> and total biomass were weakly promoted for <italic>C. glauca</italic>. The reason for these distinct responses may be attributed to the lower water potential at 50% of conductivity lost (<italic>P</italic><sub>50</sub>) for <italic>C. glauca</italic>, which enables higher hydraulic safety at the cost of a weak increase in A<sub>max</sub> due to the stomatal limitation in response to elevated N availability. Altogether, our results indicate that the deciduous <italic>L. formosana</italic> would be more susceptible to elevated N availability even if both species received similar N allocation.</p>