AUTHOR=Li Yiyong , Wang Zhaocheng , Liu Huihui , Zhang Cheng , Fu Songling , Fang Xiong 

TITLE=Responses in Growth and Anatomical Traits of Two Subtropical Tree Species to Nitrogen Addition, Drought, and Their Interactions

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 12 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.709510

DOI=10.3389/fpls.2021.709510

ISSN=1664-462X

ABSTRACT=Nitrogen (N) deposition and drought are two major stressors that influence tree growth and propagation. However, few studies have investigated their interactions. In this study, saplings of two co-occurring species, Ormosia pinnata (leguminous) and Schima superba (non-leguminous), were cultivated under two N addition rates (0 and 80 kg N ha-1 y-1) with well-watered (WW, 80% of field capacity), moderate drought (MD, 60% of field capacity), and severe drought conditions (SD, 40% of field capacity). We examined their growth, as well as multiple anatomical and non-structural carbohydrate (NSC) responses after two years. Results revealed that N addition significantly promoted the growth of MD-stressed S. superba, whereas no significant effect was detected in O. pinnata. Decreased leaf water potential (both Ψmd and Ψpd) was observed with N addition for both species under MD, but not under SD. The application of N positively impacted drought adaptive responses in stem xylem of S. superba, showing decreased stem xylem vessel diameter (DH), theoretical hydraulic conductivity (Kth) and increased vessel frequency (VF) upon drought under N addition, while such impacts were not observed in O. pinnata. Regarding leaf anatomy, N addition caused drought-stressed S. superba to generate leaves with a lower density of vein (VD) and stomata (SD). This potentially contributed to an enhanced acclimation to drought, whereas it decreased the palisade mesophyll thickness (PMT) of SD-stressed O. pinnata. Moreover, N addition increased the xylem soluble sugar and starch of MD-stressed O. pinnata, and decreased the xylem soluble sugar under SD for both species. Our results suggest that N addition does not consistently modify tree growth and anatomical traits under variable water availability. S. superba appeared to have a greater capacity to be more adaptable under the future interactive effects of N addition and drought due to major modifications in its anatomical traits.