Li Yiyong, Wang Zhaocheng, Liu Huihui, Zhang Cheng, Fu Songling, Fang Xiong
School of Forestry and Landscape Architecture, Anhui Agricultural University, Hefei, China.
Hefei Urban Ecosystem Research Station, National Forestry and Grassland Administration, Hefei, China.
Front Plant Sci. 2021 Aug 2;12:709510. doi: 10.3389/fpls.2021.709510. eCollection 2021.
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 the two co-occurring species (leguminous) and (non-leguminous) were cultivated under two N addition rates (0 and 80 kg N ha year) 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 2 years. Results revealed that N addition significantly promoted the growth of MD-stressed , whereas no significant effect was detected in . Decreased leaf water potential (both Ψ and Ψ) was also observed with N addition for both species under MD, but not under SD. Furthermore, the application of N positively impacted drought adaptive responses in the stem xylem of , showing decreased stem xylem vessel diameter ( ), theoretical hydraulic conductivity ( ), and increased vessel frequency () upon drought under N addition; such impacts were not observed in . Regarding leaf anatomy, N addition also caused drought-stressed to generate leaves with a lower density of veins () and stomata (), which potentially contributed to an enhanced acclimation to drought. However, the same factors led to a decrease in the palisade mesophyll thickness () of SDstressed . Moreover, N addition increased the xylem soluble sugar and starch of MD-stressed , and decreased the xylem soluble sugar under SD for both species. The results suggest that N addition does not consistently modify tree growth and anatomical traits under variable water availability. 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.
氮（N）沉降和干旱是影响树木生长和繁殖的两个主要压力源。然而，很少有研究调查它们之间的相互作用。在本研究中，两种共生树种（豆科）和（非豆科）的树苗在两种施氮速率（0和80千克氮·公顷⁻¹·年⁻¹）下进行培育，设置了充分浇水（WW，田间持水量的80%）、中度干旱（MD，田间持水量的60%）和重度干旱条件（SD，田间持水量的40%）。两年后，我们检查了它们的生长情况以及多种解剖学和非结构性碳水化合物（NSC）响应。结果表明，施氮显著促进了受MD胁迫的的生长，而在中未检测到显著影响。在MD条件下，两种树种施氮时叶片水势（Ψ和Ψ）均下降，但在SD条件下未下降。此外，施氮对的茎木质部干旱适应性反应有积极影响，在施氮干旱条件下，茎木质部导管直径（）、理论水力传导率（）减小，导管频率（）增加；在中未观察到此类影响。关于叶片解剖结构，施氮还导致受干旱胁迫的产生叶脉密度（）和气孔密度（）较低的叶片，这可能有助于增强对干旱的适应性。然而，相同因素导致受SD胁迫的栅栏组织厚度（）减小。此外，施氮增加了受MD胁迫的木质部可溶性糖和淀粉含量，在SD条件下两种树种的木质部可溶性糖含量均下降。结果表明，在不同水分可利用性条件下，施氮并不能始终如一地改变树木生长和解剖特征。由于其解剖特征的主要改变，在未来氮添加和干旱的交互作用下似乎具有更强的适应能力。
