Key Laboratory of Saline-alkali Vegetation Ecology Restoration, Ministry of Education, College of Life Sciences, Northeast Forestry University, Harbin City, 150040, PR China; State Key Laboratory of Tree Genetics and Breeding, Northeast Forestry University, Harbin City, 150040, PR China.
ADP International Plant Science Consulting, Talstrasse 8, D-79194, Gundelfingen, Germany.
Plant Physiol Biochem. 2019 Oct;143:94-108. doi: 10.1016/j.plaphy.2019.08.023. Epub 2019 Aug 30.
During recent decades, the southern and eastern regions of Asia have experienced high levels of atmospheric N deposition. Excess N deposition is predicted to influence tree growth and species composition in the regions, but visual or physiological assessments alone are not sufficient to determine the real effects of atmospheric N deposition. In this study, we simulated atmospheric wet deposition of inorganic N by spraying a NO solution (20 mmol⋅L) or a mixture of NO (20 mmol⋅L) plus NO (100 or 300 μmol⋅L) on leaves of hybrid poplar (Populus alba × Populus berolinensis) seedlings and examined morphoanatomical traits and physiological processes. Leaves of seedlings sprayed with single or mixed N solutions developed marginal necrosis, curling, and small cracks on the adaxial surface. The silicon (Si)-rich crystals were larger (about 100% increase in crystal diameter compared to untreated seedlings) on the adaxial leaf surface, with a significant positive correlation between the atomic percentage of N and Si on the crystal areas of the surface. Leaves were sensitive to NO compared with NO even at a low concentration; water content, dry mass, and photochemical variables significantly declined and dark respiration increased only in leaves treated with mixed N form. Mixed N foliar applications significantly increased leaf concentrations of the free amino acids Glu, Gln, and Asn and organic acids oxaloacetic acid and citric acid. Besides, mixed N treatment stimulated leaf transamination, as indicated by significant increases in Ala and Asp concentrations and activities of glutamic oxalacetic transaminase and glutamic pyruvic transaminase. However, mixed N applications led to declines in leaf concentrations of putrescine (by 65%, p = 0.01) and spermine (by 53%, p = 0.01). A higher proportion of NO (300 μmol⋅L) in mixed N solution was inhibitory to key N-metabolic enzymes and N translocation via the phloem. Our results showed that wet deposition of airborne N pollutants modified surface properties and induced additional detrimental effects related to N-compound foliar absorption. Furthermore, our findings indicate that detoxification of reactive N is apparently related to N assimilation and export from the treated leaves via the phloem.
在最近几十年，亚洲的南部和东部地区经历了高水平的大气氮沉积。过量的氮沉积预计会影响这些地区的树木生长和物种组成，但仅凭视觉或生理评估不足以确定大气氮沉积的真实影响。在这项研究中，我们通过喷洒 NO 溶液（20 mmol·L）或 NO（20 mmol·L）与 NO（100 或 300 μmol·L）的混合物模拟大气湿氮沉积，对杂种杨树（Populus alba × Populus berolinensis）幼苗的叶片进行了处理，并检查了形态解剖特征和生理过程。喷洒单一或混合氮溶液的幼苗叶片出现边缘坏死、卷曲和叶表面小裂缝。与未经处理的幼苗相比，叶片表面富硅晶体（晶体直径增加约 100%）较大，表面晶体区域的氮和硅原子百分比之间存在显著正相关。叶片对 NO 的敏感性高于 NO，即使在低浓度下也是如此；仅在施用混合氮形式的叶片中，水含量、干质量和光化学变量显著下降，暗呼吸增加。混合氮叶面处理显著增加了叶片游离氨基酸 Glu、Gln 和 Asn 以及有机酸草酰乙酸和柠檬酸的浓度。此外，混合氮处理刺激了叶片转氨基作用，表现为 Ala 和 Asp 浓度以及谷氨酸草酰乙酸转氨酶和谷氨酸丙酮酸转氨酶活性显著增加。然而，混合氮处理导致叶片腐胺（下降 65%，p=0.01）和精胺（下降 53%，p=0.01）浓度降低。混合氮溶液中较高比例的 NO（300 μmol·L）对关键氮代谢酶和韧皮部中的氮转运具有抑制作用。我们的研究结果表明，空气传播氮污染物的湿沉积改变了表面性质，并引起了与叶面吸收氮化合物相关的额外有害影响。此外，我们的研究结果表明，与氮同化和通过韧皮部从处理叶片中输出相关的氮解毒显然与氮吸收有关。
