|Hu, Yanbo -|
|Carvalho, Josirley DE Fc -|
|Sun, Guangyu -|
|Tigabu, Mulualen -|
|Wang, Liangzai -|
Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 11, 2014
Publication Date: N/A
Interpretive Summary: Chemical nitrogen dioxide is gaseous air pollutant formed by fuel combustion from transportation (through motor vehicle exhaust) and stationary sources such as electric utilities. Due to the highly interactive (oxidizing) nature of this gas, it can negatively impact the physiology, function, and chemistry of plants. The mechanisms of how the gas affects the physiology and chemistry of plants are not understood. Understanding the impact of this gas on plants will provide valuable information on the effect of gaseous chemical stress on the physiology and chemistry of higher plants. In a controlled environmental chamber the effect of nitrogen dioxide on the physiology and chemistry of leaves of poplar seedling, a model plant, was evaluated. Physiology (respiration, photosynthesis, and carbon dioxide exchange) and chemical composition of leaves, including carbon, potassium, calcium, silicon, manganese, zinc, and copper, were negatively impacted. Nitrogen percentage deposited on leaf surface of seedlings increased with higher level of nitrogen dioxide exposure. Electron microscope examination showed that, at higher concentration of nitrogen dioxide, size of leaf openings (stomata, where gas and water control occur) were significantly reduced. This research demonstrated that nitrogen dioxide at high level can alter the physiology and chemistry of poplar seedling leaves, but did not demonstrate nitrogen dioxide effects on yield or biomass. The effect of nitrogen dioxide on nutrients on leaf surface depended on the type of nutrient. The research provides the scientific communities with useful information regarding nitrogen dioxide effects on physiological processes and nutrient composition in higher plants.
Technical Abstract: Mechanisms controlling effects of gaseous nitrogen dioxide on epidermis and stomata dynamics, and photosynthesis and respirations processes are still not fully understood. In this study, we used poplar as a model plant and investigated the effects of gaseous nitrogen dioxide (4 microliters per liter) and (8 microliters per liter) on stomata-related physio-chemical processes (e.g. stomatal conductance, photosynthesis, dark- and photo-respiration) of Populus alba × Populus berolinensis hybrid leaves by using the photosynthesis system and scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) techniques. We also analyzed the changes in weight percent of chemical elements in the leaves exposed to nitrogen dioxide. The results showed that net photosynthetic and dark respiration rates were significantly reduced in leaves exposed to 4 microliters per liter nitrogen dioxide for 32-48 h as compared with CK leaves (ambient carbon dioxide 365 microliters per liter and ambient nitrogen dioxide <1 nanoliters per liter) and the leaves exposed for 14 h. Leaf temperature was an important factor affecting dark respiration rate. Postillumination carbon dioxide burst (PIB) in the exposed leaves occurred at 13-15 s after turning the light off, whereas this phenomenon was absent in CK leaves. Exposure to gaseous nitrogen dioxide for 48 h led to a decline of PIB rate. Gaseous nitrogen dioxide resulted in the changes of chemical elemental composition in leaf surface, leading to a significant increase in nitrogen percentage (from 0 to 33%) and decrease in macro- and micro-elements. In conclusion, gaseous nitrogen dioxide has significant impacts on epidermis- and stomata-related physio-chemical processes. Future work is proposed to investigate the relationship between photorespiration and foliar uptake of gaseous nitrogen dioxide and correlations of elemental composition and ultrastructure/nitrogen dioxide-N products of guard cells and mesophyll tissue adjacent to stomata.