Influence of Oxides of Nitrogen on Crop Growth and Yield: An Overview

Physiological and biochemical responses of two precious Carpinus species to high-concentration NO2 stress and their natural recovery

Carpinus betulus and Carpinus putoensis are precious species in the world. Studies on the ecosystem function of the two species are rare. This study investigated the physiological and biochemical responses of C. betulus and C. putoensis to NO₂ stress and their natural recovery. C. betulus and C. putoensis seedlings underwent fumigation with 12.0 mg/m³ NO₂ for 0, 1, 6, 12, 24, 48, and 72 h, respectively. Then, the plants were allowed to recover at room temperature for 30 d. Physiological and biochemical changes in the leaves were compared between the two species. In terms of peroxidase (POD) activity, the damage response of C. betulus under NO₂ stress appeared later than that of C. putoensis. The soluble protein content of C. betulus was noticeably higher than that of C. putoensis, and C. betulus exhibited more stable membrane lipoperoxidation. The tendency of the changes in nitrate reductase of C. betulus was less noticeable than that of C. putoensis. The variation amplitudes of N, K, Mg, Zn and Mn in the leaves of C. putoensis were greater than those of C. betulus. C. putoensis showed more sensitive metabolisms in response to NO₂ stress compared with C. betulus. High-concentration NO₂ caused damage to C. betulus and C. putoensis was reversible, and both species returned to normal growth via their own metabolism after 30-d recovery. The results of this study may provide useful reference data for quantitative assessment of the ecosystem function of C. betulus and C. putoensis and for their scientific application in urban greening.

Tansley Review No. 24 Why are atmospheric oxides of nitrogen usually phytotoxic and not alternative fertilizers?

Atmospheric pollution by the oxides of nitrogen, NO and NO₂ , can cause reductions in growth but rarely visible injury. This review considers their uptake into foliage, as well as their subsequent metabolism and physiology, and attempts to explain why these gases are often phytotoxic. The combined stresses of resisting cellular acidification, enhanced levels of nitrite (and ammonia), and the direct interference of the free radical ('N=O) with critical enzymes, reaction centres and regulatory mechanisms are thought to be the main reasons why oxides of nitrogen, especially NO, inhibit growth. If other air pollutants such as SO₂ are also present with NO or NO₂ then free radical-induced injury, similar to that caused by O₃ alone, also occurs. CONTENTS Summary 395 I. Introduction 396 II. Uptake and cycling of oxides of nitrogen 396 III. Biochemical responses to NO and NO₂ 405 IV. Physiological responses to NO and NO₂ 410 V. Combinations of NO and NO₂ with other pollutants 416 VI. Recapitulation and beyond 418 Acknowledgements 420 References 420.

FOLIAR ENTRY AND INCORPORATION OF ATMOSPHERIC NITROGEN DIOXIDE INTO BARLEY PLANTS OF DIFFERENT NITROGEN STATUS

The uptake of atmospheric NO₂ through leaf surfaces and the influence on uptake of combined nitrogen by the roots were investigated in hydroponically grown barley plants exposed to 0.3 μI 1^-1 nitrogen dioxide (NO₂ ). The response to NO₂ was dependent on the nitrogen status of the plant at the time of exposure. Only with low nitrate supplies to the roots did exposure of leaves to atmospheric NO₂ cause significant increases in the nitrogen (N) content of barley. Levels of both nitrate and reduced forms of N increased in plants in response to the pollutant and were directly due to uptake of NO₂ by leaves, since the root environment was completely sealed from atmospheric sources of NO₂ . Moreover, these increases were not due to the stimulation of nitrate uptake by the roots from the nutrient solution, although levels of activity of both nitrate and nitrite reductases were affected by exposure to NO₂ . Atmosphere NO₂ did, however, affect the ability of a plant to respond to a change in the amount of nitrate supplied to the roots, and the use of both ¹⁸ N-labelled NO₂ and nitrate indicated that the cycling of nitrogen within the plant was also influenced by exposure to atmospheric NO₂ .