Quantifying the Effects of Corn Growth and Physiological Responses to Ultraviolet-B Radiation for Modeling

Published in Agron. J. 105:1367–1377 (2013) doi:10.2134/agronj2013.0113 Copyright © 2013 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. U radiation (280–320 nm) is an integral part of sunlight that reaches the surface of Earth. Even though UV-B represents a small fraction of total solar radiation, exposure to UV-B at current and projected levels is known to elicit a variety of responses in all living organisms, including higher plants (Kakani et al., 2003; Runeckles and Krupa, 1994). Over the past 50 yr, the concentration of ozone in the stratosphere, which absorbs most of the UV-B radiation, has decreased about 5%, mainly due to release of anthropogenic pollutants such as chloroflurocarbons (Pyle, 1996). Current global distribution of mean erythemal (biologically effective/ potential for biological damage) daily dose of UV-B radiation between the latitudes 40°N and 40°S during summer ranges between 2 and 9 kJ m–2 (McKenzie et al., 2007), a level which is about 3 kJ m–2 higher than the 1994 observation (Seckmeyer et al., 1995). Elevated UV-B levels are expected to continue well into the 21st century (WMO, 2007). Model simulations suggest that the United States is already experiencing UV-B dosage that may be deleterious to crop growth and development (Lubin and Jensen, 1995). Recent estimates have shown that continued increase in ground-level UV-B radiation will occur over the next few decades, although there is considerable uncertainty between changes projected in atmospheric chemistry and associated changes in climate and their interactions (Taalas et al., 2000; Zerefos et al., 1997). Previous reviews and published studies clearly demonstrate the extent of damage caused by both ambient (Caldwell et al., 1989; Teramura, 1983; Teramura and Sullivan, 1994) and elevated UV-B radiation (Kakani et al., 2003; Krupa, 1998; Rozema et al., 1997; Searles et al., 2001; Teramura, 1983) on morphological, physiological, biochemical, and molecular components of crop plants including corn. Some of the primary effects of UV-B radiation on plant metabolic systems are DNA damage, dilation, and disintegration of cellular membranes, photooxidation of leaf pigments and phytohormones, and inhibition of photosynthesis (Correia et al., 1999; He et al., 1994; Mark and Tevini, 1997; Ros and Tevini, 1995) in association with down-regulation of genes responsible for processes such as photosynthesis and phytohormone metabolism and cell wall loosening (Casati and Walbot, 2003; Hectors et al., ABSTRACT To understand the consequences of rising levels of ultraviolet-B (UV-B) radiation on corn (Zea mays L.), two experiments were conducted using sunlit growth chambers at a wide range of UV-B radiation levels. Corn hybrids, Terral-2100 and DKC 65-44, were grown in 2003 and 2008, respectively, at four UV-B levels (0, 5, 10, and 15 kJ m–2 d–1) at 30/22°C, from 4 d after emergence to 43 d under optimum nutrient and water conditions. Plant growth, development, and photosynthetic rates were measured regularly. An inverse relationship between many growth process and dosage of UV-B radiation was recorded. Shorter plants were due to shorter internodal lengths rather than fewer internodes and the total leaf area was less due to smaller leaves. Lower biomass under enhanced UV-B was closely related to smaller leaf area and lower photosynthesis. Critical UV-B limits, defined as 90% of optimum or control, were estimated from the UV-B response indices. The critical limits for stem extension and leaf area expansion were lower in both hybrids (1.7–3.5 kJ m–2 d–1) than the critical limit for leaf number (>15 kJ m–2 d–1) and photosynthetic processes, indicating that expansion or extension rates of organs were the more sensitive to UV-B radiation. Hybrid Terral-2100 exhibited greater sensitivity to UV-B radiation than DKC 65-44 for studied parameters. Thus, both current and projected UV-B radiation can adversely affect corn growth. The functional algorithms developed in this study could be useful to enhance the corn models to predict accurately field performance.