Quantifying the effects of corn growth and physiological responses to ultraviolet-B radiation for modeling

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.