COMBINED EFFECTS OF TEMPERATURE, ULTRAVIOLET-B RADIATION, AND WATERING REGIME ON GROWTH AND PHYSIOLOGICAL PROCESSES IN CANOLA (BRASSICA NAPUS) SEEDLINGS

Relatively few studies have investigated plant responses to the combined effects of multiple environmental factors. We studied the responses of canola (Brassica napus) seedlings to combinations of temperatures (22 degrees/18 degrees C and 28 degrees/24 degrees C), ultraviolet-B (UVB) radiation levels (5 [ambient] and 10 [enhanced] kJ m(-2) d(-1)), and watering regimes (well watered and water stressed). The higher temperature decreased stem diameter, leaf area, individual organ and total-plant dry mass (DM), net CO2 assimilation (AN), water use efficiency (WUE), the chlorophyll (Chl) a-Chl b ratio, and UV-absorbing compounds but increased specific leaf mass (SLM), leaf mass ratio (LMR), shoot-root ratio (SRR), and Chl b. Enhanced UVB reduced leaf number and area, DM accumulation, SLM, LMR, AN, WUE, carotenoids, and Chl a : Chl b but increased leaf area ratio, SRR, and ethylene evolution. Water stress decreased plant growth, leaf moisture, leaf, stem, and total DM, LMR, SRR, and gas exchange but increased photosynthetic pigments, UV-absorbing compounds, epicuticular wax, and ethylene evolution. Many plant parameters were affected by two-and three-way interactions. Main factors and their interactions revealed that water stress has a larger negative influence on plants than the other two factors. We suggest that, under conditions of global climate change, water stress may have a stronger effect on plant performance than UVB radiation.