Combined effects of temperature and light quality on plants have received little attention. We investigated the single and interactive effects of temperature and light quality on growth and physiological characteristics of four canola (Brassica napus) cultivars -Clearfield 46A76 (cv 1 ), Clearfield 45H72 (cv 2 ), Roundup Ready 45H24 (cv 3 ) and Roundup Ready 45H21 (cv 4 ). Plants were grown under lower (24°/20°C) and higher (30°/26°C) temperature regimes at low red/far-red (R/ FR), normal R/FR and high R/FR light ratios in environment-controlled growth chambers (16 h light/8 h dark). Higher temperature reduced stem height and diameter; leaf number and area; dry matter of all plant parts; and specific leaf weight, but increased leaf area ratio; and chlorophyll (Chl) fluorescence (Y). Low R/FR increased stem height; Y; and ethylene, but decreased stem diameter; F v /F m ; Chl a; Chl b; and carotenoids. Among cultivars, plants from cv 4 were tallest with thickest stems and greatest dry matter. None of the main factors affected gas exchange. Higher temperature at high R/FR caused cv 3 to be shortest, whereas lower temperature at low R/FR caused cv 4 to be tallest. We conclude that heat and other stress factors will adversely affect sensitive crops, but tolerant genotypes should perform well under future climate.

Although the separate effects of light quality and temperature on plants have been studied extensively, their interactive effects have received little attention. We studied the combined effects of these two factors on the growth and physiology of velvetleaf (Abutilon theophrasti). Plants were grown under two temperature regimes (24°/20°C and 30°/26°C; 16 h day/8 h night) and three red:far-red (R:FR) light ratios (0.68, low; 1.16, normal; and 4.63, high) in controlled-environment chambers. Temperature significantly affected 3 plant parameters, light quality 17 parameters and the interaction of these two factors only 1 parameter. Plants that were grown under higher temperatures had lower water-use efficiency and chlorophyll a:b ratio, but larger root systems, than those under lower temperatures. Compared to growth at normal R:FR, plants at low R:FR were taller with higher leaf moisture, fewer leaves, reduced total biomass, lower specific leaf mass (SLM) and leaf mass ratio (LMR), lower CO 2 assimilation and light-adapted chlorophyll fluorescence, and lower chlorophyll concentration and Chl a:b ratio. Plants at low and high R:FR had lower root dry mass, SLM, LMR and chlorophyll concentration than those at normal R:FR. We found that temperature had little effect on A. theophrasti and did not regulate light quality effects on this species; thus a small degree of global warming will likely have no major effects on this species, which will probably thrive well in the future climate.