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 CO2 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.
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