Interactive Effects of Temperature and Elevated Carbon Dioxide On Early-Season Sweetpotato (Ipomoea batatas L. Lam.) Growth and Development.

Projected increase in atmospheric carbon dioxide concentration [CO₂] and temperature have fostered the need for understanding the responses of agricultural crops to [CO₂] and temperature interactions.  The potential effects of these factors on root crops particularly sweetpotato (Ipomoea batatas L. Lam.) have been inadequately studied. This study evaluates the effects of temperature and [CO₂] interactions on sweetpotato storage root initiation, early season growth and development, and physiology.  Sweetpotato cv. Beauregard slips were planted in pots filled with fine sand, and grown in sunlit, controlled environment chambers at five levels of day/night temperatures (20/12, 25/17, 30/22, 35/27, and 40/32°C) and two levels of [CO₂] (ambient, 380 and elevated, 760 µmol mol^-1), under optimum moisture and nutrient conditions. Six pots were harvested at weekly intervals, starting 15 days after transplanting to 55 days.  Storage root number, leaf area, and biomass were recorded at each harvest.  Gas exchange and other physiological parameters were also recorded.  Temperature had a significant effect (P<0.001) on storage root biomass. However, there was no interaction between [CO₂] and temperature. Storage root biomass increased with temperature up to 30/22°C, and declined by 11 and 90% at 35/27 and 40/32°C, respectively. Rate of photosynthesis increased with increasing temperature under ambient [CO₂] but was unaffected after 35/27 °C under elevated [CO₂].  On an average the stomatal conductance was reduced by 28%  under elevated [CO₂]_.  Temperature above 35°C resulted in reduction of storage root biomass significantly. Although, temperature optima for total biomass production were significantly different for two levels of [CO₂], storage root biomass was unaffected by elevated [CO₂].  Rise in atmospheric [CO₂] could not ameliorate the negative effects of high temperature on sweetpotato storage root initiation and subsequent growth and development. These functional algorithms will be useful in predicting sweetpotato storage root formation and growth.