Background
The authors write that "high temperatures can alter plant reproductive phenology, resulting in earlier or later flowering," while "high atmospheric CO2 levels have a positive fertilizing effect in plants, producing higher biomass and flower number." Hence, they decided to "quantify the effects of higher maximum temperature and atmospheric CO2 concentration on reproductive phenology in the tropical crop Habanero pepper (Capsicum chinense Jacq.)," which they did via two different sets of experiments.

What was done
Employing a set of three growth chambers, Garruņa-Hernandez et al. investigated the pertinent impacts of three different diurnal maximum temperatures (30, 35 and 40°C) in one experiment and three different atmospheric CO2 concentrations (380, 760 and 1140 ppm) in another study.

What was learned
In regard to their temperature experiment, the six scientists report that "a maximum temperature increase from 30 to 35°C caused flowering to be 6 days earlier," but they say that "at 35°C fruiting was 27 days later than at 30°C," and that "plants in the 40°C treatment could not even attain 50% flowering or fruiting." In their CO2 experiment, on the other hand, they indicate that "flowering was much earlier, flower abortion much lower and fruit production higher as CO2 concentration increased," which findings are said by them to "coincide with those of Ward and Strain (1997), who reported that a 75% rise in CO2 concentration resulted in earlier flowering by five days in Arabidopsis thaliana." In addition, the Mexican researchers report that "Habanero pepper plants at 1140 ppm CO2 increased their CO2 assimilation rate two-fold with respect to values obtained for plants at 380 ppm CO2." And they say that "increases in CO2 had a positive effect on seed number per fruit and caused flower morphology traits to augment in size."

What it means
In regard to their self-imposed question - "which factor (temperature or CO2) would have a greater effect under a climate change scenario?" - Garruņa-Hernandez et al. say their present results suggest that "a doubling of atmospheric CO2 levels in tropical-subtropical regions would promote positive changes in plants that could mitigate any deterioration caused by higher temperature, as long as this factor does not reach extremely stressful levels." And they add that "under greenhouse conditions, the present results are promising since maximum temperature can be controlled, preventing any detrimental effects, while high CO2 levels can be applied to accelerate phenological states, increase the number of flowers and fruit, and consequently improve fruit yields."

Reference
Ward, J.K. and Strain, B.R. 1997. Effects of low and elevated CO2 partial pressure on growth and reproduction of Arabidopsis thaliana from different elevations. Plant, Cell and Environment 20: 254-260.