The 2010 ASHS Annual Conference

Reducing temperatures during plant production will result in greenhouse energy savings; however, lower temperatures may lengthen the crop production time. Using elevated CO2 concentrations could help plants compensate for the reduction in growth. The goal of this experiment was to evaluate suboptimal temperatures and elevated CO2 as an alternative to reduce heating energy costs. Effects of elevated CO2 and suboptimal temperatures on plant development, nutrient uptake, and insect behavior were evaluated in a growth chamber study. Zinnias (Zinnia elegans) and petunias (Petunia×hybrida) were germinated in trays and transplanted to 6 inch pots. After transplanting, plants were grown using optimal (21 şC) or suboptimal (18 şC) temperature, ambient (390 µl•l-1) or elevated (800 µl•l-1) CO2, optimum or high nutrient levels, and presence or absence of insects. Flowering time and flower longevity were used to evaluate plant development. Concentrations of micro and micronutrients in leaves, stems and flowers were analyzed. Three weeks after transplanting, half of the plants were infested with whiteflies (Bemisia tabaci) to investigate the effect of CO2 and temperature on oviposition. Overall, results showed that total dry weight of petunias and zinnias was affected by nutrition levels and suboptimal temperature. Plants treated with high nutrition level had 35% greater biomass compared to those treated with optimum level. Zinnias grown at suboptimal temperature and ambient CO2 were taller, whereas petunias were shorter. Presence of insects did not result in any change of plant height or dry weight at any of the temperatures or CO2 regimes. Nevertheless, the presence of whiteflies caused earlier flowering in plants grown at the suboptimal temperature compared to those grown at optimal temperature. Generally, plants grown at optimal temperatures bloomed earlier and had shorter flowering duration, 5.1 days less than plants grown at suboptimal temperature, regardless of nutrition and crop type. Nutrient concentrations in various plant parts varied; although, most significant results showed a reduction in accumulation of nutrients at lower temperature. Whitefly oviposition was lower in petunias than zinnias. Results showed that the temperature and/or CO2 treatments did not affect whitefly oviposition. These partial results show that suboptimal temperatures and CO2 enrichment influence plant quality and production time, so care must be taken if this strategy is utilized to help decrease energy costs.