Interactions of CO2 Enrichment and Temperature on Carbohydrate Production and Accumulation in Muskmelon Leaves

We examined how temperature and stage of vegetative growth affect carbohydrate production and accumulation in Cucumis melo L. `Haogen' grown at various CO 2 concentrations ([CO 2 ]). Carbohydrate production was measured by net assimilation rate either on a leaf-area basis (NAR a ) or a leaf dry-weight basis (NAR w ); carbohydrate accumulation was measured by leaf starch plus sugar content. Twenty-four- and 35-day-old muskmelon plants were grown for 11 days in artificially lighted cabinets at day/night temperatures of 20/20 or 40/20C and at [CO 2 ] of 300 or 1500 μl·liter -1 . NAR a and NAR w both increased with increasing [CO 2 ], but the CO 2 effect was smaller at low temperature, especially for plants at the later stage of vegetative growth. NAR w was a better indicator of total dry-weight gain than was NAR a . Both suboptimal temperatures and CO 2 enrichment caused carbohydrates to accumulate in the leaves at both stages of vegetative growth. NAR w was correlated negatively with leaf starch plus sugar content. The rate of decrease in NAR w with increasing leaf starch plus sugar content was significantly greater for CO 2 -enriched plants. Leaf starch plus sugar content >0.03 to 0.04 kg·kg -1 of leaf residual dry weight at the end of a dark period may indicate that temperature is suboptimal for growth. Plants grown at the same temperature had higher leaf starch plus sugar content if they were CO 2 -enriched than if grown in ambient [CO 2 ], suggesting that an optimal temperature for growth in ambient [CO 2 ] may be suboptimal in elevated [CO 2 ].