Abstract
Changes in the phenology of flowering in soybeans caused by long-term growth at elevated CO2 may be important to the responses of seed yield to elevated CO2. Here we utilized near-isogenic lines of soybeans differing in three genes influencing photoperiod sensitivity to determine whether these genes affected the response of flowering time to elevated CO2. Six isolines of Harosoy 63 were grown at ambient (380 μmol∙mol−1) and elevated (560 μmol∙mol−1) CO2 concentrations in the field using free-air CO2 enrichment systems, in air-conditioned glasshouses with natural summer photoperiods, and in indoor chambers with day lengths of 11, 13, 15, and 17 hours. The effect of CO2 concentration on flowering time varied with genotype, and there was also an interaction between CO2 and photoperiod in all genotypes, as indicated by ANOVA. Elevated CO2 accelerated flowering in some cases, and delayed it in other cases. For all three of the isolines with single dominant genes, elevated CO2 decreased the days to first open flower at the longest photoperiod. At the shortest photoperiod, elevated CO2 delayed flowering in all but one isoline. The all-recessive isoline had slower flowering at elevated CO2 at both the shortest and the longest photoperiods, and also in the field and in the glasshouse. Delayed flowering at elevated CO2 in the field and glasshouse was associated with an increased final number of main stem nodes. It is concluded that the E1, E3, and E4 genes each influenced how the time to first flowering was affected by CO2 concentration at long photoperiods.
Highlights
Some experiments growing soybeans at different carbon dioxide concentrations have indicated that carbon dioxide concentration may affect the time of initial flowering
Flowering at the apical main stem node was delayed by elevated CO2 in the e1e3e4 isoline, and the number of main stem nodes at maturity was increased by elevated CO2 only in the e1e3e4 isoline (Table 2)
The effect of CO2 on flowering time of each isoline observed in the glasshouse was predictable from the responses observed in the indoor chambers with the assumption of a photoperiod of 15.5 to 16 hours in the glasshouse
Summary
Some experiments growing soybeans at different carbon dioxide concentrations have indicated that carbon dioxide concentration may affect the time of initial flowering (reviewed in Ellis et al 1995). Comparisons of soybean cultivars at ambient and elevated carbon dioxide both in indoor controlled environment chambers and in the field indicated that the duration of vegetative growth, as affected by flowering phenology, was a significant source of variation in the stimulation of yield by elevated carbon dioxide [1]. Adaptation of soybeans to rising atmospheric carbon dioxide may benefit from a better understanding of carbon dioxide effects on flowering. Both delaying and accelerating effects of elevated carbon dioxide on the time to first flowering have been found in several species in addition to soybean [3]. But not all cases, faster flowering at elevated carbon dioxide could be attributed to a generalized acceleration of development as indicated by increased rates of leaf initiation [3]. Acceleration of development at elevated carbon dioxide would not account for any delayed flowering at elevated carbon dioxide
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