Short-day Species Research Articles

Influence of sowing season on some quality indices for soybean

Soybean quality indices, like yield, can be influenced by factors such as climatic conditions, applied technology or biological material. Soybean is a short-day species with moderate temperature requirements, especially during flowering, a critical period for achieving yield and crop quality, air temperature in the range of 17-18°C is considered the biological minimum, while the range of 22-25°C is considered optimal. High temperatures during the flowering period can cause significant yield losses through flower abortion especially when correlated with insufficient humidity. This paper presents summary data obtained in soybean cultivation under the conditions of the Transylvanian Plateau at Agricultural Research and Development Turda on the influence of sowing time on some quality indices. The experiment was realized using the block method in subdivided plots with 3 factors AxBxC on a type soil chernozem, characteristic of the Transylvanian Plateau with chemical description, the soil has a neutral to low alkaline pH, neutral to high humus content, well supplied in nitrogen and potassium, medium supplied in phosphorus. During three experimental years 2021 - 2023 climatic conditions and sowing times influenced differently the protein and fat content of 5 soybean varieties. The results obtained were statistically processed by the analysis of variance method and determination of the least significant difference - LSD - (5%, 1% and 0.1%).

Several short-day species can flower under blue-extended long days, but this response is not universal

Sole-source LED lighting enables spectral flexibility to achieve desirable plant characteristics and product quality. An earlier study from our lab showed that short-day plant chrysanthemum flowers normally under long days with dynamic lighting of 11 h dichromatic red-blue LED light extended with 4 h sole blue LED light. Such dynamic LED lighting is possible in vertical farms and opens the possibility to supply a higher daily light integral (DLI) to short-day plants by providing more hours of light and thus increase growth rate. This study aims to investigate for several short-day species whether normal flowering is obtained when 11 h of red-blue is extended with 4 h of sole blue LED light. Twelve genotypes of nine short-day plants species (kalanchoe - Kalanchoe blossfeldiana, perilla - Perilla frutescens, stevia - Stevia rebaudiana, artemisia - Artemisia annua, chrysanthemum - Chrysanthemum seticuspe and Chrysanthemum morifolium, cosmos - Cosmos bipinnatus, poinsettia - Poinsettia pulcherrima and wild tomato - Solanum habrochaites) were grown at three light conditions in a climate room: 11 h red-blue short day, 11 h red-blue extended with 4 h of sole blue, and 15 h red-blue long day. Mixed red and blue light (ratio 60:40) was provided at a total photosynthetic photon flux density (PPFD) of 100 µmol m−2 s−1 and sole blue light was provided at 40 µmol m−2 s−1 PPFD. Flowering response differed among species: kalanchoe, perilla and stevia flowered only in red-blue short day. Artemisia, chrysanthemum, cosmos, poinsettia, and wild tomato flowered in red-blue short day, and blue-extended long day but not in red-blue long day. However, there was a flowering delay in cosmos, poinsettia, and wild tomato under blue-extended long days compared to short days. In blue-extended long days plants received 15 % higher DLI resulting in a 4 to 36 % increase in total dry weight compared to short days. This study shows that increasing growth rate under light-limiting growth conditions through daylength-extension with sole blue light, without compromising flowering and quality, is possible for some, but not all short-day species.

Influence of the spectral composition of light on the morphogenesis of seedlings of <i>Myrtus communis</i> L. and <i>Psidium cattleianum</i> Sabine (<i>Myrtaceae</i> Juss.) in a small pot greenhouse culture

The influence of the intensity and spectral composition of LED and fluorescent (FL) light on the morphogenesis of Myrtus communis L. and Psidium cattleianum Sabine (Myrtaceae) seedlings in a small pot greenhouse culture in the Central Botanical Garden of the National Academy of Sciences of Belarus (CBG) was studied. It was shown that in terms of plant height, the number and total surface of leaves, as well as the specific dry weight of the leaf, seedlings of both species over 120 cultivation days in all variants with irradiation surpassed control plants. The increase in dry weight per 1 cm2 of leaf (mg with respect to the control) that characterizes the photosynthesis productivity was influenced by the spectral composition of radiation, which made it possible to identify interspecies and intervariant differences. The variant with an FL Narva lamp with a total photon flux density PFD = 76.22 µmol/m2/s, with a share of the green spectrum PFD-G = 46.47 %, red – PFD-R = 20.00 % and with the value of the ratio R/FR = 5.77 in the subtropical long-day species M. communis, it was 1.24 mg, while in the tropical short-day species P. cattleianum had only 0.39 mg. In plants irradiated with an LED lamp with a photon flux density PFD = 186.20 µmol/m2/s, with a share of PFD-R = 59.34 %, and at R/FR = 54.43, the growth was 2.60 and 1.93 mg with respect to control, respectively. LED sources are the most efficient in terms of the photosynthesis productivity for both short-day and long day plants.

A long and stressful day: Photoperiod shapes aluminium tolerance in plants

Aluminium (Al), a limiting factor for crop productivity in acidic soils (pH ≤ 5.5), imposes drastic constraints for food safety in developing countries. The major mechanisms that allow plants to cope with Al involve manipulations of organic acids metabolism and DNA-checkpoints. When assumed individually both approaches have been insufficient to overcome Al toxicity. On analysing the centre of origin of most cultivated plants, we hypothesised that day-length seems to be a pivotal agent modulating Al tolerance across distinct plant species. We observed that with increasing distance from the Equator, Al tolerance decreases, suggesting a relationship with the photoperiod. We verified that long-day (LD) species are generally more Al-sensitive than short-day (SD) species, whereas genetic conversion of tomato for SD growth habit boosts Al tolerance. Reduced Al tolerance correlates with DNA-checkpoint activation under LD. Furthermore, DNA-checkpoint-related genes are under positive selection in Arabidopsis accessions from regions with shorter days, suggesting that photoperiod act as a selective barrier for Al tolerance. A diel regulation and genetic diversity affect Al tolerance, suggesting that day-length orchestrates Al tolerance. Altogether, photoperiodic control of Al tolerance might contribute to solving the historical obstacle that imposes barriers for developing countries to reach a sustainable agriculture.

The earliest maturing pigeonpea [Cajanus cajan (L.) Millspaugh] germplasm bred at ICRISAT

Adaptation of pigeonpea [Cajanus cajan (L.) Millspaugh], a short-day species, is restricted due to its sensitivity to photo-period. Earliness in this crop is reported to be linearly associated with photo-insensitivity; and this provides an opportunity to breed widely adapted cultivars through the selection for earliness. This research note reports breeding of the earliest maturing pigeonpea germplasm at ICRISAT. This germplasm, nicknamed as ‘super early’ and bred through the selection of transgressive segregants matured in < 90 days. It can be used as a source material in breeding early maturing cultivars and also can be introduced for cultivation in new production niches.

Observations on the development of plants

The influence of light intensity and daylength on four short-day species of &lt;i&gt;Chenopodium&lt;/i&gt; was analysed. The following species were tested: &lt;i&gt;Ch. ficifolium, Ch. glaucum, Ch. rubrum&lt;/i&gt; and &lt;i&gt;Ch. hybridum&lt;/i&gt;. Under short day, generative initiation was accelerated, the abundance of flowering, and growth and leaf differentiation processes were reduced. Under light of low intensity, the rhythm of development of the plants growing under long day is similar to that under short day. The development of axillary buds indicates a decrease in the intensity of vegetative differentiation and elongation growth, with an enhancement of the generative tonus; the buds in the axils of the highest growing leaves form directly inflorescences without preceding leaf differentiation. Inversion of the shape of leaves on lateral shoots was noted.

A methodology and an optimization tool to calibrate phenology of short-day species included in the APSIM PLANT model: Application to soybean

We developed a methodology and an optimization tool that simplifies calibration of the APSIM PLANT multi parameter input phenology module. The methodology and the tool were successfully applied to estimate phenological parameters for 40 soybean cultivars covering maturity groups from 00 to 6. Our approach utilized information on flowering, physiological maturity and soybean maturity group, and provided a complete set of phenological parameters for APSIM that accounted also for temperature × photoperiod interactions throughout the crop cycle. The model predicted flowering (root mean square error, RMSE = 3.1 d) and physiological maturity (RMSE = 5.5 d) very well in a range of environments across the USA (33–46°N latitude, n = 280). The relative absolute error was below 3% in all cases indicating the robustness of our approach. The APSIM PLANT phenology module is generic, thus our approach can be applied to all the short-day species included in the modelling platform.

Mobile signals in day length-regulated flowering: Gibberellins, flowering locus T, and sucrose

Despite low activity for stem growth, the gibberellins GA5 and GA6 act as long-day (LD) florigens in Lolium temulentum L. This claim is based on extensive evidence covering GA synthesis in LD in the induced leaf and their transport to the shoot apex where they act in a dose-dependent manner. GAs also act as a LD florigen in association with cold vernalization of L. perenne. In contrast, highly bioactive GA4 and, possibly, GA1 are important florigens in Arabidopsis thaliana (L.) Heynh. This species contrast reflects differences in GA deactivation, which is unimportant for Arabidopsis but dominant in L. temulentum. It is unclear if GAs participate in flowering responses of short-day (SD) species since it is LD, which up-regulate enzymes for GA biosynthesis. Sugars (sucrose) may also act directly as a florigen and, specifically, with increase in photosynthesis as in LD or when light intensity is increased in SD. In addition, in LD sucrose can indirectly cause flowering by up-regulating FT expression, the FT protein acting as a further leaf-to-apex transported florigen. Thus, there are not only multiple florigens but there can be complex interactions between the signaling pathways controlling production of these various florigens.

Two FLOWERING LOCUS T (FT) homologs in Chenopodium rubrum differ in expression patterns

FLOWERING LOCUS T (FT) like genes are crucial regulators (both positive and negative) of flowering in angiosperms. We identified two FT homologs in Chenopodium rubrum, a short-day species used as a model plant for the studies of photoperiodic flower induction. We found that CrFTL1 gene was highly inducible by a 12-h dark period, which in turn induced flowering. On the other hand, photoperiodic treatments that did not induce flowering (short dark periods, or a permissive darkness interrupted by a night break) caused only a slight increase in CrFTL1 mRNA level. We demonstrated diurnal oscillation of CrFTL1 expression with peaks in the middle of a light period. The oscillation persisted under constant darkness. Unlike FT homologs in rice and Pharbitis, the CrFTL1 expression under constant darkness was very low. The CrFTL2 gene showed constitutive expression. We suggest that the CrFTL1 gene may play a role as a floral regulator, but the function of CrFTL2 remains unknown.

The role of temperature and photoperiod in diapause induction in the brassica leaf beetle, Phaedon brassicae (Coleoptera: Chrysomelidae)

The brassica leaf beetle, Phaedon brassicae Baly (Coleoptera: Chrysomelidae), one of the pests infesting cruciferous vegetables in China and Japan, is a multivoltine species that oversummers and overwinters as an adult. The effects of both temperature and photoperiod on reproductive diapause induction were systematically investigated in this beetle. Under 16L : 8D, most of the beetles entered reproductive diapause at 12-30°C, indicating that photoperiod played a crucial role in estivation diapause induction. Under 12L : 12D, all adults developed without diapause at 28 and 30°C; less than 25% of the individuals entered reproductive diapause at 16-24°C; however, 46.1% of the individuals entered diapause at 12°C, suggesting that low temperature also had a relatively important influence on the determination of diapause. The photoperiodic response curves indicate that this species is a typical short-day species. The critical day-lengths at 20, 24 and 28°C were 13.2, 13.6 and 13.8 h, respectively. Transferring them from 16L : 8D to 12L : 12D or vice versa at different ages and/or stages during their development revealed that the photoperiod experienced by adults during the first 11 days might be important for diapause determination, even though an effect of photoperiod on the larval and pupal stages can not be excluded. Transferring individuals kept at a photoperiod of 12L : 12D from 25°C to 12°C or vice versa at different ages and/or stages during their development revealed that the temperature cue for diapause is mainly perceived by the late instar larvae and pupae.

Effects of Temperature, Light and Pre-Chilling on Seed Germination of Stevia rebaudiana (Bertoni) Bertoni Accessions

Stevia rebaudiana (Bertoni) Bertoni is a perennial shrub of the Asteraceae family native to Paraguay and Brazil where it has been used for several years as a sweetener. It is a short-day species, with a critical light requirement for flowering of roughly 13 hours. In plants whose biological cycle is strongly photoperiod-dependent, latitude is one of the major factors influencing reproduction. Late flowering may adversely affect seed production if this occurs during a season that is unfavorable to pollination. At Italian latitudes, this species often gives scanty seed production, with low germination rate and poor germination energy of seeds produced. In 2001 four accessions have been grown for seed production in a field plot experiment in Central Italy. The various accessions were found to exhibit noticeably different photoperiod requirements, which affected flowering time (from late August to the end of September) and consequently also the conditions of achene filling and ripening. Late flowering and seed ripening occurred during autumn season, unfavourable to complete seed formation, leading to an increase in the empty seed percentage recorded for each accession. Detailed germination trials were therefore undertaken using seeds collected from plants of the different accessions in order to assess the quality of the seeds produced. Various germination methods have been tested in a controlled environment adopting four different temperatures (20° C, 25° C constant temperature and 15/25° C, 20/30° C (16/8h) alternating temperature) in light or darkness with or without pre-chilling. Germination rates varied over an extensive range (germination percentage from 9 to 83%), mainly due to the divergent specific characteristics of the material examined and the different treatments studied. At all temperatures tested, the most earlier accession, showed the higher germination percentages (54-83%) while the latest accession was among those with the lowest germination values (9-44%). Overall, at the constant temperatures assayed, pre-chilling gave a higher germination percentage as compared to no pre-chilling, while at alternating temperatures higher germination rates were obtained in the absence of pre-chilling. The great variability observed between accessions for photoperiodic requirement as well as in seed germinative characteristics was probably due to the fact that this species was not subjected to any genetic improvement program.

Parental effects: Physiological age, mating pattern, and diapause duration on diapause incidence of progeny in the cabbage beetle, Colaphellus bowringi Baly (Coleoptera: Chrysomelidae)

The cabbage beetle, Colaphellus bowringi Baly, is a short-day species that has both a facultative summer and winter adult diapause. In this study, we systematically investigated the effects of parental physiological age, mating pattern (including mating frequency and delayed mating), and diapause duration on the diapause incidence of progeny in the beetle. As parents aged, progeny diapause incidences showed considerable inter-parental variability and an abnormally varying pattern, but their predicting line was approximate to horizontal when reared under constant conditions. There was significant difference in progeny diapause incidence between multiple-mating and once-mating treatments. Higher diapause incidences in the progeny were observed in delayed-mating treatments. Progeny diapause incidences increased as diapause duration in the parental generation increased, and hibernating individuals produced more diapausing progeny than aestivating ones. Reciprocal cross tests between the post-diapause adults and non-diapause adults with no diapause history showed that the effect of parental diapause duration on the progeny diapause incidence was determined by both mothers and fathers but the mothers appeared to have a stronger effect than the fathers. Our results suggest that the parental age effect in Colaphellus bowringi might not be simply age-dependent, but may be controlled by the interaction of multiple factors, including physiological, environmental, behavioral and genetic factors. We discuss the ecological and physiological significance of these findings.

Diapause induction and clock mechanism in the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae)

Photoperiodic control of diapause induction was investigated in the short-day species, Colaphellus bowringi, which enters summer and winter diapause as adult in the soil. Photoperiodic responses at 25 and 28 °C revealed a critical night length between 10 and 12 h; night lengths ≥12 h prevented diapause, whereas night lengths <12 h induced summer diapause in different degree. Experiments using non-24-h light–dark cycles showed that the duration of scotophase played an essential role in the determination of diapause. Night-interruption experiments with T=24 h showed that diapause was effectively induced by a 2-h light pulse in most scotophases; whereas day-interruption experiments by a 2-h dark break had a little effect on the incidence of diapause. The experiments of alternating short-night cycles (LD 16:8) and long-night cycles (LD 12:12) during the sensitive larval period showed that the information of short nights as well as long nights could be accumulated. Nanda–Hamner experiments showed three declining peaks of diapause at 24 h circadian intervals. Bünsow experiments showed two very weak peaks for diapause induction, one being 8 h after lights-off, and another 8 h before lights-on, but it did not show peaks of diapause at a 24 h interval. These results suggest that the circadian oscillatory system constitutes a part of the photoperiodic clock of this beetle but plays a limited role in its photoperiodic time measurement.

Age at flowering differentially affects vegetative and reproductive responses of a determinate annual plant to elevated carbon dioxide.

Plant population and community dynamics may be altered by increasing atmospheric CO(2) concentrations [[CO(2)]] through intraspecific variation in the responses of vegetative and reproductive growth. Although these responses may be regulated by age at flowering, little is known about the direct effects of age at flowering on growth responses to elevated [CO(2)]. In this study, we examined the interactive effects of elevated [CO(2)] and age at flowering on absolute and relative allocation to vegetative and reproductive growth in the determinate, short-day species Xanthium strumarium L. (common cocklebur). Six cohorts were planted at 5-day intervals in chambers maintained at either 365 or 730 micro mol mol(-1) CO(2), with an 18-h photoperiod and a non-limiting nutrient supply. All plants were simultaneously induced to flower by switching the photoperiod to 12 h for 2 days, then switching back to an 18-h photoperiod for the remainder of the experiment. All plants were harvested 15 days after the onset of flowering. Total plant biomass increased 11-41% with increasing [CO(2)] and 45% from the youngest to the oldest cohort. Vegetative growth responses to elevated [CO(2)] significantly increased with increasing age at flowering, associated with increasing sink relative to source capacity. In contrast, total fruit mass decreased 32% from the youngest to the oldest cohort and was not significantly affected by CO(2) supply. Relative biomass allocation to fruit decreased 47% from the youngest to the oldest cohort, reflecting decreased numbers of fruit, and 6-28% with increasing [CO(2)], reflecting decreased mean mass per mature fruit. Our findings suggest that elevated [CO(2)] may increase vegetative growth in Xanthium without increasing reproductive biomass, and that age at flowering may influence these responses through effects on source:sink balance. Further, changes in the allometric relationship between vegetative and reproductive growth associated with growth in elevated [CO(2)] suggest that long-term population and community-level responses to elevated [CO(2)] may differ substantially from predictions based on vegetative responses.

The role of photoperiod and temperature in determination of summer and winter diapause in the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae)

The cabbage beetle, Colaphellus bowringi, is a short-day species undergoing an imaginal summer and winter diapause. Its photoperiodic response highly depends on temperature. All adults entered diapause at ≤ 20 °C regardless of photoperiods. High temperatures strongly weakened the diapause-inducing effects of long daylengths. The diapause-averting influence of short daylengths was expressed only at high temperatures (above 20 °C). This indicates that the beetle has a cryptic ability to reproduce in summer. In fact, summer and winter diapause were induced principally by relatively low temperatures in the field, whereas photoperiod had less influence on diapause induction. The critical daylength for the autumnal population was between 12 h and 13 h. By transferring from a long day to a short day or vice versa at different times after hatching, it was shown that the sensitive stage with regard to photoperiod was the larva, whereas a long day was photoperiodically more potent than a short day. The sensitive stage to temperature encompassed the larval, pupal and adult stages. This different response pattern serves to ensure that the beetle enters summer and winter diapause in time. The selections for non-diapause trait under laboratory (at 25 °C) and natural conditions (at >24 °C) showed that the beetle could lose its sensitivity to photoperiod very rapidly.

Effect of temperature and photoperiod on the phenological development of common lambsquarters

Abstract The goal of a mechanistic model is to determine the outcome of weed–crop interference. An understanding of weed phenology is essential for construction of such models because phenological development is a major factor determining the outcome of weed–crop competition. Growth cabinet studies were conducted to determine the influence of temperature and photoperiod on the phenological development of common lambsquarters. Common lambsquarters is a short-day species adapted to a temperature range of 6.5 to 44.5 C. Phenological development of common lambsquarters grown under a constant temperature of 20 C and an 8-h photoperiod was described in terms of biological days (Bd: chronological days at the optimum photoperiod and temperature). Three development phases of common lambsquarters were described as (1) a juvenile phase of 6.3 Bd, (2) a photoperiod-sensitive inductive phase of 8.2 Bd, and (3) a photoperiod-sensitive postinductive phase of 34.4 Bd. The photoperiod sensitivity of rate of development di...

Effects of photoperiod on the phenological development of redroot pigweed (Amaranthus retroflexus L.)

Mechanistic weed models focus on determining the outcome of weed and crop interference. An understanding of weed phenology is essential for simulation model development. Phenological development is a major factor determining the outcome of weed–crop competition. Growth cabinet studies were conducted to characterize the influence of photoperiod on the phenological development of redroot pigweed (Amaranthus retroflexus L.). Results indicated that redroot pigweed is a quantitative short-day species. Four development phases of redroot pigweed were described according to its response to photoperiod: (1) a juvenile phase of 1.1 d; (2) a photoperiod-sensitive inductive phase of 7.9 d; (3) a photoperiod-sensitive post-inductive phase of 39.9 d; and (4) a photoperiod-insensitive phase of 2.2 d. This information is useful for the development of mechanistic models and for comprehending the distribution and competitive ability of redroot pigweed with crops. The utilization of these results could help in predicting the phenological development of redroot pigweed. Key words: Phenology, mechanistic weed models, juvenile phase

Validation of a Photothermal Phenology Model for Predicting Dates of Flowering and Maturity in Legume Cover Crops using Field Observations

ABSTRACT Lack of information about the specific environmental adaptation of cover crop species remains a serious constraint in the efficient design of agronomic experiments examining options for more suitable and more sustainable management of hillside farming systems in the tropics. Predictive models of crop phenology for cover crop species exist but how robust these are for legume cover crop species is largely unproven. We determined the predictive ability of phenological models, derived from glasshouse studies and driven by temperature and photoperiod, across a diverse range of cover crop genotypes and tropical hillside environments. The models were designed to predict the duration from germination to first flowering, and from first flowering to first pod maturity. Seeds of eleven legume species of cover and/or green manure crops collected from different hillside locations world-wide were sown in two groups of nurseries (tropical short-day plants in early summer and sub-tropical long-day plants in early winter) at Kabale and Namulonge in Uganda, Godavari and Lumie in Nepal, Cochabamba in Bolivia, Zamorano in Honduras, and Valenca in Brazil. Dates of sowing, first flowering and first pod maturity were taken and daily temperature data were recorded at each site. Similar observations for the same genotypes were available from independent experiments conducted at Islamabad, Pakistan, Hattiban, Nepal and at three locations in Cyprus. Model predictions were compared with field observations. The proportion of variation accounted for in the period from sowing to first pod maturity was 88% and 89% for the short-day and the long-day groups of genotypes, respectively. Likewise, the average difference from sowing to pod maturity between the model predictions and the field observations was 6.3% and 7.9% for the combined short-day species and the combined long-day species, respectively. It is clear that the model predictions, for this dataset at least, are sufficiently robust to serve as a filter for determining the environmental suitability of germplasm.

Linear Relations between Carbon Dioxide Concentration and Rate of Development Towards Flowering in Sorghum, Cowpea and Soyabean

Negative linear relations were detected (P < 0·005) between the rate of progress from sowing to panicle initiation and CO2 concentration (210-720 μmol CO2 mol-1 air) for two genotypes of sorghum [Sorghum bicolor (L.) Moench]. Relations between CO2 concentration and the rate of progress from sowing to first flowering were also negative in soyabean [Glycine max (L.) Merrill] (P < 0·025), but positive in cowpea [Vigna unguiculata (L.) Walp.] (P < 0·025), albeit that in both grain legumes sensitivity was much less than in sorghum. Thus CO2 elevation does not delay flowering in all short-day species. The considerable effect of CO2 concentration on times to panicle initiation resulted in large differences among the sorghum plants at this developmental stage; with increase in CO2 concentration, plants were taller with slightly more leaves and more pronounced apical extension. At the same time after sowing however, sorghum plants were heavier (P < 0·05) at 210 than at 360 μmol CO2 mol-1 air. In contrast, relations between the dry masses of the soyabean and cowpea plants and CO2 concentration were positive and curvilinear (P < 0·05). It is suggested that the impact of global environmental change could be severe for sorghum production in the semi-arid tropics.

Effects of elevated CO2 on time of flowering in four short-day and four long-day species

This study was undertaken to determine if the effect of elevated CO2 on flowering phenology is a function of the photoperiodic response of the species involved. Four long-day plants, Achillea millefolium, Callistephus chinensis, Campanula isophylla, and Trachelium caeruleum, and four short-day plants, Dendranthema grandiflora, Kalanchoe blossfeldiana, Pharbitis nil, and Xanthium pensylvanicum, were grown under inductive photoperiods (9 h for short day and 17 h for long day) at either 350 or 1000 μL/L CO2. Time of visible flower bud formation, flower opening, and final plant biomass were assessed. Elevated CO2 advanced flower opening in all four long-day species and delayed flowering in all four short-day species. In the long-day species, the effect of CO2 was primarily on bud initiation; all four species formed buds earlier at high CO2. Bud development, the difference in time between flower opening and bud initiation, was advanced in only one long-day species, Callistephus chinensis. Mixed results were obtained for the short-day species. Elevated CO2 exerted no effects on bud initiation but delayed bud development in Dendranthema and Kalanchoe. In Xanthium, bud initiation rather than bud development was delayed. Data on bud initiation and development were not obtained for Pharbitis. The negative effect of CO2 upon phenology in the short-day species was not associated with negative effects on growth. Elevated CO2 increased plant size in both long-day and short-day species. Key words: phenology, bud initiation, flower opening, size at flowering, photoperiodism.