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ISSN : 1225-5009(Print)
ISSN : 2287-772X(Online)
Flower Research Journal Vol.27 No.1 pp.9-16
DOI : https://doi.org/10.11623/frj.2019.27.1.02

Photosynthetic and Growth Response of Phalaenopsis Queen Beer ‘Mantefon’ to Variable CO2 Concentrations at Different Vegetative Growth Stages

Su Jung Song, Do Lee Yun††, Ah Ram Cho, Yoon Jin Kim*
Department of Horticulture, Biotechnology and Landscape Architecture, Seoul Women’s University, Seoul 01797, Korea
Current address: Useful Plant Resources Center, Korea National Arboretum, Yangpyeong 12519, Korea
Current address: Gardens and Education Division, Korea National Arboretum, Gyeonggi-do 11186, Korea
Corresponding author: Yoon Jin Kim Tel: +82-2-970-5620 E-mail: yj1082@swu.ac.kr
22/11/2018 28/02/2019 25/03/2019

Abstract


Photosynthetic characteristics and growth responses of Phalaenopsis Queen Beer ‘Mantefon’ orchid were determined in plants exposed to variable carbon dioxide (CO2) concentrations at 2-, 24-, and 36-weeks age (i.e., corresponding to juvenile, young, and mature vegetative growth stages, respectively). Plants were grown at 400 (control), 800, or 1,600 μmol·mol-1 CO2 for 6 hours during the nighttime for 32 weeks. Phalaenopsis ‘Mantefon’ in 2-and 24-week-old plants grown at 1,600 μmol·mol-1 CO2 had increased leaf number and net CO2 uptake compared with the plants grown at 400 μmol·mol-1 CO2. In 36-week-old of Phalaenopsis ‘Mantefon’, leaf number was significantly greater in plant grown at 800 and 1,600 μmol·mol-1 conditions compared with plants grown at 400 μmol·mol-1 CO2. Leaves that emerged after the start of the CO2 treatment were initially longer in the plants grown at 1,600 μmol·mol-1 CO2 than at 400 μmol·mol-1 C O2, but the final leaf length was shortest in the plants grown at 1,600 μmol·mol-1 CO2 condition. Plants showed crassulancean acid metabolism characteristic of nighttime CO2 uptake regardless plant growth stages. We found that growers may be able to promote leaf growth with increasing leaf number and reducing time to leaf initiation in the 36-week-old (i.e., mature stage) plants with 800 – 1,600 μmol·mol-1 CO2 and 2- and 24-week-old (i.e., juvenile and young stages) plants with 1,600 μmol·mol-1 C O2 for Phalaenopsis ‘Mantefon’.



초록


    Seoul Women`s University

    Introduction

    Capturing atmospheric carbon dioxide (CO2) using photosynthesis is crucial for the production of plants (Friend et al. 2009). Future changes in the global climate should affect the key processes involved in photosynthetic productivity. CO2 enrichment promotes growth in cultivated plants. Increased CO2 uptake hastens growth and facilitates the production of some combination of more and larger plant leaves, branches, flowers, and fruits. This greater yield occurs because increased CO2 concentrations promote photosynthesis (Dong et al. 2016;Nederhoff 2004). CO2 concentrations are higher during cold temperatures when the greenhouse is not vented during the nighttime and early morning hours (Reddy et al. 2010). Crassulacean acid metabolism (CAM) is a process of fixation of atmospheric CO2 during nighttime and early morning hours in some plants. CO2 has positive and negative effects on CAM plants. Biomass increases by 35% in CAM plants exposed to enriched CO2 treatment (Drennan and Nobel 2000;Xu et al. 2014). Increasing CO2 concentrations from 350 to 650 μmol·mol-1 in CAM plants increases the dry weight production of Agave deserti, Ferocactus acanthodes, and Kalanchoe hybrids (Endo and Ikusima 1997). Compared with plant responses at 380 μmol·mol-1 CO2, Selenicereus megalanthus (CAM plant) had 129%, 73%, and 68% increases in total daily net CO2 uptake, shoot elongation, and shoot dry mass, respectively, at 1,000 μmol·mol-1 CO2 (Weiss et al. 2010). However, growing Doritaenopsis at 700 – 1,000 μmol·mol-1 CO2 was not more effective than growing the plants at atmospheric CO2 conditions during the vegetative growth stages (Endo and Ikusima 1997). The excessive carbohydrates produced by elevated CO2 leads to photosynthetic acclimation, which limits production. The biomass of the CAM plant Ananas comosus grown at 712 μ mol·mol-1 CO2 was decreased by 10% compared with that of plants grown at atmospheric CO2 (Drennan and Nobel 2000).

    The CAM plant Phalaenopsis is a popular and valuable potted ornamental orchid because the grower can easily schedule growth to meet specific market dates (Lu et al. 2016). It has attractive and long lasting flowers in a variety of colors, sizes, shapes and a high wholesale value. During vegetative growth, cultivation of Phalaenopsis requires temperatures above 28°C for 18 – 20 months for leaf development (Cho et al. 2019;Wang 2007); the high temperature (> 28°C) also inhibits flowering (Blanchard and Runkle 2006). This long production time is expensive for commercial producers because every stage requires use of a controlled environment (Holley 2016). During vegetative growth, rapid production of new shoot and leaf production is essential (Tremblay and Gosselin 1998). CO2 enrichment in the greenhouse nursery might be used as a method to shorten the plant growth period.

    Plant ages can be divided into juvenile, young, and mature stages of vegetative growth in Phalaenopsis (Guo and Lee 2006). Different cultivation conditions are required at different growth stages. Commercial growers usually purchase immature plants contained in flasks. At the juvenile stage, 1- to 20-week-old Phalaenopsis are not competent to flower, even at flower induction conditions of temperatures < 26°C (Hong 2017;Lee et al. 2015). At the young stage, small bare-root plants of 24-week-old Phalaenopsis can produce flowers at relatively low temperatures (i.e., < 26°C). At the mature stage, 36-week-old Phalaenopsis (20 cm leaf span) are transplanted into the final 12 cm pots for continued vegetative growth (Blanchard et al. 2007). Growth responses are different depending on the species and plant growth stages. In Cymbidium, rates of photosynthesis in 1-year-old plants are greater compared with rates in 2-year-old plants grown at the same CO2 concentrations (Kim et al. 2013).

    In previous study, 36-week-old Doritaenopsis (Phalaenopsis × Doritis) grown under 800 and 1,600 μmol·mol-1 CO2 had increased net CO2 uptake and leaf initiation compared to the plants grown under 450 μmol·mol-1 CO2 concentration (Yun et al. 2018). Leaf span was lower in the 36-week-old Doritaenopsis grown under the 800 and 1,600 μmol·mol-1 CO2 concentration compared to the plants grown under 450 μmol·mol-1 CO2. However, no reports have been published on the effects of growth and photosynthetic response on the different growth stages in vegetative period of Phalaenopsis. In present study, we determined the photosynthetic characteristics and growth responses of 2-, 24-, and 36-week-old (i.e., juvenile, young, and mature vegetative stages, respectively), Phalaenopsis Queen Beer ‘Mantefon’ at difference CO2 concentrations.

    Materials and Methods

    Plant materials and growth conditions

    Phalaenopsis Queen Beer ‘Mantefon’ was propagated by tissue culture, 2-, 24-, and 36-week-old plants were purchased from Orchid Nursery (Goyang, Korea; 38°N latitude, 127°E longitude). The 2-week-old Phalaenopsis was cultivated after deflasking. Plants had one leaf (mean, 3.0 cm width, 6.8 cm length, and 6.8 cm leaf span) at 2 weeks, two leaves (mean, 3.3 cm width, 9.0 cm length, and 15.2 cm leaf span) at 24 weeks, and three leaves (mean, 5.0 cm width, 9.6 cm length, and 20.1 cm leaf span) at 36 weeks. The 2-, 24-, and 36-week-old plants were transplanted into their respective 6 cm, 6 cm, or 12 cm diameter pots filled with sphagnum moss (Lonquen Ltda., Puerto Montt, Chile). The air temperature was maintained at 29°C with 70% relative humidity. Three wave cool white fluorescent lamps (Phosphor fluorescent lamp, Dulux L 36W, Osram Co., Seoul, Korea) were used to maintain the photosynthetic photon flux at 160 μ mol·m-2·s-1 during 06:00 - 18:00 h at the plant canopy. The plants were fertigated by hand once every 10 days with solution of water-soluble fertilizer (electrical conductivity (EC) 1.0 ± 0.1 dS·m-1, pH 6.0 – 6.5; Newgold 20-8.7-16.7 (N-P-K), Neufarm Co., Ltd., Munster, Germany). All plants were grown in growth chamber (HB-303DHC, Hanbaek Scientific Co., Suwon, Korea).

    CO2 treatments

    The CO2 concentration was maintained using automated continuous injection of pure CO2 at 400 (control, atmospheric CO2), 800, or 1,600 μmol·mol-1 CO2. Purified CO2 (CO2 cylinders, Seoul Gas Co., Ltd, Seoul, Korea) was supplied through flowmeters at a rate of approximately 50 mL/min. The CO2 treatments were applied for 6 hour (00:00 – 06:00 h) dark periods for 32 weeks. The CO2 concentration in the chamber was monitored at 1 min intervals using automatic sensor (Air Quality Monitor Am-21, Wise Sensing Inc., ‘Younin’, Korea).

    Growth measurements

    Time to leaf initiation from the start of the CO2 treatment was measured when the first visible leaf was 0.5 cm long. Leaf number longer than 0.5 cm were counted for each plant every 4 weeks. Leaf length was measured for the first leaf initiated after CO2 treatment began. Leaf span was measured as the longest length from one leaf tip to the opposing leaf tip. Number of leaves, leaf length, and leaf span were measured for 32 weeks after the CO2 treatment began. A completely randomized design with 8 plants per treatment was used for the growth measurements.

    Photosynthetic characteristics

    Net CO2 uptake, stomatal conductance (gs), and transpiration rate (tr) were measured at 01:00 h (nighttime) and 11:00 h (daytime), r espectively. M easurements were t ak en w ith a portable photosynthesis system (Li-6400XT, Soldan Co., Seoul, Korea) using the instrument’s built-in ‘auto-program’ function. The atmospheric CO2 concentrations in the plant growth chambers were approximately 400, 800, or 1,600 μ mol·mol-1, and the same amounts of CO2 were supplied into the leaf chambers. Photosynthetic characteristics were measured at uppermost mature leaf onto 6 cm2 leaf chamber for each plant, with a light condition of 160 μ mol·m-2·s-1. Measurements were obtained at a 29°C leaf temperature and at 300 μmol·s-1 flow rate. Net CO2 uptake, gs, and tr of the 24- and 36-weeks old plants were measured at 12 weeks after the CO2 treatments began. Due to small leaf s ize of 2 -week -old p lants, n et CO2 u ptak e, gs, and tr were recorded at 32 weeks. Each measurement followed a completely randomized design with three replications per treatment.

    Statistical analysis

    Statistical analyses were performed using SAS system for Windows version 9.3 (SAS Inst. Inc., Cary, NC, USA). Differences among treatment groups were assessed using Tukey’s honestly significant difference (HSD) tests. p-values < 0.05 were considered to indicate statistically significant results. Graph module analyses were performed using Sigma Plot version 10.0 (Systat Software Inc., San Jose, CA, USA).

    Growth parameters of leaves

    The time to leaf initiation of 2- and 36-week-old plants was reduced to 35.0 and 55.0 days in plants grown at 1,600 μmol・mol-1 CO2, compared with the control plants, 58.8 and 67.7 days, respectively. (Figs. 1A and C). In 24-week-old plants, time to leaf initiation was reduced to 39.6 and 38.0 days in plants grown at 800 and 1,600 μmol・ mol-1 CO2, compared with the controls (58.4 days) (Fig. 1B). After 28 weeks, leaf numbers in 2- and 24-week-old plants grown at 1,600 μmol·mol-1 CO2 were significantly greater compared with that of plants grown at 400 μ mol·mol-1 CO2 (Figs. 2A and B). In 36-week-old plants, the numbers of leaves in plants grown at 800 and 1,600 μ mol·mol-1 CO2 were significantly greater compared with plants grown at 400 μmol·mol-1 CO2 at 20, 28, and 32 weeks (Fig. 2C). Leaf initiation and leaf number were promoted when plants were grown at the 800 - 1,600 μ mol·mol-1 CO2 range, regardless of differences in vegetative growth stage. Our previous study revealed that 60-week-old Phalaenopsis grown at 1,600 and 2,400 μ mol·mol-1 CO2 have significantly enhanced leaf numbers, leaf lengths, and leaf widths compared with plants grown at 450 and 800 μmol·mol-1 CO2 (Kim et al. 2017). More leaves are produced in plants grown at 800 and 1,600 μ mol·mol-1 CO2 compared with plants grown at 450 μmol・ mol-1 CO2, and leaves are initiated at a faster rate at 1,600 μmol·mol-1 CO2 in 36-week-old Doritaenopsis (Yun et al. 2018). Elevated CO2 concentrations promote growth in cultivated plants (Friend et al. 2009). CO2 stimulates cell division and cell expansion, which has been associated with increased plant growth rates (Huang and Xu 2015;Pritchard et al. 1999). Exposure to elevated CO2 concentrations results in shorter cell cycling in plants in both the root and shoot meristems (Kinsman et al. 1997). Shortened cell cycling appears to be supported by increased transport of assimilates and carbohydrate availability in shoot apical meristems. Compared with plants in the control group, plants grown at 1,600 μmol·mol-1 CO2 conditions had greater leaf numbers; exposure to the elevated CO2 concentration likely resulted in shortened cell cycling. New leaves in plants grown at 1,600 μmol・mol-1 CO2 also had faster initiation; the time to leaf initiation of plants grown at 1,600 μmol・mol-1 CO2 conditions was shorter than in plants grown at 400 μmol・mol-1 CO2 conditions (Figs. 1 and 2A - C). Leaf length was longer in plants grown at the 1,600 μ mol·mol-1 CO2 conditions compared with plants grown at 400 μmol・mol-1 CO2 conditions until 16 weeks of CO2 treatments in the 2-, 24-, and 36-week-old plants (Figs. 2D - F). After 16 weeks, leaf length was longer in the 2-, 24-, and 36-week-old plants grown at 400 μmol・mol-1 CO2 compared with plants grown at 1,600 μmol・mol-1 CO2. The growth of leaf length that was exposed to high CO2 concentration stopped after 16 weeks. The reason of the low growth rate of leaf length after 16 weeks is that higher CO2 concentration conditions promote new leaf development rather than the growth of leaf length. After 28, 20, and 16 weeks, leaf span in 2-, 24-, and 36-month-old plants grown at 400 μmol·mol-1 CO2 was greater than in plants grown at 800 or 1,600 μmol·mol-1 CO2 (Figs. 2G - I). Leaf span of 2-week-old plants were not statistically significant differences among different CO2 conditions until 24 weeks (Fig. 2G), because leaf length of plants in flask was longer than 2-week-old plant grown under 800 or 1,600 μ mol·mol-1 CO2 treatment (data not shown).

    Plants can be divided into source and sink components (Hofius and Börnke 2007). The source components are the locations where net fixation of CO2 occurs (e.g., older leaves). The sink components are the sites where assimilates are stored or used (e.g., younger leaves, roots, and fruits). Increased carbohydrate production associated with elevated CO2 exceeds the plant’s capacity to produce new sinks as it matures, and net photosynthetic rates decline to balance source activity and sink capacity (Thomas and Strain 1991). Acclimatization to elevated atmospheric CO2 concentrations, as is observed for many species, is usually attributed to altered source-sink relationships. Accumulation of excess soluble sugars and starch results in feedback inhibition of photosynthesis. Feedback inhibition may result in sugar and phosphate build-up, and reduced rates of starch and sucrose synthesis. A build-up of sugars may also suppress ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and result in a lowered photosynthetic rate. An imbalanced source-sink might indicate that the amounts of nutrients were inadequate to support photosynthesis and growth. Nutrient limitation is more likely to disrupt the balance between source and sink in plants growing under conditions of elevated CO2 concentrations (Baker and Thomas 1992). To alleviate nutrient deficiencies, plants should be supplied with different nutrients as CO2 concentrations vary. The small leaf span in Phalaenopsis grown at greater CO2 concentrations will be affected by nutrient deficiencies. The Phalaenopsis were fertigated using water-soluble fertilizer at EC 1.0 d·s-1, regardless of the different CO2 concentrations. In this study, the Phalaenopsis ‘Mantefon’ grown at a range of 800 - 1,600 μmol·mol-1 CO2 conditions had stimulation of leaf initiation, but the effect diminished with time and smaller-sized leaves resulted.

    Photosynthetic characteristics

    In 2-, 24-, and 36-week-old plants, during the nighttime hours net CO2 uptake was 1.95 to 5.88 μmol·m-2·s-1 compared with -0.54 to 0.61 μmol·m-2·s-1 during the daytime (Figs. 3A - C). All vegetative growth stages of Phalaenopsis ‘Mantefon’ performed CAM (i.e., CO2 u ptak e during the nighttime). Net CO2 uptake in 2-week-old plants grown at 1,600 μmol·mol-1 CO2 conditions was significantly greater than in plants grown at 400 μmol·mol-1 CO2 conditions at nighttime (Fig. 3A). In 24-week-old plants, net CO2 uptake was significantly greater under 800 - 1,600 μ mol·mol-1 CO2 conditions compared with plants grown at 400 μmol・mol-1 CO2 conditions at nighttime (Fig. 3B). Net CO2 uptake in 36-week-old plants grown at 800 μ mol·mol-1 CO2 was significantly greater than in plants grown at 400 μmol·mol-1 CO2 (Fig. 3C). During daytime, net CO2 uptake in 2-, 24-, and 36-week-old plants was not significantly different between different CO2 concentrations (Figs. 3A - C). During photosynthesis, CO2 is fixed and reduced to carbohydrate for plant growth (Huang and Xu 2015).

    Increasing photosynthesis can be due to the greater carboxylation capacity in elevated CO2 conditions. The CAM plant Selenicereus megalanthus grown at 1,000 μmol·mol-1 CO2 has a 129% increase in total daily net CO2 u ptak e compared with plants grown at atmospheric CO2 concentrations (Weiss et al. 2010). The net CO2 u ptak e increased with older plant growth stages; 2-, 24-, and 36-week-old plants grown at 400 μmol・mol-1 CO2 had 1.95, 2.30, and 3.50 μmol·m-2·s-1 uptake, respectively, at nighttime (Figs. 3A - C). Because of the increased net CO2 uptake with older plant growth stages, in 2-, 24-, and 36-week-old plants, 3.3, 5.6, and 6.8 leaves, respectively, were produced at 400 μmol・mol-1 CO2 by 32 weeks (Figs. 2A - C). During nighttime, net CO2 uptake in Phalaenopsis TS97 is lower in juvenile plants compared with young and mature plants (Guo and Lee 2006). In CAM plants, increases in net daily CO2 uptake under elevated atmospheric CO2 conditions reflect increases in both Rubisco-mediated daytime CO2 uptake and phosphoenolpyruvate carboxylase-mediated nighttime CO2 u ptak e; t he l atter results in increased nocturnal malate accumulation (Drennan and Nobel 2000). In 2-week-old plants, gs and tr were higher in the plants grown at 800 μmol·mol-1 CO2 than in plants grown at the other CO2 concentrations during nighttime (Figs. 3D and G). The gs and tr values in 24-week-old plants were higher in plants grown at 800 and 1,600 μmol·mol-1 CO2 compared with the plants grown at 400 μmol・mol-1 CO2 during nighttime (Figs. 3E and H). In 36-week-old plants, gs and tr values were not significantly different between different CO2 concentrations (Figs. 3F and I). At the cellular level, elevated CO2 concentrations induce stomata closure for increased water use efficiency (Wang et al. 2015). In 2-week-old Phalaenopsis ‘Mantefon’, gs and tr were decreased under 1,600 μmol·mol-1 CO2 conditions compared with plants grown at 800 μmol·mol-1 CO2. Decreased gs is an interactive factor and low water availability might benefit plant productivity under increased atmospheric CO2 concentrations. tr was reduced due to a lower gs (Wang et al. 2015). Maximum tr and maximum stomatal opening occur in younger leaves of tobacco plants (Václavýk 1973). gs decreases with increasing leaf age in the chaparral shrub, Lepechinia calycina, growing in its natural habitat (Field and Mooney 1983). In Phalaenopsis ‘Mantefon’, tr decreased with increasing plant growth stage, independent of CO2 concentration.

    In our present study, in 36-week-old Phalaenopsis Queen Beer ‘Mantefon’ (i.e., mature stage), leaf number were significantly greater in plant grown at 800 and 1,600 μ mol·mol-1 CO2 conditions compared with plants grown at 400 μmol·mol-1 CO2. We found that Phalaenopsis Queen Beer ‘Mantefon’ in 2- and 24-week-old (i.e., juvenile and young stages) plants grown at 1,600 μmol·mol-1 CO2 had increased net CO2 uptake, leaf number, and shorten the time to leaf initiation compared with the plants grown at 400 μmol·mol-1 CO2. With these results, using 800 - 1600 μmol·mol-1 CO2 range for 36-week-old (i.e., mature stage) and 1,600 μmol·mol-1 CO2 condition for 2- and 24-week-old (i.e., juvenile and young stages) of Phalaenopsis Queen Beer ‘Mantefon’, growers may be able to promote leaf growth faster with increasing leaf number and reducing the time to leaf initiation.

    Acknowledgments

    This work was supported by a research grant f rom Seoul Women's University (2019).

    Figure

    FRJ-27-1-9_F1.gif

    Effects of CO2 concentrations on 2-week-old (A), 24-week-old (B), and 36-week-old (C) Phalaenopsis Queen Beer ‘Mantefon’ orchids on time to leaf initiation at 32 weeks after initiation of CO2 treatments. Error bars indicate standard error of the mean values (n = 8). The different letters represent statistically significant differences as determined by results of Tukey’s HSD tests; a p-value < 0.05 was used to indicate a statistically significant difference.

    FRJ-27-1-9_F2.gif

    Changes in number of leaves (A, B, and C), leaf length (D, E, and F), and leaf span (G, H, and I) of Phalaenopsis Queen Beer ‘Mantefon’ orchids in 2- (A, D, and G), 24- (B, E, and H), or 36-week-old (C, F, and I) plants after exposure to different CO2 treatment concentrations. Error bars represent standard errors of the mean values (n = 8). The different letters above the weeks after CO2 treatments indicate statistically significant differences between different CO2 treatments at (p < 0.05) based on the results of Tukey’s HSD tests.

    FRJ-27-1-9_F3.gif

    Net CO2 uptake (A, B, and C), stomatal conductance (D, E, and F), and transpiration rate (G, H, and I) of Phalaenopsis Queen Beer ‘Mantefon’ orchids in 2- (A, D, and G), 24- (B, E, and H), or 36-week-old (C, F, and I) plants after growth at different CO2 treatment concentrations. Error bars represent standard error of the mean values (n = 3). The different letters represent significant differences as determined by the results of Tukey’s HSD tests, a p-value < 0.05 indicated a statistically significant result.

    Table

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