HORTSCIENCE 43(1):134–137. 2008.
Growth and Photosynthetic Responses of Three Lycoris Species to Levels of Irradiance Panpan Meng, Ying Ge, Qianjin Cao, Jie Chang1, Peng Pan, and Chi Liu College of Life Sciences, Zhejiang University, 368 Zijinghua Road, Hangzhou 310058, P.R. China Yijun Lu College of Life Sciences, Zhejiang University, 368 Zijinghua Road, Hangzhou 310058, P.R. China; and Hangzhou Botanical Garden, 1 Taoyuanling, Hangzhou 310013, P.R. China Scott X. Chang Department of Renewable Resources, 442 Earth Sciences Building, University of Alberta, Edmonton, Alberta, T6G 2E3, Canada Additional index words. biomass allocation, chlorophyll concentration, growth, Lycoris chinensis, L. longituba, L. sprengeri Abstract. Lycoris species have appealing characteristics for potting plants, cut flowers, and landscaping decorations, including attractive foliage, which is very similar to that of cymbidium. Lycoris species have been extensively propagated and marketed in Asia. Understanding the response of Lycoris spp. to irradiance intensity will help the horticultural industry improve the production of potting plants of those species. We studied the responses of photosynthesis, growth, and biomass allocation of potted Lycoris spp. (L. chinensis, L. longituba, and L. sprengeri) bulbs grown under three levels of irradiance, i.e., 100%, 70%, and 30% full sunlight. We found that in terms of biomass production L. chinensis can be cultivated under all levels of irradiance studied from full to 30% sunlight. For L. longituba, high irradiance levels increased the rate of net photosynthesis. For both L. chinensis and L. longituba, the full sunlight treatment produced the most attractive plants characterized by shorter, wider, and darker green leaves, features that appeal to consumers. However, none of the growth traits of L. sprengeri were affected by the irradiance treatment over the entire experimental period. It can be concluded that potting plants of L. chinensis and L. longituba are best produced under full sunlight, whereas L. sprengeri can be produced under irradiance levels from 30% to full sunlight.
Lycoris Herb., also called ‘Magic lily’, ‘Surprise lily’, or ‘Spider lily’ (Adams, 1976), is a genus of Amaryllidaceae that is native to East Asia. In many local Chinese dialects, Lycoris species have commonly been called ‘‘stone garlic,’’ referring to their onion-like bulbs, which are inedible (Qin et al., 2003). The plants have ornamental value because of their beautiful flowers and attractive foliage (Zhang and Cao, 2001) and have been used as potted and landscape plants for several hundred years. Lycoris have fasciculate, emerald or bottle-green belt leaves that are similar to those of cymbidium. In the past several decades, some of the
Received for publication 24 Aug. 2007. Accepted for publication 17 Sept. 2007. We thank Gilbert Y. Chan and Jiashu Cao for reviewing an earlier version of the manuscript. We are grateful for the funding from the National Science Foundation of China (grant no. 30570113). 1 To whom reprint requests should be addressed; e-mail
[email protected]
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Lycoris species, cultivars, and hybrids such as L. radiata (L’Her.) Herb and L. aurea (L’Her.) Herb have been used worldwide. More than 10 species and cultivars are in cultivation in Australia. The demand for Lycoris as a commercial horticultural product has been increasing steadily. There are more than 20 species in the Lycoris genus (Hsu et al., 1994), but only L. radiata and L. aurea have been widely cultivated and commanded commercial values as ornamental plants. Choi (1991) and Zhang and Cao (2001) reported that L. radiata grew best at 65% and worst at 5% of full sunlight among the irradiance levels (from 5% to 80% sunlight) studied. Lu and Xu (1988) and Zhang and Cao (2001) found that L. aurea had better cut flower quality when grown at 50% sunlight. Three other Lycoris species, L. chinensis Traub, L. longituba Xu & Fan, and L. sprengeri Comes ex Baker, have been cultivated in China for many years and the market for these species has rapidly developed in recent years. Wild populations of these species in
their natural habitat are frequently found on warm and moist sites in locations under a certain degree of shade (Qin et al., 2003). However, little information is available on the response of these Lycoris species to various irradiance levels. A better understanding of how these species respond to shade in cultivation, both in terms of growth rates and ornamental value, can greatly affect the commercial production of those species for the horticulture industry. The objective of this study was to investigate the responses in chlorophyll concentration, rate of net photosynthesis, growth, and biomass allocation of three Lycoris species to various levels of irradiance. Results from this study should provide useful information for improving the cultivation of these species. Materials and Methods The study was conducted in a greenhouse at Hangzhou Botanical Garden (12016#E, 3015#N), Zhejiang Province, located in eastern China. The three Lycoris species studied were L. chinensis, L. longituba, and L. sprengeri, all native to China. We collected bulbs of L. chinensis (3.8 cm in diameter) and L. longituba (5 cm in diameter) from Guangde, Anhui Province, and L. sprengeri (3.3 cm in diameter), from Ningbo, Zhejiang Province, in Feb. 2005. We selected 54 bulbs that were as uniform as possible for each species and planted three bulbs in each pot (16 cm in height and 20 cm in top diameter) with a mixture of field soil and vermiculite in a 2:1 ratio (by volume) in a greenhouse. There were a total of 18 pots set up for each species. The potted bulbs were grown under three levels of irradiance: 100%, 70%, or 30% sunlight. Light intensity was controlled by nylon shadecloths, which was suspended at a height of 50 cm above the pot surface. No artificial light was used and therefore the light level in each treatment changes as the natural irradiance level changes during the day or in the growing season. Eighteen pots of bulbs for each species were randomly assigned to one of the three irradiance levels, i.e., each treatment was replicated six times. All pots were well-watered to reach field capacity of the potting mix. Such a watering regime is consistent with the general practice of growing potted plants in the greenhouse. The maximum and minimum air temperatures recorded during the experiment were 39.3 C and –5.4 C, and the mean air temperature was 17.5 C. The temperature did not differ between the treatments. The walls of the greenhouse can be opened to avoid the excessive heating up of the greenhouse. One month after the treatment were applied, the rate of net photosynthesis (Pn) was measured using a portable gas exchange system (model LCA-4; ADC, Hoddesdon, UK) at vigorous vegetative growth stage (mid-Mar. 2005). Light response curves were developed using the following photosynthetic photon flux (PPF): 0, 10, 20, 50, 100, HORTSCIENCE VOL. 43(1) FEBRUARY 2008
200, 500, 1000, 1500, and 1700 mmolm–2s–1 on one randomly selected, fully expanded leaf of one plant from each of three randomly selected replications for each treatment and species. The CO2 concentration and temperature in the leaf chamber were maintained at 360 mmolmol–1 and 25 C, respectively. Light response curves were fitted by nonlinear regression using Eq. 1 with the Origin 7.0 software (Originlab, Northampton, MA) (Peek et al., 2002; Potvin et al., 1990): Pn = Pmax ½1 eAQY ðPPFD LCPÞ ð1Þ where Pmax refers to the maximum photosynthetic rate as indicated by the asymptote of the response curve, i.e., the asymptote of photosynthesis, AQY is the apparent quantum yield represented by the initial slope of the curve, LCP refers to the light compensation point (where photosynthetic uptake and respiratory CO2 release are in equilibrium), and LSP was calculated as the PPF where Pmax was reached (i.e., no further increase in the rate of photosynthesis with increasing light). After these measurements were completed, all leaves were cut from each of the three plants that were used for determining the light response curve described previously to measure chlorophyll concentration. Those leaves from each plant were combined to form a composite sample for each of the three replications. Chlorophyll was extracted using ethanol and acetone according to Peng and Liu (1992). The concentrations of chlorophylls a and b in the extract were determined spectrophotometrically at 663 and 645 nm, respectively, using a HP 751 (Hewlett Packard, Shanghai, China) spectrophotometer. Chlorophyll a and b concentrations were calculated using the equations given in Peng and Liu (1992). Four replicates were randomly selected from the six replications of each treatment and harvested for growth analysis. The length, width, area, and number of fully expanded leaves (at the end of the experiment, all leaves of the three Lycoris species were fully expanded) of each plant were measured immediately after harvesting. Leaf area was measured by WinFLORA Pro 2002a (Regent Instruments, Quebec, Canada). Root, bulb, and leaf samples were then collected and dried in an oven at 80 C for 72 h. Aboveground biomass (AB, the same as leaf biomass, because these species have no stem) and belowground biomass (BB, BB = root + bulb biomass) were determined. Specific leaf area (SLA) was calculated according to Hunt (1978). Total biomass and belowground/ aboveground biomass ratio (BB/AB) were calculated for each species–treatment combination. All data were subjected to analysis of variance (ANOVA) using the SPSS 13.0 for windows software package (SPSS, Chicago). The least significant difference test was performed on each variable when there was a significant treatment effect from the ANOVA analysis. Statistical significance was determined at a = 0.05. HORTSCIENCE VOL. 43(1) FEBRUARY 2008
Results Photosynthetic response of Lycoris spp. to PPF under various levels of irradiance. Both L. chinensis and L. longituba had significantly greater Pmax under 100% sunlight than under other irradiance levels, whereas L. sprengeri had the greatest Pmax under 70% sunlight (Table 1; Fig. 1). The LSP of L. chinensis was unaffected (a > 0.05) by the irradiance treatment; however, both L. longituba and L. sprengeri had significantly lower LSP under 30% sunlight than under the other treatments (Table 1). The greatest LCP for L. chinensis and L. longituba was observed under 100% and 30% sunlight, respectively, whereas that of L. sprengeri did not change with the level of irradiance. For L. chinensis and L. longituba, AQY had the following order: 100% sunlight > 30% sunlight > 70% sunlight, whereas for L. sprengeri, AQY increased with decreasing irradiance. Under the same irradiance level, differences between the three species were found for all four photosynthetic parameters (Pmax, LSP, LCP, and AQY) measured; there were significant interactions between species and irradiance level and therefore the ranking among the species differ depending on the level of irradiance (Table 1). Effects of irradiance treatments on chlorophyll concentration. Both L. chinensis and L. longituba had significantly higher chlorophyll a and b and total chlorophyll concentrations under the 100% sunlight than under the other two treatments. However, chlorophyll concentrations in L. sprengeri had an opposite pattern because they were higher under 30% sunlight than under the other two treatments (Table 2). Different species had different chlorophyll concentrations under the same irradiance treatment. Under the 30% sunlight treatment, chlorophyll concentrations in L. longituba were significantly lower than that in the other two species. Under 100% sunlight, the highest chlorophyll concentration was found in L. chinensis (Table 2). Effects of the irradiance treatment on leaf traits. Leaf length generally decreased with the increasing level of irradiance for L. chinensis and L. longituba but was unaffected for L. sprengeri. Significant differences in leaf length were detected between the 70% and 30% sunlight levels for L. chinensis and between the 100% and 70% of sunlight for L. longituba (Table 3). Other than this, the irradiance treatment had no effect on leaf width, leaf area, leaf biomass, or specific leaf area regardless of the species (Table 3). Differences among the species were also observed for leaf length, width, area, and biomass when evaluated for the same irradiance level; the general trend was that in most cases, the values were greater in L. chinensis than in the other two species, regardless of the level of irradiance. Effects of the irradiance treatment on growth traits. The number of leaves and aboveground biomass of L. longituba
increased with the increasing level of irradiance, and their differences were significant between the 100% and 30% sunlight levels (Table 4). Other than that, the irradiance treatment did not affect any of the growth traits of the species. In terms of biomass production, L. chinensis always had one of the greatest biomass regardless of the irradiance level, whereas L. sprengeri had the highest number of leaves regardless of the level of irradiance (Table 4). Discussion Light intensity is one of the major environmental factors that influences the growth and distribution of plant species (Boardman, 1977; Lambers et al., 1998). In return, to sustain high photosynthetic capacity or survival rates, plants modify their morphology and biomass allocation under various light conditions (Liao et al., 2006). Studying photosynthetic and morphological responses of plant species to levels of irradiance can provide information on a species’ tolerance to and growth potential in a range of light conditions. Such information would be essential for better understanding of the ecological characteristics of different plant species and be useful for the agricultural, forestry, and horticultural industries (Aleric and Kirkman, 2005). For L. chinensis, Pmax and AQY were significantly greater when plants were grown under 100% sunlight than under shade, suggesting that this species could accumulate more carbohydrate in an open habitat than under shade, because a higher AQY indicates a greater light use efficiency (Larcher, 1995). However, LCP was also higher under the full than under the 70% and 30% sunlight treatments, indicating that this species also has a lower carbon fixation ability when moved to a very low irradiance (Larcher, 1995). Our data show that, for this particular species, the greater Pmax and AQY may be countered by the higher LCP in terms of their contribution to biomass production under full sunlight. Plants grown under low light intensity generally have thin leaves resulting in a high SLA (Bj¨orkman, 1981). However, in our study, no significant differences in SLA were caused by the irradiance treatment for L. chinensis. The irradiance treatments caused no effect on LSP; although the aboveground biomass slightly increased with increasing level of irradiance, no significant differences were detected. These photosynthetic and growth characters suggest that L. chinensis is a shade-tolerant species and it can acclimatize to different light environments. For biomass production, L. chinensis can be cultivated under irradiance levels from full to 30% sunlight. Consumers prefer potting plants of Lycoris spp. with short, broad, and emerald leaves, features characteristic of orchids (Qiu et al., 2005). Lycoris chinensis and L. longituba increased leaf length and decreased leaf width in response to the decreased level of irradiance. In previous studies, shade was
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Table 1. Photosynthetic characteristics (mean) of three Lycoris species grown under 30%, 70%, or 100% sunlight (n = 3). LSPz LCPz AQYz Irradiance Pmaxz (mmolm–2s–1) (mmolm–2s–1) (mmolm–2s–1) (molmol–1) (%) 1027.7a/B 11.4a/A 0.034a/B 100 10.0a/By 70 9.2b/B 922.0a/B 3.2b/C 0.025c/B 30 9.1b/A 1085.3a/A 4.2b/B 0.030b/B L. longituba 100 10.5a/A 883.6a/B 5.3b/B 0.040a/A 70 7.9b/C 864.4a/B 5.8b/B 0.025c/B 30 7.7b/B 413.0b/B 11.9a/A 0.034b/AB L. sprengeri 100 9.9b/B 1191.0a/A 9.6a/A 0.025c/C 70 10.4a/A 1142.9a/A 9.6a/A 0.029b/A 30 9.5b/A 950.9b/A 9.6a/A 0.036a/A z Pmax = the maximum rate of photosynthesis; LSP = light saturation point; LCP = light compensation point; AQY = apparent quantum yield. y Different letters in each column indicate significant differences (a < 0.05) among irradiance treatments for the same species (lowercase letters) or among the species with the same treatment (uppercase letters). Species L. chinensis
Fig. 1. The response of the rate of net photosynthesis (Pn) to photosynthetic photon flux (PPF) for L. chinensis, L. longituba, and L. sprenger grown under 100%, 70%, or 30% sunlight. The Pn was measured at CO2 concentration of 360 mmolmol–1 and temperature of 25 C. Means ± SE of three replicates (n = 3).
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found to result in longer leaves for L. radiata and thus decreased its ornamental quality (Li et al., 2004). Therefore, our data are consistent with the literature that shade may result in lower-quality potted plants for L. chinensis and L. longituba. For L. chinensis and L. longituba, chlorophyll a or b or total chlorophyll concentrations were higher under the full sunlight treatment, whereas the opposite is true for L. sprengeri. In some species, chlorophyll concentration would be higher under shade (Lei and Lechowicz, 1997). However, it is not uncommon to find higher chlorophyll concentrations (on an area basis) in sunlit than in shade leaves (Lee et al., 2000). Higher chlorophyll concentration means darker leaves, which is also a preferred trait for ornamental plants. Our data suggest that L. chinensis and L. longituba should be cultivated under full sunlight to produce shorter, wider, and greener leaves to meet consumer preference. Lycoris longituba had the lowest Pmax but the greatest LCP at 30% sunlight; these characteristics may explain the reduction in biomass production for plants of this species grown at 30% sunlight, because high LCP means low carbon gain ability (Larcher, 1995). The biomass of L. longituba decreased with decreasing irradiance in this short-term greenhouse experiment; marked changes might be observed if the plant is grown under shade for several years. Changes at the whole plant level in response to increased light availability can be decreased biomass allocation to leaves and increased allocation to roots (Poorter and Nagel, 2000). However, no significant treatment effect on belowground to aboveground biomass ratio was detected in L. longituba; instead, leaf number increased in response to increased irradiance intensity. Our data showed that high irradiance level increased the rate of net photosynthesis and ornamental quality, including the production of a greater number of leaves, darker leaf color, and broader leaves for L. longituba. The lowest LSP and greatest AQY and chlorophyll concentration in L. sprengeri were observed at 30% sunlight. Increased chlorophyll concentration is a common adaptive response to shade, because leaves with a higher chlorophyll concentration can provide a higher light-harvesting capacity in lowlight environments (Lei and Lechowicz, 1997; Lei et al., 1996). In a previous study, chlorophyll concentration on an area basis in L. radiata was found to increase in response to shade (Li et al., 2004). However, no significant differences were observed for any of the growth traits measured for L. sprengeri, indicating that this species may be cultivated in the range of light environments studied in this experiment, because the high irradiance environments showed no advantage for growth. Dale and Causton (1992) found that chlorophyll a/b ratio can be used to assess the light environment of a plant because the chlorophyll a/b ratio is directly related to the light-harvesting capacity of the photosynthetic HORTSCIENCE VOL. 43(1) FEBRUARY 2008
Table 2. Chlorophyll (Chl) a and b concentrations and Chl a/b ratio (mean) for three Lycoris species grown under: 30%, 70%, or 100% sunlight (n = 3). Chl (a+b) Chl a/Chl b Chl b Irradiance Chl a (mgcm–2) xratio (mgcm–2) (%) (mgcm–2)z 35.7a/A 120.0a/A 2.4b/B 100 83.7a/A 70 57.5c/A 19.3c/AB 77.2c/A 3.0a/A 30 71.4b/A 26.3b/A 98.3b/A 2.7ab/A L. longituba 100 64.8a/B 22.9a/B 88.1a/B 2.8a/A 70 47.6b/B 16.6b/B 64.5b/B 2.9a/A 30 44.5b/B 15.4b/B 60.2b/B 2.9a/A L. sprengeri 100 61.0b/B 21.9b/B 83.2b/B 2.8a/A 70 56.6b/A 22.6b/A 79.6b/A 2.5b/B 30 76.1a/A 27.0a/A 103.6a/A 2.8a/A z Different letters in each column indicate significant differences (a < 0.05) among irradiance treatments for the same species (lowercase letters) or among the species with the same treatment (uppercase letters). Species L. chinensis
Table 3. The effects of irradiance level on leaf length, width, area, biomass, and specific leaf area of three Lycoris species (n = 4). Leaf biomass SLA Leaf width Leaf area Irradiance Leaf length (g/leaf) (cm2g–1) (cm) (cm2/leaf) (%) (cm)z 2.0a/A 52.6a/A 0.33a/A 158.7a/A 100 33.3b/A 70 33.3b/A 1.8a/A 53.1a/A 0.29a/A 191.7a/A 30 41.3a/A 1.6a/A 56.5a/A 0.32a/A 175.2a/A L. longituba 100 33.1b/A 1.6a/B 39.9a/B 0.28a/B 145.7a/A 70 36.9a/A 1.6a/A 51.9a/A 0.30a/A 175.3a/A 30 38.6a/B 1.5a/B 40.5a/B 0.25a/B 163.9a/A L. sprengeri 100 33.1a/A 1.0a/C 24.9a/C 0.16a/C 156.49a/A 70 35.4a/A 1.0a/B 27.5a/B 0.16a/B 224.7a/A 30 34.2a/C 1.0a/C 26.2a/C 0.16a/C 164.77a/A z Different letters in each column indicate significant differences (a < 0.05) among irradiance treatments for the same species (lowercase letters) or among the species with the same treatment (uppercase letters). SLA = specific leaf area. Species L. chinensis
Table 4. Growth variables for three Lycoris species grown under: 30%, 70%, or 100% sunlight (n = 4). Irradiance Number Aboveground Belowground BB/AB Total (%) of leaves biomass (g) biomass (g) ratioz biomass (g) 2.8a/A 17.9a/A 6.3a/A 20.7a/A 100 8.0a/By 70 7.5a/B 2.4a/A 21.8a/A 7.0a/A 24.2a/A 30 6.8a/B 2.3a/A 15.7a/A 7.0a/A 18.0a/A L. longituba 100 9.5a/AB 2.5a/A 15.5a/A 7.1a/A 18.0a/A 70 8.2ab/B 2.4ab/A 12.6a/B 5.1a/B 15.1a/B 30 7.5b/B 1.8b/B 12.7a/A 7.1a/A 14.5a/A L. sprengeri 100 12.7a/A 2.1a/A 7.4a/B 3.5a/A 9.5a/B 70 12.8a/A 2.1a/A 7.2a/B 3.5a/B 9.3a/B 30 14.2a/A 2.4a/A 9.5a/A 4.0a/A 11.9a/A z BB/AB, belowground biomass to aboveground biomass ratio. y Different letters in each column indicate significant differences (a < 0.05) among irradiance treatments for the same species (lowercase letters) or among the species with the same treatment (uppercase letters). Species L. chinensis
system. However, the chlorophyll a/b ratio of the three Lycoris species showed no consistent patterns in response to the irradiance treatment. Therefore, in the current study, the chlorophyll a/b ratio appears to be a poor indicator of the characteristics of Lycoris species’ response to the irradiance treatment. Based on the observed responses of physiological and morphological characteristics of the three Lycoris species to the levels of irradiance, we conclude that L. chinensis and L. longituba are best cultivated under full sunlight, whereas L. sprengeri can be cultivated under a range of light environments.
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