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Biogas digestates can be applied to hydroponics via nitrification. However, the low solubility of phosphorus in digestates can cause phosphorus deficiency in plants. Here, we hypothesized that acidophilic nitrification might prevent this deficiency by dissolving phosphorus in the digestate. Acidophilic and neutrophilic nitrification were conducted at a pH of 3.27 and 6.25 using biogas digestates from food wastes. Acidophilic nitrification dissolved about 3.5 times more phosphorus than neutrophilic nitrification, but the increased acidity also reduced the nitrification rate, resulting in residual ammonium. We then grew lettuce hydroponically with filtrates of these digestates. The growth performance suggested that the increased phosphorus improved growth and that the residual ammonium did not inhibit it. Acidophilic nitrification was shown to be effective for use in hydroponics, particularly to alleviate phosphorus deficiency. These findings should provide new insights into resource recycling, which is essential in both urban and space environments.Graphical abstract

In this study, wasabi plantlets were grown by photoautotrophic micropropagation under nine different day/night temperature regimes ranging from 10 °C/10 to 26 °C/26 °C. On day 28 of the culture, the dry weight and the leaf area were found to be highest under a constant air temperature of 18 °C/18 °C. Partitioning of plant biomass into stems increased whilst partitioning into leaves decreased with the increase in temperature. Whereas, partitioning of plant biomass into roots increased when the temperature increased from 10 to 18 °C but decreased with further increase in temperature to 26 °C. The shoot/root ratio showed an opposite trend compared with partitioning into roots, whereas the chlorophyll content of leaves increased when the temperature increased from 10 to 26 °C. The net photosynthetic rate of whole plantlets showed the same trend as plantlet biomass and was the highest in 18 °C/14 °C, 18 °C/18 °C, and 22 °C/18 °C treatments. By contrast, the value of the net photosynthetic rate per unit leaf area decreased sharply at temperatures ranging from 10 to 18 °C. A linear relationship between the net photosynthetic rate and RGR was clearly evident because of the large differences in the leaf area values. The specific leaf area of wasabi plantlets decreased slightly at temperatures ranging from 10 to 18 °C but increased substantially within the range of 18–26 °C; however, the leaf dry matter content showed an opposite trend. Low- and high-temperature ranges had contrasting effects on the leaf mass area and leaf nitrogen concentration. There was the high descent in dissolved oxygen concentration of culture medium at all treatments from day 0 to 7. Greater growth of wasabi plantlets in 18 °C/14 °C, 18 °C/18 °C, and 22 °C/18 °C treatments. Biomass allocation to leaves is more important than the net photosynthetic rate per leaf area for supporting a high relative growth rate.

We investigated feeding and fecundity of the two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae), on leaves of cucumber (Cucumis sativus) seedlings that had been acclimatized to different light intensities. Based on these data, we analyzed the relationships between mite performance (feeding and fecundity) and leaf properties. The cucumber seedlings were grown in controlled-environment chambers under different light intensities at a photosynthetic photon flux density of 50, 100, 150, 300, or 450 µmol m− 2 s− 1 until the first true leaves had expanded. Adult females were released on the adaxial surfaces of excised leaf samples from the seedlings of each treatment group and held under standardized light intensity (200 µmol m− 2 s− 1). Fecundity and leaf damage area increased and decreased, respectively, as the acclimatization light intensity increased, indicating indirect effects of light intensity on feeding and fecundity through changes in the host leaf properties. Leaf mass per area (LMA) and photosynthetic capacity, which increased as the acclimatization light intensity increased, was positively related to the fecundity, but was negatively related to the leaf damage area. The higher LMA and photosynthetic capacity results in an increased amount of mesophyll per unit leaf area. This would allow the mites to feed efficiently from a limited area, which may explain the increased fecundity on these leaves.

Plant responses to the red-to-far-red ratio (R:FR) of light have been investigated, but interaction between R:FR and other factors is less known. Here, we investigated the effects of R:FR × vapor-pressure deficit (VPD) on stem elongation and leaf expansion. Cucumber (Cucumis sativus) seedlings were grown in growth chambers at a VPD of 0.4 or 3.0 kPa, an air temperature of 28 °C, and an R:FR of 1.0 or 10 for 7 days after germination. Lower R:FR plus lower VPD synergistically stimulated stem elongation, likely owing to an interaction between cell-wall extensibility and turgor pressure, which (respectively) respond to changes in the proportion of active phytochrome and in evaporative demand. Leaf expansion was also stimulated at lower R:FR plus lower VPD, but unlike stem elongation, lower VPD reduced the effect of R:FR on leaf expansion. This may be explained by resource competition between stems and leaves: photosynthate allocation to leaves decreased under lower R:FR plus lower VPD. This may limit leaf expansion and thereby moderate the R:FR effect on leaf expansion, although additional factors may stimulate cell extension.

The growth of wasabi (Wasabia japonica Matsumura) plantlets was compared in four concentrations of standard Enshi nutrient solution (25%, 50%, 100%, and 150%) and two kinds of supporting materials (rockwool and vermiculite) using an in vitro hydroponic culture system for photoautotrophic micropropagation. After 28 days of culture, most of the growth parameters such as fresh weight and dry weight, shoot/root dry weight ratio, and leaf area ratio were highest in wasabi plantlets grown in 50% or 100% nutrient solution, and this enhancement was greater in vermiculite than in rockwool. Dissolved oxygen concentration decreased sharply in rockwool but only slightly in vermiculite during the course of the experiment, resulting in a dissolved oxygen concentration of 8 mg L−1 in the vermiculite and 6 mg L−1 in the rockwool. The highest root nitrogen concentration was observed at a nutrient concentration of 100% in vermiculite and rockwool. The highest net photosynthetic rates were observed on day 28 in vermiculite at nutrient concentrations of 50% and 100%. The growth of wasabi plantlets is depressed through a decrease in root water and nutrient uptake caused by low dissolved oxygen concentrations. These findings clearly demonstrate that a hydroponic system that incorporates a 50% or 100% nutrient solution concentration and vermiculite will allow high-quality wasabi plantlets to be propagated rapidly under photoautotrophic conditions.

The authors investigated whether biogas digestate could be used as a nutrient solution for rockwool culture. To do this, the authors examined growth performances of chrysanthemum cultured in rockwool and fed the filtrate of nitrified biogas digestate (f-NBD) derived from organic fraction of municipal solid waste and investigated whether application of the digestate caused nutrients to leach from the rockwool substrate. Plants that had been fed the f-NBD showed 33% lower fresh shoot weights and produced 35% fewer flowers than those that had been fed a commercial liquid fertilizer, whereas there were no significant differences in lengths of the shoots, chlorophyll contents of the leaves, numbers of days to first flowering, and maximum diameters of the flowers. Also, there were no significant differences in any of the growth parameters between plants that were cultured with the f-NBD supplemented with Mg and the commercial liquid fertilizer. These results indicate that the f-NBD could be used as a nutrient solution for chrysanthemum in rockwool culture if supplemented with Mg. In addition, a considerable amount of Fe was leached from the rockwool substrates following the application of the f-NBD, which could mitigate the expected Fe-deficiency symptoms in chrysanthemum.

The present study investigated growth properties and flowering response of seed-propagated strawberry (Fragaria ×ananassa) seedlings under artificial lighting with different photoperiods to support the development of a high-performance system for the indoor production of strawberry plug transplants. Seedlings of ‘Elan’ and ‘Yotsuboshi’ were grown for 38 days under sunlight in a greenhouse or under light-emitting diode (LED) illumination with photoperiods of 8/16, 12/12, 16/8, or 24/0 hours (light/dark) in growth chambers. The photosynthetic photon flux (PPF) in these photoperiods was maintained at 350, 230, 175, or 115 μmol·m−2·s−1, respectively, to provide the same daily light integral (DLI) of 10 mol·m−2·d−1. The average of DLI of sunlight was 9.9 mol·m−2·d−1. Seedling growth was greater with the 16- and 24-hour photoperiods than with sunlight even though all three treatments provided about the same DLI. Flower buds of the seedlings grown under longer photoperiods started significantly earlier after transplanting in ‘Elan’ but not in ‘Yotsuboshi’. Thus, strawberry transplant production under artificial lighting with an optimized photoperiod can provide high-quality transplants, although the effectiveness is cultivar-specific.

We studied growth and photosynthesis of cucumber (Cucumis sativus) seedlings under two vapor-pressure deficit levels (VPD; 0.4 and 3.0 kPa), two salinity levels (0 mM and 34 mM NaCl), and two CO2 concentrations ([CO2]; 400 and 1,000 μmol mol–1). Relative growth rate (RGR) decreased with increasing VPD, but the causal factor differed between salinity levels and CO2 concentrations. Under ambient [CO2], RGR decreased with increasing VPD at low salinity mainly due to decreased leaf area ratio (LAR), and decreased net assimilation rate (NAR) at high salinity. The decrease in intercellular [CO2] (C i) with decreasing stomatal conductance caused by high VPD did not significantly limit net photosynthetic rate (P N) at low salinity, but P N was potentially limited by C i at high salinity. At high [CO2], high VPD reduced LAR, but did not affect NAR. This is because the decrease in C i occurred where slope of P N–C i curve was almost flat.

This research investigated early hyphal development of cucurbit powdery mildew (Podosphaera xanthii) on leaves of cucumber (Cucumis sativus L.) acclimatized to different relative humidities to clarify the factors that limit it. Cucumber seedlings were acclimatized to a low (10%) or high (90%) relative humidity (RH) at 30 °C from germination. When the cotyledons had expanded and the first true leaf had begun to emerge, the plants were inoculated, and initial conidial invasion, hyphal development, and secondary haustorial formation were evaluated. The initial invasion of P. xanthii into the epidermis was slower on the low-RH leaves than on the high-RH leaves, suggesting that structural properties, such as greater leaf mass per area, physically limited the development of P. xanthii. The hyphal development and secondary haustoria of conidia that had successfully infected the epidermis were also slower on the low-RH leaves. These post-invasion behaviors indicate that conidial development was also suppressed by nonstructural properties of low-RH leaves such as nutrients, which correlate with nonstructural defense. The reduced leaf N content of the low-RH leaves may in part have inhibited the post-invasion behaviors of P. xanthii.

We evaluated the dynamics of light competition within dense cucumber (Cucumis sativus L.) plant stands and its relationship to subsequent growth under illumination with different red to far-red ratios (R:FRs). The plant stands containing seedlings with different initial degrees of mutual shading was grown under metal-halide lamps (MHLs) with spectra similar to that of sunlight (R:FR = 1.2) or fluorescent lamps (FLs) with high R:FR (11) for 6 days at a photosynthetic photon flux of 300 μmol m−2 s−1. The daily-integrated photosynthetic photon intercepted by individuals (daily PP; mol d−1 per plant) were calculated once a day from the PPF, the photoperiod, and the directly irradiated leaf area. Under MHLs, differences in the daily PP values of individual seedlings with different initial shading degrees became non-significant within 2 days, whereas under FLs, differences were preserved throughout the experimental period, indicating that the unequal competition exists between neighbors under FLs. The daily PP on day 0 and dry-weight increase of the seedlings during the experimental period were positively correlated under FLs but not under MHLs, indicating that the initial dominance of light interception by individual seedlings is likely to affect their subsequent growth under FLs. The seedlings that had lost out to neighboring seedlings could not climb over the neighbors under FLs, probably because of insufficient stimulation of shade-avoidance responses caused by the higher R:FR illumination.

We investigated the possibility of using Euglena gracilis to convert digestate from methane fermentation of organic wastes into a medium for soilless crop culture. The growth of E. gracilis cultured with aqueous solutions containing filtrate of raw digestate at 1–30% (v/v) and nitrified digestate at 10–100% (v/v) was examined. Concentrations of plant macronutrient ions in nitrified digestate before and after culturing E. gracilis were also examined. Specific growth rates in aqueous solutions containing filtrate of raw digestate at 1–10% and nitrified digestate at 10–100% showed no significant differences, respectively (0.781 ± 0.031 d−1 and 0.925 ± 0.033 d−1, mean ± standard error). The rates in the filtrate of nitrified digestate were significantly higher than those in the filtrate of raw digestate. Moreover, there were no significant differences between the concentrations of plant macronutrient ions other than in the filtrate of nitrified digestate before and after culturing E. gracilis. The con...

Light with a higher red to far-red ratio (R:FR) than sunlight reduces plant growth, but the cause has not been firmly established. In the present study, cucumber seedlings were grown under normal light (similar to sunlight; R:FR = 1.4) from metal-halide lamps or high-R:FR light (R:FR = 4.3) created by transmitting their light through FR-absorbing film, and then their growth parameters and photosynthesis were compared. The relative growth rate (RGR) at high R:FR was 92% of that under normal R:FR, although the net assimilation rate (NAR) did not differ between the treatments, indicating that changes in net photosynthesis per unit leaf area did not cause the growth inhibition at high R:FR. The CO2 exchange per unit leaf area did not differ between the treatments, which supports this hypothesis. The leaf area ratio (LAR) of total plant dry weight of high R:FR seedlings to that of normal R:FR seedlings was also 92%. This suggests that growth suppression in the high R:FR seedlings was caused mainly by decreased LAR. The specific leaf area (SLA) and leaf weight ratio (LWR), components of LAR, under high-R:FR light were 89% and 105%, respectively, of those under normal light, indicating that the smaller LAR at high R:FR mainly results from suppressed leaf enlargement per unit leaf dry matter.

The development of powdery mildew fungus (Podosphaera xanthii) is suppressed on cucumber (Cucumis sativus L.) seedlings acclimatized to higher red-to-far-red ratio (R:FR) than natural R:FR (≈1.2), but its early development and any limiting factors are still unclear. The present study evaluated conidial germination, initial invasion, and subsequent development of P. xanthii on cucumber seedlings raised under light-emitting diode (LED) lights with R:FRs of 1.2, 5.0, or 10. There were no differences in conidial germination or initial invasion between the treatments, so there was no effect of acclimatization to R:FR on either. But, the development of hyphae, hyphal cells, and haustoria after inoculation were suppressed on seedlings acclimatized to higher R:FR. Because differences occurred only after the initial invasion, nonstructural properties of the host leaves may have affected conidial development. Higher R:FR also suppressed conidial development under natural light filtered through a photo-selective film, which absorbs near-infrared (NIR)-light. However, this effect was reduced when the plants were moved to natural R:FR after inoculation, possibly because of reacclimatization of the seedlings.

The goal of this study was to establish a system for converting digestate from anaerobic digestion processes into liquid fertilizer for soilless culture. Modifications of concentrations of plant macronutrient ions during nitrification processes were investigated with digestate from a simulated municipal organic waste. Concentrations of phosphate and calcium ions in the nitrified digestate increased; the rates of increase were 15.3 mg L–1 d–1 and 17.6 mg L–1 d–1, respectively. Moreover, concentrations of macronutrient ions, except for magnesium, in the nitrified digestate were similar to those in a standard nutrient solution that is commonly applied to soilless culture.

Photoautotrophic micropropagation (PA) in a sugar-free medium can facilitate acclimatization and increase success rates when transplanting tissue cultured plants to open fields. To identify savings in production costs (time and energy) during acclimatization in wasabi plants, we used in vitro PA with four kinds of supporting material (agar, perlite, rockwool, and vermiculite) and compared their effects on subsequent ex vitro growth (in vermiculite). The study revealed that, in all aspects, the plantlets in agar and vermiculite exhibited the highest growth, whereas plantlets in rockwool showed the worst growth performance. Growth performance in vitro seemed to be correlated with the volumetric water content of the supporting material. Agar and vermiculite promoted root growth and development with increases in number of roots, root length, and root fresh weight, and the root systems in these treatments also exhibited the best growth during the ex vitro stage. In culture vessels with plantlets, dissolved oxygen concentration (DO) in agar abruptly decreased from day 0 to day 7 but then recovered by day 28. DO decreased during the culture period very slightly, slightly, and steadily, with perlite, vermiculite, and rockwool, respectively. All the wasabi plantlets from the in vitro treatments survived after transplanting to the ex vitro condition, and subsequent growth was strongly influenced by the in vitro growth performance. Growth parameters of plantlets in the agar and vermiculite treatments were highest, whereas those in rockwool were lowest.

The present study evaluated the development of powdery mildew fungus (Podosphaera xanthii) on leaves of cucumber (Cucumis sativus L.) acclimatized to different CO2 concentrations ([CO2]) to examine plant–pathogen interactions under the wide range of [CO2] that can occur in greenhouse cultivation. Seedlings of resistant and nonresistant cultivars were acclimatized to reduced (200 µmol·mol−1), ambient (400 µmol·mol−1), or elevated (1000 µmol·mol−1) [CO2]. Powdery mildew spores were inoculated onto the adaxial surface of cotyledons or first true leaves, and colonization was measured after 7 days. Colony density decreased as acclimatization [CO2] increased at the cotyledon stage but increased at the first-true-leaf stage in both cultivars. This result implies that when the effects of [CO2] on plant–pathogen interactions are described, growing stage must be specified. The acclimatization [CO2] was correlated positively with leaf mass per area, dry matter content, and carbon (C) content and negatively with nitrogen (N) content at both stages. Therefore, these leaf properties could not explain the changes in host-plant susceptibility between stages. The effect of acclimatization [CO2] was greater on the resistant cultivar than on the nonresistant cultivar, indicating that the resistant cultivar was more responsive.

We investigated the effects of morphology of host cucumber, Cucumis sativus L., leaves acclimatized to different atmospheric humidity levels on oviposition by adult females of the twospotted spider mite, Tetranychus urticae Koch. Cucumber seedlings were grown at a vapor pressure deficit (VPD) of 0.4, 1.9, or 3.0 kPa at 28°C (90%, 50%, or 20% relative humidity, respectively) in growth chambers until the second true leaves had expanded. Adult females of T. urticae were released on the adaxial surfaces of leaf squares cut from first and second true leaves in each treatment group, and held in the same humidity condition. Eggs were counted 2 d after release. The lower acclimatization humidity (higher VPD) increased trichome (leaf hair) density of the host leaves and oviposition rate, but the relationship between the trichome and oviposition differed between leaf positions. The leaf mass per area (LMA) was greater in first true leaves than in second true leaves, but was not influenced by VPD. A linear regression model with oviposition rate as the dependent variable and trichome density and LMA as independent variables showed that both variables influenced the oviposition rate approximately equally. We conclude that oviposition was accelerated under low humidity (high VPD) conditions indirectly probably through an increase in the trichome density of host leaves.

To improve the propagation of Japanese cedar (Cryptomeria japonica D. Don), we investigated the effects of apical and basal temperatures during a water soaking treatment on the adventitious root formation of 70-mm long shoot tip cuttings which have an apical bud. The basal portion of the cuttings was soaked for 28 days in water with temperatures ranging from 10 to 35 °C, at an air temperature of 5 or 10 °C. Control cuttings were soaked in water at 25 °C, with an air temperature of 25 °C. Treated cuttings were then planted in vermiculite rooting medium and grown at an air temperature of 25 °C for 35 days. Adventitious roots initiated earlier and developed more in the cuttings treated with apical temperatures of 5 or 10 °C and basal temperatures of 20–30 °C than in the control cuttings. The rooting percentage was greatest (93 %) in the cuttings treated with a 10/25 °C apical/basal temperature, whereas few control cuttings rooted (13 %). This suggests that the temperature gradient created by warming the basal portion of the cuttings while cooling their apical end stimulates adventitious root formation. When we tested seasonal variation of rootability at 10/25 °C, the rooting percentage increased from early autumn to winter, and decreased from winter to summer. The soluble sugar contents did not directly affect the formation of adventitious roots in the present study.

Grafting can improve the resistance of scions to foliar diseases, but the exact mechanism is unknown. We hypothesized that responses to a quantitative change in water relations due to transient disconnection of vascular tissues were partly responsible. Cucumber (Cucumis sativus L.) scions were grafted onto squash (Cucurbita moschata Duch.) or cucumber (self-grafting) rootstocks and allowed to heal at 28 °C and 95% relative humidity for 7 days. Spores of the cucurbit powdery mildew fungus (Podosphaera xanthii) were then inoculated onto the cotyledon leaves of the scions and of ungrafted (self-rooted) cucumber seedlings. Seven days after inoculation, colony density of P. xanthii was significantly smaller on the grafted and self-grafted scions than on the ungrafted seedlings. The adaxial epidermis of the cotyledon leaves thickened during graft healing. This is probably due to responses to water stress that protect against water loss, and may partly explain the smaller colony density. When inoculation was performed at the first-true-leaf stage 3 days after healing, the colony densities on the cotyledon and first true leaves of the grafted scions did not differ from those on ungrafted seedlings. These results suggest that the grafting transiently suppresses colony development of powdery mildew, probably through a quantitative change in water relations of host plants during graft healing.

We compared photosynthetic performance between cucumber (Cucumis sativus L.) leaves acclimated to saturating irradiances with high red: far red (R:FR = 10) and normal R:FR (= 1.4) ratios. The net photosynthetic rate (PN) and stomatal conductance (gs) of the leaves acclimated to high R:FR were greater than those of the leaves acclimated to normal R:FR; the greater gs partly explains the greater PN. The greater gs of the high-R:FR-leaves probably resulted from a higher stomatal density and/or a greater size. PN of the high R:FR leaves was still greater than that of the normal R:FR leaves at the same intercellular CO2 concentration (ci). This indicates that non-stomatal factors also increased the photosynthetic capacity of the high R:FR leaves. The maximum Rubisco carboxylase activity estimated from a PN-ci curve analysis was also greater in the high R:FR leaves, however, the intrinsic water-use efficiency (WUEi = PN/gs) of the high R:FR leaves was lower than that of the normal R:FR leaves.

This study investigated the effects of atmospheric moisture on conidia development in cucurbit powdery mildew fungus (Podosphaera xanthii) through host-plant responses. Cucumber (Cucumis sativus L.) seedlings were grown under a high vapour pressure deficit (VPD) (3.8 kPa) or a low VPD (0.4 kPa). When the cotyledons had expanded, spores of P. xanthii were inoculated onto the adaxial surface. Inoculated seedlings for both treatments were then placed in a growth chamber maintained at a VPD of 2.1 kPa. The density of visible P. xanthii colonies on the high-VPD-acclimated cotyledons was 0.46 to 0.85 times that of the low-VPD-acclimated cotyledons 7 days after inoculation. It is likely the post-germination behaviour of P. xanthii such as the infection and consequent hyphal development was affected because spore germination did not differ between the treatments. The percentage of adaxial epidermal leaf cells with haustoria was also lower in the seedlings which had acclimated to a higher VPD. The high-VPD-acclimated cotyledons were thicker and had greater dry mass per area. The water potential of cotyledons did not differ between the treatments, although the stomatal conductance of high-VPD-acclimated cotyledons was lower than that of low-VPD-acclimated cotyledons. From these results, we conclude that the inhibition of P. xanthii conidia development on high-VPD-acclimated cotyledons was mainly caused by changes in leaf morphological properties.

We investigated the effects of the soil moisture and gaseous environment on growth of sweet potato during its establishment period in order to confirm the hypothesis that elevated CO 2 concentrations in the root zone associated with elevated soil water contents lead to growth stagnation in sweet potato in a series of experiments. In Experiment 1 sweet potato was cultured on soil ridges irrigated every day, every three days, or every six days, with the mean volumetric water contents 23.4%, 15.3% and 10.2%, respectively, and the dry weight of tuberous roots irrigated every three days was greatest. In Experiment 2 sweet potato was cultured in containers filled with sand with four different water table levels (15 cm (treatment code: D15), 20 cm (D20), 25 cm (D25), and 30 cm (D30) from the soil surface), with highest volumetric water content (45%) and CO 2 concentration (3.5%) at a depth of 15 cm in D15, and reducing toward treatments with deeper water table levels (5% and 0.8%, respectively in D30). The dry masses of tuberous roots and the whole plant were greatest in D25 and smallest in D30, and D25 > D20 > D15 > D30 for the ratio of root dry mass to whole plant dry mass. In Experiment 3, sweet potato was cultured in containers in which CO 2 concentrations were adjusted to represent low (1.8%), middle (2.5%) or high (4.9%) concentrations using chemical agents that absorbed or released CO 2 to imitate the gaseous environment possibly experienced in field soil. No tuberous roots developed in the high CO 2 treatment. Furthermore, the dry masses of the whole plant and fibrous roots were 1.6 and 3 times greater, respectively, in the low CO 2 treatment than in the high CO 2 treatment. It was confirmed that elevated CO 2 concentrations in the root zone associated with elevated soil water contents suppressed growth and tuberous root development of sweet potato.

This study investigated the effects of illumination with different red-to-far-red ratios (R:FR) on height convergence pattern in cucumber ( Cucumis sativus L.) seedling stands to obtain a basic knowledge for growing plant stands uniformly under artificial light sources. Seedlings of the same age but with different initial heights (30 or 15 mm) were grown under either metal-halide lamps with spectra similar to that of natural light (R:FR = 1.2) or fluorescent lamps with a high R:FR (R:FR = 11), at a photosynthetic photon-flux (PPF) of 300 μmol m −2 s −1 and a light:dark period of 16:8 h, until the first true leaf expanded. The shoot heights of the initially taller and shorter seedlings under the metal-halide lamps converged within 4 days. In contrast, the initially shorter seedlings under fluorescent illumination remained smaller than the initially taller seedlings throughout the experimental period (8 days), although the height difference decreased gradually. The rapid height-convergence under metal-halide illumination probably resulted from shade avoidance by the shorter seedlings due to the relatively low R:FR (=0.6) and PPF (=60 μmol m −2 s −1 ) at cotyledon level under shade from the taller seedlings. The R:FR at cotyledon level for the initially shorter seedlings under fluorescent illumination was 5.5, which was higher than the value (0.6) that caused the accelerated height growth response under metal-halide light. The fact that light quality affects the structure of plant community should be considered in selecting light sources for the plant production.

We investigated the effects of warming the basal ends of Carolina poplar (Populus × canadensis Moench.) softwood cuttings at controlled low-air-temperature on their root growth and leaf damage after planting. The warming treatment was applied to the cuttings by soaking 10 mm beyond the cut end in warmed water maintained at 30 °C in a cold chamber maintained at an air temperature of 10 °C and a photosynthetic photon flux density (PPFD) of 10 μmol m−2 s−1 (near the light compensation point at 10 °C) until rooting was observed. The warmed cuttings were then grown in a growth chamber at an air temperature of 30 °C, relative humidity 85–90 %, and a PPFD of 100 μmol m−2 s−1. Control cuttings were grown in the growth chamber throughout the experiment. Rooting occurred simultaneously for both warmed and control cuttings, irrespective of air temperature. Root development was greater and leaf damage, evaluated on the basis of extent of necrosis, was less for warmed cuttings than for control cuttings. The reduction of leaf damage for warmed cuttings probably resulted from reduced post-planting water stress and leaf senescence, because of improved root development as a result of the pre-planting warming treatment. This technique could improve the propagation of cuttings of woody plants, because it would ensure that the cuttings are ready to develop roots with minimum loss of carbohydrates, irrespective of weather conditions.

This study evaluated the photosynthetic responses of Cucumis sativus leaves acclimated to illumination from three-band white fluorescent lamps with a high red:far-red (R:FR) ratio (R:FR = 10.5) and the photosynthetic responses of leaves acclimated to metal-halide lamps that provided a spectrum similar to that of natural light (R:FR = 1.2) at acclimation photosynthetic photon flux density (PPFD) of 100 to 700 μmol m−2 s−1. The maximum gross photosynthetic rate (PG) of the fluorescent-acclimated leaves was approximately 1.4 times that of the metal-halide-acclimated leaves at all acclimation PPFDs. The ratio of quantum efficiency of photosystem II (ΦPSII) of the fluorescent-acclimated leaves to that of the metal-halide-acclimated leaves tended to increase with increasing acclimation PPFD, whereas the corresponding ratios for the leaf mass per unit area tended to decrease with increasing acclimation PPFD. These results suggest that the greater maximum PG of the fluorescent-acclimated leaves resulted from an interaction between the acclimation light quality and quantity, which was mainly caused by the greater leaf biomass for photosynthesis per area at low acclimation PPFDs and by the higher ΦPSII as a result of changes in characteristics and distribution of chloroplasts, or a combination of these factors at high acclimation PPFDs.

We evaluated the preference of adult sweetpotato whitefly [SPWF (Bemisia tabaci biotype B)] to cucumber (Cucumis sativus) seedlings grown under fluorescent lamps (FLs) or metal-halide lamps (MLs) that provided a spectrum similar to that of natural light. Cucumber seedlings were grown under FLs or MLs at a photosynthetic photon flux of 350 μmol·m−2·s−1 in a 12/12-hour light/dark cycle. The red:far red (R:FR) ratio of FL was 7.0 and that of ML was 1.2. Pairs of cucumber seedlings, one grown under FLs and the other under MLs, were then placed in cages and about 100 SPWF adults were released. There were significantly fewer SPWF adults on the FL cucumber seedlings (36%) than on the ML seedlings (64%) 24 hours after release. FL cucumber seedlings had higher chlorophyll content and thicker leaves than ML seedlings. The lower attractiveness of the FL cucumber seedlings was probably due to changes in morphologic characteristics such as the leaf color and thickness resulting from high R:FR illumination of FL. The fact that light quality affects the plant attractiveness to herbivores should be considered in selecting light sources for transplant production under artificial light.

To evaluate the effect of fluorescent lamps with a high red:far-red (R:FR) light on the potential photosynthesis of transplants, we investigated the photosynthetic light responses of cucumber (Cucumis sativus L.) seedlings grown under fluorescent lamps with high R:FR light (FLH) and compared them with the responses of the seedlings grown under metal-halide lamps (ML) that provided a spectrum similar to that of natural light and under a fluorescent lamp with low R:FR light (FLL). The seedlings were grown under FLH (R:FR = 7.0), ML (R:FR = 1.2), or FLL (R:FR = 1.1) at a photosynthetic photon flux density (PPFD) of 350 μmol·m−2·s−1. The gross photosynthetic rate (Pg), quantum yield of photosystem II (ΦPSII), and photosynthetic electron transfer rate (ETR) of the foliage leaves were then evaluated at PPFDs ranging from 0 to 1000 μmol·m−2·s−1. The photosynthetic light response of FLH seedlings was similar to those of sun leaves, and the responses of ML and FLL seedlings were similar to those of shade leaves. The Pg, ETR, and ΦPSII of FLH seedlings at PPFD of 1000 μmol·m−2·s−1 was 1.38, 1.32, and 1.28 times, respectively, those of ML seedlings, and was 1.40, 1.23, and 1.22 times, respectively, those of FLL seedlings. The Pg was closely correlated with ETR in each treatment. FLH seedlings had thicker leaf and greater chlorophyll content per leaf area than ML and FLL seedlings. The greater Pg of FLH seedlings than in the other two groups of seedlings at high PPFD was probably the result of the improved ETR resulting from physiological and morphological changes in response to the high R:FR light.

SummaryA hydroponic culture system was developed for producing garlic bulbs and roots containing a precursor of ajoene. Garlic plants were cultured in a growth chamber under artificial lighting for 2 months at air temperatures of 25o/21oC (light/dark), relative humidities of 75%/90% (light/dark), a photosynthetic photon flux density of 450 µmol m–2 s–1, and a photoperiod of 12 h d–1. The growth and ajoene concentrations of garlic plants cultured hydroponically with different aeration regimes were compared in order to examine the effects of dissolved O2 levels on these parameters. The four aeration treatments included 12 h dark-time aeration (12 h-D), 12 h illuminated-time aeration (12 h-L), 24 h continuous aeration (24 h) using a pump, or no aeration (control). Dissolved O2 concentrations increased in the order: 24 h >12 h-L >12 h-D > control. Fresh weights (FW), dry weights (DW), and ajoene concentrations were increased in each part of the garlic plants by increasing the levels of dissolved O2. The FWs o...

Cuttings of cucumber (Cucumis sativus L.) grafted onto squash (Cucurbita moschata Duch.) rootstock using a hole-insertion graft were warmed at the hypocotyl of the rootstock in a cold chamber for acclimatization: they were soaked in water held at 31°C from the basal cut-end to the graft union at an air temperature of 12°C for 2 days. Warmed cuttings were planted and grown in an acclimatization chamber for 5 days. Control cuttings were planted immediately after grafting and grown in the chamber for 7 days. The fresh weight of the control scions decreased 2 days after grafting as a result of reduced water content, but that of warmed scions did not decrease. The fresh and dry weight of the warmed scions was 2.2 and 1.6 times that of the control, respectively, at 7 days after grafting. The graft development of warmed and control cuttings, evaluated based on the tensile strength, improved to a similar degree. The leaf conductance and chlorophyll fluorescence ratio (Fv/Fm) of the warmed scions, both of which indicate the degree of water stress, improved compared to those of the control at 7 days. These results demonstrate that the warming treatment does not adversely affect graft development but does reduce water stress at low air temperature during early acclimatization, and therefore improves early growth.

To evaluate the effects of plant density on gas exchanges under water stress resulting from high vapor-pressure deficit (VPD), we measured net photosynthetic rate (Pn), transpiration rate, and leaf conductance (gl) of cucumber (Cucumis sativus L.) seedlings before and after raising the VPD at different plant densities. Measurements were conducted continuously using a chamber and weighing method. Five, nine, or 12 seedlings with leaf area index (LAI) of 0.39, 0.73, and 1.10, respectively, were placed in the assimilation chamber. The average VPD in the chamber was raised from 1.1 to 3.7 kPa 30 min after the starting measurement. The Pn and gl decreased after raising the VPD above the plant community from 1.1 to 3.7 kPa. The VPD near the leaf surface (measured with 3-mm diameter humidity sensors) decreased with increasing LAI of the plant community, whereas average VPD in the whole chamber did not change with LAI. We noted significant negative correlations between the VPD near the leaf surface and Pn and gl. These results indicate that higher plant density mitigates the inhibition of photosynthesis resulting from high VPD by maintaining a lower VPD near the leaf surface with the development of a thicker boundary layer above the canopy.