Responses of native Lupinus varius (L.) to culture conditions: effects of photoperiod and sowing time on growth and flowering characteristics

The effects of photoperiod and sowing time on growth and flowering characteristics of Lupinus varius were investigated during two growing periods to determine its responses to culture conditions as a potential native cut-flower crop. The seeds were sown in an unheated plastic greenhouse on 28 September, 28 October and 28 November under natural, 14- and 16-h day-length treatments. 14- and 16-h day-lengths were established by lengthening the natural day-lengths to 14 and 16 h with the use of night break photoperiodic lighting at 1.8–1.9 μmol m⁻² s⁻¹ in 400–700 nm. Photoperiodic lighting, in particular the 16-h day-length treatments, slightly (maximally 15 days) shortened days to flowering and increased plant height in all sowing times relative to natural photoperiods. There were no significant differences in stem and branch inflorescence diameters, in lengths of branch, in main and branch inflorescences in plants grown under natural photoperiod, and 16-h day-length treatments. The highest main inflorescence diameter, the number of branches per plant, and flower numbers on main and branch inflorescences were recorded in plants grown under natural photoperiods, whereas 14-h day-length treatments did not provide sufficient specimens to allow for the measurement of most of the characteristics studied. These findings were interpreted to indicate that L. varius behaves as a facultative long day plant. Additionally, there was a particular shortening of days to flower and growth, and flowering quality decreased linearly with delayed sowing dates under all photoperiodic treatments. The earliest and latest flowering dates were recorded for plants sown in September under 16-h day-length, and plants sown in November under natural photoperiods, respectively. Therefore, sowing in September under natural photoperiods or 16-h artificial day-length resulted in earlier flowering dates and a longer time from sowing to flowering and was consequently the best sowing time with respect to all of the characteristics considered in this study.     

Day and night temperatures,daily light integral,and CO2 enrichment affect growth and flower development of Campanula carpatica ‘Blue Clips’

Campanula carpatica Jacq. ‘Blue Clips’ plants were grown in a greenhouse under nine combinations of day and night temperatures created by moving plants every 12 h among three day/night temperatures (15, 20, and 25°C). At each temperature, there were three daily light integrals (DLI; 4.2, 10.8, and 15.8 mol m⁻² per day, averaged over the experimental period) created with varying supplemental light, and ambient (≈400 μmol mol⁻¹) and enriched (≈600 μmol mol⁻¹) CO₂ concentrations. Time to flower was closely related to average daily temperature (ADT), and was not significantly affected by the day or night temperatures delivered to achieve a specific ADT. Time to flower was not largely affected by DLI or CO₂ enrichment. As plant ADT increased between 15 and 25°C, flower diameter decreased about 1 mm per degree and was not related to the difference between day and night temperatures (DIF). Flower diameter was smallest and least sensitive to changes in temperature at lower DLI and at ambient CO₂ levels. There were 10 less flower buds and 0.3 g less dry mass per plant at first flower for every 1° increase in plant ADT at high and medium DLIs. Flower bud number and dry mass were relatively low and less sensitive to changes in ADT at low DLI, and increased slightly with CO₂ enrichment at medium and high but not at low DLI. Plant height was not related to ADT, but increased linearly as DIF increased from −6 to 12°C at all DLIs, but the response was stronger under low DLI than high and medium DLIs. Flower bud number and dry mass were correlated closely with the ratio of DLI to daily thermal time (base temperature of 0°C). Flower bud number and dry mass were highest when C. carpatica plants were grown at 15°C with a DLI of 10–15 mol m⁻² per day.     

Temperature and irradiance effects on Sandersonia aurantiaca flower shape and pedicel length

Sandersonia flowers can vary from being lantern- to tubular-shaped. Lantern-shaped flowers are considered to be most commercially desirable when the ratio of the widest to the narrowest diameters of a flower, termed the ratio of hips to waist, is 1.5 or greater. Pedicel length can also affect the overall appearance of a flower stem. Short pedicels are considered more desirable. The influences of temperature and irradiance on Sandersonia aurantiaca flower shape and pedicel length were examined in controlled environment (CE) growth rooms. The growing environments were at constant temperatures of 15, 18, 21, 24 or 27 °C; or day/night temperature differentials of −6, 0, +6, +12, or +18 °C, with a mean of 21 °C. Photosynthetic photon flux densities (PPFD) were 700, 460 or 210 μmol m⁻² s⁻¹. At harvest, measurements were made of the widest and narrowest diameters of the oldest flower on each stem and the ratio of these parts was calculated. The pedicel length of the oldest flower was also measured. Environments with constant temperatures below 23 °C and the least day/night temperature differentials (−6, 0 and +6 °C) produced flowers of the most desirable shape, defined as having a hips to waist ratio of 1.5 or greater. At these temperatures, irradiance had a variable effect on flower shape. Pedicel length was also highly dependent on temperature and PPFD. As mean temperatures increased or as the temperature differential changed towards a differential of 12 °C, and as PPFD decreased, pedicel length increased significantly. Hip diameter was more sensitive to environmental changes than waist diameter and thus had a greater effect on flower shape. This work indicates to growers that they can enhance Sandersonia flower quality by producing more desirably shaped flowers with short pedicels through maintaining relatively low (less than 23 °C) mean temperatures, minimising temperature differentials, and maintaining irradiance levels as high as possible.     

Cultivation of cut flower and bulb species with saline water

The long-term effect of saline water irrigation on flower yield and quality was investigated in three herbaceous cut flower crops of commercial importance, the Emily cultivars of Japanese limonium, Trachelium caeruleum and Eustoma grandiflorum (lisianthus), and in two bulb species, Hippeastrum hybridum and Ornithogalum arabicum. Among the tested crops, limonium showed the highest resistance to salinity. Irrigation water with an electrical conductivity of up to 11.5 dS m⁻¹ had little or no effect on stem yield and length of limonium flowering stems. In Trachelium, salinity had no effect on the yield of flowering stems or the size of the inflorescence, but it markedly reduced stem weight and length. The concomitant reduction in the number of nodes to flowering was reflected in earlier flower initiation. Since delayed flower differentiation and over-elongation of Trachelium stems is a serious problem during the winter months, application of mildly saline irrigation for winter production could be used to induce earlier flower initiation and to control stem height. In lisianthus subjected to salinity from bud appearance onwards, a salinity level of 6.0 dS m⁻¹ increased stem weight and the number of flowers per stem without affecting other quality parameters. The work carried out with Trachelium and lisianthus, although limited, indicates that salinity may be used for improving the quality of some cut flowers. In contrast to its beneficial effect on the herbaceous species, salinity led to a significant reduction of bulb, leaf, and root weight of the two bulbous species, H. hybridum and O. arabicum.     

Net CO2 exchange rate of in vitro plum cultures during growth evolution at different photosynthetic photon flux density

CO₂ concentration was monitored during three 15-day subculturing cycles in vessels containing actively proliferating plum cultures of Prunus cerasifera, clone Mr.S. 2/5. The effects of two photosynthetic photon flux density regimes: 50 ± 5 μmol m⁻² s⁻¹ and 210 ± 5 μmol m⁻² s⁻¹ were compared. Three distinct phases in the CO₂ trend were distinguished during each culturing cycle of both light treatments. In the first, occurring at the beginning of the culture cycle, the amount of CO₂ emitted by the cultures during dark periods was greater than that assimilated during the light periods. In the second phase, the opposite trend was detected, while in the third, the range of CO₂ day–night fluctuations increased or remained stable according to the number of explants per vessel. The treatment with 210 ± 5 μmol m⁻² s⁻¹ did not modify the CO₂ phase trend but induced more pronounced fluctuations in day–night CO₂ concentration. Under this light treatment, cultures reached CO₂ compensation point for a period as long as 48% of the total number of light hours, while under 50 ± 5 μmol m⁻² s⁻¹, it was only 8%. The different range in CO₂ day–night fluctuations monitored throughout a subculturing cycle, appeared to be mainly induced by changes in culture growth dynamics.     

Rose productivity and physiological responses to different substrates for soil-less culture

Cultivation of roses in various soil-less media was studied with the aim to identify the optimum soil condition for rose production. Madelon roses grafted on rootstock of Rosa indica var. major were transplanted to polyethylene bags containing zeolite and perlite (at ratios of 25z:75p, 50z:50p, 75z:25p and 100z:0p, v/v) in a climate-controlled greenhouse. Net photosynthesis (A_net), stomatal conductance (g_s) and water use efficiency (WUE) of roses were followed for 5 months. Flower production and quality were recorded in three flowering flushes during a 5-month period. Analysis of variance of repeated measurements showed that even though the overall A_net did not differ among treatments (average 18.7 μmol m⁻² s⁻¹), trends in A_net seasonality for roses in 25z:75p substrate differed significantly from those in 50z:50p, 75z:25p or 100z:0p. Stomatal conductance did not show any significant seasonality or trends in response to substrate mixtures, averaging 0.89 mol m⁻² s⁻¹. Water use efficiency was significantly lower for roses in 25z:75p than in 100z:0p mixtures (1.8 ± 0.15 and 2.0 ± 0.13 μmol m⁻² s⁻¹ CO₂/mmol m⁻² s⁻¹ H₂O, respectively). Cumulative production of rose plants did not differ among substrate mixtures. Productivity significantly differed among flower stem classes. Stem class I (>70 cm) and class V (≤30 cm) exhibited the least production, contributing to only 7.6 and 3.7% of the total production, respectively. The highest productivity was observed in classes III (51–60 cm) and IV (31–50 cm), contributing to the bulk of productivity (68.4%). Class II contributed a 20.3% of the production. Results showed that zeolite and perlite acted as inert materials. Zeolite did not exert any positive effect on productivity, in contrast to what has been reported in literature recently. Use of perlite resulted in a little improvement in photosynthesis, however this improvement was not reflected by a significant increase in production.     

Analysis of rhythmic growth in holly (Ilex × meserveae) grown in controlled conditions

The influence of 24 h mean air temperature (18.3, 20.6, 23.9 and 25.8 °C) and photosynthetic photon flux (PPF; 0.6, 2.1, 3.7 and 4.7 mol m⁻² d⁻¹) on the growth cycles of vegetative growth in Ilex × meserveae (‘Blue Princess’ S.Y. Hu) was investigated. Plants propagated from top cuttings were grown in greenhouse compartments. The number of unfolded leaves was recorded continuously throughout the experiment. A modified sine function was fitted to collected data and the values for the amplitude and frequency of the growth curves were analysed. The sine function was tested as a method to evaluate the influence of climate on periodically flushing species. Both amplitude and frequency were significantly influenced by air temperature and PPF. The highest frequency of flushing was found at 23.9 °C and 3.7 mol m⁻² d⁻¹. The function resulted generally in a good fit to collected data with R² values above 0.9. Growth curves of all individual plants were categorised with respect to their growth pattern as poor synchronisation within the treatments did not allow analysis of the mean values of the growth curves.     

Daylength and photon flux density influence the growth regulator effects on morphogenesis in epicotyl segments of Troyer citrange

The optimal growth regulator addenda for adventitious shoot regeneration in epicotyl cuttings of Troyer citrange (Citrus sinensis×Poncirus trifoliata) varied with the conditions of illumination. The response to illumination and to growth regulators differed for the direct and the indirect (through callusing) pathways of regeneration. Shoot formation through the direct organogenic pathway decreased as the concentration of benzyladenine (BA) in the medium was increased in the range 2.2–22 μM, when the explants were incubated in the dark or under an 8 h daylength. For explants incubated under a 16 h daylength, the number of shoots formed increased with BA concentration. Optimal conditions of incubation for shoot formation through the direct pathway were either an 8 h daylength with a photon flux density of 74 μmol m⁻² s⁻¹ in the presence of 2.2 μM BA, or a 16 h daylength with a photon flux density of 37 μmol m⁻² s⁻¹ in the presence of 22 μM BA. Irrespective of the conditions of incubation, shoot formation through the indirect organogenic pathway was suppressed by the addition of 22 μM BA to the medium. Optimal conditions for shoot formation through this pathway were incubation under an 8 h daylength at a photon flux density of 74 μmol m⁻² s⁻¹ in the presence of 2.2 μM BA. At the optimal conditions indicated, the addition of the synthetic auxin naphtaleneacetic acid (0.54 μM) reduced shoot formation. Irrespective of the pathway of regeneration, the number of shoots formed decreased markedly with the distance of the cutting from the cotyledonary node.     

Seasonal changes in CO2 assimilation in leaves of five major Greek olive cultivars

Leaf CO₂ assimilation rate, stomatal conductance (g_s), internal CO₂ concentration (C_i), chlorophyll (a + b) content, specific leaf weight (SLW) and stomatal density were measured during the season, under field conditions, for five major Greek olive cultivars, ‘Koroneiki’, ‘Megaritiki’, ‘Konservolia’, ‘Lianolia Kerkiras’, and ‘Kalamon’, with different morphological and agronomic characteristics and diverse genetic background. Measurements were taken from current-season and 1-year-old leaves, and from fruiting and vegetative shoots, throughout the season, from March to November in years 2001 and 2002. CO₂ assimilation rates showed a substantial seasonal variation, similar in all cultivars, with higher values during spring and autumn and lower values during summer and late autumn. Stomatal conductance (g_s) followed similar trends to leaf CO₂ assimilation rates, increasing from March to July, following by a decrease during August and increasing again in autumn. ‘Koroneiki’ had the highest leaf CO₂ assimilation rate and g_s values (21 μmol m⁻² s⁻¹ and 0.45 mol m⁻² s⁻¹, respectively) while ‘Lianolia Kerkiras’ and ‘Kalamon’ showed the lowest leaf CO₂ assimilation rate and g_s values (13–14 μmol m⁻² s⁻¹ and 0.22 mol m⁻² s⁻¹, respectively). One-year-old leaves had significantly higher leaf CO₂ assimilation rate than current-season leaves from April to June, for all cultivars. From August and then, leaf CO₂ assimilation rate in current-season leaves was higher than in 1-year-old leaves. There were no significant differences in leaf CO₂ assimilation rate between fruiting and vegetative shoots. Total chlorophyll (a + b) content increased with leaf age in current-season leaves. In 1-year-old leaves chlorophyll content increased in spring, then started to decrease and increased slightly again late in the season. Chlorophyll content was higher in 1-year-old leaves than in current-season leaves throughout the season. Total specific leaf weight (SLW) increased throughout the season for all cultivars. Stomatal density in lower leaf surface was lowest for ‘Koroneiki’ (399 mm⁻²) and highest for ‘Megaritiki’ (550 mm⁻²). Our results showed differences in leaf CO₂ assimilation rate among the five different olive cultivars, with a diverse genetic background, ranging from 12 to 21 μmol m⁻² s⁻¹. From the five cultivars examined, ‘Koroneiki’, a drought resistant cultivar, performed better and was able to maintain higher leaf CO₂ assimilation rate, even under high air vapor pressure deficit. All cultivars had a pronounced seasonal variation in leaf CO₂ assimilation rate, affected by date of the year, depending on ambient conditions. The high temperatures and high air vapor pressure deficit occurring during summer caused a reduction in leaf CO₂ assimilation rate in all cultivars. Leaf CO₂ assimilation rate was also affected by leaf age for all cultivars, with old leaves having significantly higher leaf CO₂ assimilation rate than young leaves early in the season.     

Flowering of Primula malacoides in response to photoperiod and temperature

Primula malacoides Franch. ‘Prima Lilac’ was grown at 16 or 20 °C in combination with short days (SD, 8 h) or long days (LD, 16 h). In addition to uninterrupted growing conditions, plants within each temperature were moved at weekly intervals to the other photoperiod and left until termination. Temperature, but not photoperiod, significantly affected the rate of development from start of treatments (51 days from seeding) to 2 mm visible flower bud (VB). At 16 °C, VB averaged 30 days and at 20 °C, 48 days. Time to flower (first horizontal petals) at 16 °C increased from 56 to 64 days as SD increased from 1 week to continuous conditions while LD decreased time to flower from 64 to 56 days. Time to flower at 20 °C varied from 73 to 87 days with additional SD exposure resulting in slower and LD in faster flowering. These observations of the flowering response in ‘Prima’ are contrary to the photoperiodic classification of P. malacoides as a SD plant.     

Shoot induction and plant regeneration from receptacle tissues of Lilium longiflorum

An efficient system has been developed for the in vitro plant regeneration of Lilium longiflorum Thunb. by culturing receptacle sections from flower buds. The sections were cultured on one-half MS medium plus 30 g l⁻¹ sucrose, 8 g l⁻¹ agar, 5.4 μM NAA or 4.9 μM IBA plus 2.2 μM BAP. A section size of 3–4 mm was found to be optimal. After 60 days an average of 41 shoots were formed per explant. More vigorous shoots were obtained by subculturing on hormone-free medium with 20 g l⁻¹ sucrose. Rooting occurred on one-half MS medium with 1.1 μM NAA. Rooted plants were hardened-off in a greenhouse for two months, and normal flowering plants were produced.     

Determination of background pyruvic acid concentrations in onions,Allium species,and other vegetables

Background pyruvic acid concentration is a critical factor to determine onion pungency but greatly different values have been reported. This study was initiated to measure accurate background pyruvic acid levels in onion cultivars, other Allium species, and non-Allium vegetables using an HPLC method. A microwaving time of 2 min per 100 g was sufficient to deactivate alliinase and further degradation of pyruvic acid was not observed up to 6 min. Five percent trichloro acetic acid was suitable for both fresh and frozen tissues, while 80% ethanol did not stop the alliinase activity completely. The background pyruvic acid concentrations in various onion cultivars were less than 0.34 μmol ml⁻¹, while garlic and onion sprouts were 0.84–0.95 μmol ml⁻¹. Non-Allium vegetable also showed very low levels (0.09–0.34 μmol ml⁻¹) of pyruvic acid in the microwaved tissues. This study confirmed that background pyruvic acid levels in onion were minimal and could be disregarded in a routine analysis. Previous reports of high levels of the background pyruvic acid may need to be reviewed for accuracy.     

Prohexadione-calcium affects growth and flowering of petunia and impatiens grown under photoselective films

The response of petunia (Petunia x hybrida Vilm.-Andr. ‘Countdown Burgundy’) and impatiens (Impatiens wallerana Hook ‘Accent Orange Tempo’) to Prohexadione-calcium was evaluated under a clear and a far-red light absorbing greenhouse (A_FR) film to investigate the dosage effect of Prohexadione-Ca and to determine if it can overcome the flowering delay under FR deficient greenhouse environments. Prohexadione-Ca reduced stem elongation of petunia and impatiens under A_FR and clear films when applied 3 weeks after germination. Late applications were less effective. In both crops, main stem length decreased in a quadratic pattern as the concentration of Prohexadione-Ca increased. Under both films, 50–100 mg l⁻¹ Prohexadione-Ca resulted in ≈30% shorter petunia plants. Greater concentrations (500 and 1000 mg l⁻¹) resulted in excessively short plants (over 70%). Prohexadione-Ca at 100 mg l⁻¹ delayed anthesis of petunia by 8 and 3 days under the clear film and the A_FR film, respectively during less inductive photoperiods but had no effect during inductive photoperiods. In impatiens, Prohexadione-Ca at 100 mg l⁻¹ delayed anthesis over 10 days under clear or A_FR film. Greater concentrations (200 and 300 mg l⁻¹) inhibited flowering of impatiens. Prohexadione-Ca treatments significantly affected flower color development. Untreated petunia plants had dark burgundy flowers. Prohexadione-Ca treatment increased L*, a*, and C* values and decreased hue angle indicating that the flowers were faded. Flowers of untreated impatiens plants were bright orange color. Prohexadione-Ca at 100 mg l⁻¹ increased L* value and decreased a*, b*, and C* values indicating that significant petal fading had occurred. Flowers of treated plants were nearly white under both films. Although effective in height control, loss of color would be a major limitation to the use of Prohexadione-Ca on flowering crops.     

Environmental factors affecting flowering of rice flower (Ozothamnus diosmifolius,Vent.)

Rice flower (Ozothamnus diosmifolius, Vent.), native to east Australia, is a spring flowering perennial shrub. It is a new cut flower plant, recently introduced into cultivation in Australia and in Israel. Its response to environmental conditions, which affect growth and flowering, are not yet known. The purpose of the present study was to evaluate the effects of growth temperature, photoperiod and total solar energy on flowering. Experiments were conducted with plants of the cv. Cook’s Snow White. Plants were grown in three cycles under controlled conditions in the phytotron, at four day/night temperature regimes: 17/9, 20/12, 23/15 and 26/18°C. Two photoperiods — short day (SD) of 10 h natural day light and long day (LD) of 10 h natural light plus 10 h incandescent light — were employed. High temperatures enhanced vegetative growth but blocked flowering under both LD and SD. Under medium–moderate temperatures plants were absolute LD plants and did not flower under SD conditions. Under lower temperatures plants flowered under both LD and SD, but SD delayed flowering. High total solar radiation under LD did not affect flowering time but greatly promoted the number of flowering stems.     

Factors controlling high efficiency adventitious bud formation and plant regeneration from in vitro leaf explants of roses (Rosa hybrida L.)

Studies were conducted to improve adventitious bud regeneration in roses (Rosa hybrida L.), specifically to extend the protocol to different genotypes and to initiate production of multiple shoots per explant. The best results were obtained by using a two-stage procedure where excised leaflets were incubated on Murashige and Skoog (MS) (1962) induction medium with 6.8 μM TDZ plus 0.49 μM IBA in the dark for 7 days and subsequently transferred to an MS-based regeneration medium with 2.22 μM BA plus 0.049 μM IBA exposed to a PPFD of 15 μmol m⁻² s⁻¹ PAR. Bud formation capacity was also significantly affected by the genotype and the environment, such as the use of bottom cooling creating a lower RH in the vessel. The addition of silver nitrate to the induction medium also significantly improved the percentage of regeneration in three genotypes tested. Regenerated shoots failed to elongate when transferred to MS proliferation medium containing 0.5 mg l⁻¹ BA, however maximum bud development and elongation were achieved when kinetin in the range 1–2 mg l⁻¹ was used. Elongated shoots were excised and rooted best on zero growth regulator half-strength MS modified medium. Rooted plantlets were acclimatized under greenhouse conditions for evaluation of somaclonal variation.     

Effect of photoperiod and light integral on flowering and growth of Eustoma grandiflorum (Raf.) Shinn.

The aim of the study was to examine the effects of different photoperiod and light integral on floral initiation, development and subsequent growth of Eustoma grandiflorum (Raf.) Shinn. Six-weeks-old seedlings of ‘Echo Blue’ and ‘Fuji Deep Blue’ were placed under short day (SD, 10 h) and were transferred to long days (LD, 20 h) at 2-week intervals from 6 to 14 weeks after seeding. Plants initiated flower buds regardless of light regimes. Flower bud initiation was delayed by SD compared to LD; plants transferred after 6 weeks from seeding initiated flower buds at least 21 and 10 days earlier at LD at high (HL) and low (LL) daily light integral, respectively, compared to those at SD. Light regimes had little or no effect on time to flower bud development after initiation. Thus, it seems likely that LD and HL affected the initiation rather than development. Both the photoperiod and light integral strongly influenced the subsequent growth after initiation. SD delayed the time to visible bud (VB), increased the number of nodes to first open flower, number of branches, stem diameter and shoot dry weight compared to LD. HL promoted flowering and increased several shoot characteristics and flowering compared to LL.The results indicate that Eustoma is a quantitative long-day plant. LD, and more specifically HL, enhanced flower bud initiation, development and subsequent growth. An initial SD period is preferred to increase the number of branches, number of flowering buds and flowers, stem diameter and shoot dry weight.     

Effect of electrical conductivity and transpiration on production of greenhouse tomato (Lycopersicon esculentum L.)

We investigated the hypothesis that manipulating water out-flow of a plant through the shoot environment (potential transpiration, ET₀) in a glasshouse could modulate the effect of salinity/osmotic potential in the root environment upon yield of tomatoes. Contrasting root-zone salinity treatments were combined with two climate treatments — a reference (high transpiration, HET₀) and a “depressed” transpiration (low transpiration, LET₀). The salinity treatments, characterised by their electrical conductivity (EC) were 6.5, 8 and 9.5 dS m⁻¹, were always coupled with a reference treatment of EC=2 dS m⁻¹. In another experiment, concentrated nutrients (Nutrients) and nutrients with sodium chloride (NaCl) at the same EC of 9 dS m⁻¹ were compared.Marketable fresh-yield production efficiency decreased by 5.1% for each dS m⁻¹ in excess of 2 dS m⁻¹. The number of harvested fruits was not affected; yield loss resulted from reduced fruit weight (3.8% per dS m⁻¹) and an increased fraction of unmarketable harvest. At the LET₀ treatments, yield loss was only 3.4% per dS m⁻¹ in accordance with the reduction in fruit weight. Low transpiration did increase fruit fresh yield by 8% in both NaCl and Nutrients treatments at an EC=9 dS m⁻¹. Neither EC nor ET₀ affected individual fruit dry weight. Accordingly, fruit dry matter content was significantly higher at high EC than in the reference (4% per each EC unit in excess of 2 dS m⁻¹) and responded to ET₀ to a minor extent. Control of the shoot environment in a greenhouse to manipulate the fresh weight of the product may mitigate the effects of poor quality irrigation water without affecting product quality.     

Predicting dry matter production of cauliflower (Brassica oleracea L. botrytis) under unstressed conditions: I. Photosynthetic parameters of cauliflower leaves and their implications for calculations of dry matter production

Measurements of CO₂ exchange of cauliflower leaves were carried out in a field experiment which included two nitrogen fertilisation rates. Irradiance and CO₂ concentration were varied at the leaf level within a leaf cuvette and additionally a temperature treatment was applied to field grown plants moved into climate chambers. These measurements were used to estimate parameter values of a rectangular hyperbola describing cauliflower leaf CO₂ exchange as a function of irradiance and CO₂ concentration. The obtained parameter estimates were used to derive empirical regression equations with temperature and nitrogen content of the leaves as independent variables. The resulting relationships were applied within a simple photosynthesis–respiration based dry matter production model in order to derive functional relationships between light use efficiency and irradiance, leaf area index and temperature.The rectangular hyperbola was able to describe the gas exchange data as varied by irradiance and CO₂ concentration on the single leaf level with sufficient accuracy, but estimates of initial light use efficiency (about 25 μg J⁻¹) were too high because of the bias emanating from the limited flexibility of this model. Light saturated photosynthesis rate (P_max) showed an optimum response to temperature and an increase with increasing nitrogen content of leaves. The initial slope α of the rectangular hyperbola showed no consistent responses to ambient temperature and nitrogen content of leaves. The respiration per unit leaf area β increased exponentially with increasing temperature, resulting in a Q₁₀ value of 1.86. Because only a limited number of plants was evaluated in this study, additional work is needed to further substantiate the results of the gas exchange measurements.The model analysis demonstrated that LUE is independent of the light integral over a range 5–10 MJ m⁻² per day photosynthetically active radiation if one assumes an adaptation of P_max within the canopy and over time according to the incident irradiance. Acclimatisation within the canopy and higher leaf area indices, LAI, reduce the decrease of LUE with irradiance but a substantial decline remains even for LAI values of 4.     

Evaluation and modelling of greenhouse cucumber-crop transpiration under high and low radiation conditions

The main objective of this study was to analyse the transpiration time course of soilless culture cucumber plants (Cucumis sativus L.) during two cycles, at low (up to 9 MJ m⁻² d⁻¹) and high (up to 20 MJ m⁻² d⁻¹) radiation levels, and their relationship with greenhouse climate parameters (incident radiation and vapour pressure deficit, VPD) and canopy development. The coefficients of the simplified Penman–Monteith formula were calibrated in order to calculate the transpiration rate of the crop, to help improve irrigation management in substrate cultivation. The transpiration rate per ground surface area was measured by weighing plants with an electronic balance.At high radiation levels, the diurnal canopy transpiration rate was four times higher than at low radiation levels and the night transpiration rate reached values between 120 and 200 g m⁻² d⁻¹ in both cases. The leaf transpiration rate decreased during crop ontogeny and was higher in the afternoon than in the morning for the same value of radiation, whereas a linear relationship with the VPD was found even for values greater than 3 kPa. The results showed that the fitted simplified Penman–Monteith formula accounted for more than 90% of the measured hourly canopy transpiration rate, signifying that this formula could be used to predict water requirements of crops under Mediterranean conditions and improve irrigation control in a substrate culture. However, the model coefficients will have to be adjusted for specific climate and crop conditions.     

Enhancing plant diversity and mitigating BVOC emissions of urban green spaces through the introduction of ornamental tree species

Promoting the plant diversity of urban green spaces is crucial to increase ecosystem services in urban areas. While introducing ornamental plants can enhance the biodiversity of green spaces it risks environmental impacts such as increasing emissions of biogenic volatile organic compounds (BVOCs) that are harmful to air quality and human health. The present study, taking Qingdao City as a case study, evaluated the plant diversity and BVOC emissions of urban green spaces and tried to find out a solution to increase biodiversity while reducing BVOC emissions. Results showed that: (1) the species diversity and phylogenetic diversity of trees in urban green spaces were 22% and 16% lower than rural forest of this region; (2) urban areas had higher BVOC emission intensity (2.6 g C m⁻² yr⁻¹) than their rural surroundings (2.1 g C m⁻² yr⁻¹); (3) introducing the selected 11 tree species will increase 15% and 11% of species diversity and phylogenetic diversity, respectively; and (4) the BVOC emissions from green spaces will more than triple by 2050, but a moderate introduction of the selected low-emitting trees species could reduce 34% of these emissions. The scheme of introducing low-emitting ornamental species leads to a win–win situation and also has implications for the sustainable green space management of other cities.