Analysis of the effect of EC and potential transpiration on vegetative growth of tomato

This paper analyses the response of vegetative growth of greenhouse tomato to both root-zone salinity and shoot-environment (potential transpiration), with the purpose of explaining the observed lack of effect on dry matter yield. A reference salinity (EC) of 2 dS m⁻¹ was compared in three experiments with, respectively, 6.5, 8 and 9.5 dS m⁻¹. Another experiment investigated specific effects of sodium chloride, by comparing two high-EC treatments (both 9 dS m⁻¹), one with a high concentration of nutrients and one with addition of sodium chloride to a normal nutrient solution. The shoot-environment was either a “normal” climate regime or the same regime but with depressed potential transpiration, mainly by adaptation of the humidity set point. There was no detectable effect of the potential transpiration treatment, neither of the sodium chloride. Salinity effects on vegetative growth only showed up at EC exceeding 6.5 dS m⁻¹. The most evident EC effect was a reduction of leaf expansion; individual leaf area was reduced by 8% per dS m⁻¹ exceeding 6.5. This was partly compensated by a slight increase (2% per unit EC) in the number of leaves, which explains why cumulative plant leaf area decreased by about 7% per unit EC in excess of 6.5 dS m⁻¹. Therefore, leaf area index (LAI) at the highest EC was reduced by some 20% compared to the LAI at an EC of 2 dS m⁻¹. It is estimated that this would cause a reduction of less than 8% in light interception, and thus in dry matter produced. Indeed, differences observed in dry weight between the EC treatments were never significant.     

Relationships between bole and crown size for young urban trees in the northeastern USA

Knowledge of allometric equations can enable urban forest managers to meet desired economic, social, and ecological goals. However, there remains limited regional data on young tree growth within the urban landscape. The objective of this study is to address this research gap and examine interactions between age, bole size and crown dimensions of young urban trees in New Haven, CT, USA to identify allometric relationships and generate predictive growth equations useful for the region. This study examines the 10 most common species from a census of 1474 community planted trees (ages 4–16). Regressions were applied to relate diameter at breast height (dbh), age (years since transplanting), tree height, crown diameter and crown volume. Across all ten species each allometric relationship was statistically (p < 0.001) significant at an α-level of 0.05. Consistently, shade trees demonstrated stronger relationships than ornamental trees. Crown diameter and dbh displayed the strongest fit with eight of the ten species having an R² > 0.70. Crown volume exhibited a good fit for each of the shade tree species (R² > 0.85), while the coefficients of determination for the ornamentals varied (0.38 < R² < 0.73). In the model predicting height from dbh, ornamentals displayed the lowest R² (0.33 < R² < 0.55) while shade trees represented a much better fit (R² > 0.66). Allometric relationships can be used to develop spacing guidelines for commonly planted urban trees. These correlations will better equip forest managers to predict the growth of urban trees, thereby improving the management and maintenance of New England's urban forests.     

Mapping leaf area of urban greenery using aerial LiDAR and ground-based measurements in Gothenburg,Sweden

Leaf area of urban vegetation is an important ecological characteristic, influencing urban climate through shading and transpiration cooling and air quality through air pollutant deposition. Accurate estimates of leaf area over large areas are fundamental to model such processes. The aim of this study was to explore if an aerial LiDAR dataset acquired to create a high resolution digital terrain model could be used to map effective leaf area index (L_e) and to assess the L_e variation in a high latitude urban area, here represented by the city of Gothenburg, Sweden. L_e was estimated from LiDAR data using a Beer-Lambert law based approach and compared to ground-based measurements with hemispherical photography and the Plant Canopy Analyser LAI-2200. Even though the LiDAR dataset was not optimized for L_e mapping, the comparison with hemispherical photography showed good agreement (r² = 0.72, RMSE = 0.97) for urban parks and woodlands. Leaf area density of single trees, estimated from LiDAR and LAI-2200, did not show as good agreement (r² = 0.53, RMSE = 0.49). L_e in 10 m resolution covering most of Gothenburg municipality ranged from 0 to 14 (0.3% of the values >7) with an average L_e of 3.5 in deciduous forests and 1.2 in urban built-up areas. When L_e was averaged over larger scales there was a high correlation with canopy cover (r² = 0.97 in 1 × 1 km² scale) implying that at this scale L_e is rather homogenous. However, when L_e was averaged only over the vegetated parts, differences in L_e became clear. Detailed study of L_e in seven urban green areas with different amount and type of greenery showed a large variation in L_e, ranging from average L_e of 0.9 in a residential area to 4.1 in an urban woodland. The use of LiDAR data has the potential to considerably increase information of forest structure in the urban environment.     

A spatially-explicit method to assess the dry deposition of air pollution by urban forests in the city of Florence,Italy

Urban forests (UF) provide a range of important ecosystem services (ES) for human well-being. Relevant ES delivered by UF include urban temperature regulation, runoff mitigation, noise reduction, recreation, and air purification. In this study the potential of air pollution removal by UF in the city of Florence (Italy) was investigated. Two main air pollutants were considered – particulate matter (PM₁₀) and tropospheric ozone (O₃) – with the aim of providing a methodological framework for mapping air pollutant removal by UF and assessing the percent removal of air pollutant.The distribution of UF was mapped by high spatial resolution remote sensing data and classified into seven forest categories. The Leaf Area Index (LAI) was estimated spatially using a regression model between in-field LAI survey and Airborne Laser Scanning data and it was found to be in good linear agreement with estimates from ground-based measurements (R² = 0.88 and RMSE% = 11%). We applied pollution deposition equations by using pollution concentrations measured at urban monitoring stations and then estimated the pollutant removal potential of the UF: annual O₃ and PM₁₀ removal accounted for 77.9 t and 171.3 t, respectively. O₃ and PM₁₀ removal rates by evergreen broadleaves (16.1 and 27.3 g/m²), conifers (10.9 and 28.5 g/m²), and mixed evergreen species (15.8 and 31.7 g/m²) were higher than by deciduous broadleaf stands (4.1 and 10 g/m²). However, deciduous forests exhibited the largest total removal due to the high percentage of tree cover within the city. The present study confirms that UF play an important role in air purification in Mediterranean cities as they can remove monthly up to 5% of O₃ and 13% of PM₁₀.     

The overlooked carbon loss due to decayed wood in urban trees

Decayed wood is a common issue in urban trees that deteriorates tree vitality over time, yet its effect on biomass yield therefore stored carbon has been overlooked. We mapped the occurrence and calculated the extent of decayed wood in standing Ulmus procera, Platanus × acerifolia and Corymbia maculata trees. The main stem of 43 trees was measured every metre from the ground to the top by two skilled arborists. All trees were micro-drilled in two to four axes at three points along the stem (0.3 m, 1.3 m, 2.3 m), and at the tree’s live crown. A total of 300 drilling profiles were assessed for decay. Simple linear regression analysis tested the correlation of decayed wood (cm²) against a vitality index and stem DBH. Decay was more frequent and extensive in U. procera, than P. acerifolia and least in C. maculata. Decay was found to be distributed in three different ways in the three different genera. For U. procera, decay did appear to be distributed as a column from the base to the live crown; whereas, decay was distributed as a cone-shape in P. acerifolia and was less likely to be located beyond 2.3 m. In C. maculata decay was distributed as pockets of variable shape and size. The vitality index showed a weak but not significant correlation with the proportion of decayed wood for P. acerifolia and C. maculata but not for U. procera. However, in U. procera, a strong and significant relationship was found between DBH and stem volume loss (R² = 0.8006, P = 0.0046, n = 15). The actual volume loss ranged from 0.17 to 0.75 m³, equivalent to 5%–25% of the stem volume. The carbon loss due to decayed wood for all species ranged between 69–110 kg per tree. Based on model’s calculation, the stem volume of U. procera trees with DBH ≥ 40 cm needs to be discounted by a factor of 13% due to decayed wood regardless of the vitality index. Decayed wood reduces significantly the tree’s standing volume and needs to be considered to better assess the carbon storage potential of urban forests.     

The impact of photoperiod and irradiance on flowering of several herbaceous ornamentals

Forty-one herbaceous species were grown under short-days (8 h photoperiod, ambient irradiance averaged 12–13.2 and 6.4–8.3 mol m⁻² day⁻¹ for Experiments I and II, respectively) with or without supplemental high-pressure sodium lighting (+50, 100, or 150 μmol m⁻² s⁻¹); or under long-days delivered using natural day lengths and irradiance with night interruption lighting (2200–0200 h at 2 μmol m⁻² s⁻¹ from incandescent lamps) or under ambient daylight plus supplemental irradiance during the day and as a day extension to 18 h (0800–0200 h) with supplemental high pressure sodium lighting (+50, 100, or 150 μmol m⁻² s⁻¹) to identify the impact of photoperiod and irradiance on flowering of each species. Days to first open flower, leaf number below first flower, and mean dry weight gain per day (MDWG) were measured when the first flower opened. Twenty-seven species were photoperiodic with examples of five photoperiodic response groups represented: obligate short-day (2), facultative short-day (5), obligate long-day (16), facultative long-day (4); 13 were day neutral (no photoperiod response in flowering). One species, Salvia sclarea L., did not flower. A facultative irradiance response was observed with 10 species; 28 species were irradiance indifferent; 2 had delayed flowering as irradiance increased. Photoperiod affected MDWG of 30 species. Increasing irradiance affected MDWG with 14 species. Photoperiod interacted with irradiance to affect MDWG of 11 species. Cobaea scandens had the greatest MDWG (0.40 g day⁻¹) while Amaranthus hybridus had the least MDWG (0.01 g day⁻¹) across photoperiod and irradiance levels.     

Estimation of broad-leaved canopy growth in the urban forested area using multi-temporal airborne LiDAR datasets

Inter-annual canopy growth is one of the key indicators for assessing forest conditions, but the measurements require laborious field surveys. Up-to-date LiDAR remote sensing provides sufficient three-dimensional morphological information of the ground to monitor canopy heights on a broad scale. Thus, we attempted to use multi-temporal airborne LiDAR datasets in the estimation of vertical canopy growth, across various types of broad-leaved trees in a large urban park.The growth of broad-leaved canopies in the EXPO '70 urban forest in Osaka, Japan was assessed with 19 plots at the stand level and 39 selected trees at the individual-tree level. Airborne LiDAR campaigns repeatedly observed the park in the summers of 2004, 2008, and 2010. We acquired canopy height models (CHMs) for each year from the height values of the uppermost laser returns at every 0.5 m grid. The annual canopy growth was calculated by the differences in CHMs and validated with the annual changes in field-measured basal areas and tree heights.LiDAR estimations revealed that the average annual canopy growth from 2004 to 2010 was 0.26 ± 0.11 m m⁻² yr⁻¹ at the plot level and 0.26 ± 0.10 m m⁻² yr⁻¹ at the individual-tree level. This result showed that growing trends were consistent at different scales through 2004 to 2010 despite uncertainty in estimating short-term growth for small crown areas at the individual-tree level. This LiDAR-estimated canopy growth shows a moderate relation to field-measured increase of basal areas and average heights. The estimation uncertainties seem to result from the complex canopy structure and irregular crown shape of broad-leaved trees. Challenges still remain on how to incorporate the growth of understory trees, growth in the lateral direction, and gap dynamics inside the canopy, particularly in applying multi-temporal LiDAR datasets to the large-scale growth assessment.     

Optimising the organic components of topsoil mixtures for urban grassland

In order to optimise the organic components of topsoil mixtures for urban grassland, we conducted two pot experiments, each with seven topsoil mixtures and perennial ryegrass (Lolium perenne) as the experimental crop. The mineral base material of the topsoil mixtures was a blend of crushed bedrock (0–2 mm), sand and agricultural topsoil. The organic components comprised three types of organic waste-based products (WBP), namely sewage sludge (SS), water sludge (WS) and garden-park compost (GPC), which were added in varying ratios to a total amount of 0.3 m³ WBP m^?3. In both experiments, mineral nitrogen (N) availability was the key limiting factor for plant growth. Plant growth increased with increasing amounts of the N-rich SS, whereas WS and/or GPC alone resulted in sparse biomass production. Topsoil mixtures with 0.1 m³ m^?3 each of SS, WS, GPC or with 0.1 m³ SS m^?3 and 0.2 m³ WS m^?3 resulted in favourable growth patterns and acceptable soil chemical properties. Topsoil mixtures containing ≤0.1 m³ SS m^?3 can therefore be recommended for the establishment of urban grassland. With >0.1 m³ SS m^?3, N and phosphorus (P) were applied in excess, causing intensive plant growth and strongly increased readily available phosphorus (P-AL) content in topsoil. We therefore suggest revision of the current Norwegian regulations, which permit inclusion of 0.3 m³ SS m^?3 in topsoil mixtures for urban greening.     

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.     

Varying evapotranspiration and salinity level of irrigation water influence soil quality and performance of perennial ryegrass (Lolium perenne L.)

Increasing use of recycled water that is often high in salinity warrants further examination of irrigation practices for turfgrass health and salinity management. A study was conducted during 2011–2012 in Riverside, CA to evaluate the response of perennial ryegrass (Lolium perenne L.) ‘SR 4550’ turf to varying quality and quantity of irrigation water. A modified line-source sprinkler irrigation system provided a salinity gradient (EC_w ∼0.6–4.2 dS m⁻¹) in between lines. Irrigation was scheduled in four separate irrigation zones perpendicular to the irrigation lines according to 80, 100, 120, and 140% ET_o. Changes in turf quality (R² = 0.30***), were primarily driven by the number of days that the area had been irrigated with saline water. When data were separated by irrigation amount, both time and water quality accounted for 54% and 46% of the variability (P < 0.001) in quality and cover, respectively at 80% ET_o. A model was created to quantify decline in turf quality in relationship to %ET_o replacement and salinity accumulation in the rootzone (R² = 0.57). Our results suggest that perennial ryegrass requires irrigation scheduling at 140% ET_o, irrigation water quality below EC_w ∼1.7 dS m⁻¹, and EC_e below 3.8 dS m⁻¹ to maintain acceptable quality for 442 d in Riverside, CA.     

Allometric equations for estimating the aboveground volume of five common urban street tree species in Daegu,Korea

Quantifying urban tree biomass and carbon (C) storage by using allometric equations is required for various studies such as assessing the inventory, modelling, and measuring ecosystem services of urban trees. However, the lack of urban-specific allometric equations leads to uncertainty when estimating urban tree biomass and C storage. Therefore, we followed a nondestructive approach and developed allometric equations specifically for Acer buergerianum Miq., Ginkgo biloba L., Platanus orientalis L., Prunus yedoensis Matsum., and Zelkova serrata (Thunb.) Makino in Daegu, Korea. Diameter at breast height (DBH)-based and DBH-and-height-based allometric equations were highly accurate at estimating the aboveground volume (R² > 0.92), while the allometric equations for P. orientalis and Z. serrata developed for traditional forests overestimated volume by 68% and 427%, respectively. The addition of a height variable into the DBH-based allometric equations did not increase the reliability of the allometric equations at a local level. The mean aboveground C storage of urban street trees was 24.9 Mg C/ha except for P. orientalis with a mean of 69.7 Mg C/ha, and the total aboveground C storage of urban street trees in Daegu was 10.6 Gg C. Alternatively, a generalized allometric equation which compiled species-specific equations can be applied for large-scale estimation. The generalized equations developed in this study and those found in the literature may suggest a constant value (～2.3–2.4) for the scaling exponent in the generalized equations. Allometric equations developed from natural or artificial stands may overestimate the volume of urban street trees; therefore, estimating urban tree biomass and C storage requires urban-specific allometric equations.     

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.     

The influence of small green space type and structure at the street level on urban heat island mitigation

The purpose of this study was to determine the types and structures of small green spaces (SGs) that effectively reduce air temperature in urban blocks. Six highly developed blocks in Seoul, South Korea served as the research sites for this study. Air temperature was measured at the street level with mobile loggers on clear summer days from August to September in 2012. The measurements were repeated three times a day for three days. By analyzing the spatial characteristics, SGs within the six blocks were categorized into the four major types: polygonal, linear, single, and mixed. The result revealed that the polygonal and mixed types of SGs showed simple linear regression at a significant level (p < 0.01). It indicated that the blocks’ urban heat island (UHI) mitigation (ΔT_Rmn) increased in a linear fashion when the area and volume of these two types of green spaces increased. The area and volume of a polygonal SG with mixed vegetation, over 300 m² and 2300 m³, respectively, lowered the ΔT_Rmn by 1 °C; SG with an area and volume of larger than 650 m² and 5000 m³, respectively, lowered the ΔT_Rmn by 2 °C. The results of this study will be useful to urban planners and designers for determine the types and structures of urban green spaces to optimize the cooling effect, as well as how such green spaces should be designed and distributed.     

Density,diversity and richness of woody plants in urban green spaces: A case study in Chennai metropolitan city

A tree diversity inventory was carried out in urban green spaces (UGSs) of Chennai metropolitan city, India. This inventory aims to study the diversity, density and richness of trees in UGSs of Chennai. A total of one hundred 10 m × 10 m (total 1 ha) plots were laid to reveal tree diversity and richness of UGSs. Trees with ≥10 cm girths at breast height (gbh) were inventoried. We recorded 45 species in 42 genera and 21 families. Caesalpiniaceae and Fabaceae each with 6 species dominated the study area followed by Arecaceae (3). Density and stand basal area of the present study were 500 stems ha^?1 and 64.16 m², respectively. Most of the inventoried trees were native (31 species) and deciduous (28 species). Fabaceae and Caesalpiniaceae dominated the present study area in terms of stand basal area and density. The Shannon diversity index and evenness of study area were 2.79 and 0.73, respectively. The most important species and families based on species important value index (IVI) and family important value index were Albizia saman, Polyalthia longifolia and Azadirachta indica; Fabaceae, Caesalpiniaceae and Annonaceae respectively. We find Chennai's urban forest is relatively superior to many urban forests of the world in terms of stand basal area and species richness. Results emphasize the importance of enhancement of urban green spaces in Chennai metropolitan city.     

The effects of NaCl pre-treatments on salt tolerance of melons grown under long-term salinity

The response of melon (Cucumis melo) plants to long-term salinity was investigated to determine the availability of the NaCl pre-treatments (seed priming + seedling conditioning) as an interesting strategy for increasing the salt tolerance. Seeds of melon cultivars “Hasanbey” and “Kirkagac” were primed with 18 dS m⁻¹ NaCl solution for 3 days at 20 °C. During emergence and seedling growth, non-primed seeds were irrigated with local irrigation water (EC: 0.3 dS m⁻¹) whereas primed groups were treated with 9.0 dS m⁻¹ saline solution for 35 days. Seedlings derived from pre-treated (P) and non-pre-treated (NP) groups were transplanted to 8 l pots. After transplanting, salinity treatments were started with the first irrigation. The salinity treatments consisted of five levels (control, 4.5, 9.0, 13.5 and 18.0 dS m⁻¹) of irrigation solution for a period of 90 days. NaCl pre-treatments diminished the inhibiting effect of salinity on growth of melon plants. However, competence for salt adaptation varied with cultivar and the level of salinity. The physiological response of the P plants was also maintained in the long-term. Stomatal conductance and relative chlorophyll content of P plants tended to be higher than those of the NP ones. In addition, NaCl pre-treatments enhanced K and Ca concentrations of leaves and stems, and prevented toxic effects of salinity because less Na accumulated in stems. These results suggest that the use of NaCl pre-treatments could be a useful strategy to increase the salt tolerance of melon plants in the long-term and also to permit the establishment of melon crop by direct sowing in a saline medium.     

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.     

Production of high quality Ardisia plants by stem tip cuttings

To produce commercially acceptable Ardisia plants, stem tip cuttings from mature plants were rooted and forced in greenhouses. Ten centimeter long cuttings were either treated with 200 ppm 1-naphthalene acetic acid (NAA) for 2 h, 2000 ppm indole-3-yl-butyric acid (IBA) for 10 s, or 0.5 and 1.0% IBA powder prior to sticking them in the rooting medium. Rooting percentage at 45 days exceeded 76% with 2000 ppm IBA treatment which was a significant increase over non-treated control. Rooted cuttings developed into three types of plants: those forming only vegetative shoots without flowers, those forming reproductive shoots with flowers, and those forming both vegetative and reproductive shoots. The ideal plant produced only vegetative shoots when rooted cuttings were transplanted into pots. About 50% rooted cuttings were forced to finish, producing 31 or 40% of high quality plants when rooted cuttings with vegetative shoots were grown in a greenhouse (GH) at temperatures higher than 21/19 °C (day/night) in 1995 or 21/18 °C GH in 1997, respectively. This method shortened the total production time to less than 2 years as compared to 4 years when starting from seeds.     

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.     

Spatiotemporal dynamics of plant diversity in response to farmers’ evolved settlements in Shanghai

The expansion of the Shanghai metropolitan region has caused a substantial amount of farmland to become urbanized. Most farmers have lost their land and have been relocated from villages to new collective settlements, resulting in dramatic changes in the landscape pattern. This study explores the effects of this transformation on the spatiotemporal dynamics of plant diversity. We randomly sampled 22 plots comprising 294 subplots within two crossed transects that pass through 5 traditional villages and 17 new settlements. The results show that resettlement has exerted significant effects on plant species diversity, both temporally and spatially. Temporally, the Gleason index (GI) of total species over time could be ordered as 1990s > 2000s > 1980s, while Shannon’s diversity index (SHDI) was ordered as 2000s > 1990s > 1980s. Spatially, the GI of total species decreased from the urban center to the exurbs or from the inside to the outside of the built-up areas. SHDI was highest in suburbs or ecotones. Furthermore, the GI of total species had significant correlations with those of indigenous species, exotic species, and planted species (r > 0.90, p < 0.01) as well as with the region and location of settlement (r < −0.48, p < 0.01). Both indigenous and exotic species had significant positive correlations with total species richness at 0.01 levels. Generally, compared with traditional settlements, new settlements displayed greater richness and diversity of plant species, primarily because of the exotic species present in new settlements. The farmers’ socio-economic status was found to be the primary cause of differences in species richness. To protect indigenous and wild species, it is necessary to take into account local knowledge in villages to encourage Chinese farmers to participate actively in community greening. A bridge should be built between traditional villages and modern settlements and between the past and future for farmers.     

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.