Non-shaded Conditions Research Articles

A screening model to predict microalgae biomass growth in photobioreactors and raceway ponds

A microalgae biomass growth model was developed for screening novel strains for their potential to exhibit high biomass productivities under nutrient-replete conditions in photobioreactors or outdoor ponds. Growth is modeled by first estimating the light attenuation by biomass according to Beer-Lambert's Law, and then calculating the specific growth rate in discretized culture volume slices that receive declining light intensities due to attenuation. The model uses only two physical and two species-specific biological input parameters, all of which are relatively easy to determine: incident light intensity, culture depth, as well as the biomass light absorption coefficient and the specific growth rate as a function of light intensity. Roux bottle culture experiments were performed with Nannochloropsis salina at constant temperature (23°C) at six different incident light intensities (10, 25, 50, 100, 250, and 850 µmol/m(2) s) to determine both the specific growth rate under non-shading conditions and the biomass light absorption coefficient as a function of light intensity. The model was successful in predicting the biomass growth rate in these Roux bottle batch cultures during the light-limited linear phase at different incident light intensities. Model predictions were moderately sensitive to minor variations in the values of input parameters. The model was also successful in predicting the growth performance of Chlorella sp. cultured in LED-lighted 800 L raceway ponds operated in batch mode at constant temperature (30°C) and constant light intensity (1,650 µmol/m(2) s). Measurements of oxygen concentrations as a function of time demonstrated that following exposure to darkness, it takes at least 5 s for cells to initiate dark respiration. As a result, biomass loss due to dark respiration in the aphotic zone of a culture is unlikely to occur in highly mixed small-scale photobioreactors where cells move rapidly in and out of the light. By contrast, as supported also by the growth model, biomass loss due to dark respiration occurs in the dark zones of the relatively less well-mixed pond cultures. In addition to screening novel microalgae strains for high biomass productivities, the model can also be used for optimizing the pond design and operation. Additional research is needed to validate the biomass growth model for other microalgae species and for the more realistic case of fluctuating temperatures and light intensities observed in outdoor pond cultures.

EFFECT OF SHADING AND GRAFTING TECHNIQUE ON GROWTH AND FRUIT PRODUCTION OF SWEET PEPPER PLANTS

Horticultural cultivation in Mediterranean greenhouses requires the implementation of refrigeration systems to avoid stress situations, particularly under spring-summer conditions. The effect of the temperature and high solar radiation in the greenhouse can be decreased by shade screen. The use of grafting onto adequate rootstocks could be an interesting alternative to maintain commercial fruit yield and quality under stress conditions. The effects of using aluminised screens offering different degrees of shading combined with two transplant types (grafted or ungrafted) were analyzed in sweet pepper plants. Simultaneous comparisons were made among greenhouse that were either non-shaded (control) or covered with reflective aluminized shadecloth that attenuated 40% (T40) and 60% (T60) of direct sunlight. The shadecloth was applied at the start of warm weather in May. The greenhouses were shaded for the rest of the summer, and fruit being picked until August. The use of shadecloth proved to be efficient in improving vegetative growth and reducing the unmarketable yield, compared to non-shaded conditions. The results showed that fruit yield was highest in the T40 treatment, presented significantly different, and the T60 treatment had a lower production. On the other hand the use of the grafting promoted vegetative growth. Grafting increased the marketable yield compared to the ungrafted plants under shade and non-shade conditions.

Effects of the modification of light intensity by color shade nets on yield and quality of tomato fruits

The photoselective netting concept was studied in a tomato ‘Vedeta’ cultivation in the south part of Serbia (Aleksinac) under high solar radiation, using four different colored shade-nets (pearl, red, blue and black) with different relative shading (40% and 50% PAR). Exposure to full sunlight was used as a control. Red and pearl nets with 40% shade significantly increased the total yield. Shading reduced the appearance of tomato cracking and eliminated sunscalds on tomato fruits and accordingly, increased the marketable tomato production by about 35% compared to non-shading conditions. Changing the light intensity by color shade nets affected the biosynthesis of lycopene and β-carotene in tomatoes. Thus, significantly higher lycopene content was observed in greenhouse tomato integrated with red shade netting technologies (64.9μgg−1) than in field-grown tomatoes (48.1μgg−1). By contrast, shaded fruits have lower content of β-carotene. The photo-selective, light-dispersive shade nets appear as interesting tools that can be further implemented within protected cultivation practices.

Grafting is an efficient alternative to shading screens to alleviate thermal stress in greenhouse-grown sweet pepper

Sweet pepper crop yield and quality in some Mediterranean regions are negatively affected by the high radiation and temperature during the spring–summer harvesting period. Although the use of shading screens is a common, although expensive, strategy to minimize the impact of thermal stress, the use of grafting onto adequate rootstocks could be an interesting alternative to maintain commercial fruit yield and quality under non-shaded conditions, in addition to providing other advantages such as resistance to soil-borne diseases. In order to test this hypothesis, we studied the behaviour of ‘Herminio’ plants ungrafted and grafted onto three different commercial rootstocks (Atlante, Creonte and Terrano) under non-shaded and shaded conditions. The use of shading screen proved to be efficient in improving vegetative growth, photosynthesis, transpiration and leaf water status, and for reducing the unmarketable yield, especially the incidence of the sunscalded fruits, compared to non-shaded conditions. In general, the grafted plants performed better than the ungrafted ones under both growing conditions, but the differences were more evident under non-shaded conditions. The plants grafted onto Atlante produced up to 40% more leaf area than the other combinations but did not increase yield nor reduce the incidence of the sunscald disorder. However, grafting onto Creonte did not significantly affect leaf biomass but increased the total and marketable fruit yield by 30% and 50% under non-shaded and shaded conditions compared to the ungrafted plants, respectively. Moreover, this rootstock maintained 30–60% higher leaf photosynthetic activity and reduced the amount of sunscalded fruits by 6% during the harvest period in non-shaded conditions. However some fruit nutritional parameters were affected. These results suggest that improved protection of the photosynthetic apparatus is more efficient for increasing yield and for reducing sunscald disorder than more foliage per se under non-shaded conditions, in the absence of any other imposed stress. The use of the rootstock Creonte is an efficient alternative to using shading screens in greenhouse-grown sweet peppers.

Effects of short-term treatment with various light intensities and hydroponic solutions on nitrate concentration of lettuce

A glasshouse experiment was conducted to investigate the effects of five days’ treatment before harvest with various light intensities and seven hydroponic solutions on nitrate reduction in lettuce. The results showed that SPAD of new and expanded leaves were elevated by most of the hydroponic solutions under shading compared with the full nutrient solution, while no effect was demonstrated under non-shading. Additionally, lettuces under non-shading presented slightly higher leaf SPAD than those under shading. Nitrate concentrations of lettuce new leaves, expanded leaves and petiole were lowered significantly by all hydroponic solutions under shading and non-shading conditions compared with the full nutrient solution. Under non-shading, the efficiencies of seven hydroponic solutions varied largely, but no efficiency differences were showed under shading. N-free solution, 0.75 mM potassium sulphate solution and 5×10−5 mM ammonium molybdate solution functioned more efficiently in reducing nitrate concentration both in expanded leaves and petiole of lettuce before harvest. In conclusion, proper light intensity is a key important factor that determines the efficiencies of nitrogen-free hydroponic solution treatments in lowering nitrate concentrations in leaf blades and petioles of lettuce before harvest.

Effects on microclimate, crop production and quality of a tomato crop grown under shade nets

SummaryThe effects of four shade nets with different colour transmission properties and shading intensities (two black nets with shading intensities of 40% and 49%, a green net with a shading intensity of 34%, and a mixed green and black shade net with a shading intensity of 40%) on the screenhouse microclimate, and on the growth and development of a tomato crop, were investigated. Experiments were carried out during Spring and Summer 2003 in New Anchialos, a coastal area of Eastern Central Greece. Tomato seedlings were planted in soil and the following environmental variables were recorded at regular intervals: solar radiation, air temperature and relative humidity, leaf temperature, and several variables related to crop growth and development. Air temperature and vapour pressure deficit (VPD) values were similar under all four shade nets and without shading. However, canopy temperature and, accordingly, the canopy-to-air VPD were significantly lower under shading than without shading. Shading did not reduce the total plant dry matter content, but increased the leaf area index, the number of fruit per plant, and the total fresh tomato yield. Shading reduced losses caused by tomato cracking by 50%, and thus increased the marketable tomato fruit yield by approx. 50% compared to growth under non-shaded conditions.

The Effect of Light and Water Supply on Growth, Net CO2 Assimilation Rate and Mineral Content of Salak (Salacca zalacca (Gaertn.) Voss) Seedlings

The study was carried out in a greenhouse of at the Institute for Horticultural Sciences of the Humboldt Universität zu Berlin. Seven-months-old seedlings of salak cultivars “pondoh” from Indonesia were used for the study. At this age, plants are usually transferred from the nursery to the field in the growing region. An experimental block design was arranged for the study. A total of 48 experimental plants was separated into two blocks, namely shading (S) and non-shading (N). Three water supply treatments were assigned to each block. At the beginning of the study, the seedlings for N treatment were moved from shading to non-shading tables in the greenhouse. Three water supply treatments were assigned to each block. At the beginning of the study, the seedlings for N treatment were moved from shading to non-shading tables in the greenhouse. Two additional 400 W lamps (HQI-TS/D, OSRAM, Germany) were placed 2 m above the seedlings in the N treatment. Three watering treatments, applied to each block, were W1 (100 ml distilled water per plant every 2 days), W2 (100 ml per plant every 4 days) and W3 (100 ml per plant every 6 days). Therefore, the combinations of the treatments were SW1, SW2, SW3, NW1, NW2 and NW3. Responses to be analysed were shoot and root dry weight, increment of shoot length and leaf area, net CO2 assimilation rate (PN) and plant mineral contents, i.e. N, P, K, Ca and Mg. In addition, water content of the growing media was recorded. The study results showed that shading, which reduced sunlight by 70 %, was not beneficial for 7-months-old salak seedlings, due to lower growth rate, PN and N content as compared with plants in non-shading conditions. On the other hand, light intensities above 800 µmol m-2 s-1 (PAR) possibly cause leaf bleaching and should be avoided. Salak plants did not tolerate drought conditions. However, different water supply did not affect PN and mineral uptake (N, P, K, Ca, Mg) of salak plants.

Preadapted for invasiveness: do species traits or their plastic response to shading differ between invasive and non-invasive plant species in their native range?

Aim Species capable of vigorous growth under a wide range of environmental conditions should have a higher chance of becoming invasive after introduction into new regions. High performance across environments can be achieved either by constitutively expressed traits that allow for high resource uptake under different environmental conditions or by adaptive plasticity of traits. Here we test whether invasive and non-invasive species differ in presumably adaptive plasticity. Location Europe (for native species); the rest of the world and North America in particular (for alien species). Methods We selected 14 congeneric pairs of European herbaceous species that have all been introduced elsewhere. One species of each pair is highly invasive elsewhere in the world, particularly so in North America, whereas the other species has not become invasive or has spread only to a limited degree. We grew native plant material of the 28 species under shaded and non-shaded conditions in a common garden experiment, and measured biomass production and morphological traits that are frequently related to shade tolerance and avoidance. Results Invasive species had higher shoot–root ratios, tended to have longer leaf-blades, and produced more biomass than congeneric non-invasive species both under shaded and non-shaded conditions. Plants responded to shading by increasing shoot–root ratios and specific leaf area. Surprisingly, these shade-induced responses, which are widely considered to be adaptive, did not differ between invasive and non-invasive species. Main conclusions We conclude that high biomass production across different light environments pre-adapts species to become invasive, and that this is not mediated by plasticities of the morphological traits that we measured.

Effect of Light Intensity on Arundinaria gigantea Growth and Physiology

The once dominant Arundinaria gigantea canebrake ecosystems have been reduced to fragmented populations less than 2% of their former extent resulting in a critically endangered ecosystem. Restoration of canebrakes is thus necessary for maintaining and enhancing biodiversity in the southeastern United States. Contemporary fragments of canebrakes are trapped between anthropogenic development and closed canopy forests. The goal of this study was to assess the impact of light intensity on rivercane growth and physiology in both laboratory and field studies and thereby enhance restoration success. A laboratory experiment was conducted to test light (partial shading and no shading) and nitrogen (0, 0.5, 5.0, 25, and 100 g/L) effects on seedling growth. Potential interaction occurred between light and nitrogen. Levels of nitrogen up to ten times the commercially recommended amount (0.5 g/L) significantly increased seedling growth when plants were grown under non-shaded conditions. A thinning site was established in an existing rivercane population and forest canopy was reduced 60% by girdling overstory trees. Number of new shoots and new shoot diameter were both increased by thinning. In addition, light response curves demonstrated that rivercane had a typical C3 light response pattern and field readings showed that rivercane maintained net photosynthetic activity throughout the dormant season. Results indicate that rivercane growth is enhanced with increased light levels. Reduction of overstory canopy is a potential management tool for enhancing survival and growth of existing populations.

Survival of Sporangia of New Clonal Lineages of Phytophthora infestans in Soil Under Semiarid Conditions.

Currently, there is no information on the viability of sporangia in soil of the new metalaxyl-resistant genotypes of Phytophthora infestans in the semiarid Columbia Basin of Washington and potato-growing regions throughout the world. Sporangia of metalaxyl-resistant US-8 and US-11 clonal lineages of P. infestans survived a maximum of 23 to 30 days in a Shano silt loam and a Quincy loamy fine sand. There were no significant differences between soil types in area under the spore survival curve (AUSSC) in two trials, however, sporangia of P. infestans in the Quincy sand had a significantly greater mean maximum days of sporangia survival (MDSS) than did the Shano silt loam in one of two trials. AUSSC and MDSS were significantly greater (P < 0.05) for sporangia in wet soil than in dry soil under shaded conditions. Mean AUSSC and MDSS significantly decreased (P < 0.01) under nonshaded conditions versus shaded conditions. Three metalaxyl-resistant isolates (two US-8 and one US-11) of P. infestans did not significantly differ (P < 0.05) in AUSSC and MDSS.

Alteration in Intra-plant Distribution of δ15N in Response to Shading in Legumes

The intra-plant distribution of 15N in common bean, cowpea and soybean having different levels of responses to shading and N2-fi xing ability were analyzed under shaded and non-shaded conditions. Maize was used as a reference (non N2-fixing) plant. Seedlings were grown in pot soils for 3 weeks then transferred to shaded (55% of control) and non-shaded (control) conditions in a greenhouse, and sampled at 13 days and 24 days after shading. The proportion of plant N derived from N2-fixation (%Ndfa) estimated by the natural 15N abundance method was higher in cowpea and soybean (74.91%) than in common bean (37.38%). Shade treatment reduced %Ndfa signifi cantly in cowpea and soybean. The difference in δ15N between shoot and root (Δδ 15Ns-r) was the highest in maize followed by common bean, cowpea and soybean. Shading increased Δδ 15Ns-r in each legume species, particularly in cowpea and soybean. A signifi cant negative correlation was found between Δδ 15Ns-r and %Ndfa in all legumes at both sampling dates (R2 = 0.67.0.96, P<0.1). The slope and Y-intercept of the regression line was similar at the sampling dates, but varied with the species. The slope was –0.05 in cowpea, –0.06 in common bean, and –0.11 in soybean. The Δδ 15Ns-r value estimated by extrapolation of the regression line was 2.9, 2.5 and 8.6%. at 0 %Ndfa, and –3.2, –2.8 and –2.6%. at 100 %Ndfa, in common bean, cowpea and soybean, respectively. The consistent relationships between Δδ 15Ns-r and %Ndfa found among legume species suggest that Δδ 15Ns-r could be used as a parameter for estimating %Ndfa without using a reference plant, although the component of regression line was characteristically different among legume species.

Survival of Phytophthora infestans in Surface Water

ABSTRACT Coverless petri dishes with water suspensions of sporangia and zoospores of Phytophthora infestans were embedded in sandy soil in eastern Washington in July and October 2001 and July 2002 to quantify longevity of spores in water under natural conditions. Effects of solar radiation intensity, presence of soil in petri dishes (15 g per dish), and a 2-h chill period on survival of isolates of clonal lineages US-8 and US-11 were investigated. Spores in water suspensions survived 0 to 16 days under nonshaded conditions and 2 to 20 days under shaded conditions. Mean spore survival significantly increased from 1.7 to 5.8 days when soil was added to the water. Maximum survival time of spores in water without soil exposed to direct sunlight was 2 to 3 days in July and 6 to 8 days in October. Mean duration of survival did not differ significantly between chilled and nonchilled sporangia, but significantly fewer chilled spores survived for extended periods than that of nonchilled spores. Spores of US-11 and US-8 isolates did not differ in mean duration of survival, but significantly greater numbers of sporangia of US-8 survived than did sporangia of US-11 in one of three trials.

SHADE-INDUCED PLASTICITY AND ITS ECOLOGICAL SIGNIFICANCE IN WILD POPULATIONS OF ARABIDOPSIS THALIANA

In laboratory studies of Arabidopsis thaliana, plants shaded by neighboring vegetation (or subject to treatments mimicking shade) flower at a younger developmental stage, and sometimes earlier in time. We examined whether this shade avoidance response varies among and within natural populations of A. thaliana, and whether it corresponds to variable selection regimes at shaded and unshaded field sites, by conducting a two-year reciprocal transplant study and a parallel greenhouse study that manipulated the presence and timing of shade. In the field, shading had limited or inconsistent impacts on survivorship across several phases of the growing season. The date of bolting was earlier at the shadier site compared to the less shady site, but in the greenhouse there was no significant shade- induced plasticity for this trait. In both studies, we detected directional selection gradients favoring earlier bolting in shade, but gradients favoring earlier bolting were as strong in nonshaded conditions. The number of rosette leaves at bolting (i.e., the developmental stage of flowering) was significantly reduced by shade in both studies. However, there was either no directional selection on this trait, or selection to flower with more rather than fewer leaves. Despite the contrast in habitats, there was limited differentiation between populations for survivorship, reproductive fitness, size-related or flowering time traits, and no differ- entiation for trait plasticities. Some traits were variable among families within populations. A trade-off between age and developmental stage may limit the response to selection for flowering time, possibly explaining limited local adaptation. The adaptive significance of shade-induced flowering time plasticity remains equivocal. Future studies of the plasticity of flowering time in A. thaliana should investigate the effects of shading regimes together with other environmental variables on size- and timing-related traits.

Effects of light availability on attachedRhinanthus minor (L.), an angiospermatic root hemiparasite

We studied the effect of light availability on the growth of an angiospermatic root hemiparasite,Rhinanthus minor. When attached to its host, height growth increased in response to shading, demonstrating thatR. minor was able to detect alterations in light quality and/or quantity. However, this reduced illumination did not affect its biomass, number of haustoria, or the amount of15N transferred from the hosts, compared with its performance under non-shaded conditions. Therefore,R. minor is unlikely to have difficulty in extracting host resources under shading. This result may have been mediated by a loweredR. minor transpiration rate in response to fluctuations in external conditions, including shading and water stress, compared with non-parasitic plants. Therefore, we suggest that, as long as the extent of resources diverted from host to parasite is not significantly altered by shading, growth of the attachedR. minor will be unaffected by reduced light availabilityper se.

Roles of succession, light, nutrients and disturbance on population vigor and maintenance of the rare plant Solidago shortii (Asteraceae)

Results of field and glasshouse experiments on Solidago shortii, and our observations on this species over many years, were used to construct a conceptual model of the roles of succession, light, soil nutrients and disturbance on population vigor and maintenance of this federal-endangered species. As cover of woody vegetation increased at a population site between 1986 and 1992, number of flowering ramets of S. shortii significantly decreased but number of vegetative ramets remained nearly constant. Adult plants transplanted into a redcedar thicket and those shaded in a glasshouse produced many fewer flowering ramets and capitula per flowering ramet and less biomass and had higher mortality than those in the open. Seedlings/juveniles shaded in a glasshouse had significantly less dry biomass; lower RGR, NAR, leaf area and root/shoot ratio and higher LAR, SLA and LWR than nonshaded ones. In a field site and glasshouse, fertilized plants (NPK) consistently had more flowering ramets and capitula per flowering ramet than nonfertilized ones. Hierarchy of dry weight of plants grown in a glasshouse in soils derived from five types of bedrock was phosphatic limestone > calcareous shale > sandstone > black shale = dolomite. Flowering and biomass production in the field-fertilizer and soil-type experiments were associated closely with levels of P. Number of flowering ramets significantly increased in plants transferred from shaded to nonshaded glasshouse conditions, but no such increase occurred after opening the canopy above plants in a thicket. Both high light and high nutrient levels apparently are necessary to maintain high vigor of S. shortii. In areas subject to invasion by woody plants, periodic high intensity disturbance may be required to prevent population extirpation.

Leaf surface fine-structures in rice plants cultured under shaded, and non-shaded conditions.

Leaf surface fine-structures in rice plants cultured under shaded, and non-shaded conditions.