Kaolin Film Increases Gas Exchange Parameters of Coffee Seedlings During Transference From Nursery to Full Sunlight

Increases in water use efficiency (WUE) and the reduction of negative impacts of high temperatures associated with high solar radiation are being achieved with the application of fine particle film of calcined and purified kaolin (KF) on the leaves and fruits of various plant species. KF was applied on young Coffea arabica and Coffea canephora plants before their transition from nursery to full sunlight during autumn and summer. The effects of KF were evaluated through the responses of leaf temperature (Tleaf), net CO2 assimilation rate (A), stomatal conductance (gs), transpiration (E), WUE, crop water stress index (CWSI), index of relative stomatal conductance (Ig), initial fluorescence (F0), and photosynthetic index (PI) in the first 2–3 weeks after the plant transitions to the full sun. All measurements were performed at midday. In Coffea plants, KF decreased the Tleaf up to 6.7°C/5.6°C and reduced the CWSI. The plants that were not protected with KF showed lower A, gs, E, and Ig than those protected with KF. C. canephora plants protected with KF achieved higher WUE compared with those not protected by 11.23% in autumn and 95.58% in summer. In both Coffea sp., KF application reduced F0, indicating reduced physical dissociation of the PSII reaction centers from the light-harvesting system, which was supported with increased PI. The use of KF can be recommended as a management strategy in the transition of Coffea seedlings from the nursery shade to the full sunlight, to protect leaves against the excessive solar radiation and high temperatures, especially in C. canephora during the summer.

Response of Plant Growth and Development, and Accumulation of Hydroxyl-cinnamoyl Acid Derivatives to Selected Shade Nets and Seasonality of Field-grown Bush Tea (Athrixia phylicoides DC.)

Horticultural practices and quality of bush tea (Athrixia phylicoides DC.) are critical for herbal tea industrialization. The objective of the current study was to determine the effect of selected shade nets and seasonal variation on plant growth and development, and hydroxycinnamic acid content of field-grown bush tea. The trial was laid out in a randomized complete block design consisting of three shade nets (black, green, and white) and control or full sunlight with three different light intensities (40%, 50%, and 80%) replicated three times. Proportion of intercepted radiation by the canopy, chlorophyll content, plant height, and fresh and dry mass were measured, and hydroxycinnamic acid accumulation was determined. In addition, hydroxycinnamic acid composition was determined using liquid chromatography linked to mass spectrometry (LC-MS). The application of shade nets resulted in plant growth and yield reduction as compared with the plants exposed to full sunlight during summer followed by white shade net. The accumulation of hydroxycinnamic acid was higher in 80% white shade net plots compared with unshaded plants (control) and the other shade nets. Therefore, lack of shading provides a conducive environment to enhance plant growth and development of bush tea. The white shade net (80%) was an effective microclimate tool to enhance accumulation of caffeoylquinic acid (m/z 353), p-coumaric acids (m/z 337), dicaffeoylquinic acid (m/z 515), and tricaffeoylquinic acids of bush tea. This study is the first to demonstrate light as a determining factor for production of chlorogenates in bush tea plants. Future studies will be conducted to determine the effect of light on extracts of the bush tea using different solvents.

Acclimating Cucumber Plants to Blue Supplemental Light Promotes Growth in Full Sunlight

Raising young plants is important for modern greenhouse production. Upon transfer from the raising to the production environment, young plants should maximize light use efficiency while minimizing deleterious effects associated with exposure to high light (HL) intensity. The light spectrum may be used to establish desired traits, but how plants acclimated to a given spectrum respond to HL intensity exposure is less well explored. Cucumber (Cucumis sativus) seedlings were grown in a greenhouse in low-intensity sunlight (control; ∼2.7 mol photons m–2 day–1) and were treated with white, red, blue, or green supplemental light (4.3 mol photons m–2 day–1) for 10 days. Photosynthetic capacity was highest in leaves treated with blue light, followed by white, red, and green, and was positively correlated with leaf thickness, nitrogen, and chlorophyll concentration. Acclimation to different spectra did not affect the rate of photosynthetic induction, but leaves grown under blue light showed faster induction and relaxation of non-photochemical quenching (NPQ) under alternating HL and LL intensity. Blue-light-acclimated leaves showed reduced photoinhibition after HL intensity exposure, as indicated by a high maximum quantum yield of photosystem II photochemistry (Fv/Fm). Although plants grown under different supplemental light spectra for 10 days had similar shoot biomass, blue-light-grown plants (B-grown plants) showed a more compact morphology with smaller leaf areas and shorter stems. However, after subsequent, week-long exposure to full sunlight (10.7 mol photons m–2 day–1), B-grown plants showed similar leaf area and 15% higher shoot biomass, compared to plants that had been acclimated to other spectra. The faster growth rate in blue-light-acclimated plants compared to other plants was mainly due to a higher photosynthetic capacity and highly regulated NPQ performance under intermittent high solar light. Acclimation to blue supplemental light can improve light use efficiency and diminish photoinhibition under high solar light exposure, which can benefit plant growth.

Adaptability of Siamese Rosewood and Teak Seedlings to Varying Light Conditions

Rosewood and Teak are valuable timber species, which have been heavily logged from both natural forests and plantations. Climate change has also contributed to a reduction in their numbers. We studied their light adaptability at the seedling stage to quantify the growth and physiological characteristics under 10% and 100% of full sunlight. Rosewood performed better, as indicated by the relative growth rate, chlorophyll content, and chlorophyll efficiency, under both shade and sunlight. We also simulated a sudden change in light intensity (gap opening up in the canopy) by exposing seedlings, previously under shade, to full sunlight. Rosewood seedlings responded faster (higher relative growth rate) to changing light conditions relative to Teak. We conclude that Rosewood seedlings can be planted either under shade, or in full sunlight, or in a location experiencing sudden change from shade to sunlight, while Teak seedlings should be planted under at least 10% sunlight, but not in full sunlight, as it can lead to chlorophyll and tissue damage.

Organization of leaf vascular system and gas exchange in seedlings of Guazuma ulmifolia Lam. in different light conditions

In tropical forests, different physiological characteristics of leaves in tree species are evidenced by variations in different incident light conditions. We aim to evaluate gas exchange and organization of leaf vascular system in Guazuma ulmifolia Lam. seedlings under different light conditions. Seedlings were obtained from seeds germinated under greenhouse conditions with controlled environment. Ninety days after germination, seedlings in 8kg pots were transferred to the experimental site to allow acclimatization under sun and shade conditions. The experimental design was completely randomized, with two treatments: full sunlight and artificial shading, limiting the luminosity to about 5% of irradiance. Seedlings were maintained under these conditions for 120 days before measuring gas exchange parameters. We measured photosynthetic rate, stomatal conductance, sub-stomatic CO2 concentration, transpiration, and chlorophyll content. Anatomical analysis measured distance between veins, distance from veins to abaxial epidermis, distance from veins to adaxial epidermis, distance from veins to stomata, total leaf thickness, abaxial epidermis thickness, adaxial epidermis thickness, palisade parenchyma thickness, and spongy parenchyma thickness of foliar gas exchange of G. ulmifolia which presented significant differences between light environments. Photosynthetic rate and stomatal conductance were reduced by 78% and 39%, respectively, in shade, while stomatal conductance increased by 31% in full sunlight. Transpiration showed no significant difference between the two treatments, but chlorophyll content was 30% lower in full sunlight. Distance between veins and distance from veins to stomata showed no difference between treatments, but the other parameters increased in full sunlight. Thus, the results showed that the pioneer species G. ulmifolia presented leaf gas exchange acclimated to environments with high luminosity.

Transcriptional response of Asarum heterotropoides Fr. Schmidt var. mandshuricum (Maxim.) Kitag. leaves grown under full and partial daylight conditions

Background Asarum heterotropides Fr. Schmidt var. mandshuricum (Maxim.) Kitag. is an important medicinal and industrial plant, which is used in the treatment of various diseases. The main bioactive ingredient is the volatile oil having more than 82 identified components of which methyleugenol, safrole, myristicin, and toluene account for about 70% of the total volume. As a sciophyte plant, the amount of light it absorbs through leaves is an important factor for growth and metabolism. Results We grew Asarum plants under full, 50, 28, and 12% sunlight conditions to investigate the effect of different light irradiances on the four major volatile oil components. We employed de novo transcriptome sequencing to understand the transcriptional behavior of Asarum leaves regarding the biosynthetic pathways of the four volatile oil components, photosynthesis and biomass accumulation, and hormone signaling. Our results demonstrated that the increasing light conditions promoted higher percent of the four components. Under full sunlight conditions, cinnamyl alcohol dehydrogenase and cytochrome p450719As were upregulated and led the increased methyleugenol, safrole, and myristicin. The transcriptomic data also showed that Asarum leaves, under full sunlight conditions, adjust their photosynthesis-antenna proteins as a photoprotective response with the help of carotenoids. Plant hormone-signaling related genes were also differentially expressed between full sunlight and low light conditions. Conclusions High light induces accumulation of major bioactive ingredients A. heterotropides volatile oil and this is ascribed to upregulation of key genes such as cinnamyl alcohol dehydrogenase and cytochrome p450719As. The transcriptome data presented here lays the foundation of further understanding of light responses in sciophytes and provides guidance for increasing bioactive molecules in Asarum.

Study on the Effect of Shading on Performance of Leafy Vegetables

A field experiment was conducted at Sher-e-Bangla Agricultural University, Sher-e-Bangla, Dhaka, Bangladesh during the period from March, 2019 to June, 2019. The aim of the study was to select best summer leafy vegetables, suitable for holding under different shade condition in agroforestry systems. The selected vegetables were also grown in control i.e., open field condition or in full sunlight. The vegetables were Indian Spinach, Stem Amaranth, and Red Amaranth and treatments were T0= planting summer leafy vegetables under full sunlight, T1= planting summer leafy vegetables under 50% shade condition (reduced light intensity) and T2 = planting summer leafy vegetables under 75% shade condition (reduced light intensity). The experiment was laid out following single factor RCBD design. Three replications were used for each treatment for each crop. During the study period maximum light intensity reduction was recorded in Red Amaranth (48.28%) in 75% shade condition and minimum light intensity was reduced in case of Indian Spinach (26.14%) under 50% shade condition. The reduced light intensity had substantial effects on various growth parameters of the summer leafy vegetables. From the experiment, significant result was observed in all morphological characteristics for all leafy vegetables under reduced light intensity. Apart from this, highest yield was found in Stem Amaranth (22.33 ton/ha) and Indian Spinach (13.83 ton/ha) in 75% shade condition. Highest yield of Indian Spinach (19.40 ton/ha), Stem Amaranth (27.25 ton/ha) and Red Amaranth (11.30 ton/ha) was recorded under full sunlight. Considering shade condition, Stem Amaranth and Indian Spinach were best suitable for growing in Agroforestry systems.

Maranta arundinacea (arrowroot).

Maranta arundinacea is a perennial plant, native to Mexico, Central and South America, that has been introduced and cultivated for its starch-rich root (known as arrowroot), and as an ornamental and medicinal plant. It has escaped from cultivation and can be found naturalized in a wide variety of substrates and habitats, ranging from open areas with full sunlight to deep-shaded sites. It can reproduce sexually by seeds and vegetatively by rhizomes and suckers. The pieces of rhizome left in the soil after harvest often pose a weed problem because they re-sprout easily and are difficult to eradicate.

Effects of Light and Fertilizer Amounts on Seedling Growth of Brachychiton populneus (Schott & Endl.)

Nutrient application and light intensity are two important abiotic factors that affect the plant growth and development. This study was carried out to determine the effect of different NPK fertilizer amount, viz. 0, 1, 2, 3 and 4 g.pot-1, light regimes, viz. 50% full sunlight (inside the lath house) and 100% full sunlight (the open area) and their interactions on the growth, chlorophyll contents and biomass of potted Brachychiton populneus seedlings. At the end of the experiment, (after six months) growth parameter including plant height (cm), stem diameter (mm) and leaf numbers, chlorophyll contents and biomass allocation were measured. The results indicate that the greatest stem height increment, stem diameter increment, leaf number increment, stem dry weight and leaf dry weight were obtained from the seedlings grown in the open area. However, the highest chlorophyll content and root dry weight were observed from the seedlings grown inside the lath house. In addition, the seedlings fertilized with 3 and/or 4 g NPK every two months recorded higher growth traits, chlorophyll content and biomass allocation than other amounts of the fertilizer. Thus, the present study suggests that in order to obtain optimum growth of B. populneus potted seedlings, it should be grown in the open area and fertilized with 3 or 4 g NPK every two months.