High Tunnel Coverings Alter Crop Productivity and Microclimate of Tomato and Lettuce

The implementation of high tunnels has shown to increase marketability and/or yield of tomato (Solanum lycopersicum) and lettuce (Lactuca sativa) crops compared with open-field systems. These structures provide the opportunity to alter light intensity and spectral quality by using specific polyethylene (poly) films and/or shadecloth, which may affect microclimate and subsequent crop productivity. However, little is known about how specific high tunnel coverings affect these parameters. The overall goal of this study was to evaluate the impact of various high tunnel coverings on the microclimate and crop productivity of tomato and lettuce. The coverings included standard, ultraviolet (UV)-stabilized poly film (standard); diffuse poly (diffuse); full-spectrum clear poly (clear); UV-A/B blocking poly (block); standard + 55% shadecloth (shade); and removal of standard poly 2 weeks before initial harvest to simulate a movable tunnel (movable). Microclimate parameters that were observed included canopy and soil temperatures, canopy growing degree-days (GDD), and photosynthetic active radiation (PAR), and crop productivity included yield and net photosynthetic rate. Hybrid red ‘BHN 589’ tomatoes were grown during the summer, and red ‘New Red Fire’ and green ‘Two Star’ leaf lettuce were grown in both spring and fall in 2017 and 2018. Increased temperature, GDD, and PAR were observed during the spring and summer compared with the fall. The soil temperatures during the summer increased more under the clear covering compared with the others. For tomato, the shade produced lower total fruit yield and net photosynthetic rate (Pn) compared with the other treatments, which were similar (P < 0.001 and <0.001, respectively). The greatest yield was 7.39 kg/plant, which was produced under the clear covering. For red leaf lettuce grown in the spring, the plants under the clear, standard, and diffuse coverings had significantly greater yield than the movable and shade coverings (P < 0.001). The coverings had less effect on the yield during the fall lettuce trials, which may have been attributed to the decrease in PAR and environmental temperatures. The findings of this study suggest that high tunnel coverings affect both microclimate and yield of lettuce and tomato.

Effects of Potassium Silicate Fertilizer on Photosynthetic Characteristics and Yield in Winter Wheat (Triticum Aestivum L.)

Effects of different dosages of potassium silicate fertilizer on photosynthetic characteristics and yield of winter wheat under field conditions were studied. Four different dosages: 0, 45, 90 and 135kg/ha were applied. Results showed that the chlorophyll content, net photosynthetic rate of wheat flag leaf firstly increased and then decreased with the increase of levels of potassium silicate fertilizer. By the change of SPAD values after flowering, when the application of potassium silicate fertilizer was 90 kg/ha, the existence time of chlorophyll in flag leaf was significantly long, and the net photosynthetic rate was significantly increased. The 1000-grain weight of winter wheat significantly increased and the yield the highest. Overall, when the applied amount of potassium silicate fertilizer was 90 kg/ha, the performances of winter wheat were best. Bangladesh J. Bot. 50(4): 1127-1132, 2021 (December)

Effect of Enhanced UV-B Radiation on Fruit Maturity and Quality, and Leaf Photosynthesis in ' Guifei ' Mango

(1) Background: Investigating the characteristics of photosynthetic physiological changes of leaves in Mangifera indica L. cv. 'GuIfei' under enhanced UV-B radiation, natural light exposed trees were regarded as control, and 96 kJ&middot;m-2&middot;d-1enhanced UV-B radiation was artificially simulated in the field; (2) Methods: The changes of fruit maturity and fruit quality, leaf net photosynthetic rate (Pn), photosynthetic pigments contents, photochemical reaction, activities of photosynthetic enzymes and their genes expressions were determined; (3) Results: Compared with CK, the percentage of mature fruits of the treatment was significantly increased, and fruit quality was better. The net photosynthetic rate (Pn), the contents of photosynthetic pigment, Hill reaction activity and photochemical quenching coefficient (qP) of the treatment leaves showed a significantly higher trend than CK. The activities of Rubisco and RCA, and the expression of Rubisco genes rbcL and rbcS were significantly increased; (4) Conclusions: 96 kJ&middot;m-2&middot;d-1 enhanced UV-B radiation treatment improved Rubisco activity through increasing the expression of Rubisco genes rbcL and rbcS, thereby enhancing the CO2-fixing capacity and dark reaction capacity of leaves. Based on this, it raised the net photosynthetic rate of leaves, which promoted the early maturity of 'Guifei' mango by the fast accumulating photosynthetic products.

Light control of catechin accumulation is mediated by photosynthetic capacity in tea plant (Camellia sinensis)

Background Catechins are crucial in determining the flavour and health benefits of tea, but it remains unclear that how the light intensity regulates catechins biosynthesis. Therefore, we cultivated tea plants in a phytotron to elucidate the response mechanism of catechins biosynthesis to light intensity changes. Results In the 250 μmol·m− 2·s− 1 treatment, the contents of epigallocatechin, epigallocatechin gallate and total catechins were increased by 98.94, 14.5 and 13.0% respectively, compared with those in the 550 μmol·m− 2·s− 1 treatment. Meanwhile, the photosynthetic capacity was enhanced in the 250 μmol·m− 2·s− 1 treatment, including the electron transport rate, net photosynthetic rate, transpiration rate and expression of related genes (such as CspsbA, CspsbB, CspsbC, CspsbD, CsPsbR and CsGLK1). In contrast, the extremely low or high light intensity decreased the catechins accumulation and photosynthetic capacity of the tea plants. The comprehensive analysis revealed that the response of catechins biosynthesis to the light intensity was mediated by the photosynthetic capacity of the tea plants. Appropriately high light upregulated the expression of genes related to photosynthetic capacity to improve the net photosynthetic rate (Pn), transpiration rate (Tr), and electron transfer rate (ETR), which enhanced the contents of substrates for non-esterified catechins biosynthesis (such as EGC). Meanwhile, these photosynthetic capacity-related genes and gallic acid (GA) biosynthesis-related genes (CsaroB, CsaroDE1, CsaroDE2 and CsaroDE3) co-regulated the response of GA accumulation to light intensity. Eventually, the epigallocatechin gallate content was enhanced by the increased contents of its precursors (EGC and GA) and the upregulation of the CsSCPL gene. Conclusions In this study, the catechin content and photosynthetic capacity of tea plants increased under appropriately high light intensities (250 μmol·m− 2·s− 1 and 350 μmol·m− 2·s− 1) but decreased under extremely low or high light intensities (150 μmol·m− 2·s− 1 or 550 μmol·m− 2·s− 1). We found that the control of catechin accumulation by light intensity in tea plants is mediated by the plant photosynthetic capacity. The research provided useful information for improving catechins content and its light-intensity regulation mechanism in tea plant.

The Effect Mechanism and Model Optimization of Pulsed Light Dark Duration on Lettuce

Background: Despite its rapid development, the costs of crop artificial light source technology are still high. In addition, both the luminous efficiency and photosynthetic light supplement efficiency of the light source require further improvement. This study aims to improve the photosynthetic light supplement efficiency by altering the luminescence mode of the light source, transforming the conventional continuous supplementary light source into a pulse light source, and exploring how to further reduce energy consumption and improve the light supplement efficiency without influencing the light supplement effect of Lettuce.Results: For this purpose, Lettuce (Lactuca sativa L.) was selected as the experimental material to investigate the effects of varying the duty ratio, frequency and dark duration on the Pn (net photosynthetic rate) of leaves. The results revealed that Pn values under each duty ratio treatment increased with frequency and gradually stabilized to a level similar to that of continuous light. At higher duty ratios, the lettuce leaf Pn under pulse light reached a stable state at a lower frequency, with Pn leveling showing an overall upward trend with the decreasing dark period duration and a large increase in the early stage. For dark period durations lower than a certain value (0.000683594 s), variations in Pn among treatments were minimal, with a gradual increasing trend until no significant differences are observed with continuous light (CK); Under the D3 (weak light) condition, plants were easy to spindling(excessive growth)and exhibited narrow and slender leaves. Plants under the D2 condition (The duration period duration was 0.000465468s) presented the strongest roots and stems, with wide leaves and a compact growth. The following trend in Pn was observed across all duty ratios D2>D1 (0.000046547s)>CK>D3 (0.004654685s). Conclusions: The dominant influencing factor of the plant net photosynthetic rate was determined as the ratio of the frequency and duty ratio (i.e., dark period duration). Compared with continuous light, pulsed light is more beneficial to plant growth and utilization.

Responses of Leaf Hydraulic Traits of Schoenoplectus Tabernaemontani To Increasing Temperature and CO2 Concentrations

Background Against the background of a changing climate, the responses of functional traits of plateau wetland plants to increasing temperatures and CO2 concentrations need to be understood. Hydraulic traits are the key for plants to maintain their ecological functions and affect their growth and survival. However, few studies have comprehensively considered the response strategies of wetland plants' hydraulic traits to environmental changes in the context of water and matter transport, loss, and retention. According to the latest IPCC prediction results, we performed experiments under increased temperature (2℃) and CO2 levels (850 µmol/mol) in an artificial Sealed-top Chamber (STC) to investigate the responses of the hydraulic characteristics of Schoenoplectus tabernaemontani, the dominant species in plateau wetlands in China. Results Compared with the CK group, net photosynthetic rate, transpiration rate, stomatal length, cuticle thickness, vascular bundle length, vascular bundle width, and vascular bundle area of S. tabernaemontani in the ET group were significantly reduced, whereas stomatal density and vein density increased significantly. Compared with the CK group, the hydraulic traits of S. tabernaemontani in the EC group were reduced considerably in stomatal length and cuticle thickness but increased dramatically in stomatal density, and there were no significant differences between other parameter values and the control group. Net photosynthetic rate was significantly positively correlated with stomatal length, cuticle thickness, and vascular bundle length, and stomatal conductance was significantly positively correlated with cuticle thickness. The transpiration rate was significantly positively correlated with cuticle thickness, epidermal cell area, vascular bundle length, vascular bundle width, and vascular bundle area. Regarding the hydraulic traits, there was a significant negative correlation between stomatal density and stomatal length, or cuticle thickness, and a significant positive correlation between the latter two. The epidermal cell area was significantly positively correlated with epidermal thickness, vascular bundle length, vascular bundle width, and vascular bundle area Conclusions Increased temperature and CO2 levels are not conducive to the photosynthetic activity of S. tabernaemontani. Photosynthetic rate, stomatal density and size, vein density, epidermal structure size, and vascular bundle size play an essential role in the adaptation of this species to changes in temperature and CO2 concentration. In the process of adaptation, hydraulic traits are not isolated from each other, and there is a functional association among traits. This study provide a scientific basis for the management and protection of plateau wetlands.

Shading Reduces Water Deficit in Strawberry (Fragaria × ananassa Duch.) Plants during Vegetative Growth

Strawberry (Fragaria × ananassa Duch.) is a commercially important crop with high water requirements, for which it is necessary to find strategies that mitigate the influence of water deficit on plant growth. This study was aimed to evaluate the effects of shading on the vegetative growth of strawberry cv. Sweet Ann under water deficit. The treatments consisted of the combination of two levels of shading (light intensity reduced on 47% vs. non-shaded plants) and two levels of water availability (water deficit vs. well-watered plants). The water deficit reduced the leaf water potential from -1.52 to -2.21 MPa, and diminished stomatal conductance, net photosynthetic rate (from 9.13 to 2.5 μmol m-2 s-1), photosystem II photochemical efficiency (from 0.79 to 0.67), and biomass accumulation, while increased the electrolyte leakage. The shading allowed the water-deficient plants to maintain water potential (-1.58 MPa) and photosystem II efficiency (0.79) and to increase water use efficiency (from 14.80 to 86.90 μmol CO2/mmol H2O), net photosynthetic rate (from 2.40 to 9.40 μmol m-2 s-1) and biomass of leaves, crowns, and roots compared to non-shaded plants without water limitation. These results suggest that a reduction in incident light intensity attenuates the effects of stomatic and non-stomatic limitations caused by water deficit during vegetative growth of strawberry.

Changes in peanut canopy structure and photosynthetic characteristics induced by an arbuscular mycorrhizal fungus in a nutrient-poor environment

A well-developed canopy structure can increase the biomass accumulation and yield of crops. Peanut seeds were sown in a soil inoculated with an arbuscular mycorrhizal fungus (AMF) and uninoculated controls were also sown. Canopy structure was monitored using a 3-D laser scanner and photosynthetic characteristics with an LI-6400 XT photosynthesis system after 30, 45 and 70 days of growth to explore the effects of the AMF on growth, canopy structure and photosynthetic characteristics and yield. The AMF colonized the roots and AMF inoculation significantly increased the height, canopy width and total leaf area of the host plants and improved canopy structure. AMF reduced the tiller angle of the upper and middle canopy layers, increased that of the lower layer, reduced the leaf inclination of the upper, middle and lower layers, and increased the average leaf area and leaf area index after 45 days of growth, producing a well-developed and hierarchical canopy. Moreover, AMF inoculation increased the net photosynthetic rate in the upper, middle and lower layers. Plant height, canopy width, and total leaf area were positively correlated with net photosynthetic rate, and the inclination angle and tiller angle of the upper leaves were negatively correlated with net photosynthetic rate. Overall, the results demonstrate the effects of AMF inoculation on plant canopy structure and net photosynthetic rate.