Explore the vast range of titles available.

Red and blue light are traditionally believed to have a higher quantum yield of CO 2 assimilation ( QY , moles of CO 2 assimilated per mole of photons) than green light, because green light is absorbed less efficiently. However, because of its lower absorptance, green light can penetrate deeper and excite chlorophyll deeper in leaves. We hypothesized that, at high photosynthetic photon flux density ( PPFD ), green light may achieve higher QY and net CO 2 assimilation rate ( A n ) than red or blue light, because of its more uniform absorption throughtout leaves. To test the interactive effects of PPFD and light spectrum on photosynthesis, we measured leaf A n of “Green Tower” lettuce ( Lactuca sativa ) under red, blue, and green light, and combinations of those at PPFD s from 30 to 1,300 μmol⋅m –2 ⋅s –1 . The electron transport rates ( J ) and the maximum Rubisco carboxylation rate ( V c,max ) at low (200 μmol⋅m –2 ⋅s –1 ) and high PPFD (1,000 μmol⋅m –2 ⋅s –1 ) were estimated from photosynthetic CO 2 response curves. Both QY m,inc (maximum QY on incident PPFD basis) and J at low PPFD were higher under red light than under blue and green light. Factoring in light absorption, QY m,abs (the maximum QY on absorbed PPFD basis) under green and red light were both higher than under blue light, indicating that the low QY m,inc under green light was due to lower absorptance, while absorbed blue photons were used inherently least efficiently. At high PPFD , the QY inc [gross CO 2 assimilation ( A g )/incident PPFD ] and J under red and green light were similar, and higher than under blue light, confirming our hypothesis. V c,max may not limit photosynthesis at a PPFD of 200 μmol m –2 s –1 and was largely unaffected by light spectrum at 1,000 μmol⋅m –2 ⋅s –1 . A g and J under different spectra were positively correlated, suggesting that the interactive effect between light spectrum and PPFD on photosynthesis was due to effects on J . No interaction between the three colors of light was detected. In summary, at low PPFD , green light had the lowest photosynthetic efficiency because of its low absorptance. Contrary, at high PPFD , QY inc under green light was among the highest, likely resulting from more uniform distribution of green light in leaves.

Trees play a key role in the global hydrological cycle and measurements performed with the thermal dissipation method (TDM) have been crucial in providing whole-tree water-use estimates. Yet, different data processing to calculate whole-tree water use encapsulates uncertainties that have not been systematically assessed. We quantified uncertainties in conifer sap flux density (F d) and stand water use caused by commonly applied methods for deriving zero-flow conditions, dampening and sensor calibration. Their contribution has been assessed using a stem segment calibration experiment and 4 yr of TDM measurements in Picea abies and Larix decidua growing in contrasting environments. Uncertainties were then projected on TDM data from different conifers across the northern hemisphere. Commonly applied methods mostly underestimated absolute F d. Lacking a site- and species-specific calibrations reduced our stand water-use measurements by 37% and induced uncertainty in northern hemisphere F d. Additionally, although the interdaily variability was maintained, disregarding dampening and/or applying zero-flow conditions that ignored night-time water use reduced the correlation between environment and F d. The presented ensemble of calibration curves and proposed dampening correction, together with the systematic quantification of data-processing uncertainties, provide crucial steps in improving whole-tree water-use estimates across spatial and temporal scales.

Vertical farming is becoming increasingly popular for production of leafy vegetables and herbs, with basil ( Ocimum basilicum L.) as one of the most popular herbs. In basil most research has focused on increasing secondary metabolites with light spectra. However, knowledge about the effect of light intensity (photosynthetic photon flux density, PPFD) and spectra on growth and morphology is key for optimizing quality at harvest. The impact of PPFD and spectrum on plant growth and development is species dependent and currently few studies in basil are available. Understanding the response to End-Of-Production (EOP) light of growth and morphology is important for successful vertical farming. We performed a comprehensive series of experiments, where the effects of EOP PPFD, fraction of blue and their interaction on the growth and morphology were analyzed in two green and one purple basil cultivar. In addition, the impact of different EOP intensities and duration of far-red were investigated. We found that increasing the PPFD increased fresh mass, dry matter content and plant height in all three cultivars. The responses were linear or quadratic depending on the cultivar. A high fraction of blue (>90%) increased plant height and decreased the dry mass partitioning to the leaves. The only interaction found between the fraction of blue and overall PPFD was on plant height in the green cultivar whereas other growth parameters and morphology responded stronger to PPFD than to the fraction of blue light. Plant dry matter production was increased with the addition of far-red. Far-red EOP intensity treatments enhanced the fraction of dry mass partitioned to the leaves, whereas a prolonged far-red treatment enhanced partitioning to the stem. Both plant fresh mass and dry matter content were improved by applying high PPFD shortly before harvest. Light spectra were found to be of less importance than PPFD with respect to plant dry matter content. Light use efficiency (LUE) based on fresh mass decreased with increasing PPFD whereas LUE based on dry mass increased with increasing PPFD, when given as EOP treatments. The overall physiological mechanisms of the light intensity and spectral effects are discussed.

Plants compete for sunlight and have evolved to perceive shade through both relative increases in the flux of far-red photons (FR; 700 to 750 nm) and decreases in the flux of all photons (intensity). These two signals interact to control stem elongation and leaf expansion. Although the interacting effects on stem elongation are well quantified, responses for leaf expansion are poorly characterized. Here we report a significant interaction between far-red fraction and total photon flux. Extended photosynthetic photon flux density (ePPFD; 400 to 750 nm) was maintained at three levels (50/100, 200 and 500 µmol m -2 s -1 ), each with a range of 2 to 33% FR. Increasing FR increased leaf expansion in three cultivars of lettuce at the highest ePPFD but decreased expansion at the lowest ePPFD. This interaction was attributed to differences in biomass partitioning between leaves and stems. Increased FR favored stem elongation and biomass partitioning to stems at low ePPFD and favored leaf expansion at high ePPFD. In cucumber, leaf expansion was increased with increasing percent FR under all ePPFD levels showing minimal interaction. The interactions (and lack thereof) have important implications for horticulture and warrant further study for plant ecology.

This paper investigates the effect of augmented rail geometry on rail gun key parameters such as mutual inductance gradient between the main and augmented rail (M’), maximum current density, and maximum magnetic flux density distribution in the rail cross-section, as well as repulsive force acting on the rails. The research study was conducted using a rectangular main rail with several augmented rail designs, including rectangular T, rectangular E, rectangular U, rectangular Convex, and rectangular Concave under inward and outward modes. The ANSYS MAXWELL 2-D eddy current field solver, which computes the magnetic field distributions for a given configuration using the finite element method, was used to calculate the rail gun essential parameters. Using the obtained results, a comparison study was conducted. It was found that the rectangular main rail with the inward circular convex augmented form rail cross-section had a greater value of M’ than other geometries; hence, it could be utilized to increase the armature’s velocity.

In this work, a one-dimensional simulation model is developed to investigate a transient high heat flux density thermal management system. A specific heat capacity at constant pressure equivalent model is applied to simulate the capacity of the phase change heat storage heat exchanger. Based on the experimental results, the simulation model is validated, with which the simulation accuracy ranges from 92.3% to 98.3%. Then, the cooling plate inlet temperature, vapor cycle system cooling capacity and compressor power are numerically analyzed. The comparison with a thermal management system without using phase change heat exchanger is also conducted. The simulation results demonstrate that the system using phase change heat exchanger exhibits a smoother variation in cooling plate inlet temperature, which can be maintained at around 15°C. The results from this work can help to better understand and then design a transient high heat flux density thermal management system.

The effects of photosynthetic photon flux density (PPFD) fluctuations in sunlight have already been investigated; however, the spectral photon flux density distribution (SPD) has hardly been considered. Here, sunlight SPD fluctuations recorded for 200 min in October in Tokyo, Japan were artificially reproduced using an LED-artificial sunlight source system. The net photosynthetic rate ( P n ) of cucumber leaves under reproduced sunlight was measured and compared with the P n estimated from a steady-state PPFD– P n curve for the same leaves. The measured and estimated P n agreed except when the PPFD was low, where the measured P n was lower than the estimated P n . The ratio of measured P n to estimated P n was 0.94–0.95 for PPFD ranges of 300–700 μmol m –2 s –1 , while the value was 0.98–0.99 for 900–1,300 μmol m –2 s –1 , and the overall ratio was 0.97. This 3% reduction in the measured P n compared with the P n estimated from a steady-state PPFD– P n curve was significantly smaller than the approximately 20–30% reduction reported in previous experimental and simulation studies. This result suggests that the loss of integral net photosynthetic gain under fluctuating sunlight can vary among days with different fluctuation patterns or may be non-significant when fluctuations in both PPFD and relative SPD of sunlight are taken into consideration.

Leafy vegetable production under controlled environment using artificial lighting has many advantages over conventional greenhouses and open-field production. However, high initial investment and operation costs are restricting the wide application of this technology. In order to design an optimal artificial lighting environment for lettuce production, effects of different combinations of light intensity, photoperiod, and light quality on growth, quality, photosynthesis, and energy use efficiency of lettuce (Lactuca sativa L. cv Ziwei) were investigated under a closed plant factory. Lettuce transplants were grown under photosynthetic photon flux density (PPFD) at 150 µmol/m2·s, 200 µmol/m2·s, 250 µmol/m2-s, and 300 µmol/m2·s provided by fluorescent lamps (FL) with a red to blue ratio (R:B ratio) of 1.8 and light-emitting diode (LED) lamps with R:B ratio of 1.2 and 2.2, in combination with photoperiod of 12 and 16 h/d. In order to examine the \"long term\" photosynthetic characteristics, net photosynthetic rates of hydroponic lettuce leaves were continuously measured for 2 d (15th and 16th day after transplanting) before harvest. There was no difference in leaf fresh weight (FW) between PPFD of 250 µmol/m2·s and 300 µmol/m2·s with photoperiod of 16 h/d, regardless of light quality, and same results showed in contents of nitrate, soluble sugar, and vitamin C, respectively. The results of continuous measurements of net photosynthetic rate of lettuce leaves before harvest indicated that plants grown at PPFD of 250 µmol/m2·s had consistently higher compared to those grown at PPFD of 300 µmol/m2·s. Combining the results from growth, photosynthesis, quality, and energy consumption, it can be concluded that PPFD at 250 µmol/m2·s with photoperiod of 16 h/d under LED with R:B ratio of 2.2 is a suitable light environment for maximum growth and high quality of commercial lettuce (cv. Ziwei) production under indoor controlled environment.

In Northern Europe, the use of light–emitting diodes (LEDs) is widely adopted in protected horticulture, enabling to enhance plant growth by ensuring needed radiative fluxes throughout seasons. Contrarily, the use of artificial lighting in Mediterranean greenhouse still finds limited applications. In this study, the effects of supplemental LED interlighting on vegetative development, fruit growth, yield, and fruit quality of high-wire tomato plants (Solanum lycopersicum L. cv. ‘Siranzo’) during spring and summer season were addressed in a hydroponic greenhouse in Italy. Plants were either grown under natural solar radiation (control), or by adding supplemental LED interlighting. LED treatment featured red (R) and blue (B) light (RB ratio of 3) and a photosynthetic photon flux density of 170 µmol m−2 s−1 for 16 h d−1. Supplemental LED interlighting enhanced yield as a result of increased fruit weight and dimension. While no effects on soluble solids content and fruit color at harvesting were observed, supplemental LED interlighting accelerated ripening by one week in spring and two weeks in summer and this also resulted in increased cumulated productivity (+16%) as compared to control treatment. Overall, supplemental LED interlighting can represent a feasible technology for tomato greenhouse production also in the Mediterranean region.

The cost of providing lighting in greenhouses and plant factories can be high. In the case of variable electricity prices, providing most of the light when electricity prices are low can reduce costs. However, it is not clear how plants respond to the resulting fluctuating light levels. We hypothesized that plants that receive a constant photosynthetic photon flux density (PPFD) will produce more biomass than those grown under fluctuating light levels. To understand potential growth reductions caused by fluctuating light levels, we quantified the effects of fluctuating PPFD on the photosynthetic physiology, morphology, and growth of ‘Little Gem’ and ‘Green Salad Bowl’ lettuce. Plants were grown in a growth chamber with dimmable white LED bars, alternating between high and low PPFDs every 15 min. The PPFDs were ∼400/0, 360/40, 320/80, 280/120, 240/160, and 200/200 μmol⋅m −2 ⋅s –1 , with a photoperiod of 16 h and a DLI of ∼11.5 mol⋅m −2 ⋅day –1 in all treatments. CO 2 was ∼800 μmol⋅mol –1 . Plants in the 400/0 μmol⋅m −2 ⋅s –1 treatment had ∼69% lower A n , 30 (net assimilation averaged over 15 min at high and 15 min at low PPFD) than plants grown at a PPFD of 320/80 μmol⋅m −2 ⋅s –1 (or treatments with smaller PPFD fluctuations). The low A n , 30 in the 400/0, and to a lesser extent the 360/40 μmol⋅m −2 ⋅s –1 treatment was caused by low net assimilation at 360 and 400 μmol⋅m −2 ⋅s –1 . Plants grown at 400/0 μmol⋅m −2 ⋅s –1 also had fewer leaves and lower chlorophyll content compared to those in other treatments. The four treatments with the smallest PPFD fluctuations produced plants with similar numbers of leaves, chlorophyll content, specific leaf area (SLA), dry mass, and leaf area. Chlorophyll content, A n , 30 , and dry mass were positively correlated with each other. Our results show that lettuce tolerates a wide range of fluctuating PPFD without negative effects on growth and development. However, when fluctuations in PPFD are extreme (400/0 or 360/40 μmol⋅m −2 ⋅s –1 ), chlorophyll levels and A n , 30 are low, which can explain the low poor growth in these treatments. The ability of lettuce to tolerate a wide range of fluctuating light levels suggests that PPFD can be adjusted in response to variable electricity pricing.