Photosynthetically Active Radiation Transmission Research Articles

Calculations of Arctic Ice‐Ocean Interface Photosynthetically Active Radiation (PAR) Transmittance Values

AbstractSea ice algae play an important role in the Arctic Ocean ecosystem, driving primary production in the spring and sequestering carbon to the deep ocean. Up to 45% of Arctic Ocean primary production occurs in ice‐covered areas; photosynthetically active radiation (PAR) is fundamental to driving this production. Sea ice, and particularly snow, strongly scatter and reflect light, reducing the amount of PAR transmitted to the ice‐ocean interface. The effect that varying thicknesses of sea ice (0.2–3.5 m) and snow (0.01–1 m) have on the value of PAR transmittance at the ice‐ocean interface are considered for a Winter, Spring, and Summer scenario. When characteristic Arctic Ocean conditions (2 m sea ice and ∼0.2 m snowpack) are modeled, there is roughly a two‐fold difference in PAR transmittance at the ice‐ocean interface between the Winter (0.003) and Spring (0.007) scenarios and an order of magnitude difference with the Summer scenario (0.04). The modeled values correlate within one standard deviation of measured values and show good agreement with extended pan‐Arctic Ocean field campaign measurements. The results also indicate that simple exponential decay methods may lead to inaccurate results, and radiative‐transfer modeling is required to accurately predict PAR transmittance at the ice‐ocean interface. Therefore, this study offers a novel mathematical technique to predict the value of PAR transmittance at the ice‐ocean interface. Coupled with year‐round near‐real‐time sea ice and snow thickness remote sensing data, this technique may improve understanding of primary production and carbon budgets in the changing Arctic Ocean.

Factors influencing the variation in canopy light extinction coefficient (k) among pisifera parents of two oil palm origins

Summary The canopy light extinction coefficient (k) is defined as the exponential decline in the amount of light passing through the leaf layers as a function of leaf area index (LAI). This definition is standard in oil palm breeding trials and models of canopy photosynthesis, where k is sometimes assumed to have a fixed value. The present experiment aims to validate the alleged constancy of k. Therefore, k was inferred from the fractional transmission of photosynthetically active radiation (PAR) and LAI, as obtained from dura x pisifera test crosses of Nigeria and Ghana pisifera origins. The palms were planted at two densities (135 and 160 palms ha−1) in North Sumatra in 2010. At the age of 7.5 years after planting, the area of newly opened leaves approached a maximum. Transmission of PAR remained very low and was only weakly related to k. By contrast, LAI exerted a strong negative effect on k, which generated, under both densities, considerable differences in k between both origins and among pisifera within an origin. The assumption of applying a fixed k value for a certain genotype or palm density, as obtained during leaf expansion at closed canopy, may therefore not be realistic. The present study suggests that the relationship of k with LAI over time merits further investigation, starting just before canopy closure.

Transmission of photosynthetically active radiation and the productivities of soybean and maize in agroforestry systems

AbstractIn integrated crop‐livestock‐forestry (ICLF) systems, an agroforestry model, the forestry component influences the distribution of photosynthetically active radiation (PAR) and alters grain productivity. The aim of this study was to evaluate the effects of systematic and selective thinning of eucalyptus stands on the productivity of soybean and maize grown. The randomized block‐designed experiment comprised three treatments, namely crops grown under full sunlight (CFS) and in ICLF plots subjected to systematic and selective thinning to leave single‐row (ICLFS) and triple‐row (ICLFT) tree configurations. Soybean and maize were planted in succession between the tree stands and PAR incidence/transmittance and crop productivities were evaluated in the north and south sun‐exposed faces of the plots during three cultivation cycles after thinning. In comparison with CFS, PAR transmittance in the ICLF systems decrease varied according to the time of day, period of the year, distance of the sampling position from the trees, the sun‐exposed area (north and south faces) and time after thinning. Soybean productivities in ICLFS were similar to those of CFS in the first and second crop cycles, but significantly lower (p < 0.05) in the third crop cycle. In the ICLFT system, soybean productivity was similar to that of CFS in the second crop cycle but significantly lower in the first and third crop cycles. With regard to the maize crop, productivities decreased in the order CSF > ICLFS > ICLFT in all cultivation cycles. Our results showed that PAR transmittance and soybean/maize productivities were positively influenced by thinning of eucalyptus stands, particularly in ICLFS system.

Effects of Shade Nets on The Microclimate and Growth of Tomato

This study evaluated the effects of the shading nets with photoselective features, with an open-field control. The green-shade net with shading intensity of 40% and the blue, pearl, and yellow-shade nets with shading intensity of 75% were used as netting materials. The total radiation and photosynthetically active radiation (PAR) transmittance of the shade nets were analyzed. The environment conditions such as air temperature, relative humidity and canopy temperature were measured with the aid of appropriate sensors. Tomato growing was realized in the aim to determine the effects of shade nets on the crops cultivated under the shade nets, in contrast to the open field conditions. Vegetative growing parameters, fruit quality parameters and the yield were assessed in the study. This investigation revealed that shading resulted in an evident increase in the total yield and the pearl-shade nets should be the better choice for producing a high quality tomato crop, based on PAR transmittance (between 44.8 and 52.8%).

Fertilizer Reduction Combined with Organic Liquid Fertilizer Improved Canopy Structure and Function and Increased Cotton Yield

The application of organic liquid fertilizer combined with chemical fertilizer is one of the key technologies used to simultaneously improve cotton yield and efficiently utilize resources. However, organic fertilizer is usually applied once as a base fertilizer during production, and few studies have been conducted on topdressing with water during the growth period. Therefore, in this study, Xinluzao 74 was used as the experimental material, and a single fertilizer application (CF) was used as a control in 2019–2020 under the conditions of integrated control of water and fertilizer with mulch drip irrigation. Five combinations of reduction in chemical fertilizer combined with organic fertilizer (OF1, OF2, OF3, OF4, and OF5) were used to investigate the influences of chemical fertilizer combined with organic liquid fertilizer on the leaf area index (LAI), canopy openness (DIFN), mean foliage tilt angle (MTA), photosynthetically active radiation (PAR), canopy apparent photosynthesis (CAP), and yield and quality of cotton. The results show that among the different fertilization treatments, the OF2 treatment had the best results, not only ensuring a suitable LAI (4.8) and maintaining a large DIFN (0.1) but also increasing the light transmittance of the middle and lower canopies (0.02–0.03). At the same time, CAP increased significantly compared with that in the CF treatment, with an average increase of 12.8%. The high value lasted for a long time, and the late decay stage remained at 8.9 μmol m−2 s−1. The ratio of the population respiration rate to total photosynthesis (CR/TCAP) decreased significantly, with an average decrease of 13.5%. Compared with that in CF, the lint yield increased by 27.0% in the other treatments. The correlation analysis showed that lint yield was positively correlated with the relative chlorophyll content (SPAD value), PAR transmittance (PARU) and CAP in the upper canopy (p < 0.05) and significantly negatively correlated with PAR transmittance (PARM) in the middle canopy and PAR transmittance (PARD) and CR/TCAP in the lower canopy (p < 0.05). Therefore, under mulch drip irrigation, the OF2 treatment (OF + 80% CF) improved the canopy structure of cotton at the late growth stage, increased the population photosynthetic rate, and increased lint yield significantly; thus, this approach can be used as an effective fertilization method to achieve the goal of decreasing costs and increasing efficiency in cotton production.

Eucalyptus tree influence on spatial and temporal dynamics of fine-root growth in an integrated crop-livestock-forestry system in southeastern Brazil

Integrated farming systems are promising strategies towards land-use efficiency and sustainable agriculture. The integrated crop-livestock-forestry (ICLF) system stablish complex interactions were synergies or competition depend on the arrangements throughout time and space. Fine root (≤2 mm) growth dynamics of crops, pasture and trees remains unclear when these species are integrated. We aimed to assess root growth dynamics after Eucalyptus urograndis introduction into an integrated crop-livestock (ICL) system. Previous ICL area was used as a reference. We assessed ICLF 1.9, 4.3 and 7.5 m distances from tree rows, starting the study when trees had three years of age. Eucalyptus rows were spaced 15 m apart and integrated to annual crops and pasture. We evaluated the root growth under two different successional periods: (i) corn cultivation interspaced with palisade grass (Urochloa brizantha); and (ii) a pasture, when palisade grass was grazed. We tracked fine root length using the minirhizotron technique, capturing 3200 images scanning up to 70 cm soil depth. Data of photosynthetically active radiation (PAR) transmission, soil bulk density, rainfall and air temperature were used as complementary information to support the discussion. Our results showed that Eucalyptus trees impaired root growth of annual crops cultivated in the interrow position, regardless of distance from the row. From 31 to 80 days after corn germination, root length production in ICLF was reduced by 120–179 cm m−2.d−1 along the tree interrow space. For the pasture period, total produced root length density reduced 6% at 1.9 m but increased 25% at 4.3 and 7.5 m, when compared to ICL. Shade of Eucalyptus trees at ICLF 1.9 m position, with PAR transmission mainly below 60%, sharply impaired root growth. Eucalyptus roots represented 12% from total root length produced in ICLF system, and 38% of these roots had positive ectomycorrhizal status. In conclusion, under Eucalyptus trees higher than 20 m, pasture of palisade grass is more adaptable than corn when considering the root growth dynamics of our studied ICLF arrangement. Based on our findings, corn intercropped with palisade grass should not be introduced in future management of the ICLF system, unless part of the trees is chopped to reduce light competition. However, implemented pasture of palisade grass showed belowground synergies with Eucalyptus, increasing root growth in intermediary interrow positions and emerging new fungal symbiosis, which could be playing important functions in soil, as soil carbon storage and nutrient cycling.

Semi-Transparent Organic Photovoltaics Applied as Greenhouse Shade for Spring and Summer Tomato Production in Arid Climate

Recognizing the growing interest in the application of organic photovoltaics (OPVs) with greenhouse crop production systems, in this study we used flexible, roll-to-roll printed, semi-transparent OPV arrays as a roof shade for a greenhouse hydroponic tomato production system during a spring and summer production season in the arid southwestern U.S. The wavelength-selective OPV arrays were installed in a contiguous area on a section of the greenhouse roof, decreasing the transmittance of all solar radiation wavelengths and photosynthetically active radiation (PAR) wavelengths (400–700 nm) to the OPV-shaded area by approximately 40% and 37%, respectively. Microclimate conditions and tomato crop growth and yield parameters were measured in both the OPV-shaded (‘OPV’) and non-OPV-shaded (‘Control’) sections of the greenhouse. The OPV shade stabilized the canopy temperature during midday periods with the highest solar radiation intensities, performing the function of a conventional shading method. Although delayed fruit development and ripening in the OPV section resulted in lower total yields compared to the Control section (24.6 kg m−2 and 27.7 kg m−2, respectively), after the fourth (of 10 total) harvests, the average weekly yield, fruit number, and fruit mass were not significantly different between the treatment (OPV-shaded) and control group. Light use efficiency (LUE), defined as the ratio of total fruit yield to accumulated PAR received by the plant canopy, was nearly twice as high as the Control section, with 21.4 g of fruit per mole of PAR for plants in the OPV-covered section compared to 10.1 g in the Control section. Overall, this study demonstrated that the use of semi-transparent OPVs as a seasonal shade element for greenhouse production in a high-light region is feasible. However, a higher transmission of PAR and greater OPV device efficiency and durability could make OPV shades more economically viable, providing a desirable solution for co-located greenhouse crop production and renewable energy generation in hot and high-light intensity regions.

Smart glass impacts stomatal sensitivity of greenhouse Capsicum through altered light.

Optical films that alter light transmittance may reduce energy consumption in high-tech greenhouses, but their impact on crop physiology remains unclear. We compared the stomatal responses of Capsicum plants grown hydroponically under control glass (70% diffuse light) or the smart glass (SG) film ULR-80, which blocked >50% of short-wave radiation and ~9% of photosynthetically active radiation (PAR). SG had no significant effects on steady-state (gs) or maximal (gmax) stomatal conductance. In contrast, SG reduced stomatal pore size and sensitivity to exogenous abscisic acid (ABA), thereby increasing rates of leaf water loss, guard cell K+ and Cl- efflux, and Ca2+ influx. SG induced faster stomatal closing and opening rates on transition between low (100 µmol m-2 s-1) and high PAR (1500 µmol m-2 s-1), which compromised water use efficiency relative to control plants. The fraction of blue light (0% or 10%) did not affect gs in either treatment. Increased expression of stomatal closure and photoreceptor genes in epidermal peels of SG plants is consistent with fast stomatal responses to light changes. In conclusion, stomatal responses of Capsicum to SG were more affected by changes in light intensity than spectral quality, and re-engineering of the SG should maximize PAR transmission, and hence CO2 assimilation.

Simulation of Radiation and Crop Activity in a Greenhouse Covered with Semitransparent Organic Photovoltaics

A solution to the problem of reduction of available photosynthetically active radiation (PAR) due to the cover with conventional opaque photovoltaics (PV) of greenhouses is the use of semitransparent PV. The question is how dense the semitransparent PV should be and how dense the coverage should be in order not to burden plant growth. The present paper assesses the effect of the use of semitransparent organic photovoltaics (OPV) on the greenhouse roof cover on the available PAR inside the greenhouse. The method used is to simulate the transmission of radiation through the cover and into the greenhouse with computational fluid dynamics (CFD) using the discrete ordinates (DO) model. Three combinations of OPV/cover that give a normal (perpendicular) transmittance to PAR of 30%, 45%, and 60%, defining the required PV covering, were examined. Then the radiation transmission during eight indicative solar days was simulated. The results are given in terms of available PAR radiation inside the greenhouse and of crop photosynthesis rate, comparing them with the results of a polyethylene cover without OPVs and external conditions. The reduction observed to the mean daily PAR radiation integral for the cases with normal PAR transmittance of 30%, 45%, and 60% in relation to the bare polyethylene (PE) was 77%, 66%, and 52%, respectively while the respective simulated reduction to the daily average photosynthesis rate was 33%, 21%, and 12%, respectively. Finally, the yearly power production from the OPV per greenhouse length meter for the cases with normal PAR transmittance of 30%, 45%, and 60% was 323, 242, and 158 kWh m−1 y−1, respectively. The results of this work could be further used for the optimization of greenhouse design for maximizing the PAR at the crop level.

Temperature and Light Characterization during Winter Production Season in High Tunnels in the Southwestern United States

Replicated temperature data from passively heated high tunnels are lacking, especially in the southwestern United States. Field studies were conducted over three seasons in two locations in New Mexico—a southern site in Las Cruces and a northern site in Alcalde—to characterize the crop environment in three high-tunnel designs during the winter growing season (October–March). High tunnels were 16 × 32 ft and oriented with the long edge running east to west. Heavyweight woven plastic covered the single-layer (SL) high-tunnel design. Double-layer designs (DL) were covered with a lightweight woven plastic on the bottom, followed by a second layer of the heavyweight plastic inflated with a fan. A heat sink was created using 16 55-gal barrels painted black, filled with water, and aligned along the north side of the double layer for the DL+B design. Soil temperature (3 inches deep) and air temperature (1 ft above the soil surface) were recorded inside the high tunnel, inside the high tunnel under a floating rowcover, and outside the high tunnel. In addition, photosynthetically active radiation (PAR) was recorded inside and outside the high tunnels during or near the winter solstice each year of the study. Daily air and soil temperature minimums were highest in the DL+B design and lowest in the SL design. Maximum air and soil temperatures did not significantly differ between high-tunnel designs, although the DL+B design measurements were consistently lower. During season 1, the SL design had significantly higher PAR transmission than the other two designs. In the northern location, the difference became insignificant during seasons 2 and 3, likely due to dust accumulation and plastic aging. In the southern location, the SL design maintained higher PAR transmission throughout the study, possibly due to plastic cleaning. Data collected in this study can help inform the decisions of high-tunnel growers and researchers in the region.

Leaf and Crown Optical Properties of Five Early-, Mid- and Late-Successional Temperate Tree Species and Their Relation to Sapling Light Demand

The optical properties of leaves and canopies determine the availability of radiation for photosynthesis and the penetration of light through tree canopies. How leaf absorptance, reflectance and transmittance and radiation transmission through tree canopies change with forest succession is not well understood. We measured the leaf optical properties in the photosynthetically active radiation (PAR) range of five Central European early-, mid- and late-successional temperate broadleaf tree species and studied the minimum light demand of the lowermost shade leaves and of the species’ offspring. Leaf absorptance in the 350–720 nm range varied between c. 70% and 77% in the crown of all five species with only a minor variation from the sun to the shade crown and between species. However, specific absorptance (absorptance normalized by mass per leaf area) increased about threefold from sun to shade leaves with decreasing leaf mass area (LMA) in the late-successional species (Carpinus betulus L., Tilia cordata Mill., Fagus sylvatica L.), while it was generally lower in the early- to mid-successional species (Betula pendula Roth, Quercus petraea (Matt.)Liebl.), where it changed only a little from sun to shade crown. Due to a significant increase in leaf area index, canopy PAR transmittance to the forest floor decreased from early- to late-successional species from ~15% to 1%–3% of incident PAR, linked to a decrease in the minimum light demand of the lowermost shade leaves (from ~20 to 1%–2%) and of the species’ saplings (from ~20 to 3%–4%). The median light intensity on the forest floor under a closed canopy was in all species lower than the saplings’ minimum light demand. We conclude that the optical properties of the sun leaves are very similar among early-, mid- and late-successional tree species, while the shade leaves of these groups differ not only morphologically, but also in terms of the resource investment needed to achieve high PAR absorptance.

Growth and development of soybean under changing light environments in relay intercropping system

BackgroundMaize-soybean relay-intercropping (MSR) is a famous system of crop production in developing countries. However, maize shading under this system directly affects the light quality and intensity of soybean canopy. This is a challenging scenario in which to implement the MSR system, in terms of varieties selection, planting pattern, and crop management since the duration of crop resource utilization clearly differs.MethodsTherefore, this experiment aimed to elucidate the effect of leaf excising treatments from maize top to fully clarify the needs and balance of light quality and intensity of intercrop-soybean under MSR in field conditions. The effects of different leaf excising treatments (T0, no removal of leaves; T2, removal of two topmost leaves; T4, removal of four topmost leaves; T6, removal of six topmost leaves from maize plants were applied at first-trifoliate stage (V1) of soybean) on photosynthetically active radiation transmittance (PART), red to far-red ratio (R:FR), morphological and photosynthetic characteristics and total biomass production at second-trifoliate stage (V2), fifth-trifoliate stage (V5), and flowering-stage (R1) of soybean were investigated through field experiments for 2-years under MSR.ResultsAs compared to T0, treatment T6 increased the PART and R:FR ratio at soybean canopy by 77% and 37% (V2), 70% and 34% (V5), and 41% and 36% (R1), respectively. This improved light environment in T6 considerably enhanced the leaf area index, SPAD values and photosynthetic rate of soybean plants by 66%, 25% and 49% at R1, respectively than T0. Similarly, relative to control, T6 also increased the stem diameter (by 29%) but decreased the plant height (by 23%) which in turn significantly increased stem breaking strength (by 87%) by reducing the lodging rate (by 59%) of soybean plants. Overall, under T6, relay-cropped soybean produced 78% of sole soybean seed-yield, and relay-cropped maize produced 81% of sole maize seed-yield. Our findings implied that by maintaining the optimum level of PART (from 60% to 80%) and R:FR ratio (0.9 to 1.1), we can improve morphological and photosynthetic characteristics of soybean plants in MSR. Therefore, more attention should be paid to the light environment when considering the sustainability of MSR via appropriate planting pattern selection.

The optimal size of a Paulownia-crop agroforestry system for maximal economic return in North China Plain

Intercropping system has been widely adopted in China to reduce soil erosion, disease and pest damage, to increase biodiversity and land productivity over the last four decades. However there is no clear guideline on what is the optimal size of an intercropping system for maximizing the economic return in the region. In this study, we measured the effects of a two to five-year old Paulownia tree belt on winter wheat and summer maize yield in a 160 m by 320 m Paulownia-crop intercropping system in North China Plain. Field measurements showed that tree shading reduced the incoming photosynthetically active radiation (PAR) at crop by up to 26% for winter wheat and up to 38% for summer maize at the location near the tree belt over their respective growing season, and the effect of tree shading became insignificant at a distance of more than 15 m from the tree belt. The effect of tree shading on crop yield was proportional to the effect on incoming PAR at a rate of 0.32 g mol−1 for summer maize and 0.11 g mol−1 for winter wheat at the study site. A model of PAR transmission was also validated using field measurements and was then used to estimate the reduction of crop yield as a result of shading by the tree belt at different tree age or size for a range of plot size of a Paulownia-crop intercropping system. Together with the estimated cost and benefit, we found that the optimal size of a typical Paulownia-crop intercropping system was 26 ha with two rows of tree at 4 m spacing with pruning at the study site. The optimal size increases with grain price and decreases with timber price. The approached we developed here can be used to guide the future design of Paulownia-crop intercropping systems in North China Plain.

Long-term variation in light intensity on a coral reef

An important goal of coral reef science is to understand the roles played by environmental conditions in determining benthic community structure. Pursuit of this goal typically involves testing for associations between community structure and environmental conditions, and in recent years, attention has focused on temperature and seawater pH. Such analyses are helpful in projecting coral reef community structure into the future, but their efficacy depends on the extent to which changes in community structure are correctly associated with causative processes, and whether future conditions are a subset of those experienced in the past. Here, we describe variation from 2014 to 2017 in one environmental factor, photosynthetically active radiation (PAR), at 19-m depth on the reefs of St. John, US Virgin Islands, and evaluate the extent to which this factor could cause changes in benthic community structure. The transmission of downwelling surface PAR to 19-m depth (TPAR-19) varied from 2.0 to 40.0% among days, and from 4.8 to 15.8% among months within a year, and was lower and more variable in the autumn versus other seasons. Monthly TPAR-19 was inversely associated with monthly rainfall, suggesting that runoff affected seawater clarity. The monthly diffuse attenuation coefficient (Kd-PAR) varied 1.7-fold from 0.097 to 0.164 m−1 and was within the range expected for coral reefs. Given the high temporal variation in underwater light intensity, and its importance to foundational reef taxa, understanding of the response of coral reefs to temperature and pH (and other factors) will remain incomplete without closer attention to this physical environmental condition.

Forage productivity and nutritive value during pasture renovation in integrated systems

Integrated crop-livestock-forestry systems are strategies to diversify production in the same area, aiming at higher sustainability. Corn is one of the most used crops in integrated systems due to its multiple uses on the farm. The objective of this study was to evaluate the effect of light restriction on morphological and productive characteristics of the forage components (corn for silage and pastures) in integrated livestock production systems. The experiment was carried out on Embrapa’s integrated systems in Sao Carlos, SP, Brazil, during two growing seasons. In the integrated crop-livestock (iCL) system corn was sown simultaneously with Piata-grass. In the integrated crop-livestock- forestry (iCLF) system, besides corn and Piata-grass, Eucalyptus urograndis trees were planted in single 15 × 2 m rows. Corn productivity and pasture yield and nutritive value were evaluated in iCL and iCLF systems. In iCLF, evaluations were made in four positions relative to the tree lines: 1.5, 3.75, 7.5, and 11.25 m. Photosynthetically active radiation (PAR) transmission by trees was also measured in the same positions. Results of the corn crop indicated that the position relative to the tree lines affected (P < 0.001) all morphological characteristics and production parameters. Production was not affected by position relative to the tree lines in the first year but was lower in the position closer to the trees in the second year. As an average of all positions evaluated in iCLF, corn DM production in the first agricultural year was 43.3% inferior compared to the second year (5266.1 vs. 9816.7 kg DM ha−1). In iCL, the average corn DM production for the two years was 10082 kg DM ha−1. For the corn, the relationship between PAR transmission and the relative yield (production in each position in iCLF divided by the production in iCL) was influenced by drought in the 2013/2014 growing season. Considering the results for the renovated pastures, position relative to the tree lines affected pasture height (P < 0.0001), specific leaf area (P < 0.0012), digestibility (P < 0.0085) and crude protein (P < 0.0001).

Turfgrass Cover Sources Vary in Temperature, Light and Moisture Penetration, and Weight

Turfgrass managers apply covers to manipulate grass and soil environments. This study evaluated how various cover compositions and colors affect winter temperatures under cover, light and moisture penetration, and wet and dry weights of covers in the field. Seven covers including interwoven translucent polyethylene, gray, white, or orange nonwoven geotextiles, black and white woven polypropylene, and aluminized high‐density polyethylene strips were tested in Blacksburg, VA. Covers were in place December to March of 2013–2014 and 2014–2015 to evaluate bermudagrass (Cynodon dactylon × transvaalensis Burtt‐Davy, ‘Patriot’) surface temperature moderation. Cover effects on photosynthetically active radiation (PAR), moisture penetration (measured as percent change in soil volumetric water content [%SVWC] at 5‐cm soil depth under cover prior to and following a minimum 1.25 cm rain event), as well as cover dry and wet weights in the field prior to and after 0.1 cm irrigation were collected in spring 2016. Considering mean minimum extreme low temperatures, all covers provided significantly higher temperatures than uncovered control in 2013–2014, while in 2014–2015 all covers except for interwoven translucent polythethylene and aluminized high‐density polyethylene strips exceeded the control. Of standard covers, translucent polyethylene had the highest PAR transmission and was always in the top statistical category for mean maximum and daily range temperatures. Orange geotextile had the greatest dry and wet weights and gray and orange geotextiles had the lowest change in %SVWC on a 3% sloped native soil. Understanding differences in cover parameters will aid turfgrass managers in appropriate cover selection.

Windows in Arctic sea ice: Light transmission and ice algae in a refrozen lead

AbstractThe Arctic Ocean is rapidly changing from thicker multiyear to thinner first‐year ice cover, with significant consequences for radiative transfer through the ice pack and light availability for algal growth. A thinner, more dynamic ice cover will possibly result in more frequent leads, covered by newly formed ice with little snow cover. We studied a refrozen lead (≤0.27 m ice) in drifting pack ice north of Svalbard (80.5–81.8°N) in May–June 2015 during the Norwegian young sea ICE expedition (N‐ICE2015). We measured downwelling incident and ice‐transmitted spectral irradiance, and colored dissolved organic matter (CDOM), particle absorption, ultraviolet (UV)‐protecting mycosporine‐like amino acids (MAAs), and chlorophyll a (Chl a) in melted sea ice samples. We found occasionally very high MAA concentrations (up to 39 mg m−3, mean 4.5 ± 7.8 mg m−3) and MAA to Chl a ratios (up to 6.3, mean 1.2 ± 1.3). Disagreement in modeled and observed transmittance in the UV range let us conclude that MAA signatures in CDOM absorption spectra may be artifacts due to osmotic shock during ice melting. Although observed PAR (photosynthetically active radiation) transmittance through the thin ice was significantly higher than that of the adjacent thicker ice with deep snow cover, ice algal standing stocks were low (≤2.31 mg Chl a m−2) and similar to the adjacent ice. Ice algal accumulation in the lead was possibly delayed by the low inoculum and the time needed for photoacclimation to the high‐light environment. However, leads are important for phytoplankton growth by acting like windows into the water column.

Community dynamics of bottom-ice algae in Dease Strait of the Canadian Arctic

Sea ice algae are a characteristic feature in ice-covered seas, contributing a significant fraction of the total primary production in many areas and providing a concentrated food source of high nutritional value to grazers in the spring. Algae respond to physical changes in the sea ice environment by modifying their cellular carbon, nitrogen and pigment content, and by adjusting their photophysiological characteristics. In this study we examined how the ratios of particulate organic carbon (POC) to nitrogen (PON), and POC to chlorophyll a (chl a), responded to the evolving snow-covered sea ice environment near Cambridge Bay, Nunavut, during spring 2014. We also estimated photosynthesis-irradiance (PI) curves using oxygen-optodes and evaluated the resulting time-series of PI parameters under thin and thick snow-covered sites. There were no significant differences in PI parameters between samples from different overlying snow depths, and only the maximum photosynthetic rates in the absence of photoinhibition (PsB) and photoacclimation (IS) parameters changed significantly over the spring bloom. Furthermore, we found that both these parameters increased over time in response to increasing percent transmission of photosynthetically active radiation (TPAR) through the ice, indicating that light was a limiting factor of photosynthesis and was an important driver of temporal (over the spring) rather than spatial (between snow depths) variability in photophysiological response. However, we note that spatial variability in primary production was evident. Higher TPAR over the spring and under thin snow affected the composition of algae over both time and space, causing greater POC:chl a estimates in late spring and under thin snow cover. Nitrogen limitation was pronounced in this study, likely reducing PsB and algal photosynthetic rates, and increasing POC:PON ratios to over six times the Redfield average. Our results highlight the influence of both light and nutrients on ice algal biomass composition and photophysiology, and suggest a limitation by both resources over a diel period.

Changes of the light transmittance of the LDPE films during the service life for greenhouse application

In this study, changes on light transmittance of greenhouse covering materials produced by CO-EX technology with multi-layered CO-EX UV+IR+EVA and UV+IR+EVA+AD additives was investigated during their service life of 24 months. As physical properties, global solar radiation (GSR) and photosynthetically active radiation (PAR) transmittance of greenhouse covering materials were determined. Initial GSR transmittances were determined as 92.7% and 83.6% for UV+IR+EVA and UV+IR+EVA+AD added PE, respectively. The plastic films of UV+IR+EVA and UV+IR+EVA+AD had losses of GSR transmittances of 7.3% and 13.2% at the end of their service life, respectively. These losses were due to accumulation of dust and dirt on the exterior surface of films. Initial PAR transmittance of UV+IR+EVA and UV+IR+EVA+AD films were determined as 80.1% and 83.0%, respectively. Both of the plastic films of UV+IR+EVA and UV+IR+EVA+AD had PAR transmittance losses of 6.2% and 4.9% at the end of their service life, respectively.

Vine growth and physiological performance of two red grape cultivars under natural and reduced UV solar radiation

Background and Aims Under natural conditions the grapevine has shown different growth and physiological responses to high UV radiation. We evaluate the effect of natural and reduced UV-B, UV-A and photosynthetically active radiation (PAR) on vine growth, physiological status and berry composition in Bovale Grande (syn. Carignan) and Cannonau (syn. Grenache) field-grown grapes. Methods and Results During the two seasons of the trial, UV-screening treatments Visible + UV-A and Visible, imposed with plastic tunnels from pea size onward, promoted a significant difference in UV and PAR transmission as compared with that of plants exposed to natural sunlight, but did not reduce canopy growth and yield. Plants adjusted leaf gas exchange and water status to both high and reduced UV and PAR radiation. The concentration of phenolic substances of berries was significantly higher under natural UV, whereas accumulation of anthocyanins responded differently in the two cultivars according to the duration of high temperature. Conclusions The results indicate that red grapes of Mediterranean origin are able to adapt growth and physiological responses to high natural UV and temperature, but accumulation of berry anthocyanins and phenolic substances can vary considerably according to sensitivity of cultivars to these abiotic factors. Significance of the Study Increasing knowledge on the acclimation responses to high UV and solar irradiance environments by grape cultivars may help to improve management practices towards greater adaption to global warming conditions and projected climate change.