Maximum Photosynthetically Active Radiation Research Articles

Solar radiation effects on growth, anatomy, and physiology of apple trees in a temperate climate of Brazil.

The aim of study was to characterize patterns of interception and distribution of photosynthetically active radiation (PAR) in an apple orchard and to examine its relationship with morphophysiological characteristics of "Royal Gala" and "Fuji Suprema" apple trees. The experiments were conducted during three production cycles in two distinct orchard areas, one covered by black anti-hail netting and another uncovered (control). We analyzed PAR characteristics with data from meteorological sensors installed on the canopy, as well as growth, anatomical, and physiological variables of apple trees. The reduction of PAR by netting influenced the components of radiation balance. PAR intercepted, absorbed, transmitted, and reflected by the canopy under netting decreased by 33%, 31%, 32%, and 46%, respectively, in comparison to uncovered canopy. When leaf area index (LAI) was 1.5 (under netting) and 2.5 (uncovered), maximum PAR interception efficiency was reached. During the three production cycles, a light extinction coefficient of 1.09 and 0.76 was found under netting and in the control, respectively. Plant height was greater under netting in all three cycles for both cultivars. Number of leaves, LAI, and shape index did not differ between treatments. At stage 85, leaves of "Royal Gala" under netting showed lower chlorophyll content and thinner parenchymas in comparison to the control. However, physiological and anatomical characteristics of Fuji "Suprema" did not change under anti-hail netting.

New continuous total ozone, UV, VIS and PAR measurements at Marambio, 64° S, Antarctica

Abstract. A ground-based ultraviolet (GUV) multi-filter radiometer was set up at Marambio, 64∘ S, 56∘ W, Antarctica, in 2017. The instrument continuously measures ultraviolet (UV) radiation, visible (VIS) radiation and photosynthetically active radiation (PAR). The measurements are designed for providing high-quality long-term time series that can be used to assess the impact of global climate change in the Antarctic region. The quality assurance includes regular absolute calibrations and solar comparisons performed at Marambio and at Sodankylä, Finland. The measurements continue observations at Marambio that were performed with (Norwegian Institute for Air Re-search UV Radiometer (NILU-UV) radiometers between 2000 and 2010 as part of the Antarctic NILU-UV network. These measurements are ideally suited for assessing the effects of the ongoing stratospheric ozone recovery on the ecosystem, as the data products include information on radiation at various wavelengths ranging from UV to VIS so that changes on biologically effective radiation due to ozone can be separated from those due to other factors. Data products include total ozone, photosynthetically active radiation (PAR), visible (VIS) radiation at 555 nm, UV index, UV irradiance at 5 channels, UVB and UVA dose rate and daily dose, and biologically weighted UV dose rate and daily dose, calculated with 10 different action spectra. The data from the last 5 d and the daily maximum UV index time series are plotted and updated daily on the following web page: http://fmiarc.fmi.fi/sub_sites/GUVant/ (last access: 17 April 2020). The first 2 years of UV measurements were very different in terms of the results: for October, November and December the monthly average of daily maximum UVB dose rates were clearly higher in 2018 than in 2017. The largest difference was observed in October, when the average of daily maximum UVB dose rates was 76 and 102 µW cm−2 in 2017 and 2018, respectively. Monthly averages of the 3 months were similar in 2018, while in 2017 the monthly average of October was lower than those of November and December. The VIS and PAR time series show that daily maxima in 2018–2019 exceed those in 2017–2018 during late spring and summer (mid-November–January). The studied dataset, including daily maximum irradiances at five UV channels and one VIS channel; daily maximum UVB, UVA, and PAR dose rates; noon UVB, UVA, and PAR dose rates; noon total column ozone; and UVB and UVA daily doses, is freely accessible at https://doi.org/10.5281/zenodo.3688700 (Lakkala et al., 2019).

Energetic and Environmental Constraints on the Community Structure of Benthic Microbial Mats in Lake Fryxell, Antarctica

ABSTRACTEcological communities are regulated by the flow of energy through environments. Energy flow is typically limited by access to photosynthetically active radiation (PAR) and oxygen concentration (O2). The microbial mats growing on the bottom of Lake Fryxell, Antarctica, have well-defined environmental gradients in PAR and (O2). We analyzed the metagenomes of layers from these microbial mats to test the extent to which access to oxygen and light controls community structure. We found variation in the diversity and relative abundances of Archaea, Bacteria and Eukaryotes across three (O2) and PAR conditions: high (O2) and maximum PAR, variable (O2) with lower maximum PAR, and low (O2) and maximum PAR. We found distinct communities structured by the optimization of energy use on a millimeter-scale across these conditions. In mat layers where (O2) was saturated, PAR structured the community. In contrast, (O2) positively correlated with diversity and affected the distribution of dominant populations across the three habitats, suggesting that meter-scale diversity is structured by energy availability. Microbial communities changed across covarying gradients of PAR and (O2). The comprehensive metagenomic analysis suggests that the benthic microbial communities in Lake Fryxell are structured by energy flow across both meter- and millimeter-scales.

Diurnal variation of carbon dioxide flux above growing cowpea (<i>Vigna unguiculata [L] Walp.</i>) at an agricultural site in Ile-Ife, Nigeria

The goal of this study was to investigate the diurnal variation of carbon dioxide (CO ) flux above cowpea 2 (Vigna unguiculata [L.] Walp) in relation to its phenological stages of growth. The experimental site was an agricultural area located at the Teaching and Research farm of Obafemi Awolowo University, Ile-Ife, Nigeria.. The planting of cowpea covered two cycles, March-June and August-November, 2015, which represented dryto-wet and wet-to-dry seasonal transitions in the area respectively. An eddy covariance system was deployed on site from which turbulent flux of carbon dioxide had been determined. In addition, net radiation, photosynthetically active radiation (PAR), leaf surface temperature, soil moisture and thermal parameters were measured within the plant environment. Concentration of CO at the study location decreased by about 50 % to 2 -3 -2 minimum values, 650 mgm at 1500 hrs (LT), which is coincident with maximum PAR value of 1800 Wm . -2 -1 From sunset until dawn, the CO flux measured increased steadily from about 0.2 mgm s around 1800 hrs (LT) 2 -2 -1 to reach maximum value, about 0.5 mgm s at 0300 hr. Irrespective of growth stage of the plant, CO flux was 2 maximum during nighttime. Keywords: Cycles, Phenological stages, Plant environment, Seasonal transitions, Turbulent flux

Photosynthesis ecophysiology of polar Vaucheria sp. – inter-annual comparison

The Vaucheria sp. microbial mats represent the most important primary producer in the tidal flat in Adventdalen, Svalbard. Its photosynthetic activity was monitored ex situ in a microcosm in late Arctic summer in 2016 and 2017 using variable chlorophyll fluorescence measurements with blue and red excitation lights. The effective quantum yield (FPSII) was measured, and the photosynthetic relative electron transport rate (rETR) was calculated. During the measurement period, the microclimate data, air temperature and photosynthetically active radiation (PAR), were recorded as well. Year 2016 was slightly warmer than year 2017. Despite of higher maximum PAR values found in 2016, the mean irradiance reached higher values in 2017 than 2016. When using red light excitation, the rETR and effective quantum yield values were lower than those measured using blue excitation light in 2016. However, opposite results were recorded in 2017, indicating thus rather sample-specific differences. According to redundancy analysis, the PAR was confirmed as the main driver of photosynthesis in late Arctic summer in both years. No serious photoinhibition, expressed as serious systematic decline of the rETR, was observed in both years indicating rapid photoacclimation of Vaucheria sp. photosynthesis to changing light environment. The air temperature was found to be less important driver of the photosynthetic activity. The inter-annual comparisons showed increased photosynthetic activity in 2017, probably caused by higher PAR in 2017, by differences in microcosmos design and/or heterogeneity of samples.

Shade netting reduces sunburn damage and soil moisture depletion in ‘Granny Smith’ apples

The benefits associated with the use of protective netting for apple orchards have been assessed in several growing regions, but no studies exist for Washington State, USA. This region experiences semi-arid conditions characterized by long days, high light intensity and high temperatures which increases the risk of plant stress and fruit sunburn damage. The aim of this study was to assess the effect of anti-hail nets on orchard microclimate, soil moisture and fruit sunburn. Seven-year-old ‘Granny Smith’/‘M9-T337’ apple trees were covered in 2014 with 20% white shade net sheltering a rectangular area. Uncovered trees served as control. Shade net reduced the maximum daily photosynthetically active radiation (PAR) by 32%, with a maximum PAR value on a sunny day of 1649 and 1222 μmol m-2 s-1 in the control and netted areas, respectively. Canopy air temperature was slightly lower during the day and higher at night under the net compared to the control. Shade nets reduced soil moisture depletion at 0-30 cm depth, resulting 20% higher than the control. No significant differences were observed deeper in the soil profile. Netting significantly decreased fruit sunburn, with 92% of harvested fruit having no sunburn damage compared to control in which 51% had no sunburn damage in 2014. Although preliminary, these results show that shade netting has the potential to reduce sunburn damage in ‘Granny Simith’ apples and water requirements in semi-arid environments and might represent an important tool for increasing yields of high quality fruit.

Climatic oscillations in the production of Eucalyptus benthamii x E. dunnii shoots in mini-clonal hedge

Detailed knowledge on the factors influencing the production of minicuttings, especially focusing on management and environmental optimization is important. Therefore, this study aimed at evaluating the influence of temperature, relative humidity and PAR (photosynthetically active radiation) and their oscillations in mini-clonal hedges of three E. benthamii x E. dunnii hybrid clones regarding survival, vigor and productive capacity of ministumps. A mini-clonal hedge with a semi-hydroponic system was formed, with five replicates of five ministumps per clone, submitted to 41 successive collections of minicuttings during one year. A multiple linear regression model for minicutting production was adjusted according to maximum, average and minimum climatic variables, considering a period from 0 until 16 weeks before collection. Ministumps from three clones showed 100 % survival throughout the year. Clone 1 showed higher production (8,000 minicuttings m-2 month-1) and clone 3 showed the lowest values for this variable (less than 5,000 minicuttings m-2 month-1). The adjusted multiple linear regression model was formed by the maximum PAR, maximum humidity and temperature range of different weeks before collection. Maximum PAR (1,440-1,600 μmol m-² s-1) was the most influential variable in the adjusted model and positively related to minicutting productivity. Based on ideal climatic values found by the regression model, it is possible to suggest that climatic oscillations do not favor ministump development.

Effects of cumulus clouds on microclimate and shoot-level photosynthetic gas exchange in Picea engelmannii and Abies lasiocarpa at treeline, Medicine Bow Mountains, Wyoming, USA

Here we describe the dynamic effects of cumulus clouds on microclimate and shoot-level photosynthetic gas exchange in saplings of two treeline conifer species—Picea engelmannii and Abies lasiocarpa. Measurements were made during both clear-sky and partly cloudy conditions (∼10–70% cumulus cloud cover) throughout the 2012 growing season within an alpine-treeline ecotone. Cumulus clouds generated dynamic fluctuations in photosynthetically active radiation (PAR), higher maximum PAR (>2500μmolm−2s−1), 2–4 fold increases in diffuse PAR, reduced daily mean and cumulative PAR, lower needle temperatures, and reduced leaf-to-air vapor pressure differences relative to clear-sky conditions. Onset of cloud-shade corresponded with declines in photosynthesis, needle temperatures, and evapotranspiration, which were proportional to cloud duration and opacity. Despite increased diffuse light and greater sunlight intensity during cloud-gaps, photosynthesis was never higher on partly cloudy days compared to clear days in either species, during cloud-gaps or cloud-shade. However, reduced transpiration paired with photosynthesis comparable with clear-sky levels during cloud-gaps resulted in greater instantaneous water use efficiency relative to clear-sky measurements. There was no apparent photoinhibition of photosynthesis reflected in gas exchange measurements in response to abrupt and dramatic changes in PAR levels caused by cumulus clouds. We conclude that cumulus clouds reduce instantaneous and daily carbon gain, although lower needle temperatures and associated reductions in transpirational water loss may alleviate daily and seasonal water stress, thereby enhancing carbon gain over the growing season.

Analysis of photosynthetically active radiation under various sky conditions in Wuhan, Central China

Observations of photosynthetically active radiation (PAR) and global solar radiation (G) at Wuhan, Central China during 2005-2012 were first reported to investigate PAR variability at different time scales and its PAR fraction (F(p)) under different sky conditions. Both G irradiances (I(g)) and PAR irradiances (I(p)) showed similar seasonal features that peaked in values at noon during summer and reached their lower values in winter. F(p) reached higher values during either sunrise or sunset; lower values of F p appeared at local noon because of the absorption effects of water vapor and clouds on long-wave radiation. There was an inverse relationship between clearness index (K(t)) and F(p); the maximum I(p) decreased by 22.3 % (39.7 %) when sky conditions changed from overcast to cloudless in summer (winter); solar radiation was more affected by cloudiness than the seasonal variation in cloudy skies when compared with that in clear skies. The maximum daily PAR irradiation (R(p)) was 11.89 MJ m⁻² day⁻¹ with an annual average of 4.85 MJ m⁻² day⁻¹. F p was in the range of 29-61.5 % with annual daily average value being about 42 %. Meanwhile, hourly, daily, and monthly relationships between R p and G irradiation (R g) under different sky conditions were investigated. It was discovered that cloudy skies were the dominated sky condition in this region. Finally, a clear-sky PAR model was developed by analyzing the dependence of PAR irradiances on optical air mass under various sky conditions for the whole study period in Central China, which will lay foundations for ecological process study in the near future.

The study of microclimate in response to different plant community association in tropical moist deciduous forest from northern India

The data on microclimate were collected between 2010 and 2011 in five forest communities (dry miscellaneous, sal mixed, lowland miscellaneous, teak and savannah) in a tropical moist deciduous forest in Katerniaghat Wildlife Sanctuary, Uttar Pradesh, India to compare how vegetation structure affects microclimate. Diurnal variations in microclimatic variables [photosynthetically active radiation (PAR) at forest understory level, air temperature, soil surface temperature, ambient CO2, air absolute humidity] were measured with LI-COR 840, LI-COR 191, LI-COR 190 SZ, LI-1400-101 and LI-1400-103 (LI-COR; Lincoln, NE, USA) at centre of three 0.5 ha plots in each forest community. The diurnal trend in microclimatic parameters showed wide variations among communities. PAR at forest floor ranged from 0.0024 to 1289.9 (μmol m−2s−1) in post-monsoon season and 0.0012 to 1877.3 (μmol m−2s−1) in mid-winter season. Among the five communities, the highest PAR value was observed in savannah and lowest in sal mixed forest. All the forest communities received maximum PAR at forest floor between 1000 and 1200 h. The ambient air temperature ranged from 19.15 to 26.69°C in post-monsoon season and 11.31 to 23.03°C in mid-winter season. Soil temperature ranged from 13.54 to 36.88°C in post-monsoon season and 6.39 to 29.17°C in mid-winter season. Ambient CO2 ranged from 372.16 to 899.14 μmol mol−1 in post-monsoon season and 396.65 to 699.65 μmol mol−1 in mid-winter season. In savannah ecosystem, diurnal trend of ambient CO2 was totally different from rest four communities. According to Canonical correspondence analysis, PAR and ambient CO2 are most important in establishment of forest community, among microclimatic variables.

Grapevine row orientation affects light environment, growth, and development of black nightshade (Solanum nigrum)

Row orientation in vineyards can affect the quantity of light intercepted by the crop's canopy. Consequently, the light available to weeds growing under the canopy might also be affected, with potential implications for their physiology, growth, and productivity. This hypothesis was tested in 2003 and 2004 in a central California vineyard having rows oriented east–west (EW) and north–south (NS) in a randomized complete block design. In April of both years, potted black nightshade seedlings were placed under grapevines of both row orientations and grown for about 10 wk. Photosynthetically active radiation (PAR) at the weed canopy zone (WCZ) of NS rows was bimodal, with peaks occurring at about 09:30 A.M. and 4:30 P.M. At those times, PAR approached 500 μmol m−2 s−1 (between 30 and 40% of full sun). In contrast, maximum PAR in the WCZ of EW rows was generally less than 75 μmol m−2 s−1 throughout the day. The ratio of red to far-red light was also greater in NS than EW rows in the morning and afternoon. In both row orientations, PAR was suboptimal for nightshade because maximum net photosynthesis occurred at light levels ≥ 500 μmol m−2 s−1, but nightshade in the NS rows had higher net photosynthetic rates than those in EW rows when subjected to higher ambient PAR. Stem extension and phenology of nightshade was not affected by vine row orientation, but plants in EW rows had greater leaf areas, leaf area ratios, leaf weight ratios, and lower specific leaf weights than plants in NS rows. Berry mass, seeds per berry, and estimated seed production was 40, 7, and 20% lower, respectively, for plants in the EW than in the NS rows. Dry mass and total nonstructural carbohydrates (TNC) of nightshade roots were also 25 and 45% lower, respectively, in EW than in NS plants. Thus, grapevine row orientation may affect nightshade fecundity by reducing light in the WCZ.

Assessment of Leitneria floridana in Disjunct Native Habitats: Implications for Horticulture and Conservation

Tolerance of shade, flooding, drought, and nutrient-poor substrate is desirable among ornamental plants installed in managed landscapes. Many attractive native taxa have not been evaluated for their resistance to environmental stressors. We assessed Florida corkwood (Leitneria floridana Chapman) in its natural habitat in four disjunct populations in the United States and tested the physical and chemical properties of the soil at the study sites. Measures at all sites were made within two weeks in late June, 2003. Leaf area, plant height, length of new shoots, and the rate of photosynthesis were higher among plants receiving more than 600 μmol·m-2·s-1 of photosynthetically active radiation (PAR) compared to plants that occurred where maximum PAR was lower. Soil texture ranged from clay loam to fine sand, and soil pH across sites was 4.5 to 6.6. Concentration of nitrate-nitrogen, phosphorus, and potassium ranged from 3 to 75 mg·L-1, 7 to 11 mg·L-1, and 3 to 64 mg·L-1, respectively. Bases of plants in Florida were submersed in water, while soil moisture percentages in Missouri and Texas were 6 to 30. The apparent tolerance of L. floridana to shade, low and high soil moisture, and nutrient-poor soil in native habitats indicates that it could be used in a wide range of managed landscapes. Its capacity to adapt to shade may permit the use of L. floridana as an understory species in managed landscapes, but stewards of natural areas may need to maintain open sites within its native habitat to allow expansion of populations. Because this assessment of L. floridana included native populations across the natural range of the species, our results are uniquely suited for both horticultural and ecological interpretation and application.

Microenvironmental and vegetational heterogeneity induced by phytogenic nebkhas in an arid coastal ecosystem

The nebkhas of woody plants represent distinct habitats in arid and semiarid ecosystems. Nebkhas are mounds composed of wind-borne sediment within or around shrub canopies. We studied the effects of widely spaced nebkhas of Retama raetam shrub on their microenvironment and associated herbaceous vegetation in the Mediterranean coast of Sinai Peninsula. Our measurements included nebkha size (height and width) and shrub size (canopy height and diameter). We identified four distinct microsites at each nebkha: crest, mid-slope, edge, and internebkha space. We measured soil temperature and moisture, photosynthetically active radiation (PAR), and soil properties. The plant species grown at each microsite were identified and their densities were measured. Average soil temperature and PAR were highest at internebkha space and lowest at nebkha crest. The maximum diurnal temperature and PAR of internebkhas exceeded that of nebkhas. Soil moisture and nutrient concentrations showed a gradient of spatial heterogeneity and were highest at the nebkha edge. Regression analysis indicated that total herbaceous plant density was significantly related to nebkha size, and to shrub canopy diameter and area. Detrended correspondence analysis indicated that patterns of species composition were correlated with the spatial variability in soil moisture and nutrient content along the gradient of increasing distance from the nebkha crest. It is assumed that shrub canopy and its nebkha interact in governing ecosystem functioning in this environment.

Light absorption and water loss in overwintered and spring–sown evening primrose ( Oenothera spp.) crops

Evening primrose ( Oenothera spp.) is a high-value oilseed crop for temperate areas which may be either overwintered or spring–sown. Light absorption, light use efficiency, water loss and biomass water ratio were compared between overwintered and spring–sown crops of cv. Merlin in two years of field trials. An overwintered crop of cv. Peter was also studied in year two. The energy content of evening primrose plant material was shown to be similar to other crops. Both overwintered and spring–sown crops can achieve full canopy closure and maintain high fractional photosynthetically active radiation (PAR) interception for long periods but canopy closure occurred much later than in other temperate seed crops. In spring–sown evening primrose, maximum PAR interception did not occur until August, by which time incident light levels were declining and consequently the proportion of incident light energy captured during the main growing season was low. Most light was intercepted by green leaves and very little shading by senescent tissue and flowers occurred. Light conversion efficiencies for the main growing period were comparable with other temperate C 3 crops, but in year two a steep decline in light conversion efficiency was observed as the crops matured and the soil water deficit exceeded 60 mm. In year one, water loss from both the overwintered and spring–sown crops were low and the soil water deficit increased relatively slowly. By contrast, in the year two crop water loss was high and the soil water deficit built up very rapidly between the end of June and crop maturity. No significant differences in biomass water ratio (water use efficiency) were recorded between overwintered and spring–sown crops but ratios were 50% higher in year one than in year two. Although no relationship was detected between biomass water ratio corrected for vapour pressure deficit (“normalised”) and soil water deficit, after canopy closure normalised daily water loss declined with increasing soil water deficit. Earlier canopy closure, particularly in the spring crop, and the avoidance of soil water deficits through irrigation, would lead to substantial improvements in the size and consistency of seed yields of evening primrose crops.

Microenvironmental Heterogeneity and Space Utilization by Desert Vines within their Host Trees

The three-dimensional biomass distribution and the microenvironments experienced by several desert vine species growing within the canopy of host trees were studied at the Centro Ecológico de Sonora in México. The light environment within the crown of the host tree Cercidium microphyllum showed a horizontal and vertical gradient from the base of the trunk to the edges of the canopy. Within this gradient total daily photosynthetically active radiation (PAR) varied from 47.8 mol m−2outside the crown to 4.6 mol m−2at the centre of the crown and close to the ground. Maximum air temperature was 3 °C lower beneath the crown than outside. Within the canopy, most vines experienced less than 50% of the daily available PAR outside the canopy. For most of the day, leaves of vines received 15% or less of the maximum available PAR. Our study shows that vines do not grow towards full sunlight but rather they exploit different habitat possibilities within their host tree crown. Leaves along the stems of vines experienced a wide range of light environments, showing coefficients of variation (CV) in total daily PAR from 36.4 to 94.6%. Daily courses of PAR also showed that leaves within the canopy experienced short-term temporal variation in the light environment. Differences in CV of daily PAR values and preferences in heterogeneous light microenvironments among species suggested that different vine species might be spatially separated in the canopy. We suggest that in desert habitats, conditions within the crown of host trees result in an important microhabitat that vines can exploit, allowing them to avoid the high light, temperature and water deficits found in the surrounding environment.

Far‐red enrichment and photosynthetically active radiation level influence leaf senescence in field‐grown sunflower

Basal leaves frequently senesce before anthesis in high population density crops. This paper evaluates the hypothesis that quantitative and qualitative changes in the light environment associated with a high leaf area index (LAI) trigger leaf senescence in sunflower (Helianthus annuus L.) canopies. Mean leaf duration (LD, time from achievement of maximum leaf area) of leaf 8 was significantly (P < 0.05) reduced from 51 to 19 days as crop population density was increased from 0.47 to 4.76 plants m−2. High compared to low plant population density was associated with earlier reduction in the photosynthetically active radiation (PAR) and red/far‐red ratio (R/FR) reaching the target leaf. However the changes in R/FR preceded those in PAR. When the light environment of individual leaves of isolated plants growing under field conditions was manipulated using filters and FR‐reflecting mirrors, LD was positively and linearly related with the mean daily PAR (MDR) received in the FR‐ (no FR enrichment) treatments. FR enrichment of light reaching the abaxial surface of the leaf significantly (P < 0.05) reduced LD by 9 days at intermediate PAR levels with respect to FR‐controls, but did not affect LD at the maximum PAR used in these experiments. However, when light reaching both leaf surfaces was enriched with FR, LD (for leaves receiving maximum PAR) was 13 days shorter than that of the FR‐ control. These results show that basal leaf senescence in sunflower is enhanced both by a decrease in PAR and by a decrease in R/FR.