Photosynthetically Active Radiation Levels Research Articles

Spatiotemporal variability and drivers of modeled primary production rates in the Northern Humboldt Current System

A coupled physical-biogeochemical model was employed to explore the spatiotemporal dynamics of primary production (PP) rates within the Northern Humboldt Current System (NHCS). The coastal zone spanning 250 km from the shore, from 3°to 18°S, stands out as a highly productive upwelling region, exhibiting an average surface PP value of 2.5 mol C m−3 yr−1. Correspondingly, the average vertically integrated PP within the euphotic layer amounts to 13 mol C m−2 yr−1. In this context, summer emerges as the peak of productivity, yielding 18 mol C m−2 yr−1, while winter signifies the period of least productivity, with 9 mol C m−2 yr−1. Our study revealed that surface PP variability is primarily driven by changes in surface chlorophyll and phytoplanktonic biomass (mainly diatoms), followed by changes in photosynthetically active radiation (PAR) levels. During summertime, these three drivers contribute to substantial positive anomalies in surface PP. However, the reduction in nutrient availability resulting from weakened upwelling-favorable winds has a slight negative impact on surface PP rates. Yet, this decline is offset by a positive thermal effect during the warmer season. In contrast, during the winter season, a significant decrease in surface chlorophyll concentrations due to a vertical redistribution into a deeper mixed layer significantly diminishes surface PP. Furthermore, the reduction in both PAR levels and biomass concentrations has a comparable effect, further contributing to the decrease in surface PP rates during wintertime. At a depth of 20 m, changes in PP are primarily driven by variations between the opposing influences of PAR and chlorophyll concentrations. While PAR adheres to the seasonal cycle of warming and cooling throughout the year, chlorophyll-driven anomalies exhibit an inverse pattern to those at the surface, influenced by the vertical dilution effect within the mixed layer. Overall, this study provides valuable insights into the complex interplay of drivers that govern PP dynamics across various depths within one of the world’s most productive marine regions.

The influence of the hydrometeorological factors on the CO2 fluxes from the oligotrophic bog surface.

The influence of the hydrometeorological factors on the CO2 fluxes from the oligotrophic bog surface.

Shading and PAR under different density agrivoltaic systems, their simulation and effect on wheat productivity

The introduction of renewable energy to mitigate climate change and the need for sufficient land to increase food production are mutually exclusive. Agrivoltaic systems (AVS) integrate the production of agricultural crops and electric power on the same piece of land but the main issue is the reduced availability of light to crops below the AVS, which restricts optimum crop growth and yield. This study examines the radiation and shade distribution over the crop surface among three densities of photovoltaic (PV) panels {Partial density (PD), Half density (HD) and Full density (FD)} under the AVS. Wheat variety GW 496 was chosen to grow under the AVS with line sowing and drip irrigation. Among three densities of photovoltaic (PV) panels, the proportion of shaded area over the crop surface was found highest in full density plot and lowest in partial density plot. The shaded area under AVS varied from 24.1% to 75.4% of the total area. The shaded area under different density plots, adversely affects the availability of photosynthetically active radiation (PAR) over the crop surface. The reduction of PAR under the AVS was more affected by panel density. Maximum reduction in PAR under AVS was observed in FD plot and minimum in the PD plot. A sharp increase in the PAR level was observed from shading to open sun conditions. The lowest value of PAR level (56 μmol m−2 s1) was recorded in just below the panel’s array. The consistent overestimation of PAR was observed during the crop growing period in all the PVPs density plots. The result revealed that the grid points under shade conditions showed a better association between observed and simulated incident PAR than unshaded grid points. Furthermore, the simulation results revealed that the model modeled PAR better in PD plot. The study also found that wheat grown under no shade yielded 4.51 t/ha over reduced light either in PD (3.06 t/ha), HD (2.77 t/ha), and FD plots (2.62 t/ha). Shading treatments showed that the crop yield decreased with an increase in shading intensity.

Lichen substances are more important for photoprotection in sun than shade collections of lichens from the same species

Photosynthetic organisms possess a great diversity of mechanisms to protect themselves from the potentially stressful effects of high PAR (photosynthetically active radiation). A distinctive response to longer term exposure to high levels of PAR in lichens is the synthesis of a variety of substances in the upper cortex that can protect photobionts from photoinhibition. In the present study, lichen substances were removed harmlessly from lichens using the “acetone rinsing” method. This enabled us to compare the importance of the substances in photoprotection in sun and shade collections of four species of Afromontane lichens. While all species normally grow in more exposed microhabitats, it is easy to make collections of more shaded thalli. Using chlorophyll fluorescence, we show that collections of lichens from sunny microhabitats have higher tolerance to photoinhibition than those from shaded locations. Furthermore, removal of lichen substances increases sensitivity to photoinhibition, suggesting that even although colorless, they have a role in protecting against high PAR. Sensitivity was increased much more in sun than shade collections, implying that substances play a greater role in photoprotection in lichens from sunny microhabitats. Nevertheless, following the removal of lichen substances, most sun collections still possess higher tolerance to photoinhibition than shade collections. Therefore, the additional tolerance of sun collections appears derive from a combination of both lichen substances and other, probably more biochemical tolerance mechanisms.

Tracking diurnal to seasonal variations of gross primary productivity using a geostationary satellite, GK-2A advanced meteorological imager

The diurnal sampling capability of geostationary satellites provides unprecedented opportunities for monitoring canopy photosynthesis at multiple temporal scales. At the diurnal scale, only geostationary satellites can currently provide sub-daily data at regular intervals, also it can help to minimize data gaps due to clouds at the seasonal scale. However, the potential of geostationary satellites for monitoring photosynthesis has not been explored in depth. In this study, we tracked diurnal to seasonal variations in gross primary production (GPP) using the product of near-infrared reflectance of vegetation and photosynthetically active radiation (PAR) (NIRvP) over deciduous forests, mixed forests and a rice paddy during the growing season. For this purpose, we generated three levels of reflectance and PAR from Geostationary Korea Multi-Purpose Satellite-2A (GK-2A). We examined how NIRvP derived from GK-2A tracked in-situ GPP data collected from five flux tower sites in South Korea. Bi-directional Reflectance Distribution Function (BRDF) normalized NIRvP agreed well with in-situ GPP over the course of the growing season at hourly (R2 = 0.68–0.77) and daily timesteps (R2 = 0.71–0.83). Atmospheric correction and BRDF normalization improved the performance of NIRvP in tracking GPP at both the diurnal and seasonal time scales. Also, GK-2A showed a much higher percentage of available high-quality BRDF data over the whole growing season for all study sites than the Moderate Resolution Imaging Spectroradiometer (MODIS) (GK-2A: 85%; MODIS: 39%), especially during the cloudy monsoon period. Our findings demonstrated that the unique observation characteristics of geostationary satellites can contribute to large-scale monitoring of diurnal to seasonal GPP dynamics.

Interactive effects of nitrogen, UV and PAR on barley morphology and biochemistry are associated with the leaf C:N balance

Environmental conditions to which plants acclimate prior exposure to abiotic or biotic stressors can greatly affect their subsequent resilience. This may have a significant impact on the response to ongoing climate change and can be useful for increasing the food security under adverse weather conditions associated with climate change.Within this study, we tested the hypothesis that plant morphological and biochemical acclimation to radiation conditions and nitrogen (N) availability is closely linked with carbon (C) and N balance. Four barley (Hordeum vulgare) varieties, differing in their morphological characteristics and sensitivity to photooxidative stress, were grown at two levels of N supply and four radiation regimes combining distinct levels of ultraviolet (UV) and photosynthetically active radiation (PAR). Changes in root and shoot morphology, accumulation of phenolic compounds, amino acids, and sugars were studied together with the analysis of C and N content in leaves.Both UV and PAR reduced leaf length and increased root-to-shoot ratio (R:S). Such effect was more pronounced under high N availability. High N supply reduced R:S, but this effect showed significant interactions with UV and PAR, and also with barley variety. Changes in R:S were positively related to C:N ratio in leaves that varied in response to both N availability and radiation treatments. UV radiation, particularly in combination with high PAR intensity, led to increases in most phenolic compounds (particularly flavones such as saponarin, homoorientin and isovitexin) which was also closely associated with changes in C:N ratio, while specifically phenolic acids (vanillic and syringic acids) decreased under high levels of UV and PAR, and hydroxycinnamic acids responded positively mainly to PAR. Although high N availability generally reduced the accumulation of phenolic compounds, this effect was genotype-specific and modulated by the radiation regime.A similar antagonistic effect of radiation treatment and N availability was also found for the accumulation of sugars (pentoses), resulting in a close relationship between the accumulation of pentoses and C:N ratio. The accumulation of most amino acids, in contrary to phenolic compounds, increases at high N and is also stimulated by high PAR and UV intensities.We conclude that radiation conditions and N availability have opposite effects on plant morphology and accumulation of most phenolic compounds and modulate the amino acid and sugar metabolism. Strong associations of these responses with changes in C:N ratio indicates that plant stoichiometry integrates acclimation processes and induction of relevant defence mechanisms.

Solar-induced chlorophyll fluorescence intensity has a significant correlation with negative air ion release in forest canopy

Forest vegetation is an essential source of negative air ion (NAI) and influencing factor of the process. A number of studies have focused on the temporal and spatial changes of NAI in different forest communities and their relationship with meteorological factors; however, there is no literature on the relationship between solar-induced chlorophyll fluorescence intensity (SIF) and NAI, and quantitative research on relationship between NAI and photosynthesis of forest vegetation is comparatively limited. In this study, we investigated the dynamic changes NAI, SIF, and meteorological parameters in canopy during the growing season by using a flux tower at the sites Xiaolangdi and Minquan in a warm-temperate monsoon climate zone from June to September of 2019 and 2020. Results showed that the canopy NAI, SIF, and photosynthetically active radiation (PAR) showed significant diurnal and seasonal dynamic change characteristics, and that the changes in the observed indicators at different times were significantly different. The seasonal change characteristics of canopy NAI and SIF were relatively similar, and canopy SIF could accurately capture the dynamic changes of NAI. Additionally, the NAI–SIF relationship was increasingly significant at higher PAR levels, and the coefficient of determination (R2) of the two sites reached 0.652 and 0.570. It showed that when vegetation photosynthesis was fully activated, the dynamic change process of the canopy NAI provided a more robust correlation and more accurate estimation in the vegetation's main growth stage, thus demonstrating the reliability of SIF as an indicator for tracking NAI seasonal changes. In the future, automatic, continuous SIF observations could provide reliable understanding of the photosynthetic characteristics of terrestrial ecosystems, thereby quantifying the contribution potential of forest to NAI application in ground-based optical measurement and airborne and satellite remote sensing. This provides a working foundation for direct assessment of spatial and temporal distribution patterns of global seasonal NAI.

The Impact of Light Spectrum and Intensity on the Growth, Physiology, and Antioxidant Activity of Lettuce (Lactuca sativa L.).

This study focused on the physiology, growth and antioxidant activity response of hydroponically grown lettuce (Lactuca sativa L.) under sole-source LED lighting of differing spectra. Lighting spectra were provided by differing combinations of LEDs of three different peak wavelengths, (Blue 435, Blue 450, and Red 663 nm) with ratios of B450/R663: 1.25 ± 0.1, B450/R663: 1.25 ± 0.1, and B450/R663 1:1 at two light intensities of photosynthetically active radiation (PAR) (270 μmol m−2 s−1 and 60 μmol m−2 s−1). A further experiment was conducted, in which Blue and Red LEDs were supplemented with Green (Blue 450, Red 663, and Green 520 nm) with ratios of B435/R663: 1.25 ± 0.1, B450/R663/G520: 1/0.73/0.26, and B450/R663: 1.25 ± 0.1. LED light intensities under the different spectra were adjusted to deliver the same level of PAR (270 ± 20 μmol m−2 s−1). Results from the first experiment showed that increased fraction of blue 435 nm in combination with red light at 663 nm at high irradiance enhanced the physiology of lettuce (i.e., significantly increased assimilation rate, stomatal conductance and transpiration rate) and increased the yield while having no significant effect on antioxidant activity. At the lower irradiance, the B435/R663 significantly increased antioxidant activity compared to other spectra. Results from the second experiment showed no significant effect of the spectra of LEDs on the physiology and yield of lettuce, but antioxidant activity was very significantly induced by B450/R663 at the ratio of 1.25 ± 0.1. However, the amount was still less than that obtained by B435/R663 1.25 ± 0.1 from the first experiment. This study indicates that LED light with a spectrum of B435/R663 at a ratio of 1.25 ± 0.1 significantly improves lettuce yield and antioxidant activity.

Comparison of Measured and Calculated Carboxylation Rate, Electron Transfer Rate and Photosynthesis Rate Response to Different Light Intensity and Leaf Temperature in Semi-closed Greenhouse with Carbon Dioxide Fertilization for Tomato Cultivation

This study aimed to estimate the photosynthetic capacity of tomato plants grown in a semi-closed greenhouse using temperature response models of plant photosynthesis by calculating the ribulose 1,5-bisphosphate carboxylase/ oxygenase maximum carboxylation rate (Vcmax), maximum electron transport rate (Jmax), thermal breakdown (hightemperature inhibition), and leaf respiration to predict the optimal conditions of the CO2-controlled greenhouse, for maximizing the photosynthetic rate. Gas exchange measurements for the A-Ci curve response to CO2 level with different light intensities {PAR (Photosynthetically Active Radiation) 200μmol·m -2 ·s -1 to 1500μmol·m -2 ·s -1 } and leaf temperatures (20°C to 35°C) were conducted with a portable infrared gas analyzer system. Arrhenius function, net CO2 assimilation (An), thermal breakdown, and daylight leaf respiration (Rd) were also calculated using the modeling equation. Estimated Jmax, An, Arrhenius function value, and thermal breakdown decreased in response to increased leaf temperature (> 30°C), and the optimum leaf temperature for the estimated Jmax was 30°C. The CO2 saturation point of the fifth leaf from the apical region was reached at 600ppm for 200 and 400μmol·m -2 ·s -1 of PAR, at 800ppm for 600 and 800μmol·m -2 ·s -1 of PAR, at 1000ppm for 1000μmol of PAR, and at 1500ppm for 1200 and 1500μmol·m -2 ·s -1 of PAR levels. The results suggest that the optimal conditions of CO2 concentration can be determined, using the photosynthetic model equation, to improve the photosynthetic rates of fruit vegetables grown in greenhouses.

Increased CO2 Relevant to Future Ocean Acidification Alleviates the Sensitivity of a Red Macroalgae to Solar Ultraviolet Irradiance by Modulating the Synergy Between Photosystems II and I.

While intertidal macroalgae are exposed to drastic changes in solar photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) during a diel cycle, and to ocean acidification (OA) associated with increasing CO2 levels, little is known about their photosynthetic performance under the combined influences of these drivers. In this work, we examined the photoprotective strategies controlling electron flow through photosystems II (PSII) and photosystem I (PSI) in response to solar radiation with or without UVR and an elevated CO2 concentration in the intertidal, commercially important, red macroalgae Pyropia (previously Porphyra) yezoensis. By using chlorophyll fluorescence techniques, we found that high levels of PAR alone induced photoinhibition of the inter-photosystem electron transport carriers, as evidenced by the increase of chlorophyll fluorescence in both the J- and I-steps of Kautsky curves. In the presence of UVR, photoinduced inhibition was mainly identified in the O2-evolving complex (OEC) and PSII, as evidenced by a significant increase in the variable fluorescence at the K-step (Fk) of Kautsky curves relative to the amplitude of FJ−Fo (Wk) and a decrease of the maximum quantum yield of PSII (Fv/Fm). Such inhibition appeared to ameliorate the function of downstream electron acceptors, protecting PSI from over-reduction. In turn, the stable PSI activity increased the efficiency of cyclic electron transport (CET) around PSI, dissipating excess energy and supplying ATP for CO2 assimilation. When the algal thalli were grown under increased CO2 and OA conditions, the CET activity became further enhanced, which maintained the OEC stability and thus markedly alleviating the UVR-induced photoinhibition. In conclusion, the well-established coordination between PSII and PSI endows P. yezoensis with a highly efficient photochemical performance in response to UVR, especially under the scenario of future increased CO2 levels and OA.

A climate-based analysis of photosynthetically active radiation availability in large-scale greenhouses across China

Photosynthetically Active Radiation (PAR) is critically required for sustaining plant and vegetable growth. This study investigated PAR availabilities in two typical large-scale greenhouses using an advanced method of climate-based solar modelling in China. Seven Chinese locations in terms of daylight (solar) climate zones and latitudes were studied. The PAR prediction was conducted via RADIANCE (ray-tracing solar and light simulation package). Key findings were: 1) A climate-based analysis was proved as more practical than the methods based on only clear sky and solar geometries. 2) A ray-tracing solar modelling could effectively predict PAR levels at specific positions (e.g. vertical planes), which could benefit the development of vertical farming activities. 3) The PAR availability could receive insignificant impact from roof configuration in these large-scale greenhouses. 4) For the approach of vertical farming, the vertical arrangement of planting system could be significantly affected by greenhouse orientations, while horizontally no such effect can be found. These findings could be developed into design strategies to support greenhouse planning.

The inhibitory effects of the antifouling compound Irgarol 1051 on the marine diatom Skeletonema sp. across a broad range of photosynthetically active radiation.

The release of anthropogenic organic pollutants has resulted in extensive environmental risks to coastal waters. Among pollutants released, the most common antifoulant, Irgarol 1051, is an effective inhibitor of photosystem II of photoautotrophs; thus, the continuous release of this compound into surrounding seawater would potentially threaten marine algae. To investigate this, we grew the model marine diatom Skeletonema sp. at different concentrations of Irgarol 1051 and levels of photosynthetically active radiation (PAR). Irgarol did not affect the photochemical capacity when cells were incubated in the dark, but photochemical yields all significantly decreased, and relative inhibition by Irgarol increased once cells were exposed to even the lowest PAR, with lower photochemical yields observed under increased level of Irgarol. In addition, the rate of decrease in yield increased with Irgarol concentration but was unchanged among PAR treatments. The growth rates showed a similar pattern to photochemical yields, with lower values under higher Irgarol concentrations, but with no significant differences in the effect of Irgarol observed between the light levels employed. The ratio of repair to damage rates of PSII clearly shows that this ratio decreased with light intensity, largely due to increases in damage rates and that the PAR level at which repair balanced damage decreased under a high level of Irgarol. Our results suggest that the inhibitory effects of Irgarol become obvious after PAR exposure even at a relatively low light level, suggesting that Irgarol would affect phytoplankton throughout the daytime, and may therefore have a broad environmental risk, potentially limiting coastal primary production.

Intercepted Photosynthetically Active Radiation (PAR) and Spatial and Temporal Distribution of Transmitted PAR under High-Density and Super High-Density Olive Orchards

We quantified the photosynthetically active radiation (PAR) interception in a high-density (HD) and a super high-density (SHD) or hedgerow olive system, by measuring the PAR transmitted under the canopy along transects at increasing distance from the tree rows. Transmitted PAR was measured every minute, then cumulated over the day and the season. The frequencies of the different PAR levels occurring during the day were calculated. SHD intercepted significantly but slightly less overall PAR than HD (0.57 ± 0.002 vs. 0.62 ± 0.03 of the PAR incident above the canopy) but had a much greater spatial variability of transmitted PAR (0.21 under the tree row, up to 0.59 in the alley center), compared to HD (range: 0.34–0.43). This corresponded to greater variability in the frequencies of daily PAR values, with the more shaded positions receiving greater frequencies of low PAR values. The much lower PAR level under the tree row in SHD, compared to any position in HD, implies greater self-shading in lower-canopy layers, despite similar overall interception. Therefore, knowing overall PAR interception does not allow an understanding of differences in PAR distribution on the ground and within the canopy and their possible effects on canopy radiation use efficiency (RUE) and performance, between different architectural systems.

Ultraviolet Radiation Stimulates Activity of CO2 Concentrating Mechanisms in a Bloom-Forming Diatom Under Reduced CO2 Availability.

The diatom Skeletonema costatum is cosmopolitan and forms algal blooms in coastal waters, being exposed to varying levels of solar UV radiation (UVR) and reduced levels of carbon dioxide (CO2). While reduced CO2 availability is known to enhance CO2 concentrating mechanisms (CCMs) in this diatom and others, little is known on the effects of UV on microalgal CCMs, especially when CO2 levels fluctuate in coastal waters. Here, we show that S. costatum upregulated its CCMs in response to UVR (295–395 nm), especially to UVA (320–395 nm) in the presence and absence of photosynthetically active radiation (PAR). The intensity rise of UVA and/or UVR alone resulted in an increase of the activity of extracellular carbonic anhydrase (CAe); and the addition of UVA enhanced the activity of CCMs-related CAe by 23–27% when PAR levels were low. Such UV-stimulated CCMs activity was only significant at the reduced CO2 level (3.4 μmol L−1). In addition, UVA alone drove active HCO3− uptake although it was not as obvious as CAe activity, another evidence for its role in enhancing CCMs activity. In parallel, the addition of UVA enhanced photosynthetic carbon fixation only at the lower CO2 level compared to PAR alone. In the absence of PAR, carbon fixation increased linearly with increased intensities of UVA or UVR regardless of the CO2 levels. These findings imply that during S. costatum blooming period when CO2 and PAR availability becomes lower, solar UVR (mainly UVA) helps to upregulate its CCMs and thus carbon fixation, enabling its success of frequent algal blooms.

Effects of feeding on the physiological performance of the stony coral Pocillopora acuta

Reef-building corals rely on both heterotrophy and endosymbiotic dinoflagellate autotrophy to meet their metabolic needs. Those looking to culture these organisms for scientific or industrial purposes must therefore consider both feeding regimes and the light environment. Herein the effects of three photosynthetically active radiation (PAR) levels were assessed in fed and unfed specimens of the model coral Pocillopora acuta that were cultured in a recirculating aquaculture system (RAS). Half of the corals were fed Artemia sp. brine shrimp in a separate feeding tank to prevent biofouling, and fragments were exposed to PAR levels of 105, 157, or 250 μmol quanta m−2 s−1 over a 12-h period each day. All cultured corals survived the 140-day treatment, and the physiological response variables assessed-buoyant weight, specific growth rate, linear extension, color, and Fv/Fm-were significantly influenced by feeding, and, to a lesser extent, light. Specifically, fed corals grew faster and larger, and presented darker pigmentation; corals fed at the highest light levels grew at the fastest rate (6 cm year−1 or 175 mg g−1 week−1). Given the high physiological performance observed, we advocate the active feeding of brine shrimp in RAS by those looking to cultivate P. acuta, and likely other corals, over long-term timescales.

Interannual Variability of Primary Production in the East Siberian Sea

Interannual variability (2002–2018) of primary production, surface seawater temperature (T0), photosynthetically active radiation (PAR) and ice cover area in the East Siberian Sea (ESS) was studied based on the data of the MODIS-Aqua ocean color scanner. The annual total primary production (PPtot) decreased by 1.7 TgC over 17 years. The multi-year negative trend in PPtot was 0.1 TgC y–1 (1.38% y–1). The decrease in PPtot was accompanied by the decrease in the area-specific primary production (IPP). Over the investigated period the annual mean IPP decreased by 13 mgC m–2 d–1. The multi-year negative trend in IPP was 0.76 mgC m–2 d–1 y–1 (0.84% y–1). The decrease in PPtot and IPP was accompanied by statistically insignificant increase in T0 (R2 = 0.09) and statistically significant decline in PAR (R2 = 0.29). Over the 17 years, T0 in ESS increased by 0.68°С (0.04°С y–1 or 3.2% y–1) and PAR declined by 3.4 Ein m–2 d–1 (0.2 Ein m–2 d–1 y–1 or 1.9% y–1). The ice-free area slightly diminished during the study period (R2 = 0.10) by 64.94×103 km2. The statistically insignificant negative multi-year trend in the ESS ice-free area was 3.82 × 103 km2 y–1 (0.87% y–1). Long-term variability in PPtot in ESS from 2002 to 2018 depended not only on the decrease in the ice cover but also on PAR level and IPP.

Water Use Efficiency of Acacia seyal (Del.) in extreme arid environment prevails in South-Western Desert, Egypt

The present investigation involves the studies of water use efficiency of Acacia seyal (Del.) seedlings under extreme arid conditions. Experiments were performed in a hyper arid environment to study the effects of drought stress using different water regimes at 12%, 9%, 6%, 4% and 2%. Calculated instantaneous water use efficiency was measured under full Photosynthetic Active Radiation range (0-2500μmols-1m-2). Acacia seyal showed maximum photosynthesis rate at 9% soil moisture content, and at high Photosynthetic Active Radiation levels. Maximum transpiration rate recorded at 9% soil moisture content at highest Photosynthetic Active Radiation. The maximum instantaneous water use efficiency was noticed at 4% soil moisture content at high Photosynthetic Active Radiation level. Acacia seyal maximized photosynthesis rate and minimized transpiration rate, giving maximum instantaneous water use efficiency at the high Photosynthetic Active Radiation and low soil moisture content levels.

Energy dissipation and photosynthetic electron flow during the transition from juvenile red to mature green leaves in mango (Mangifera indica L.)

Leaf colouration during development from juvenile red to mature green leaves is a genetically controlled process in mango (Mangifera indica L.). This study aimed to determine the pigmentation pattern and electron transport flow in both red and green leaves under varied light intensity. In this study, 5- and 10-day old juvenile red and mature green leaves, respectively, were used. Three different photosynthetic active radiation levels (600 ± 5, 1000 ± 5 and 1200 ± 5 µmol m−2 s−1) were chosen to examine chlorophyll a fluorescence (O-J-I-P) transients. The vacuole of spongy cells in mesophyll contained anthocyanin in the juvenile leaf and rapidly degraded during the colour transition from red to green. A significant difference in chlorophyll, carotenoid and anthocyanin pigments was observed in both leaf types. The O-J-I-P parameters revealed that light intensity has a greater influence on the PSII electron transport chain than on PSI. Furthermore, the PSI of both leaves appeared to be more tolerant than that in PSII. The red leaf performed more energy dissipation than the green leaf after elevated light intensity exposure. O-J-I-P transients can be used as a sensitive, non-destructive method for measuring energy dissipation induced by intense radiation in plants.

Seasonal variation in the lipid profile of Acropora millepora at Halfway Island, Great Barrier Reef

To understand how environmental conditions and reproductive events affect coral energetic status, seasonal variations in lipid and fatty acid profiles of the common scleractinian coral, Acropora millepora, were studied from pre-spawning in November 2009 until post-spawning in November 2010 at Halfway Island (in the Keppel Island Group, Southern Great Barrier Reef, Australia). Seasonal chlorophyll levels, photosynthetically active radiation (PAR), rainfall and water temperature were major drivers of the overall coral lipid profile, and this was particularly pronounced in correlations with the important, high-energy lipid, triacylglycerol. This likely reflected changing food sources and feeding modes (i.e. phototrophy vs heterotrophy), which corresponds to the opportunistic feeding behaviour of corals. Water temperature was also a major influencer of the coral fatty acid profile. In particular, saturated fatty acids correlated positively with water temperature, while polyunsaturated fatty acids correlated negatively, reflecting cell membrane fluidity regulation, which is necessary for coral to tolerate changing temperatures. Spawning and maternal provisioning also proved to be a major driver of change in the coral lipid profile. The mass spawning events in spring for both 2009 and 2010 caused reductions in the important coral egg constituents: wax ester, triacylglycerol, phosphatidylcholine and fatty acid 10:0. Interestingly, lipid accumulation was significantly lower in the 2010 spawn compared to 2009, possibly due to lower PAR and chlorophyll levels, reflecting reduced photosynthetic activity and phytoplankton availability. Regardless, in 2010, resource provisioning to egg production was greater than in 2009, suggesting increased reproductive effort in the face of environmental stress. This study demonstrates the strong influence of opportunistic heterotrophy and autotrophy and maternal provisioning on the coral lipid profile. Such information is fundamental to understanding the environmental and biochemical processes underlying coral health and predicting how anomalous events and climate-driven changes will affect coral reef assemblages.

Photosynthetically active radiation impacts significantly on root and cell hydraulics in barley (Hordeum vulgare L.).

Photosynthetically active radiation (PAR) affects transpirational water loss, yet we do not know through which mechanisms root water uptake is adjusted in parallel. Here, we exposed hydroponically grown barley plants to three levels of PAR [Normal (control), Low, High] and focused on the role which aquaporins (AQPs), apoplastic barriers (Casparian bands, suberin lamellae) and root morphology play in the adjustment of root hydraulic conductivity (Lp). Plants were analyzed when they were 14-18 days (d) old. Root and cell Lp, which involves AQP activity, was determined through exudation and cell pressure probe measurements, respectively. Gene expression of AQPs was analyzed through qPCR. The formation of apoplastic barriers was studied through staining of cross-sections. The rate of transpirational water loss per plant and unit leaf area increased in response to high-PAR and decreased in response to low-PAR treatments, both during day and night. Hydraulic conductivity in roots decreased significantly at organ and cell level in response to Low-PAR, and increased (organ) or did not change (cell level) in response to High-PAR. The formation of apoplastic barriers was little affected by PAR. Gene expression of AQPs tended to be highest in the Low-PAR treatment. Lateral roots, showing few apoplastic barriers, contributed the least in Low- and the most to root surface area in High-PAR plants. It is concluded that barley plants which experience changes in shoot transpirational water loss in response to PAR adjust root water uptake through changes in root Lp, and that these changes are mediated through altered AQP activity and root morphology.