High Photosynthetically Active Radiation Research Articles

Empirical analysis of the influence of vegetation photosynthetic productivity on negative air ions in forest ecosystems driven by solar radiation

Air pollution stands as the single largest environmental risk to human health globally, and negative air ions (NAIs) serve as essential indicators for measuring regional air quality. They play a crucial role in alleviating the pressure and risks posed by air pollution. NAIs are notably abundant in forests, where the photosynthesis of vegetation serves as a significant factor influencing their presence. However, a dearth of quantitative research exists regarding the relationship between vegetation photosynthesis and NAIs. Current literature only offers qualitative insights, suggesting that vegetation photosynthesis may foster NAIs production. The mechanisms through which the photosynthetic process influences NAIs and the potential contribution of forest vegetation to NAIs remain unclear, lacking quantitative investigation. In this study, Quercus variabilis, a typical tree species in the warm temperate zone, was chosen as the research subject. We examined the dynamic changes in NAIs and net ecosystem productivity (NEP) from 2019 to 2021. The results demonstrated a strong correlation between NAIs and NEP at the ecosystem scale during the primary vegetation growing season. NEP effectively tracked daily changes in NAIs and exhibited a good fit. Notably, the scatter plots of NAIs and NEP exhibited clear stratification under varying photosynthetically active radiation (PAR) intensities. The correlation between NAIs and NEP was significantly higher under high PAR conditions compared to low PAR conditions, with R2 values of 0.458 and 0.367, respectively. Consequently, NEP emerges as a superior indicator for tracking NAIs variation characteristics at the ecosystem scale compared to PAR. This finding offers a rapid and accurate evaluation method for discerning the spatial and temporal distribution patterns of NAIs within forest ecosystems. Such insights provide a theoretical foundation for further assessing the potential contribution of forest vegetation to NAIs.

Morphological and Pigment Responses to Far-Red and Photosynthetically Active Radiation in an Olive Cultivar Suitable for Super-High-Density Orchards.

Plant density is increasing in modern olive orchards to improve yields and facilitate mechanical harvesting. However, greater density can reduce light quantity and modify its quality. The objective was to evaluate plant morphology, biomass, and photosynthetic pigments under different red/far-red ratios and photosynthetically active radiation (PAR) combinations in an olive cultivar common to super-high-density orchards. In a greenhouse, young olive trees (cv. Arbequina) were exposed to low (L) or high (H) PAR with or without lateral FR supplementation (L+FR, L-FR, H+FR, H-FR) using neutral-density shade cloth and FR light-emitting diode (LED) modules. Total plant and individual organ biomass were much lower in plants under low PAR than under high PAR, with no response to +FR supplementation. In contrast, several plant morphological traits, such as main stem elongation, individual leaf area, and leaf angle, did respond to both low PAR and +FR. Total chlorophyll content decreased with +FR when PAR was low, but not when PAR was high (i.e., a significant FR*PAR interaction). When evaluating numerous plant traits together, a greater response to +FR under low PAR than under high PAR appeared to occur. These findings suggest that consideration of light quality in addition to quantity facilitates a fuller understanding of olive tree responses to a light environment. The +FR responses found here could lead to changes in hedgerow architecture and light distribution within the hedgerow.

Daily variations on photosynthesis, pigmentation and photoprotection of Plocamium cartilagineum (Plocamiaceae, Rhodophyta)

ABSTRACT Field studies are a useful tool to understanding how seaweeds develop protective mechanisms against environmental variation and acclimate to them. These mechanisms can include morphological changes, inhibition of electron transportation rate, pigments and UV-absorbing compounds production. The present paper evaluates the daily cycle of photosynthesis and biochemistry of Plocamium cartilagineum from Spain under varying radiation and temperature conditions. For this purpose, four sites were chosen at La Herradura beach, Spain. Photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) were measured in situ at the sites, and ETR in situ (electron transport rate) as an estimator of photosynthetic capacity was determined. Algal thalli from each site were sampled throughout the day at 09:30, 11:00, 13:00, 15:30, 17:00, 19:30 h, to quantify photosynthetic pigments, UV-photoprotective compounds (i.e. mycosporine-like amino acids, MAAs), and antioxidant capacity. Higher irradiance and temperature at two sites directly influenced ETR in situ . Algae from the site with highest PAR and UV radiation had dynamic photoinhibition when compared to algae from a more shaded site during certain periods of the day. Lower pigment concentrations were observed in algae that received higher irradiances, suggesting photoacclimation. Samples found at the site exposed to the highest ultraviolet-A radiation had the highest concentrations of mycosporine-like amino acids between 15:30 h and 19:30 h. MAAs proportion varied among the sites and during the day. We conclude that environmental conditions in the short-term influenced photosynthetic parameters and the accumulation of pigments and MAAs in P. cartilagineum showing its high physiological plasticity.

UV-A and UV-B combined with photosynthetically active radiation change plant growth, antioxidant capacity and essential oil composition of Pelargonium graveolens

BackgroundThe different wavelengths of solar radiation incident on earth [herein: Photosynthetically Active Radiation (PAR) , Ultra Violet-A (UV-A) and Ultra Violet-B (UV-B)] and their spectral balance not only have an impact on plants’ growth, morphology and physiology, but also are important for the quality and quantity of plant secondary metabolites.Material and methodsIn an outdoor study we addressed the effects of PAR intensity and UV-A and UV-B on the growth, yield, phenolic and flavonoid content, antioxidant activity and essential oil composition of Pelargonium graveolens L’Hér. The experiment was performed with split plots in a randomized complete block design with three replications. During the growth, two PAR intensities (ambient PAR and reduced PAR) and four UV treatments (ambient UV, enhanced UV-A, enhanced UV-B and enhanced UVA + B) were applied.ResultsHigh PAR intensity decreased the length and width of leaf, the height of plant and fresh weight of aerial parts, and increased the dry weight of aerial parts. Enhanced UV-B irradiation was associated with reduced plant height, leaf expansion and fresh and dry weight of aerial parts. Interestingly, the negative effect of UV-B radiation on morphology and growth of plant was largely alleviated by high PAR intensity. The amount of total phenols and flavonoids, antioxidant activity and essential oil production of P. graveolens strongly increased with the increase of UV-B irradiation and PAR. On the other hand, UV-A radiation did not significantly influence total phenol and flavonoid content, antioxidant activity and essential oil composition. Moreover, the combination of high PAR intensity and UV-B led to further increases in total flavonoid content and antioxidant capacity. Both high PAR intensity and enhanced UV-B increased the percentage of geraniol in essential oil, leading to a slight reduction of citronellol/geraniol ratio which is a marker of quality for rose geranium essential oil.ConclusionsOverall, we conclude that UV-B irradiation was associated to reduction of plant growth and yield, while, the adverse effect of UV-B irradiation on the plant was mitigated by high PAR intensity. On the other hand, both high PAR and enhanced UV-B boosted the production of phenols, flavonoids and essential oil. Considering that the lower citronellol/geraniol ratio is the most important indicator for the economic value of rose geranium essential oil, reducing citronellol/geraniol ratio under enhanced UV-B radiation and/or high PAR is likely to be favorable.

Compensation of adverse growing media effects on plant growth and morphology by supplemental LED lighting.

There is an increasing interest in alternatives to peat in growing media due to environmental constraints. However, plants grown in peat substitutes often show impaired growth compared to plants grown in peat-based media. Hence, it would be interesting to know whether these deficiencies can be compensated by supplementing other growth factors, e.g. light. The present study aims to investigate the interactive nature between growing media and supplemental lighting on plant growth and morphology, and to examine whether supplemental light emitting diode (LED) lighting may compensate adverse growing media effects. Basil (Ocimum basilicum L.) and Chinese cabbage (Brassica rapa subsp. pekinensis) were grown in different growing media consisting of peat, green compost, coconut pulp, wood fibre, perlite and sphagnum moss under blue, red and far-red supplemental LED lighting. We found significant interactions between growing media and supplemental photosynthetically active radiation (PAR) on plant growth, morphology and development. At low light intensities, peat-based and substituted growing media performed similarly, whereas with increasing light intensities the peat-based growing media significantly outperformed their alternatives. The substrate choice determines the required amount of supplemental light to compensate for adverse growing media effects and the amount varies depending on plant species and season. Thereby, it was indicated that red light alleviates adverse growing media effects best. We also found that far-red light is not effective when background PAR is low and becomes more effective under high background PAR. The implications and prospects of the results are discussed.

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.

Underwater light attenuation inhibits native submerged plants and facilitates the invasive co‐occurring plant Cabomba caroliniana

AbstractAimDecreasing in the diversity and distribution of native submerged plants have been widely observed in recent decades. Global underwater darkening, which is mainly caused by radiation dimming and a decrease in transparency due to, e.g. eutrophication, has emerged as a general trend that strongly hampers the growth of submerged plants in lakes by decreasing the light available for photosynthesis. However, few studies have attempted to compare the responses of native and invasive submerged plants to underwater darkening. In this study, we aimed to compare the effects of light attenuation on the growth and photosynthesis traits of native and invasive submerged plants.LocationEast China.MethodThrough field investigations and a mesocosm experiment, the responses of functional traits of two representative native [water thyme (Hydrilla verticillata), Eurasian watermilfoil (Myriophyllum spicatum)] and one invasive [Carolina fanwort (Cabomba caroliniana)] plant species to various environmental factors, notably to underwater light attenuation, were studied.ResultsUnderwater photosynthetically active radiation (PAR) exerted a substantial effect on the relative coverage and abundance of the three studied submerged plants in their natural freshwater habitats. Invasive C. caroliniana showed relatively superior growth (total biomass and relative growth rate) and photosynthesis traits (maximum quantum yield of photosystem II Fv/Fm, chlorophyll a content, chlorophyll b content and the ratio of Chl a and b contents) compared to the two native plants under low underwater PAR conditions. In contrast, under high underwater PAR conditions, C. caroliniana showed the opposite response.Main ConclusionsLight attenuation inhibits the growth of native submerged plants but facilitates the growth of invasive plant species. Restoration of freshwater lakes by reducing deterioration from underwater darkening (for instance, by reducing of external nutrients loading) may therefore constrain the growth and spread of the invasive C. caroliniana.

Solar radiation, temperature and the reproductive biology of the coral Lobactis scutaria in a changing climate

Coral reefs worldwide are at risk due to climate change. Coral bleaching is becoming increasingly common and corals that survive bleaching events can suffer from temporary reproductive failure for several years. While water temperature is a key driver in causing coral bleaching, other environmental factors are involved, such as solar radiation. We investigated the individual and combined effects of temperature, photosynthetically active radiation (PAR), and ultraviolet radiation (UVR) on the spawning patterns and reproductive physiology of the Hawaiian mushroom coral Lobactis scutaria, using long-term experiments in aquaria. We examined effects on spawning timing, fertilisation success, and gamete physiology. Both warmer temperatures and filtering UVR altered the timing of spawning. Warmer temperatures caused a drop in fertilisation success. Warmer temperatures and higher PAR both negatively affected sperm and egg physiology. These results are concerning for the mushroom coral L. scutaria and similar reproductive data are urgently needed to predict future reproductive trends in other species. Nonetheless, thermal stress from global climate change will need to be adequately addressed to ensure the survival of reef-building corals in their natural environment throughout the next century and beyond. Until then, reproduction is likely to be increasingly impaired in a growing number of coral species.

Elevated CO2 modulates the physiological responses of Thalassiosira pseudonana to ultraviolet radiation.

Diatoms account for a large proportion of marine primary productivity, they tend to be the predominant species in the phytoplankton communities in the surface ocean with frequent and large light fluctuations. To understand the impacts of increased CO2 on diatoms' capacity in exploitation of variable solar radiation, we cultured a model diatom Thalassiosira pseudonana with 400 or 1000ppmv CO2 and exposed it to high photosynthetically active radiation (PAR) alone or PAR plus ultraviolet radiation (UVR) to examine its physiological performances. The results showed that the maximum photochemical efficiency (Fv/fm) was significantly reduced by high PAR and PAR+UVR in T. pseudonana, UVR-induced inhibition on PSII activity was exacerbated by high CO2. PSII activity drops coincide approximately with PsbA content in the cells exposed to high PAR or PAR+UVR, which was pronounced at high CO2. The removal of PsbD in T. pseudonana cells declined under high CO2 during UVR exposure, limiting the repair capacity of PSII. In addition, high CO2 reversed the induction of energy-dependent form of NPQ by UVR to the increase of Y(No), indicating the severe damage of the photoprotective reactions. Our findings suggest that the adverse impacts of UVR on PSII function of T. pseudonana were aggravated by the elevated CO2 through modulating its capacity in repair and protection, which thereby would influence its abundance and competitiveness in phytoplankton communities.

Management and landscape of shelterbelts contribute to butterfly and flowering plant diversity in northern Japan

AbstractA considerably large number of shelterbelts were established in Japan to increase crop yields in agricultural landscapes. Shelterbelt landscapes have multiple functions; they not only help to control wind damage but also to conserve biodiversity, including forest and grassland species. However, previous studies on biodiversity conservation in shelterbelts, and the target taxa were limited since this aspect of shelterbelts has not received much attention in Japan. This study examines the effects of shelterbelts and their regeneration on the diversity of butterflies and flowering plants in the Tokachi region of Hokkaido, Japan. Using a transect method, we compared environmental factors, butterfly, and flowering plant diversity in four habitats: inside forest, forest edge, regeneration sites, and semi‐natural grasslands which include shelterbelts and surrounding landscapes. There were significant differences in photosynthetically active radiation (PAR) among habitats, with higher PAR corresponding to higher numbers of butterfly species and individuals, and flowering plant species and flowers. Nonmetric multidimensional scaling results also showed that the species composition of flowering plants and butterflies differed among habitats. In addition, indicator value analysis showed that semi‐natural grasslands and regeneration sites were characterized by endangered butterflies and their host plants. Our results indicated that shelterbelt regeneration and the surrounding environment (e.g., semi‐natural grasslands) contributed to the diversity of butterflies and flowering plants, including endangered species. Future studies evaluating the diversity of various taxa would provide a more comprehensive understanding of the effects of shelterbelts on biodiversity conservation.

Hydrogen Peroxide Variation Patterns as Abiotic Stress Responses of Egeria densa.

In vegetation management, understanding the condition of submerged plants is usually based on long-term growth monitoring. Reactive oxygen species (ROS) accumulate in organelles under environmental stress and are highly likely to be indicators of a plant’s condition. However, this depends on the period of exposure to environmental stress, as environmental conditions are always changing in nature. Hydrogen peroxide (H2O2) is the most common ROS in organelles. The responses of submerged macrophytes, Egeria densa, to high light and iron (Fe) stressors were investigated by both laboratory experiments and natural river observation. Plants were incubated with combinations of 30–200 μmol m–2 s–1 of photosynthetically active radiation (PAR) intensity and 0–10 mg L–1 Fe concentration in the media. We have measured H2O2, photosynthetic pigment concentrations, chlorophyll a (Chl-a), chlorophyll b (Chl-b), carotenoid (CAR), Indole-3-acetic acid (IAA) concentrations of leaf tissues, the antioxidant activity of catalase (CAT), ascorbic peroxidase (APX), peroxidase (POD), the maximal quantum yield of PSII (Fv Fm–1), and the shoot growth rate (SGR). The H2O2 concentration gradually increased with Fe concentration in the media, except at very low concentrations and at an increased PAR intensity. However, with extremely high PAR or Fe concentrations, first the chlorophyll contents and then the H2O2 concentration prominently declined, followed by SGR, the maximal quantum yield of PSII (Fv Fm–1), and antioxidant activities. With an increasing Fe concentration in the substrate, the CAT and APX antioxidant levels decreased, which led to an increase in H2O2 accumulation in the plant tissues. Moreover, increased POD activity was proportionate to H2O2 accumulation, suggesting the low-Fe independent nature of POD. Diurnally, H2O2 concentration varies following the PAR variation. However, the CAT and APX antioxidant activities were delayed, which increased the H2O2 concentration level in the afternoon compared with the level in morning for the same PAR intensities. Similar trends were also obtained for the natural river samples where relatively low light intensity was preferable for growth. Together with our previous findings on macrophyte stress responses, these results indicate that H2O2 concentration is a good indicator of environmental stressors and could be used instead of long-term growth monitoring in macrophyte management.

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.

利用叶片荧光参数估算油蒿灌丛群落生态系统生产力

PDF HTML阅读 XML下载 导出引用 引用提醒 利用叶片荧光参数估算油蒿灌丛群落生态系统生产力 DOI: 10.5846/stxb202103210750 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（32071842，31901366，32071843） Estimating ecosystem productivity from leaf chlorophyll fluorescence parameter in Artemisia ordosica shrub community Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:生态系统生产力（GEP）在全球碳循环中具有重要意义，但其准确估算仍然是一个挑战。近年来，叶绿素荧光和冠层GEP的关联成为生态学的研究热点，关系尚不清楚且存在广泛争议。于2015年对宁夏盐池毛乌素沙地荒漠灌木油蒿（Artemisia ordosica）灌丛生态系统碳交换（NEE）特征进行连续观测，使用多通道荧光监测仪对通量贡献区内油蒿叶片的实时荧光（Fs）和光下荧光（Fm'）进行原位连续监测，叶面积指数（LAI）、归一化植被指数（NDVI）以及环境因子同步观测。利用光合有效辐射（PAR）、LAI和实际光化学效率（ΦPSII）等参数构建基于叶绿素荧光的生态系统生产力（GEPChlF）模型，探究叶片和冠层尺度不同参数对环境因子波动的响应，比较分析GEPChlF和基于涡度相关法监测生态系统生产力（GEPEC）相关性及GEPChlF的适用性。研究发现，ΦPSII和NEE日变化规律一致，ΦPSII、GEPChlF和GEPEC由PAR控制，受空气温度（Ta）和饱和水汽压差（VPD）调控，土壤含水量（SWC）和ΦPSII呈显著正相关（P<0.01）。PAR处于400-800 μmol m-2 s-1时，GEPChlF与GEPEC线性关系最优，斜率为0.627（R2=0.67，P<0.01）；弱光下GEPChlF的低估可能是由于冠层实际光能拦截率高造成；强光下GEPChlF显著高于GEPEC，呈非线性关系，可能是GEPEC基于夜间温度敏感性所拟合的生态系统呼吸（Re）无法预测光呼吸部分所导致。GEPChlF具有荧光参数的特性，对环境波动更加敏感，和环境因子相关性优于GEPEC。结果表明，高辐射、极端温度、高蒸腾和干旱是限制叶片和冠层尺度下油蒿光合过程的主要胁迫因素。本研究构建的荒漠生态系统光合过程模型GEPChlF能够替代GEPEC作为一个良好的冠层尺度生态参数，所提出的空间尺度上推方法可为促进区域可持续发展提供数据支撑和决策参考。 Abstract:Accurate estimation of gross ecosystem productivity (GEP) remains a challenge despite its importance in the global carbon cycle. Recently, the relationship between chlorophyll fluorescence and canopy GEP becomes an important scientific concern in plant ecology. However, it remains unclear how they are linked at multiple spatial scales across the growing season. In this study, continuous measurements of net ecosystem CO2 exchange (NEE) were made in a desert shrub (Artemisia ordosica) ecosystem using eddy covariance (EC) technique from May to October 2015 in Mu Us desert. The real-time fluorescence (Fs) and fluorescence under light (Fm') were also measured in situ using the Monitoring-PAM multi-channel fluorometer. Leaf area index (LAI), the normalized difference vegetation index (NDVI), and environmental factors including photosynthetically active radiation (PAR), air temperature (Ta), vapor pressure deficit (VPD), soil water content (SWC) and precipitation (PPT) were measured simultaneously within the range of carbon flux contribution. We developed a chlorophyll fluorescence-based model with input variables of photochemical efficiency (ΦPSII), PAR, and LAI to estimate ecosystem productivity (GEPChlF). We then compared the applicability of GEPChlF with EC-based GEP (GEPEC) and examined the responses of different parameters to environmental factors at leaf and canopy scales. As a result, the diurnal pattern of ΦPSII was similar to that of NEE, being mainly controlled by PAR and modified positively by Ta and VPD (P<0.01). The ΦPSII had a significantly positive correlation with SWC (P<0.01). The GEPChlF agreed well with GEPEC when PAR was 400-800 μmol m-2 s-1, with a slope of 0.627 (R2=0.67, P<0.01). The GEPChlF was likely to be underestimated under low PAR, leading to a high light interception rate of canopy, thus resulting in a low absorbed photosynthetically active radiation (APAR) in the model. The GEPChlF was significantly higher than GEPEC under high PAR and their relationship was nonlinear, which may be due to Artemisia ordosica released excessive sunlight energy for photo-respiration, nitrogen metabolism, Miller reaction and other processes. It was noted that photo-respiration was difficult to predict accurately because the daytime ecosystem respiration (Re) was simulated on the basis of nocturnal temperature sensitivity. Compared with GEPEC, chlorophyll fluorescence-derived GEPChlF was more sensitive to environmental fluctuations and had a better relation with environmental factors. Our results confirmed that the GEPChlF from chlorophyll fluorescence-based model could replace GEPEC as a good ecological parameter at canopy scale in consideration of the plant physiological status. We found that excessive radiation, extreme temperature, high transpiration and drought were the main stress factors limiting the photosynthetic process of Artemisia ordosica at different spatial scales. The study provides a method for estimating ecosystem productivity under the stressed environmental conditions on the basis of monitoring chlorophyll fluorescence in relation to environmental factors. The present results may scientifically support decision-making for promoting regional sustainable development. 参考文献 相似文献 引证文献

A comparison of physiological responses between attached and pelagic populations of Sargassum horneri under nutrient and light limitation

Large-scale Sargassum blooms have been increasingly observed in coastal zones in recent years. Sargassum horneri (Turner) C. Agardh blooms (pelagic) have been observed in Jeju Island (Korea) and the southwest of the Korean Peninsula, causing serious problems for seaweed and abalone farms as well as for fisheries, tourism and recreational industries. The present study explored the physiological responses of attached and pelagic S. horneri populations cultivated under different nutrient concentrations (HN: 50 μM of nitrogen and 5 μM of phosphorus; LN: 5 μM of nitrogen and 0.5 μM of phosphorus) and photosynthetically active radiation (PAR) (H-PAR: 250; M-PAR: 150; L-PAR: 50 μmol photons m−2 s−1) for 25 days. Relative growth rates (RGR) were significantly lower in the pelagic population than that in the attached population. All thalli from the pelagic population died within 20 days. Chlorophyll a and c, and carotenoids were significantly higher at HN than at LN, and decreased as PAR increased for both populations. For the attached population, photosynthetic rate, tissue nitrogen, and carbon and nitrogen removal were also significantly higher at HN than at LN. These results suggest that high nutrient and lower PAR increased the biomass accumulation of attached populations in coastal areas. Nutrient limitation and high PAR may accelerate senescence of the pelagic populations while traveling on the sea surface from their point of origin.

Upwelling Irradiance below Sea Ice—PAR Intensities and Spectral Distributions

Upwelling and downwelling spectral (320–920 nm) distributions and photosynthetic active radiation (PAR) intensities were measured below a first-year land-fast sea ice in a western Greenland fjord with and without a snow cover. Time-series of surface upwelling PAR, downwelling PAR, and under-ice PAR were also obtained. Spectral distributions of upwelling and downwelling irradiances were similar except for reduced intensities in the UV, the red, and NIR parts of the spectrum when the ice was snow-covered. Upwelling PAR amounted to about 10% of downwelling intensities, giving 5.1 µmol photons m−2 s−1 at the bottom of the ice with a snow cover and 8.2 µmol photons m−2 s−1 without. PAR partitioning analyses showed that the upwelling was related to scattering by suspended particles in the water column. A snow melt increased under-ice daily maximum downwelling PAR from 50 to 180 µmol photons m−2 s−1 and overall under-ice PAR of 55 and 198 µmol photons m−2 s−1 with 10% upwelling. It is concluded that upwelling PAR below sea ice might be an important factor regarding sea ice algae photophysiology and performance with a 10% higher PAR; specifically when PAR &gt; Ek the light saturation point of the sea ice algae.

Grapevine morphological shade acclimation is mediated by light quality whereas hydraulic shade acclimation is mediated by light intensity

Plants acclimate to shade by sensing light signals such as low photosynthetic active radiation (PAR), low blue light (BL) levels and low red-to-far red ratios (R:FR) trough plant photoreceptors cross talk. We previously demonstrated that grapevine is irresponsive to variations in R:FR and that BL-attenuation mediates morphological and architectural responses to shade increasing light interception and absorption efficiencies. However, we wondered if grapevine respond to low R:FR when BL is attenuated at the same time. Our objective was to evaluate if morphological, architectural and hydraulic acclimation to shade is mediated by low R:FR ratios and BL attenuation. To test this, we carried out experiments under natural radiation, manipulating light quality by selective sunlight exclusion and light supplementation. We grew grapevines under low PAR (LP) and four high PAR (HP) treatments: HP, HP plus FR supplementation (HP + FR), HP with BL attenuation (HP–B) and HP with BL attenuation plus FR supplementation (HP–B + FR). We found that plants grown under HP-B and HP-B + FR had similar morphological (stem and petiole length, leaf thickness and area), architectural (laminae’ angles) and anatomical (stomatal density) traits than plants grown under LP. However, only LP plants presented lower stomata differentiation, lower δ13C and hence lower water use efficiency. Therefore, even under a BL and R:FR attenuated environment, morphological and architectural responses were modulated by BL but not by variation in R:FR. Meanwhile water relations were affected by PAR intensity but not by changes in light quality. Knowing grapevine responses to light quantity and quality are indispensable to adopt tools or design new cultural management practices that manipulate irradiance in the field intending to improve crop performance.

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.

Long-term straw incorporation increases rice yield stability under high fertilization level conditions in the rice–wheat system

Straw incorporation is a global common practice to improve soil fertility and rice yield. However, the effect of straw incorporation on rice yield stability is still unknown, especially under high fertilization level conditions. Here, we reported the effect of straw returning on rice yield and yield stability under high fertilization levels in the rice–wheat system over nine years. The results showed that straw incorporation did not significantly affect the average rice yield of nine years. Straw incorporation reduced the coefficient of variation of rice yield by 25.8% and increased the sustainable yield index by 8.2%. The rice yield positively correlated with mean photosynthetically active radiation (PAR) of rice growth season and the effects of straw incorporation on rice yield depended on the PAR. Straw incorporation increased the rice yield by 5.4% in the low PAR years, whereas it did not affect the rice yield in the high PAR years. Long-term straw incorporation lowered soil bulk density but improved the soil organic matter, total N, available N, available P, and available K more strongly than straw removal. Our findings suggest that straw incorporation can increase rice yield stability through improving the resistance of rice plant growth to low PAR.

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.

Shady business: the darkening of estuaries constrains benthic ecosystem function

Coastal intertidal soft-sediment habitats provide ecosystem services to millions of people worldwide, yet are under intense pressure from land-use change and sea-level rise (SLR). Both pressures interact to reduce light reaching the seafloor, thereby disrupting benthic primary producers and the ecosystem functions and services they provide. This study considers the implications of altered light climate on microphytobenthic (MPB) production in shallow estuaries. Continuous measurements of seafloor photosynthetically active radiation (PAR) were made over 9 mo on intertidal sandflats in 14 New Zealand estuaries spanning a turbidity gradient. A literature summary of benthic photosynthesis-irradiance curves was used to predict PAR limitation at sampling sites. Estimates of the proportion of time MPB would be light limited during emersion ranged from a median of 32-64% compared to a median of 55-100% during immersion. For estuaries close to 100% PAR limitation during immersion, emerged intertidal areas represent a refuge for MPB production which is vulnerable to SLR. Based on hypsometric curves (a representation of estuary bathymetry), the intertidal area of our study estuaries is predicted to decrease by 27-94% in response to SLR of 1.4 m. The combination of high PAR limitation during immersion and large losses of intertidal area will increase vulnerability to the loss of MPB production and the associated ecosystem services, which will push these ecosystems towards tipping points. The research highlights how the interplay between local and global scale stressors may ultimately trigger ecological collapse under future global change.