Photophysiological Characteristics Research Articles

A mesophilic relative of common glacier algae, Ancylonema palustre sp. nov., provides insights into the induction of vacuolar pigments in zygnematophytes.

The green algae of the genus Ancylonema, which belong to the zygnematophytes, are prevalent colonizers of glaciers worldwide. They display a striking reddish-brown pigmentation in their natural environment, due to vacuolar compounds related to gallic acid. This pigmentation causes glacier darkening when these algae bloom, leading to increased melting rates. The Ancylonema species known so far are true psychrophiles, which hinders experimental work and limits our understanding of these algae. For instance, the biosynthesis, triggering factors, and biological function of Ancylonema's secondary pigments remain unknown. In this study, we introduce a mesophilic Ancylonema species, A. palustre sp. nov., from temperate moorlands. This species forms the sister lineage to all known psychrophilic strains. Despite its morphological similarity to the latter, it exhibits unique autecological and photophysiological characteristics. It allows us to describe vegetative and sexual cellular processes in great detail. We also conducted experimental tests for abiotic factors that induce the secondary pigments of zygnematophytes. We found that low nutrient conditions combined with ultraviolet B radiation result in vacuolar pigmentation, suggesting a sunscreen function. Our thriving, bacteria-free cultures of Ancylonema palustre will enable comparative genomic studies of mesophilic and extremophilic zygnematophytes. These studies may provide insights into how Ancylonema species colonized the world's glaciers.

Photophysiological Characterization of Phytoplankton by Measuring Pigment Production Rates: A Description of Detail Method and a Case Study

Each phytoplankton species has intrinsic pigments, which result in different photophysiological characteristics in response to natural light conditions. Therefore, phytoplankton pigments provide important information on the photosynthetic activity that produces the basic food source for marine ecosystems. This study addresses the challenge of accurately measuring pigment production rates in phytoplankton communities. Two strategies are proposed for improving measurement sensitivity. Firstly, increasing the injection of 13C substrate into incubation bottles up to 15% of the total dissolved inorganic carbon is recommended, with minimal impact on pigment production rate determinations. Secondly, optimizing sample injection volume for high-performance liquid chromatography balances analysis time and dilution effects. The in situ field experiments conducted in this study for pigment production measurements revealed diminished activity of photoprotective mechanisms involving zeaxanthin and diatoxanthin during the study period. Furthermore, the results showed that the notable production rates of chl-b (0.069–0.105 ng C L–1 h–1, 74–89% of total accessary pigment production rates), an accessory pigment mainly attributed to prasinophytes, potentially due to restricted light availability. Prioritization of chl-b production over primary production (negative correlation between primary and chl-b production; R2 = 0.6662) highlights the potential impact of compensatory pigment-related activities on overall phytoplankton productivity. In conclusion, this study underscores the significance of directly quantifying pigment production rates to enhance our comprehension of phytoplankton photophysiology and the production mechanisms specific to various pigments.

The interacting effect of prolonged darkness and temperature on photophysiological characteristics of three Antarctic phytoplankton species.

Photophysiological characteristics of the Southern Ocean phytoplankton species Phaeocystis antarctica, Geminigera cryophila, and Chaetoceros simplex were assessed during 7 weeks of darkness and subsequent recovery after darkness at 4 and 7°C. Chlorophyll a fluorescence and maximum quantum efficiency of PSII decreased during long darkness in a species-specific manner, whereas chlorophyll a concentration remained mostly unchanged. Phaeocystis antarctica showed the strongest decline in photosynthetic fitness during darkness, which coincided with a reduced capacity to recover after darkness, suggesting a loss of functional photosystem II (PSII) reaction centers. The diatom C. simplex at 4°C showed the strongest capacity to resume photosynthesis and active growth during 7 weeks of darkness. In all species, the maintenance of photosynthetic fitness during darkness was clearly temperature dependent as shown by the stronger decline of photosynthetic fitness at 7°C compared to 4°C. Although we lack direct evidence for this, we suggest that temperature-enhanced respiration rates cause stronger depletion of energy reserves that subsequently interferes with the maintenance of photosynthetic fitness during long darkness. Therefore, the current low temperatures in the coastal Southern Ocean may aid the maintenance of photosynthetic fitness during the austral winter. Further experiments should examine to what extent the species-specific differences in dark survival are relevant for future temperature scenarios for the coastal Southern Ocean.

Photoinhibition of the Picophytoplankter Synechococcus Is Exacerbated by Ocean Acidification

The marine picocyanobacterium Synechococcus accounts for a major fraction of the primary production across the global oceans. However, knowledge of the responses of Synechococcus to changing pCO2 and light levels has been scarcely documented. Hence, we grew Synechococcus sp. CB0101 at two CO2 concentrations (ambient CO2 AC:410 μatm; high CO2 HC:1000 μatm) under various light levels between 25 and 800 μmol photons m−2 s−1 for 10–20 generations and found that the growth of Synechococcus strain CB0101 is strongly influenced by light intensity, peaking at 250 μmol m−2 s−1 and thereafter declined at higher light levels. Synechococcus cells showed a range of acclimation in their photophysiological characteristics, including changes in pigment content, optical absorption cross section, and light harvesting efficiency. Elevated pCO2 inhibited the growth of cells at light intensities close to or greater than saturation, with inhibition being greater under high light. Elevated pCO2 also reduced photosynthetic carbon fixation rates under high light but had smaller effects on the decrease in quantum yield and maximum relative electron transport rates observed under increasing light intensity. At the same time, the elevated pCO2 significantly decreased particulate organic carbon (POC) and particulate organic nitrogen (PON), particularly under low light. Ocean acidification, by increasing the inhibitory effects of high light, may affect the growth and competitiveness of Synechococcus in surface waters in the future scenario.

Spatial and temporal drivers of fluorescence quantum yield variability in the Southern Ocean

AbstractFluorescence quantum yield is a powerful tool for assessing phytoplankton photophysiology and photosynthetic efficiency, but there is a paucity of in situ studies. Here we present the first wavelength‐specific fluorescence quantum yield data from high spatial and temporal resolution real‐time measurements made in the Southern Ocean. This dataset represents both winter and summer conditions across a broad latitudinal range of the Atlantic and Indian South Ocean and the presented analysis assesses the potential influence of a range of physical, chemical, and biological drivers of variability. The results indicate that both light history and potential iron limitation play significant roles in constraining the magnitude of fluorescence quantum yield on a seasonal basis, with links to specific pigment composition of carotenoids involved in fluorescence quenching. Whereas community structure and associated pigment content play a strong role in dictating the spectral shape of fluorescence quantum yield both seasonally and spatially, with larger diatom‐dominated communities fluorescing more in the blue region of the spectrum and smaller phycoerythrin‐containing phytoplankton fluorescing more in the green‐orange region of the spectrum. This study provides a better understanding of the drivers of variability of in situ fluorescence quantum yield, which is useful for informing interpretations of studies based on remotely sensed signals, which are essential for investigating spatial and temporal variability in photophysiological characteristics on longer time scales.

Photophysiological Mechanism of Dense Planting to Increase the Grain Yield of Intercropped Maize with Nitrogen-Reduction Application in Arid Conditions

Leaf photophysiological characteristics are the main indexes that determine crop yield formation. However, it remains unclear whether photosynthesis is systematically regulated via the cropping pattern and nitrogen supply when maize crops are planted with a high density. So, a field experiment that had a three-factor split-plot arrangement of treatments was conducted from 2020 to 2021. The main plot was two cropping patterns that included the sole cropping of maize and wheat–maize intercropping. The split plot had two nitrogen application rates: a traditional nitrogen application rate (N2, 360 kg ha−1) and one reduced by 25% (N1, 270 kg ha−1) for maize. The split–split plot had three planting densities: a traditional density (M1, 78,000 plant ha−1), a medium density (M2, 10,400 plant ha−1), and a high density (M3, 129,000 plant ha−1) for sole maize; the corresponding densities of intercropped maize were 45,000, 60,000, and 75,000 plant ha−1, respectively. The grain yield, the photosynthetic traits, and chlorophyll a fluorescence of the maize were assessed. The results showed that a 25% nitrogen reduction and dense planting had a negative impact on the individual maize’s photosynthesis. However, intercropping could alleviate these drawbacks. When the maize was grown in the intercropping system at a lower nitrogen level and a medium planting density (IN1M2), the photosynthetic traits were better or similar to those of the traditional treatment (SN2M1) at the reproductive growth stage. Moreover, IN1M2 improved the light energy distribution among photochemistry, photo-protective and heat dissipation process of maize compared with SN2M1. A grey relation analysis demonstrated that the Pn and Tr of the individual maize played the most significant role in the group’s productivity. Thus, the IN1M2 treatment achieved the highest grain yield and can be recommended as a feasible agronomic practice in oasis-irrigated regions.

Yield, Flower Quality, and Photo-Physiological Responses of Cut Rose Flowers Grafted onto Three Different Rootstocks in Summer Season

The thermal stress caused by high temperatures on cut rose flowers grown in greenhouses is a major environmental impact that reduces the yield of growing cut rose flowers during summer. To confirm the resistance of grafted cut rose flowers to high-temperature stress, roses were grown in a greenhouse during the summer season and analyzed for yield, quality, root activity, and photo-physiological characteristics. A morphological change was observed in the stomata of the grafted cut rose flowers, which were larger in size than the scion or rootstocks. As a result of cultivating cut rose flowers by lowering the temperature of the greenhouse through shading in summer, it was confirmed that all of the scions, rootstocks, and grafted cut rose flowers were not in a stressed state by observing the maximal quantum yield of primary photochemistry (FV/FM) values on the chlorophyll-a fluorescence. However, the rate of electron transport flux from the primary acceptor (QA) to the secondary acceptor (QB) per the photosystem II reaction center (ET0/RC) value was found to be significantly higher on grafted cut rose flowers, compared with that of the scions. The efficiencies of the photosynthesis rate, the transpiration rate, and the stomatal conductance were increased when grafted compared with non-grafted. When the root activity was confirmed by the formazan content, it was found that the root activity was improved grafting. Furthermore, when grafted, morphological changes such as flower size and the number of petals on spray roses were also observed. Although there was a difference depending on the type of rootstock, the yield of the grafted cut rose flowers increased by 11–20%, compared with the scion rose. Therefore, grafting cultivation during the summer season with high temperatures is an effective method in terms of photo-physiological response and yield.

Cultivation and Photophysiological Characteristics of Desmids in Moderately Saline Aquaculture Wastewater

Although desmids typically inhabit freshwater environments characterized by low amounts of nutrients and low salinity, several desmid species have been recorded in eutrophic waters, indicating their adaptation to elevated pollution and conductivity. This study aimed to determine whether desmids could be used for remediation of moderately saline aquaculture wastewater (AWW) from a fish farm situated in the southeast of Sweden. Fourteen desmid strains isolated from different climates (tropical to polar) and trophic conditions (oligo- to eutrophic) were cultivated in diluted AWW and we estimated their growth rates, biomass, nutrient removal efficiency, chlorophyll fluorescence parameters, and cellular C, N, and P quotas. Despite being grown at moderate salinity, unfavourable N:P ratio, and relatively low light/temperature regime the eutrophic strains, Cosmarium humile, C. laeve, and a meso-oligotrophic species C. impressulum, completely absorbed nitrate and phosphate from AWW media after 7 days, indicating their potential for remediation of fish effluents in colder climates. These species, along with the typical eutrophic species, C. meneghinii and Staurastrum chaetoceras, had biomass in the range 0.45 to 1.19 g · L-1 while maximum growth rates ranged from 0.36 - 0.51 · d-1 , similar to published rates for several fast-growing green microalgae cultivated in various AWW types. Tropical desmids had distinctly high values of saturating irradiance (Ik > 1000 µmol photons · m-2 · s-1 ), and, along with eutrophic desmids, had high potential electron transport (rETRmax > 155 rel. units). Hence, the desmids studied demonstrated inherent photophysiological responses corresponding to their climate and trophic origin under the suboptimal growth conditions.

Vertical structure in chlorophyll profiles: influence on primary production in the Arctic Ocean.

Subsurface chlorophyll maximum (SCM) layers are prevalent throughout the Arctic Ocean under stratified conditions and are observed both in the wake of retreating sea ice and in thermally stratified waters. The importance of these layers on the overall productivity of Arctic pelagic ecosystems has been a source of debate. In this study, we consider the three principal factors that govern productivity within SCMs: the shape of the chlorophyll profile, the photophysiological characteristics of phytoplankton and the availability of light in the layer. Using the information on the biological and optical parameters describing the vertical structure of chlorophyll, phytoplankton absorption and photosynthesis–irradiance response curves, a spectrally resolved model of primary production is used to identify the set of conditions under which SCMs are important contributors to water-column productivity. Sensitivity analysis revealed systematic errors in the estimation of primary production when the vertical distribution of chlorophyll was not taken into account, with estimates of water-column production using a non-uniform profile being up to 97% higher than those computed using a uniform one. The relative errors were shown to be functions of the parameters describing the shape of the biomass profile and the light available at the SCM to support photosynthesis. Given that SCM productivity is believed to be largely supported by new nutrients, it is likely that the relative contribution of SCMs to new production would be significantly higher than that to gross primary production. We discuss the biogeochemical and ecological implications of these findings and the potential role of new ocean sensors and autonomous underwater vehicles in furthering the study of SCMs in such highly heterogeneous and remote marine ecosystems.This article is part of the theme issue ‘The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.

Annual patterns in phytoplankton phenology in Antarctic coastal waters explained by environmental drivers

AbstractCoastal zones of Antarctica harbor rich but highly variable phytoplankton communities. The mechanisms that control the dynamics of these communities are not well defined. Here we elucidate the mechanisms that drive seasonal species succession, based on algal photophysiological characteristics and environmental factors. For this, phytoplankton community structure together with oceanographic parameters was studied over a 5‐year period (2012–2017) at Rothera Station at Ryder Bay (Western Antarctic Peninsula). Algal pigment patterns and photophysiological studies based on fluorescence analyses were combined with data from the Rothera Time‐Series program. Considerable interannual variation was observed, related to variations in wind‐mixing, ice cover and an El Niño event. Clear patterns in the succession of algal classes became manifest when combining the data collected over the five successive years. In spring, autotrophic flagellates with a high light affinity were the first to profit from increasing light and sea ice melt. These algae most likely originated from sea‐ice communities, stressing the role of sea ice as a seeding vector for the spring bloom. Diatoms became dominant towards summer in more stratified and warmer surface waters. These communities displayed significantly lower photoflexibility than spring communities. There are strong indications for mixotrophy in cryptophytes, which would explain much of their apparently random occurrence. Climate models predict continuing retreat of Antarctic sea‐ice during the course of this century. For the near‐future we predict that the marginal sea‐ice zone will still harbor significant communities of haptophytes and chlorophytes, whereas increasing temperatures will mainly be beneficial for diatoms.

Development of temperature-based algorithms for the estimation of microphytobenthic primary production in a tidal flat: A case study in Daebu mudflat, Korea

This study presents the results of field experiments that were designed to investigate the photophysiological characteristics of microphytobenthos (MPB) and to estimate primary production (PP) in Daebu mudflat, which is located at the west coast of Korea. A typical seasonal (or monthly) fluctuation of intertidal MPB PP was found in association with biotic (benthic Chl-a) and/or abiotic parameters (irradiance and temperature) over a period of three years. From a series of field-laboratory experiments using the oxygen micro-profiling method (totaling 28 surveys), three consistent phenomena were observed: 1) winter to early spring algal blooms, 2) seasonal changes in Q10, and 3) temperature dependent MPB photosynthesis-irradiance (P-I). In particular, both the chlorophyll-specific maximum photosynthetic capacity (Pbmax) and the saturated light intensity (Ik), derived from 126 P-I curves (1870 data sets of oxygen micro-profiling in the sediment), were significantly correlated with sediment temperature (p < 0.01). To develop an empirical MPB PP model, the relationships between P-I parameters and environmental variables were parameterized following established exponential forms (e.g., Q10). It was possible to estimate the MPB PP in Daebu mudflat area by using easily accessible explanatory factor, suitable to be used for future explorations of parameters such as sediment temperature, irradiance, chlorophyll concentration, and tidal height. The estimated annual MPB PP based on the empirical PP model were found to be greater than that in the Wadden Sea and average annual PP in the temperate zones of the world. Authors believe that the present approach of the MPB PP estimation could be combined with remote-sensing techniques (e.g., satellites) to support coastal ecosystem management.

Distribution of Phaeocystis antarctica-dominated sea ice algal communities and their potential to seed phytoplankton across the western Antarctic Peninsula in spring

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 586:91-112 (2018) - DOI: https://doi.org/10.3354/meps12367 Distribution of Phaeocystis antarctica-dominated sea ice algal communities and their potential to seed phytoplankton across the western Antarctic Peninsula in spring Virginia Selz1,*, Kate E. Lowry1, Kate M. Lewis1, Hannah L. Joy-Warren1, Willem van de Poll2, Sandip Nirmel1, Amy Tong1, Kevin R. Arrigo1 1Department of Earth System Science, Stanford University, Stanford, CA 94305, USA 2Department of Ocean Ecosystems, Energy and Sustainability Research Institute Groningen, University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands *Corresponding author: vselz@stanford.edu ABSTRACT: The western Antarctic Peninsula has experienced extreme changes in the timing of sea ice melt and freeze up, shortening the duration of the seasonal sea ice cycle. While previous research demonstrated connections between multiple pelagic trophic levels and the physics of the sea ice, few studies have assessed the sea ice ecosystem or its linkage to the ocean ecosystem in this region. Through a field survey and shipboard experiments, our study focused on characterizing the spring ice algal bloom and elucidating its role in seeding phytoplankton communities post-ice melt in high and low light conditions. Field data revealed that algal communities in slush layers, often formed from the flooding of seawater (infiltration layers), dominated biomass distributions in the sea ice throughout the region, and showed distinct photophysiological characteristics from interior or bottom ice communities. Sea ice algal biomass reached 120 mg chl a m-2 and was often dominated by Phaeocystis antarctica. Shipboard growth experiments showed that prior light history (ice or water column), rather than community composition (phytoplankton and ice algae were composed of similar taxa), primarily drove physiological responses to high and low light. P. antarctica generally dominated the community in growth experiments at the end of the 6 d incubation period. Settling column experiments suggested that P. antarctica’s higher sinking rates relative to other taxa may explain its minor contributions to the summer phytoplankton community in single-cell form and its absence in colonial form, observed in the long-term ecological record of this region. KEY WORDS: Photophysiology · Diatoms · Ice-ocean coupling · Community composition Full text in pdf format PreviousNextCite this article as: Selz V, Lowry KE, Lewis KM, Joy-Warren HL and others (2018) Distribution of Phaeocystis antarctica-dominated sea ice algal communities and their potential to seed phytoplankton across the western Antarctic Peninsula in spring. Mar Ecol Prog Ser 586:91-112. https://doi.org/10.3354/meps12367 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 586. Online publication date: January 11, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Phytoplankton blooms during austral summer in the Ross Sea, Antarctica: Driving factors and trophic implications.

During the austral summer of 2014, an oceanographic cruise was conducted in the Ross Sea in the framework of the RoME (Ross Sea Mesoscale Experiment) Project. Forty-three hydrological stations were sampled within three different areas: the northern Ross Sea (RoME 1), Terra Nova Bay (RoME 2), and the southern Ross Sea (RoME 3). The ecological and photophysiological characteristics of the phytoplankton were investigated (i.e., size structure, functional groups, PSII maximum quantum efficiency, photoprotective pigments), as related to hydrographic and chemical features. The aim was to identify the mechanisms that modulate phytoplankton blooms, and consequently, the fate of organic materials produced by the blooms. The observed biomass standing stocks were very high (e.g., integrated chlorophyll-a up to 371 mg m-2 in the top 100 m). Large differences in phytoplankton community composition, relative contribution of functional groups and photosynthetic parameters were observed among the three subsystems. The diatoms (in different physiological status) were the dominant taxa in RoME 1 and RoME 3; in RoME 1, a post-bloom phase was identified, whereas in RoME 3, an active phytoplankton bloom occurred. In RoME 2, diatoms co-occurred with Phaeocystis antarctica, but were vertically segregated by the upper mixed layer, with senescent diatoms dominating in the upper layer, and P. antarctica blooming in the deeper layer. The dominance of the phytoplankton micro-fraction over the whole area and the high Chl-a suggested the prevalence of non-grazed large cells, independent of the distribution of the two functional groups. These data emphasise the occurrence of significant temporal changes in the phytoplankton biomass in the Ross Sea during austral summer. The mechanisms that drive such changes and the fate of the carbon production are probably related to the variations in the limiting factors induced by the concurrent hydrological modifications to the Ross Sea, and they remain to be fully clarified. The comparison of conditions observed during summer 2014 and those reported for previous years reveal considerably different ecological assets that might be the result of current climate change. This suggests that further changes can be expected in the future, even at larger oceanic scales.

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

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

Effects of soil drought on photosynthetic traits and antioxidant enzyme activities in Hippophae rhamnoides seedlings

Water deficit is one of the major limiting factors in vegetation recovery and reconstruction in the semi-arid area of loess hilly regions. Leaf photosynthesis in Hippophae rhamnoides Linn., a common tree grown in this region, decreases under water stress, but the mechanism responsible is not clear. The objective of this study was to investigate the effects of drought stress on photosynthesis and the relationship between photosynthetic variables and soil water contents to help us better understand the photo-physiological characteristics of H. rhamnoides under water stress and guide cultivation in the loess hilly region. Here, gas exchange, chlorophyll fluorescence and antioxidant enzyme activity in leaves of 3-year-old saplings of H. rhamnoides grown in pots were tested under eight soil water conditions. When soil water content (RWC) was between 38.9 and 70.5 %, stomatal limitation was responsible for the reduced net photosynthetic rate (P N). When RWC was lower than 38.9 %, nonstomatal limitation was the main factor restricting P N. Moderate water stress improved the water use efficiency (WUE) of the leaf. Water stress significantly influenced fluorescence variables and the antioxidant enzyme system. When RWC was between 38.9 and 70.5 %, nonphotochemical quenching (NPQ) increased and then decreased, indicating that thermal energy dissipation was a significant photoprotection mechanism. Antioxidant enzymes were activated when RWC ranged from 48.3 to 70.5 %; under severe water stress (RWC < 38.9 %), the antioxidant enzyme system was damaged, the activity of the antioxidant enzymes declined, and membranes were damaged. In the semiarid loess hilly region, RWC between 58.6 and 70.5 % was the economic water threshold value that maintained higher WUE and P N, and the maximum soil water deficit level that could sustain H. rhamnoides was RWC of 38.9 %.

Depth-integrated and depth-resolved models of Kara Sea primary production

Primary production (PP) models of the Kara Sea are developed based on data collected on fall expeditions (September–October 1993, 2007, and 2011) and their precision assessment utilizes the dataset collected in September 2013. The algorithms for different model types (depth-integrated and depth-resolved) are compared. The depth-resolved model performs slightly better than the depth-integrated one (the rootmean- square-difference (RMSD) are 0.29 and 0.31, respectively). These algorithms utilize the daily assimilation number (DAN) and photosynthetic efficiency (ψ) as the model coefficients, and surface chlorophyll a (chl a) and photosynthetically active radiation (PAR) as input variables. These algorithms perform better than the models that use chl a alone. Our results suggest that an increase in the performance of the Kara Sea PP models depends on the input of the photophysiological characteristics of phytoplankton (DAN and ψ) and PAR. To a lesser extent, this concerns the advantages of the depth-resolved model over the depth-integrated one. The constructed region-specific Kara Sea PP models combined with satellite-derived chl a and PAR can be used to estimate annual values and long-term variation of PP in hydrologically and hydrochemically similar waters of the Arctic Ocean.

Contrasting Photophysiological Characteristics of Phytoplankton Assemblages in the Northern South China Sea.

The growth of phytoplankton and thus marine primary productivity depend on photophysiological performance of phytoplankton cells that respond to changing environmental conditions. The South China Sea (SCS) is the largest marginal sea of the western Pacific and plays important roles in modulating regional climate and carbon budget. However, little has been documented on photophysiological characteristics of phytoplankton in the SCS. For the first time, we investigated photophysiological characteristics of phytoplankton assemblages in the northern South China Sea (NSCS) using a real-time in-situ active chlorophyll a fluorometry, covering 4.0 × 105 km2. The functional absorption cross section of photosystem II (PSII) in darkness (σPSII) or under ambient light (σPSII’) (A2 quanta-1) increased from the surface to deeper waters at all the stations during the survey period (29 July to 23 August 2012). While the maximum (Fv/Fm, measured in darkness) or effective (Fq’/Fm’, measured under ambient light) photochemical efficiency of PSII appeared to increase with increasing depth at most stations, it showed inverse relationship with depth in river plume areas. The functional absorption cross section of PSII changes could be attributed to light-adapted genotypic feature due to niche-partition and the alteration of photochemical efficiency of PSII could be attributed to photo-acclimation. The chlorophyll a fluorometry can be taken as an analog to estimate primary productivity, since areas of higher photochemical efficiency of PSII coincided with those of higher primary productivity reported previously in the NSCS.

黄土丘陵区土壤水分对黄刺玫叶片光响应特征参数的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 黄土丘陵区土壤水分对黄刺玫叶片光响应特征参数的影响 DOI: 10.5846/stxb201501310256 作者: 作者单位: 山东农业大学,山东农业大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家重点基础研究发展计划项目（2012CB416904） Effects of soil moisture on the photosynthetic light reaction of Rosa xanthina L. in a loess hilly region Author: Affiliation: Shandong Agricultural University,Shandong Agricultural University 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:在半干旱黄土丘陵区，以3年生黄刺玫（Rosa xanthina L.）植株为材料，采用盆栽控水试验，利用CIRAS-2型便携式光合作用测定系统，在8个土壤水分含量下测定了黄刺玫叶片的光响应过程。探讨了黄刺玫光合生理参数与土壤水分的定量关系及土壤水分效应等级划分问题。结果表明：黄刺玫的净光合速率（Pn）、光合量子效率（Φ）、水分利用效率（WUE）、胞间CO2浓度（Ci）和蒸腾速率（Tr）对土壤水分都具有明显阈值响应特征。土壤相对含水量（RWC）在36.2%-81.2%范围内，黄刺玫在强光下的Pn和WUE水平较高，光合作用不会发生明显的光抑制。RWC为66.5%左右时，Φ与Pn达到最高水平，表现出较强的光能利用潜力；RWC为81.2%为时，Tr达最大值，RWC为44.5%时，WUE为最大值。依据黄刺玫叶片Pn、Ci、Tr和WUE与土壤水分的定量关系，确定RWC在低于36.2%时为"低产低效"等级，在36.2%-44.5%之间为"低产高效"等级，44.5%-66.5%为"高产高效"等级，66.5%-81.2%为"高产中效"等级，在高于81.2%时为"低产低效"等级。 Abstract:Water is a vital macronutrient and an important environmental factor, and is required for plants to conduct photosynthesis, which insufficient or excessive soil moisture will negatively affect. The soil water deficit is a key factor affecting plant physiological activity, restricting plant productivity and vegetative restoration. Rosa xanthina L. is one of the most widely distributed types of secondary vegetation in mountainous and hilly region in North China. Because of its high level of ecological adaptability, resistance to stress, and ecological functions, Rosa xanthina shows great potential value for development and application to the reconstruction of vegetation in the ecologically fragile Loess Plateau. Thus far, previous studies of Rosa xanthina have focused on such features as its root structure and soil reinforcement capabilities, the structure and ecological adaptations of its associated community, the morphology and anatomical structure of its leaves, and its photosynthetic characteristics. However, few studies have investigated the response relationship between photosynthesis and soil moisture, or the effective use of soil moisture by Rosa xanthina in arid habitats. The objectives of this study are to explore both the photosynthetic response to soil moisture and light and their quantitative relationship, and to attempt to identify the threshold effect of soil moisture on photosynthesis in Rosa xanthina L. In addition, this study aims to determine the species' photosynthetic productivity classification using physiological photosynthesis data. This new information will provide references that will help further our understanding of the water use and photophysiological characteristics of Rosa xanthina under drought stress. Three-year-old Rosa xanthina seedlings which were collected from the nursery and then potted in buckets were taken as materials in the semiarid loess hilly and gully regions. Sufficient water was provided to each seedling to saturate the soil in the bucket two days before the determination of photosynthetic parameters, and the soil water content was then monitored with no further watering. We measured soil water content and the photosynthetic parameters every two days until the seedlings withered. Using a CIRAS-2 portable photosynthesis system, the light reaction processes of Rosa xanthina plants were measured under eight soil moisture conditions found in the semiarid loess hilly region. The result showed that the net photosynthetic rate (Pn), quantum yield (Φ), and water use efficiency (WUE) exhibit clear threshold response characteristics. Higher photosynthetic rates (Pn) and WUE were observed in Rosa xanthina leaves when the relative soil water content (RWC) increased from 36.2% to 81.2%, and there was no significant photoinhibition of photosynthesis. When RWC was approximately 66.5%, Φ and Pn peaked, exhibiting strong potential energy utilization. The transpiration rate (Tr) and WUE peaked when RWC respectively were 81.2% and 44.5%. Based on the quantitative relationship between RWC and the plants' physiological photosynthetic characteristics, the RWC values measured when Pn, Φ, Tr, and WUE reached their respective maxima, and when RWC corresponded to the inflectional values of intercellular CO2 concentration (Ci) were designated as points of differentiation. Thus, we propose a metric for the grading of soil moisture availability according to its effect on Rosa xanthina photosynthesis. Soils with an RWC lower than 36.2% are considered "low productivity and low efficiency" grade, those with an RWC of 36.2%-44.5% are considered "low productivity and high efficiency" grade, those with an RWC of 44.5%-66.5% are considered "high productivity and high efficiency" grade, those with an RWC of 66.5%-81.2% are considered "high productivity and medium efficiency" grade, and those with an RWC greater than 81.2% are considered "low productivity and low efficiency" grade. 参考文献 相似文献 引证文献

Tradeoffs to Thermal Acclimation: Energetics and Reproduction of a Reef Coral with Heat TolerantSymbiodiniumType-D

The photo-physiological characteristics of thermo-tolerantSymbiodiniumtypes have been postulated to have negative effects on the energetics of the reef corals by reducing fitness. To investigate this, two key and inextricably coupled indicators of fitness, lipids and reproduction, were monitored in colonies of the broadcast-spawning coralAcropora milleporaover a two-year period that included a natural bleaching event. In the absence of bleaching ITS1-type clade D predominant colonies had 26% lower stored lipids compared to C2 colonies. At spawning time, this correlated with 28% smaller eggs in type-D colonies. This energetic disparity is expected to have reduced larval duration and settlement-competency periods in type-D compared to type-C2 colonies. More importantly, irrespective of the effect of genotype, the fitness of all corals was adversely affected by the stress of the bleaching event which reduced prespawning lipids by 60% and halved the number of eggs compared to the previous year. Our results extend work that has shown that direct temperature stress and symbiont change are likely to work in concert on corals by demonstrating that the lipids and reproduction of the reef building corals on tropical reefs are likely to be impaired by these processes as our climate warms.

Physiological basis for high resistance to photoinhibition under nitrogen depletion in Emiliania huxleyi

We quantified and compared the photophysiological characteristics of Emiliania huxleyi with two marine diatoms Thalassiosira pseudonana and Coscinodiscus sp. under nitrogen‐ and phosphorus‐replete and ‐depleted conditions. Under nitrogen‐depleted conditions, E. huxleyi maintained significant photosystem II (PSII) function over at least 38 d, whereas for both diatoms, PSII function declined to marginal levels within 8‐10 d of nitrogen depletion. In contrast, under phosphorus‐depleted conditions, PSII function in E. huxleyi declined sharply within 7 d and in T. pseudonana within 3 d. Under nutrient‐replete conditions, E. huxleyi had one of the highest PSII repair rate constants among phytoplankton examined to date. Under nitrogen depletion, E. huxleyi exhibited a decrease in susceptibility to photoinactivation of PSII, while the diatoms showed no significant change in susceptibility. The superior ability of E. huxleyi relative to the diatoms to limit PSII photoinactivation as well as to maintain PSII repair for many days of nitrogen depletion could help to explain why E. huxleyi is able to form blooms under the low‐nitrate, high‐light conditions that frequently occur in stratified surface waters.