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Capó-Bauçà S, Iñiguez C, Galmés J. The diversity and coevolution of Rubisco and CO 2 concentrating mechanisms in marine macrophytes. THE NEW PHYTOLOGIST 2024; 241:2353-2365. [PMID: 38197185 DOI: 10.1111/nph.19528] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/26/2023] [Accepted: 12/15/2023] [Indexed: 01/11/2024]
Abstract
The kinetic properties of Rubisco, the most important carbon-fixing enzyme, have been assessed in a small fraction of the estimated existing biodiversity of photosynthetic organisms. Until recently, one of the most significant gaps of knowledge in Rubisco kinetics was marine macrophytes, an ecologically relevant group including brown (Ochrophyta), red (Rhodophyta) and green (Chlorophyta) macroalgae and seagrasses (Streptophyta). These organisms express various Rubisco types and predominantly possess CO2 -concentrating mechanisms (CCMs), which facilitate the use of bicarbonate for photosynthesis. Since bicarbonate is the most abundant form of dissolved inorganic carbon in seawater, CCMs allow marine macrophytes to overcome the slow gas diffusion and low CO2 availability in this environment. The present review aims to compile and integrate recent findings on the biochemical diversity of Rubisco and CCMs in the main groups of marine macrophytes. The Rubisco kinetic data provided demonstrate a more relaxed relationship among catalytic parameters than previously reported, uncovering a variability in Rubisco catalysis that has been hidden by a bias in the literature towards terrestrial vascular plants. The compiled data indicate the existence of convergent evolution between Rubisco and biophysical CCMs across the polyphyletic groups of marine macrophytes and suggest a potential role for oxygen in shaping such relationship.
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Affiliation(s)
- Sebastià Capó-Bauçà
- Research Group on Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears-INAGEA, 07122, Palma, Balearic Islands, Spain
| | - Concepción Iñiguez
- Research Group on Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears-INAGEA, 07122, Palma, Balearic Islands, Spain
- Department of Ecology, Faculty of Sciences, University of Malaga, Boulevard Louis Pasteur s/n, 29010, Málaga, Spain
| | - Jeroni Galmés
- Research Group on Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears-INAGEA, 07122, Palma, Balearic Islands, Spain
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He Y, Ding N, Yu G, Sunahara GI, Lin H, Zhang X, Ullah H, Liu J. High-resolution imaging of O 2 dynamics and metal solubilization in the rhizosphere of the hyperaccumulator Leersia hexandra Swartz. JOURNAL OF HAZARDOUS MATERIALS 2023; 455:131580. [PMID: 37167872 DOI: 10.1016/j.jhazmat.2023.131580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2022] [Revised: 04/25/2023] [Accepted: 05/03/2023] [Indexed: 05/13/2023]
Abstract
The mobilization of trace metals in the rhizosphere can be affected by the redox potential, which is closely related to the O2 dynamics. This study examined the distributions of O2 and trace metals in the rhizosphere of the subaquatic hyperaccumulator Leersia hexandra Swartz under chromium (Cr) stress using planar optodes and the diffusive gradients in thin films technique coupled with laser ablation inductively coupled plasma mass spectrometry. The O2 concentrations and oxidized areas in the rhizosphere significantly increased with increases in the light intensity, air humidity, and atmospheric CO2 concentrations (p < 0.05). The O2 concentration first increased with increasing ambient temperatures, then decreased when the temperature increased from 25 to 32 ℃. The O2 concentration in the rhizosphere was significantly decreased under Cr stress (p < 0.05), with a prolonged response time to the altered ambient temperature. Cr stress led to decreased mobilities of As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Sb, V, W, and Zn in the rhizosphere, which were negatively correlated with the concentrations of O2. These results provide new insights into the role of changes in the O2 concentration induced by the roots of hyperaccumulator plants in controlling the mobility of trace metals in soils.
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Affiliation(s)
- Yao He
- College of Environmental Science and Engineering, Guilin University of Technology, Guilin, China
| | - Na Ding
- College of Environmental Science and Engineering, Guilin University of Technology, Guilin, China
| | - Guo Yu
- College of Environmental Science and Engineering, Guilin University of Technology, Guilin, China; Guangxi Collaborative Innovation Center for Water Pollution Control and Water Safety in Karst Areas, Guilin University of Technology, 541000 Guilin, China.
| | - Geoffrey I Sunahara
- Department of Natural Resource Sciences, McGill University, Montreal, Quebec, Canada
| | - Hua Lin
- College of Environmental Science and Engineering, Guilin University of Technology, Guilin, China; Guangxi Collaborative Innovation Center for Water Pollution Control and Water Safety in Karst Areas, Guilin University of Technology, 541000 Guilin, China.
| | - Xuehong Zhang
- College of Environmental Science and Engineering, Guilin University of Technology, Guilin, China; Guangxi Collaborative Innovation Center for Water Pollution Control and Water Safety in Karst Areas, Guilin University of Technology, 541000 Guilin, China
| | - Habib Ullah
- Department of Environmental Science, Zhejiang University, Hangzhou, Zhejiang, China
| | - Jie Liu
- College of Environmental Science and Engineering, Guilin University of Technology, Guilin, China; Guangxi Collaborative Innovation Center for Water Pollution Control and Water Safety in Karst Areas, Guilin University of Technology, 541000 Guilin, China
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Capó-Bauçà S, Iñiguez C, Aguiló-Nicolau P, Galmés J. Correlative adaptation between Rubisco and CO 2-concentrating mechanisms in seagrasses. NATURE PLANTS 2022; 8:706-716. [PMID: 35729266 DOI: 10.1038/s41477-022-01171-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Accepted: 05/13/2022] [Indexed: 05/19/2023]
Abstract
Submerged angiosperms sustain some of the most productive and diverse ecosystems worldwide. However, their carbon acquisition and assimilation mechanisms remain poorly explored, missing an important step in the evolution of photosynthesis during the colonization of aquatic environments by angiosperms. Here we reveal a convergent kinetic adaptation of Rubisco in phylogenetically distant seagrass species that share catalytic efficiencies and CO2 and O2 affinities up to three times lower than those observed in phylogenetically closer angiosperms from terrestrial, freshwater and brackish-water habitats. This Rubisco kinetic convergence was found to correlate with the effectiveness of seagrass CO2-concentrating mechanisms (CCMs), which probably evolved in response to the constant CO2 limitation in marine environments. The observed Rubisco kinetic adaptation in seagrasses more closely resembles that seen in eukaryotic algae operating CCMs rather than that reported in terrestrial C4 plants. Our results thus demonstrate a general pattern of co-evolution between Rubisco function and biophysical CCM effectiveness that traverses distantly related aquatic lineages.
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Affiliation(s)
- Sebastià Capó-Bauçà
- Research Group on Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears-INAGEA, Palma, Spain
| | - Concepción Iñiguez
- Research Group on Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears-INAGEA, Palma, Spain.
| | - Pere Aguiló-Nicolau
- Research Group on Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears-INAGEA, Palma, Spain
| | - Jeroni Galmés
- Research Group on Plant Biology under Mediterranean Conditions, Universitat de les Illes Balears-INAGEA, Palma, Spain
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Enhancement of diatom growth and phytoplankton productivity with reduced O 2 availability is moderated by rising CO 2. Commun Biol 2022; 5:54. [PMID: 35031680 PMCID: PMC8760321 DOI: 10.1038/s42003-022-03006-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2021] [Accepted: 12/23/2021] [Indexed: 11/09/2022] Open
Abstract
Many marine organisms are exposed to decreasing O2 levels due to warming-induced expansion of hypoxic zones and ocean deoxygenation (DeO2). Nevertheless, effects of DeO2 on phytoplankton have been neglected due to technical bottlenecks on examining O2 effects on O2-producing organisms. Here we show that lowered O2 levels increased primary productivity of a coastal phytoplankton assemblage, and enhanced photosynthesis and growth in the coastal diatom Thalassiosira weissflogii. Mechanistically, reduced O2 suppressed mitochondrial respiration and photorespiration of T. weissflogii, but increased the efficiency of their CO2 concentrating mechanisms (CCMs), effective quantum yield and improved light use efficiency, which was apparent under both ambient and elevated CO2 concentrations leading to ocean acidification (OA). While the elevated CO2 treatment partially counteracted the effect of low O2 in terms of CCMs activity, reduced levels of O2 still strongly enhanced phytoplankton primary productivity. This implies that decreased availability of O2 with progressive DeO2 could boost re-oxygenation by diatom-dominated phytoplankton communities, especially in hypoxic areas, with potentially profound consequences for marine ecosystem services in coastal and pelagic oceans. Sun et al. investigate the effects of current ambient and potential future oxygen levels on phytoplankton growth and photosynthesis with field observations and mesocosm and lab experiments. Their results demonstrate positive effects of low O2 on phytoplankton growth, photosynthesis, and inorganic carbon acquisition at current and future high levels of CO2.
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Chen B, Liu J, Xu G, Li G. Lowering pO 2 Interacts with Photoperiod to Alter Physiological Performance of the Coastal Diatom Thalassiosira pseudonana. Microorganisms 2021; 9:microorganisms9122541. [PMID: 34946142 PMCID: PMC8704836 DOI: 10.3390/microorganisms9122541] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 11/30/2021] [Accepted: 12/03/2021] [Indexed: 11/16/2022] Open
Abstract
Exacerbating deoxygenation is extensively affecting marine organisms, with no exception for phytoplankton. To probe these effects, we comparably explored the growth, cell compositions, photosynthesis, and transcriptome of a diatom Thalassiosira pseudonana under a matrix of pO2 levels and Light:Dark cycles at an optimal growth light. The growth rate (μ) of T. pseudonana under a 8:16 L:D cycle was enhanced by 34% by low pO2 but reduced by 22% by hypoxia. Under a 16:8 L:D cycle, however, the μ decreased with decreasing pO2 level. The cellular Chl a content decreased with decreasing pO2 under a 8:16 L:D cycle, whereas the protein content decreased under a 16:8 L:D cycle. The prolonged photoperiod reduced the Chl a but enhanced the protein contents. The lowered pO2 reduced the maximal PSII photochemical quantum yield (FV/FM), photosynthetic oxygen evolution rate (Pn), and respiration rate (Rd) under the 8:16 or 16:8 L:D cycles. Cellular malondialdehyde (MDA) content and superoxide dismutase (SOD) activity were higher under low pO2 than ambient pO2 or hypoxia. Moreover, the prolonged photoperiod reduced the FV/FM and Pn among all three pO2 levels but enhanced the Rd, MDA, and SOD activity. Transcriptome data showed that most of 26 differentially expressed genes (DEGs) that mainly relate to photosynthesis, respiration, and metabolism were down-regulated by hypoxia, with varying expression degrees between the 8:16 and 16:8 L:D cycles. In addition, our results demonstrated that the positive or negative effect of lowering pO2 upon the growth of diatoms depends on the pO2 level and is mediated by the photoperiod.
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Affiliation(s)
- Bokun Chen
- Institute of Marine Science and Technology, Shandong University, Qingdao 266237, China; (B.C.); (G.X.)
- Joint Laboratory for Ocean Research and Education of Dalhousie University, Shandong University and Xiamen University, Qingdao 266237, China
| | - Jihua Liu
- Institute of Marine Science and Technology, Shandong University, Qingdao 266237, China; (B.C.); (G.X.)
- Joint Laboratory for Ocean Research and Education of Dalhousie University, Shandong University and Xiamen University, Qingdao 266237, China
- Correspondence:
| | - Ge Xu
- Institute of Marine Science and Technology, Shandong University, Qingdao 266237, China; (B.C.); (G.X.)
- Marine Environmental Monitoring Centre of Ningbo, East China Sea Bureau of Ministry of Natural Resources, Ningbo 315016, China
| | - Gang Li
- Key Laboratory of Tropical Marine Bio-Resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510530, China;
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Elgetti Brodersen K, Kühl M, Trampe E, Koren K. Imaging O 2 dynamics and microenvironments in the seagrass leaf phyllosphere with magnetic optical sensor nanoparticles. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2020; 104:1504-1519. [PMID: 33037691 DOI: 10.1111/tpj.15017] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2020] [Revised: 09/17/2020] [Accepted: 09/23/2020] [Indexed: 06/11/2023]
Abstract
Eutrophication leads to epiphyte blooms on seagrass leaves that strongly affect plant health, yet the actual mechanisms of such epiphyte-induced plant stress remain poorly understood. We used magnetic optical sensor nanoparticles in combination with luminescence lifetime imaging to map the O2 concentration and dynamics in the heterogeneous seagrass phyllosphere under changing light conditions. By incorporating magnetite into the sensor nanoparticles, it was possible to image the spatial O2 distribution under flow over seagrass leaf segments in the presence of a strong magnetic field. Local microniches with low leaf surface O2 concentrations were found under thick epiphytic biofilms, often leading to anoxic microhabitats in darkness. High irradiance led to O2 supersaturation across most of the seagrass phyllosphere, whereas leaf microenvironments with reduced O2 conditions were found under epiphytic biofilms at low irradiance, probably driven by self-shading. Horizontal micro-profiles extracted from the O2 images revealed pronounced heterogeneities in local O2 concentration over the base of the epiphytic biofilm, with up to 52% reduction in O2 concentrations in areas with relatively thick (>2 mm), compared with thin (≤1 mm), epiphyte layers in darkness. We also present evidence of enhanced relative internal O2 transport within leaves with epiphyte overgrowth, compared with bare seagrass leaves, in light as a result of limited mass transfer across thick outward diffusion pathways. The local availability of O2 was still markedly reduced in the epiphyte-covered leaves, however. The leaf phyllosphere is thus characterized by a complex microlandscape of O2 availability that strongly affects microbial processes occurring within the epiphytic biofilm, which may have implications for seagrass health, as anoxic microhabitats have been shown to promote the microbiological production of reduced toxic compounds, such as nitric oxide.
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Affiliation(s)
- Kasper Elgetti Brodersen
- Marine Biological Section, Department of Biology, University of Copenhagen, Strandpromenaden 5, Helsingør, 3000, Denmark
| | - Michael Kühl
- Marine Biological Section, Department of Biology, University of Copenhagen, Strandpromenaden 5, Helsingør, 3000, Denmark
| | - Erik Trampe
- Marine Biological Section, Department of Biology, University of Copenhagen, Strandpromenaden 5, Helsingør, 3000, Denmark
| | - Klaus Koren
- Marine Biological Section, Department of Biology, University of Copenhagen, Strandpromenaden 5, Helsingør, 3000, Denmark
- Department of Biology, Section for Microbiology, Aarhus University Centre for Water Technology, Ny Munkegade 114, Aarhus C, 8000, Denmark
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Nguyen HM, Kim M, Ralph PJ, Marín-Guirao L, Pernice M, Procaccini G. Stress Memory in Seagrasses: First Insight Into the Effects of Thermal Priming and the Role of Epigenetic Modifications. FRONTIERS IN PLANT SCIENCE 2020; 11:494. [PMID: 32411166 PMCID: PMC7199800 DOI: 10.3389/fpls.2020.00494] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2020] [Accepted: 04/01/2020] [Indexed: 05/30/2023]
Abstract
While thermal priming and the relative role of epigenetic modifications have been widely studied in terrestrial plants, their roles remain unexplored in seagrasses so far. Here, we experimentally compared the ability of two different functional types of seagrass species, dominant in the Southern hemisphere, climax species Posidonia australis and pioneer species Zostera muelleri, to acquire thermal-stress memory to better survive successive stressful thermal events. To this end, a two-heatwave experimental design was conducted in a mesocosm setup. Findings across levels of biological organization including the molecular (gene expression), physiological (photosynthetic performances and pigments content) and organismal (growth) levels provided the first evidence of thermal priming in seagrasses. Non-preheated plants suffered a significant reduction in photosynthetic capacity, leaf growth and chlorophyll a content, while preheated plants were able to cope better with the recurrent stressful event. Gene expression results demonstrated significant regulation of methylation-related genes in response to thermal stress, suggesting that epigenetic modifications could play a central role in seagrass thermal stress memory. In addition, we revealed some interspecific differences in thermal responses between the two different functional types of seagrass species. These results provide the first insights into thermal priming and relative epigenetic modifications in seagrasses paving the way for more comprehensive forecasting and management of thermal stress in these marine foundation species in an era of rapid environmental change.
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Affiliation(s)
| | - Mikael Kim
- Seagrass Ecology Group, Oceanographic Center of Murcia, Spanish Institute of Oceanography, Murcia, Spain
| | - Peter J. Ralph
- Seagrass Ecology Group, Oceanographic Center of Murcia, Spanish Institute of Oceanography, Murcia, Spain
| | - Lázaro Marín-Guirao
- Stazione Zoologica Anton Dohrn, Villa Comunale, Naples, Italy
- Climate Change Cluster (C3), University of Technology Sydney, Sydney, NSW, Australia
| | - Mathieu Pernice
- Seagrass Ecology Group, Oceanographic Center of Murcia, Spanish Institute of Oceanography, Murcia, Spain
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Brodersen KE, Koren K, Revsbech NP, Kühl M. Strong leaf surface basification and CO 2 limitation of seagrass induced by epiphytic biofilm microenvironments. PLANT, CELL & ENVIRONMENT 2020; 43:174-187. [PMID: 31429088 DOI: 10.1111/pce.13645] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2019] [Revised: 08/07/2019] [Accepted: 08/09/2019] [Indexed: 06/10/2023]
Abstract
Coastal eutrophication is a growing problem worldwide, leading to increased epiphyte overgrowth of seagrass leaves. Yet little is known about how epiphytes affect key biogeochemical conditions and processes in the seagrass phyllosphere. We used electrochemical microsensors to measure microgradients of O2 , pH, and CO2 at the bare and epiphyte-covered leaf surface of seagrass (Zostera marina L.) to determine effects of epiphytes on the leaf chemical microenvironment. Epiphytes result in extreme daily fluctuations in pH, O2 , and inorganic carbon concentrations at the seagrass leaf surface severely hampering the plant's performance. In light, leaf epiphyte biofilms and their diffusive boundary layer lead to strong basification, markedly reducing the CO2 and HCO3- availability at the leaf surface, leading to reduced photosynthetic efficiency as a result of carbon limitation and enhanced photorespiration. With epiphytes, leaf surface pH increased to >10, thereby exceeding final pH levels (~9.62) and CO2 compensation points for active photosynthesis. In darkness, epiphyte biofilms resulted in increased CO2 and hypoxia at the leaf surface. Epiphytes can lead to severe carbon limitation in seagrasses owing to strong phyllosphere basification leading to CO2 depletion and costly, yet limiting, HCO3- utilization, increasing the risk of plant starvation.
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Affiliation(s)
| | - Klaus Koren
- Department of Bioscience, Aarhus University Centre for Water Technology, Aarhus C, Denmark
| | - Niels Peter Revsbech
- Department of Bioscience, Aarhus University Centre for Water Technology, Aarhus C, Denmark
| | - Michael Kühl
- Marine Biological Section, Department of Biology, University of Copenhagen, Helsingør, Denmark
- Climate Change Cluster, Faculty of Science, University of Technology Sydney, Sydney, Australia
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Kim M, Pernice M, Watson-Lazowski A, Guagliardo P, Kilburn MR, Larkum AWD, Raven JA, Ralph PJ. Effect of reduced irradiance on 13C uptake, gene expression and protein activity of the seagrass Zostera muelleri. MARINE ENVIRONMENTAL RESEARCH 2019; 149:80-89. [PMID: 31181418 DOI: 10.1016/j.marenvres.2019.06.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Revised: 05/30/2019] [Accepted: 06/05/2019] [Indexed: 06/09/2023]
Abstract
Photosynthesis in the seagrass Zostera muelleri remains poorly understood. We investigated the effect of reduced irradiance on the incorporation of 13C, gene expression of photosynthetic, photorespiratory and intermediates recycling genes as well as the enzymatic content and activity of Rubisco and PEPC within Z. muelleri. Following 48 h of reduced irradiance, we found that i) there was a ∼7 fold reduction in 13C incorporation in above ground tissue, ii) a significant down regulation of photosynthetic, photorespiratory and intermediates recycling genes and iii) no significant difference in enzyme activity and content. We propose that Z. muelleri is able to alter its physiology in order to reduce the amount of C lost through photorespiration to compensate for the reduced carbon assimilation as a result of reduced irradiance. In addition, the first estimated rate constant (Kcat) and maximum rates of carboxylation (Vcmax) of Rubisco is reported for the first time for Z. muelleri.
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Affiliation(s)
- Mikael Kim
- University of Technology Sydney, Climate Change Cluster, Ultimo, NSW, 2007, Australia
| | - Mathieu Pernice
- University of Technology Sydney, Climate Change Cluster, Ultimo, NSW, 2007, Australia.
| | - Alexander Watson-Lazowski
- Hawkesbury Institute for the Environment, University of Western Sydney, Penrith, Australia; ARC Centre of Excellence for Translational Photosynthesis, Australian National University, Canberra, Australia
| | - Paul Guagliardo
- Centre for Microscopy, Characterisation and Analysis, University of Western Australia, Perth, WA, Australia
| | - Matt R Kilburn
- Centre for Microscopy, Characterisation and Analysis, University of Western Australia, Perth, WA, Australia
| | - Anthony W D Larkum
- University of Technology Sydney, Climate Change Cluster, Ultimo, NSW, 2007, Australia
| | - John A Raven
- University of Technology Sydney, Climate Change Cluster, Ultimo, NSW, 2007, Australia; Division of Plant Science, University of Dundee at the James Hutton Institute, Invergowrie, Dundee, DD2 5DA, UK
| | - Peter J Ralph
- University of Technology Sydney, Climate Change Cluster, Ultimo, NSW, 2007, Australia
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Oscar MA, Barak S, Winters G. The Tropical Invasive Seagrass, Halophila stipulacea, Has a Superior Ability to Tolerate Dynamic Changes in Salinity Levels Compared to Its Freshwater Relative, Vallisneria americana. FRONTIERS IN PLANT SCIENCE 2018; 9:950. [PMID: 30022993 PMCID: PMC6040085 DOI: 10.3389/fpls.2018.00950] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2017] [Accepted: 06/12/2018] [Indexed: 05/30/2023]
Abstract
The tropical seagrass species, Halophila stipulacea, originated from the Indian Ocean and the Red Sea, subsequently invading the Mediterranean and has recently established itself in the Caribbean Sea. Due to its invasive nature, there is growing interest in understanding this species' capacity to adapt to new conditions. One approach to understanding the natural tolerance of a plant is to compare the tolerant species with a closely related non-tolerant species. We compared the physiological responses of H. stipulacea exposed to different salinities, with that of its nearest freshwater relative, Vallisneria americana. To achieve this goal, H. stipulacea and V. americana plants were grown in dedicated microcosms, and exposed to the following salt regimes: (i) H. stipulacea: control (40 PSU, practical salinity units), hyposalinity (25 PSU) and hypersalinity (60 PSU) for 3 weeks followed by a 4-week recovery phase (back to 40 PSU); (ii) V. americana: control (1 PSU), and hypersalinity (12 PSU) for 3 weeks, followed by a 4-week recovery phase (back to 1 PSU). In H. stipulacea, leaf number and chlorophyll content showed no significant differences between control plants and plants under hypo and hypersalinities, but a significant decrease in leaf area under hypersalinity was observed. In addition, compared with control plants, H. stipulacea plants exposed to hypo and hypersalinity were found to have reduced below-ground biomass and C/N ratios, suggesting changes in the allocation of resources in response to both stresses. There was no significant effect of hypo/hypersalinity on dark-adapted quantum yield of photosystem II (Fv/Fm) suggesting that H. stipulacea photochemistry is resilient to hypo/hypersalinity stress. In contrast to the seagrass, V. americana exposed to hypersalinity displayed significant decreases in above-ground biomass, shoot number, leaf number, blade length and Fv/Fm, followed by significant recoveries of all these parameters upon return of the plants to non-saline control conditions. These data suggest that H. stipulacea shows remarkable tolerance to both hypo and hypersalinity. Resilience to a relatively wide range of salinities may be one of the traits explaining the invasive nature of this species in the Mediterranean and Caribbean Seas.
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Affiliation(s)
- Michelle A. Oscar
- French Associates Institute for Agriculture and Biotechnology of Drylands, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel
- Dead-Sea & Arava Science Center, Neve Zohar, Israel
| | - Simon Barak
- French Associates Institute for Agriculture and Biotechnology of Drylands, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel
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