Antioxidative responses of Nostoc ellipsosporum and Nostoc piscinale to salt stress

Authors

Maryam Rezayian, Vahid Niknam, Mohammad Ali Faramarzi

The responses of the cyanobacteria Nostoc ellipsosporum and Nostoc piscinale to salt stress during various growth stages were studied. Nostoc ellipsosporum was more NaCl tolerant and attained more biomass under salinity than N. piscinale. Accumulation of proline was detected in N. ellipsosporum under salinity stress. Malondialdehyde content decreased in both species on day 9 (mid log phase) under salt stress. A similar trend was detected in hydrogen peroxide (H₂O₂) content in N. ellipsosporum. Strong induction in catalase (CAT) activity was observed in N. ellipsosporum on day 9 in the presence of salt. The increase in CAT activity of N. piscinalewas observed only at higher concentrations of NaCl. In contrast to N. ellipsosporum, induction in peroxidase and polyphenol oxidase (PPO) activities on day 9 was stronger in N. piscinale. Salinity enhanced superoxide dismutase (SOD) and PPO activity in N. ellipsosporum at all growth stages. Moreover, different isoforms of CAT and SOD were detected in these cyanobacteria. Apparently, selection pressure in these cyanobacteria has led to the evolution of SODs and CATs as the main antioxidant enzymes against reactive oxygen species. Phycobiliprotein content in N. ellipsosporum under all conditions was significantly higher than that in N. piscinale. NaCl at moderate concentrations significantly increased phycobiliprotein content in the middle of the log phase in both species. Moreover, contrary to N. piscinale, the size of phycobilisomes [phycoerythrin + phycocyanin / allophycocyanin] in N. ellipsosporumincreased significantly under salt stress at the mid of log phase and later. The increase in size of phycobilisomes in N. ellipsosporum could help this species to withstand salt stress by enhancing energy transfer capacity. These results suggest that N. ellipsosporum cells could be better protected against salinity-induced oxidative damage by maintaining higher levels of antioxidative enzymes, proline, and phycobiliproteins than the cells of N. piscinale.

Seasonal changes in photosynthesis, growth, nitrogen accumulation, and salinity tolerance of Chaetomorpha crassa (Cladophorales, Chlorophyceae)

Authors

Xu Gao, Hikaru Endo, Yukio Agatsuma

Mass cultivation of the chlorophyte Chaetomorpha crassa has the potential to serve as a biological filter for the reduction of eutrophication in summertime Japanese waters. In order to clarify the suitability of C. crassa for this purpose, seasonal changes in its photosynthesis, growth, NO₃–N uptake, nitrogen content, and salinity tolerance were investigated trimonthly from May 2011 to February 2012, with samples collected in Nagatsuraura Lagoon, northern Japan. Significant effects of seawater temperature on photosynthesis, growth, and nitrogen accumulation were also detected in all four seasons, and all parameters at summer temperatures (24–28 °C) were significantly greater than those at the temperatures of other seasons (8–20 °C). Moreover, compared to the other three seasons, C. crassa showed significantly higher growth rates at 16–4 psu and higher survival percentages at 8–2 psu during the summer. In conclusion, due to its high capacity for growth and nitrogen accumulation, and greater physiological tolerance of low salinity during the elevated temperature period, large-scale cultivation of C. crassa could play a significant role in the bioremediation of both saline and brackish waters during summer.

Coastal eutrophication and freshening: Impacts on Pseudo-nitzschia abundance and domoic acid allelopathy

Authors

Elise Van Meerssche, Dianne I. Greenfield, James L. Pinckney

Species of the diatom genus Pseudo-nitzschia can produce domoic acid (DA), a neurotoxin responsible for amnesic shellfish poisoning. This release of DA by toxic Pseudo-nitzschia species in the water column may be a way to help the cells to outcompete other phytoplankton species (i.e. allelopathy). In this study, the influence of salinity and nutrient inputs on the effect of DA on natural phytoplankton community compositions was investigated using bioassays to measure phytoplankton responses to 400 ng DA ml⁻¹. Dissolved DA (dDA) was added to natural phytoplankton assemblages from a low salinity site dominated by river runoff and from a relatively pristine, high salinity site in which nutrients were added simultaneously with dDA. At the low salinity site, the percent inhibition of cryptophytes and diatoms induced by the addition of dDA was negatively correlated with salinity. However, at the high salinity site with nutrients added, no correlation with salinity was observed. This study highlights how environmental factors such as salinity and nutrients can play important roles on toxin allelopathy by alleviating or exacerbating its effect.

Dynamics of exopolymeric carbon pools in relation with phytoplankton succession along the salinity gradient of a temperate estuary (France)

Authors

Jérôme Morelle, Mathilde Schapira, Sylvaine Françoise, Gaëlle Courtay, Francis Orvain, Pascal Claquin

In parallel to phytoplankton community dynamics, transparent exopolymeric particles (TEP) and exopolymeric substances (EPS) were investigated along the salinity gradient of a temperate estuary (Seine estuary, Normandy, France) over the course of a year. The phytoplankton community was mainly dominated by marine diatom species (especially Skeletonema sp., Nitzschia sp., and Paralia sulcata) associated with a spring bloom of pico-eukaryotes and the development of Cryptophyceae in summer. The decreases in species richness and salinity were correlated along the estuary and a significant exponential relationship between species richness and primary production was identified. Concentrations of TEP and EPS (soluble and bound carbohydrates) are highly dynamic in this estuary and can reach respectively 69 mgC L−1, and 33 mgC L−1. TEP distribution was mainly related to physical factors (hydrodynamics, maximum turbidity zone formation and sediment resuspension) probably produced by stressed or dying phytoplankton, while EPS appeared to be excreted during the phytoplankton spring bloom. Soluble and bound EPS appear to be related to Skeletonema sp. and Cryptophyceae occurrences. This paper presents the dynamic pattern of these carbon pools, which play an important role in the trophic network and influence the flocculation processes involved in the fate of both organic and inorganic matter.

 

Assessing phytoplankton composition and structure within micro-estuaries and micro-outlets: a community analysis approach

Authors

Tatenda Dalu, Mandla L. Magoro, Jonathan D. Tonkin, Lucienne R. D. Human, Renzo Perissinotto, Shaun H. P. Deyzel, Janine B. Adams, Alan K. Whitfield

Micro-estuaries and micro-outlets represent small coastal waterbodies that differ in their relative salinity and size, with the former being larger, more saline (mesohaline versus oligohaline), and exchanging with the sea more often than the latter. There are thousands of these waterbodies along the world’s coastline, yet few of these very small systems have been identified and studied. We investigated systematic differences between micro-estuaries and micro-outlets in terms of phytoplankton community composition, including spatio-temporal variation in both community structure and biomass (chlorophyll-a). A multivariate analysis was used to assess differences in environmental variables, biomass and phytoplankton community composition across four seasons and the two waterbody types. A total of 260 (63 families) and 244 (74 families) phytoplankton taxa were identified within the micro-estuaries and micro-outlets, respectively. Nano- and picoplankton were the dominant groups in micro-estuaries, and pico- and microplankton in micro-outlets. Micro-estuaries were rich in phytoplankton taxa representative of marine, estuarine and freshwater conditions, with a successional sequence in dominance evident, from Chlorophyta during winter to Bacillariophyta in spring and Cyanophyta in summer. By contrast, micro-outlets were mostly dominated by freshwater taxa, with Chlorophyta remaining the dominant group across all four seasons. Higher phytoplankton biomass was recorded during the winter when increased nutrients were available following catchment flooding. Seasonal switching in phytoplankton was reflected not only in changing dominance patterns in both habitat types but also in complete replacement of some species in micro-outlets, despite Chlorophyta remaining dominant. Such temporal turnover, which is often accompanied by predictable seasonal changes in environmental conditions, can promote overall species richness by allowing more taxa to coexist in a single environment through temporal niche segregation.

Seasonal and diurnal evaporation from a deep hypersaline lake: The Dead Sea as a case study

Authors

I. Hamdani, S. Assouline, J. Tanny, I. M. Lensky, I. Gertman, Z. Mor, N. G. Lensky

Evaporation plays a major role in lake systems, as it affects the water, energy and solutes budgets. Water salinity reduces evaporation, and as a result affects the energy budget of the lake, including stored heat. In this study, we explore the seasonal and diurnal variations of evaporation and other energy fluxes over the Dead Sea, the deepest and saltiest hypersaline lake on Earth. We present two consecutive years observations using Eddy Covariance system, meteorological stations and a buoy station measuring the water column properties. These observations reveal the effects of synoptic and mesoscale atmospheric circulation on lake evaporation. The seasonal cycle of evaporation is characterized by two peaks. The summer evaporation peak is related to high radiation inputs. The winter peak stem from the high heat storage of the deep lake, with evaporation driven by high vapor pressure demand, combined with synoptic scale wind systems and thermal instability. In summer, the synoptic circulation is stable, providing a weak background wind velocity (Persian trough), hence, the dominant diurnal wind pattern is induced by the Mediterranean Sea Breeze (mesoscale circulation). The two years of eddy covariance measurements in the hypersaline Dead Sea, located in a hyperarid region, revealed annual evaporation rate of 1.13 ± 0.13 m yr−1. We explored several evaporation models versus the directly measured evaporation, and found that the most reliable is a mass transfer model, that was calibrated here for the Dead Sea.

Regeneration and colonization abilities of the invasive species Elodea canadensis and Elodea nuttallii under a salt gradient: implications for freshwater invasibility

Authors

Lise Thouvenot, Gabrielle Thiébaut

Salinity plays an important role in macrophyte distribution. The current increase in salinization of native freshwaters could modify their susceptibility to invasion. In this study, we determined the tolerance to salt of two invasive macrophytes: Elodea canadensis and Elodea nuttallii. We analysed their growth, regeneration and colonization abilities and the influence of their phenological stage in their response to salt in a laboratory experiment. Traits of both Elodea species varied according to the season and the salt concentration: they were more affected by salt in autumn than in spring, demonstrating higher salt tolerance in spring than in autumn. The two species were sensitive to different thresholds of salinity, although they were both strongly reduced at 3 g l⁻¹ of salt in autumn. Consequently, salt marshes and brackish waters (salt concentration inferior to 3 g l⁻¹ of salt) are likely to be invaded by both species, but the effect of salt levels superior to 3 g l⁻¹ on plant invasiveness needs to be investigated.

River plume and bottom boundary layer – Hotspots for nitrification in a coastal bay?

Authors

Ines Bartl, Iris Liskow, Kirstin Schulz, Lars Umlauf, Maren Voss

Coastal zones, impacted by major rivers, comprise distinct environments, such as river plumes and bottom boundary layers (BBL). These environments are characterized by high nutrient concentrations and high microbial activities and thus offer favourable conditions for nitrification, a key process in the coastal nitrogen cycle. Because nitrification provides substrates for both primary production and denitrification, elucidation of its magnitude and regulation is crucial for understanding the nitrogen cycle in coastal zones. During three research cruises covering three seasons, the enhancement of nitrification rates and their regulation by environmental variables, including salinity, temperature, oxygen, and inorganic and organic nitrogen were investigated in river plume and BBL of the Vistula Estuary (Bay of Gdansk, Southern Baltic Sea). Nitrification rates were not enhanced in the river plume (39 ± 38 nmol L−1 d−1) compared to coastal surface water (45 ± 18 nmol−1 d−1) but the relationship to salinity and particulate organic nitrogen changed, suggesting different regulatory mechanisms along the salinity gradient. Nitrification rates in the BBL covered a range from 1 to 227 nmol L−1 d−1 and did not differ seasonally. NH4+ turnover was dominated by assimilation into biomass in summer and by nitrification in winter and spring. In summer, rates were only slightly enhanced in the BBL and clearly related to particulate organic nitrogen and carbon concentrations, indicating particle attachment of nitrifiers and close coupling to organic matter degradation. The lack of correlations between nitrification and environmental variables in winter and spring suggested other regulatory mechanisms than in summer. Short-term changes, including the oxygenation of anoxic deep offshore water and particle resuspension clearly enhanced nitrification and further highlighted the variable mechanisms regulating nitrification in the Bay of Gdansk. Although nitrification rates did not greatly differ between seasons or water layers, the variability in regulatory mechanisms and the seasonal switch in NH4+ recycling are likely to have implications on coastal N-turnover and hence on the filter function of coastal waters.

Patterns of Vegetation Dynamics across Mild Disturbance Gradient in a Freshwater Wetland System in Southern India

Authors

P. V. Jyothi, S. Sureshkumar

Ponnani Kole wetlands, the northward extension of Vembanad Kole Ramsar site in Kerala, Southern India, is facing environmental pressures due to increases in human population, changes in land use pattern, improper watershed management and urban developments. The current study describes the community assemblage pattern of macrophytes and their variations within and among areas affected by environmental disturbances in Ponnani Kole wetland system. The macrophyte community structures in the study site were characterized with reference to areas of saline intrusion, intense agricultural activities and sewage disposal. Sphaeranthus africanus and Colocasia esculenta were specific to sewage; Rotala indica, Hedyotis corymbosa, Limnophila heterophylla and Eriocaulon setaceum were specific to agriculture; while, Acanthus ilicifolius, and Mariscus dubius were specific to areas of saline intrusion in the study site. Mean diversity did not vary significantly among the different zones of disturbance with the exception of saline intruded areas. Taxonomically, similar species flourished well in all regions of the study except in the saline intrusion area. In undisturbed areas, considered as control, the occurrence of all macrophytes was observed in equal proportions with the exception of mangroves and suspended hydrophytes. However, in sewage disposal areas, the occurrence of 45 species was observed with unequal predominance of all taxa, viz. class, order and family of macrophytes. The implementation of decision supporting tools to aid strategy and policy makers explore land-use options and disturbance scenarios along with ecological tools assessing multiple ecosystem services will see Ponnani Kole wetland become established as a macrophyte dominated ecological regime which can be further developed as a conservation and educational site for tropical aquatic macrophytes.

Responses of Tidal Freshwater and Brackish Marsh Macrophytes to Pulses of Saline Water Simulating Sea Level Rise and Reduced Discharge

Authors

Fan Li, Steven C. Pennings

Coastal low-salinity marshes are increasingly experiencing periodic to extended periods of elevated salinities due to the combined effects of sea level rise and altered hydrological and climatic conditions. However, we lack the ability to predict detailed vegetation responses, especially for saline pulses that are more realistic in nature than permanent saline presses. In this study, we exposed common freshwater and brackish plants to different durations (1–31 days per month for 3 months) of saline water (salinity of 5). We found that Zizaniopsis miliacea was more tolerant to salinity than the other two freshwater species, Polygonum hydropiperoides and Pontederia cordata. We also found that Zizaniopsis miliaceabelowground and total biomass appeared to increase with salinity pulses up to 16 days in length, although this relationship was quite variable. Brackish plants, Spartina cynosuroides, Schoenoplectus americanus and Juncus roemerianus, were unaffected by the experimental treatments. Our experiment did not evaluate how competitive interactions would further affect responses to salinity but our results suggest the hypothesis that short pulses of saline water will increase the cover of Zizaniopsis miliacea and decrease the cover of Polygonum hydropiperoides and Pontederia cordata in tidal freshwater marshes, thereby reducing diversity without necessarily affecting total plant biomass.