Production of the rotifer Brachionus plicatilis for aquaculture in Kuwait

Macrophytes, plankton samples, salinity and depth data were collected from wetlands in October 1981. Species diversity and distributions are recorded and relationships drawn between macrophytes and plankton occurrence. An examination of the data of Geddes et al. (1981) enables comparisons of species composition in a similar range of Western Australian lakes in 1978 at a different stage in the seasonal cycle. Comparison with the biota of salt lakes in Australia's eastern states and elsewhere lead to biogeographical speculations for the macrophytes and for some of the planktonic species.     

Temporal Changes between Ecological Regimes in a Range of Primary and Secondary Salinised Wetlands

Many rivers and wetlands in south-western Australia are threatened by salinisation due to rising saline watertables, which have resulted from land clearing and the replacement of deep-rooted perennial species with shallow-rooted annual species. A four to six weekly sampling program of water quality, submerged macrophytes and macroinvertebrates was undertaken at six wetlands, from September 2002 to February 2004, to investigate seasonal variation in a range of primary and secondary saline systems. The wetlands dried and filled at different times in response to local rainfall patterns, and salinities varied accordingly with evapoconcentration and dilution. Two types of clear-water wetlands were recognised; those dominated by submerged aquatic macrophytes (Ruppia, Lepilaena and Lamprothamnium) and those dominated by benthic microbial communities. Two types of turbid wetlands were also recognised; those with high concentrations of phytoplankton and those with high concentrations of suspended sediments. A primary saline lake and two lakes that have only recently been affected by secondary salinisation persisted in a clear, macrophyte-dominated regime throughout most of the study period, except during drying and filling. Two lakes with a long history of secondary salinisation (70 years) moved between regimes over the study period. A clear, benthic microbial community – dominated regime only persisted at the wetland which contained permanent water throughout the study period. The turbid regimes were only present during drying and refilling phases. A richer and more abundant macroinvertebrate fauna was associated with the clear, macrophyte- dominated wetlands. Our results suggest that the development of management guidelines that recognise the presence of different ecological regimes and that consider the interactions between water regime, salinity, and primary and secondary production will be more useful in protecting biodiversity and ecological function in these systems than managing salinity as a single factor.     

A review of the salt sensitivity of the Australian freshwater biota

In Victoria, Australia, both dryland salinity and salinity in irrigation regions are serious agricultural problems. One option to control the latter is to pump groundwater to maintain it below the surface. However, this leaves a saline wastewater for disposal, probably into local streams or wetlands. This review of the salt sensitivity of the biota of Australian streams and wetlands gives information of interest to those responsible for developing controls on these discharges. The review addresses the lethal and sub-lethal effects of salinity on microbes (mainly bacteria), macrophytes and micro-algae, riparian vegetation, invertebrates, fish, amphibians, reptiles, mammals, and birds. Data suggest that direct adverse biological effects are likely to occur in Australian river, stream and wetland ecosystems if salinity is increased to around 1 000 mg L⁻¹. The review highlights a general lack of data on the sensitivity of freshwater plants and animals to salinity increases.     

A study of the salt lakes and salt springs of Eyre Peninsula, South Australia

An 18-month-study of 40 saline wetlands, ranging from 6 to 336 g l⁻¹, on the west and southern coasts of Eyre Peninsula yielded 88 species of invertebrates, some aquatic plants and a fish. The invertebrates are taxonomically diverse and include 38 crustaceans, 28 insects, 12 molluscs and significantly an aquatic spider, a nemertean, two polychaetes, two sea anemones, a sponge and a bryzoan. Most were tolerant of wide fluctuations in salinity, there being 51 halobionts, 21 halophils and only 16 salt-tolerant freshwater species. Many invertebrates are restricted to the thalassic springs where marine molluscs dominated. Athalassic wetlands were dominated by crustaceans and were of two basic types—coastal and continental. There is evidence of the former evolving biologically into the later, and for some lakes to be still in transition. There is also evidence of increasing salinity in recent decades and already two lakes exhibit severe secondary salinity. Like other salt lakes in Australia the fauna is regionally distinctive. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest Editors: J. John & B. Timms Salt Lake Research: Biodiversity and Conservation—Selected papers from the 9th Conference of the International Society for Salt Lake Research     

Efficiency of three halophyte species in removing nutrients from saline water: a pilot study

Saline wetlands may be well suited for purifying contaminated water from saline agriculture and aquaculture or from freshwater-based agriculture in areas subject to increased salinity. However, case studies on the nutrient removal efficiency of halophyte species are scarce, especially for temperate regions. Here we tested the nutrient removal efficiency and ability to store nutrients in aboveground and belowground biomass of three halophyte species, Aster tripolium, Bolboschoenus maritimus subsp. compactus, and Spartina anglica, in a greenhouse microcosm experiment at two salinity levels. Nutrient removal from water differed among the species: Spartina had the highest nitrogen removal, Bolboschoenus and Spartina had the highest phosphorus removal. The species also differed in the allocation of the nutrient uptake. Bolboschoenus had the highest absolute uptake of nitrogen and phosphorus in shoots, whereas Spartina had the highest uptake of nitrogen and phosphorus in roots. The applicability of these three species in constructed saline wetlands depends on the local salinity and water regime.     

Habitat Use by Migrant Shorebirds in Saline Lakes of the Southern Great Plains

Abstract Shorebirds migrating through the Southern Great Plains of North America use saline lakes as stopovers to rest and replenish energy reserves. To understand how availability of invertebrates, salinity, freshwater springs, vegetation, and water influence the value of saline lakes as migration stopovers, we compared lakes used and not used by migrant shorebirds. Shorebirds used lakes that had freshwater springs, mudflats and standing water, sparse vegetation (≤1% cover), low to moderate salinities (x = 30.87 g/L), and mean invertebrate biomass of 0.79 g/m². Lakes that were not used were generally dry or had hypersaline water (x = 82.56 g/L), lacked flowing springs and vegetation, and had few or no invertebrates (x = 0.007 g/m²). Our results suggest that reduced spring flows and increased salinity negatively affect availability of shorebird habitats and aquatic invertebrates. We recommend preservation of the freshwater springs discharging in the saline lakes. Because the springs are discharged from the Ogallala aquifer, which is recharged through the playa wetlands, the entire complex of wetlands in the Great Plains and the Ogallala aquifer should be managed as an integral system.     

闽江河口区淡水和半咸水潮汐沼泽湿地土壤产甲烷菌多样性

为认识盐度对河口潮汐沼泽湿地土壤产甲烷菌的影响,应用PCR-RFLP技术及测序分析对闽江河口区淡水-半咸水盐度梯度上分布的4个短叶茳芏潮汐沼泽湿地土壤产甲烷菌群落结构进行研究。闽江河口区短叶茳芏潮汐沼泽湿地土壤产甲烷菌群落结构受盐度影响明显,位于下洋洲和塔礁洲的短叶茳芏潮汐淡水沼泽湿地土壤产甲烷菌的香农-威纳多样性指数值分别为2.81和2.65,位于蝙蝠洲和鳝鱼滩的短叶茳芏潮汐半咸水沼泽湿地土壤产甲烷菌香农-威纳多样性指数值分别仅为2.33和2.27。系统发育分析表明:短叶茳芏沼泽湿地土壤产甲烷菌类群主要有甲烷杆菌目(Methanobacteriales),包括Methanobacterium、Methanobrevibacter和Methanobacteriaceae;甲烷微菌目(Methanomicrobiales),主要有Methanoregula,以及甲烷八叠球菌目(Methanosarcinales),主要有Methanosarcina和Methanococcoides。闽江河口区短叶茳芏潮汐淡水沼泽湿地土壤主要的优势产甲烷菌有Methanoregula、Methanosarcina和Methanobacterium,而短叶茳芏潮汐半咸水沼泽湿地土壤主要的优势产甲烷菌则转化为仅以Methanoregula为主。     

Increasing fluctuations of soil salinity affect seedling growth performances and physiology in three Neotropical mangrove species

Background

Micro-tidal wetlands are subject to strong seasonal variations of soil salinity that are likely to increase in amplitude according to climate model predictions for the Caribbean. Whereas the effects of constant salinity levels on the physiology of mangrove species have been widely tested, little is known about acclimation to fluctuations in salinity.

Aims and methods

The aim of this experiment was to characterize the consequences of the rate of increase in salinity (slow versus fast) and salinity fluctuations over time versus constant salt level. Seedling mortality, growth, and leaf gas exchange of three mangrove species, Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle were investigated in semicontrolled conditions at different salt levels (0, 685, 1025, and 1370 mM NaCl).

Results

Slow salinity increase up to 685 mM induced acclimation, improving the salt tolerance of A. germinans and L. racemosa, but had no effect on R. mangle. During fluctuations between 0 and 685 mM, A. germinans and R. mangle were not affected by a salinity drop to zero, whereas L. racemosa took advantage of the brief freshwater episode as shown by the durable improvement of photosynthesis and biomass production.

Conclusions

This study provides new insights into physiological resistance and acclimation to salt stress. We show that seasonal variations of salinity may affect mangrove seedlings’ morphology and physiology as much as annual mean salinity. Moreover, more severe dry seasons due to climate change may impact tree stature and species composition in mangroves through higher mortality rates and physiological disturbance at the seedling stage.     

Hydrochemistry from Sr and Mg contents of ostracodes in Pleistocene lacustrine deposits,Baza Basin (SE Spain)

A reconstruction of the early Pleistocene paleohydrochemistry based on the Mg, Sr and Ca content of the Cyprideis valves is presented for shallow lacustrine sequences of the Baza basin. A large number of environmental changes in this marginal area has been recorded by the recurrent alternation of two fossil assemblages which differ in their salinity requirements. Measurements of the Sr/Ca and Mg/Ca ratios of individual calcite shells of Cyprideis show that the water in the higher saline stages (with thalassic organisms indicating marine-like conditions) was of non-marine origin. The Sr/Ca values of Cyprideis valves from sands deposited during a saline water phase show lower values than those from an overlying carbonate sequence which was formed under lower salinity conditions. These unexpected values are assumed to be the result of major changes in the chemical composition of the water in shallow, littoral ponded areas of a hydrologically complex lake. In the sequences that originated in these areas, Sr/Ca values may be used only as salinity indicators within each portion of the sequence formed in a single, continuous evolution. In more open areas, the wide fluctuations of Sr/Ca and Mg/Ca recorded in ostracodes from individual layers of rippled ostracode-shell sands probably reflect the mixing of valves from changing short-term environmental conditions.     

Development of a salinity-secondary flow-approach model to predict mangrove spreading

This paper presents a new salinity-secondary flow-approach (SSA) model for identifying areas likely to be colonized by mangrove species based on two indices: water salinity concentration and river secondary flow intensity, R/W (the ratio of radius of curvature to river width). The mangrove Kandelia obovata is spreading rapidly in the Tanshui River system and therefore resulting in flooding impact to riparian wetlands; however, few studies have examined the dispersal characteristics of this species on the reach scale. According to the literature review and our observation, the salinity is the major factor in determining the spreading capabilities of mangroves. In addition, the effect of secondary flow can also facilitate mangrove invasion through the creation of bare mudflats.The case study of the Tanshui River system shows that the SSA model can be used for the determination of the habitat requirements and thus the dispersal capabilities of K. obovata. The results of the study show that the optimum conditions for the growth and dispersal of K. obovata exist in waters with mean annual salinity levels that are higher than 5 ppt (parts per thousand). Although K. obovata can survive in brackish wetlands with mean annual salinity levels lower than 5 ppt, its spreading capability is impaired. In tidal freshwater wetlands with mean annual salinity levels that are lower than 0.1 ppt, K. obovata cannot survive. The study also found that the R/W lower than 3 led to large mudflats, which provide an ideal environment for the growth of mangroves, due to the secondary flow.It shows that the SSA model can identify the potential habitat of mangrove in tidal region, so it might help with not only estuarine wetland management but also mangrove restoration project, especially for the sea level rise effect and its impact on potential mangrove invasion.     

Seasonal Changes in Fungal Production and Biomass on Standing Dead Scirpuslacustris Litter in a Northern Prairie Wetland

Decaying macrophytes are an important source of carbon and nutrients in fungal and bacterial communities of northern prairie wetlands. Dead macrophytes do not collapse into the water column immediately after death, and decomposition by fungi and bacteria begins while the plants are standing. The seasonal variations in fungal biomass and production on Scirpus lacustris stems, both above and below water, were measured to assess which environmental factors were dominant in affecting these variations in a typical prairie wetland. Fungal biomass and production were measured from early May to November, just prior to freeze-up. Fungal decomposition began and was greatest in the spring despite low water temperatures. The fungal production, as measured by the incorporation of [1-¹⁴C]acetate into ergosterol, ranged from 1.8 to 376 μg of C g of ash-free dry mass (AFDM)⁻¹ day⁻¹, and the biomass, as estimated by using ergosterol, ranged from nondetectable to 5.8 mg of C g of AFDM⁻¹. There was no significant difference in biomass or production between aerial and submerged portions of Scirpus stems. The water temperature was correlated with fungal production (r = 0.7, P < 0.005) for aerial stem pieces but not for submerged pieces. However, in laboratory experiments water temperature had a measurable effect on both biomass and production in submerged stem pieces. Changes in fungal biomass and productivity on freshly cut green Scirpus stems decaying in the water either exposed to natural solar radiation or protected from UV radiation were monitored over the summer. There was no significant difference in either fungal biomass (P = 0.76) or production (P = 0.96) between the two light treatments. The fungal biomass and rates of production were within the lower range of the values reported elsewhere, probably as a result of the colder climate and perhaps the lower lability of Scirpus stems compared to the labilities of the leaves and different macrophytes examined in other studies performed at lower latitudes.     

Sex-related differences in leaf traits in an androdioecious shrub under contrasting levels of soil salinity

This study explores whether male and hermaphrodite plants of Phillyrea angustifolia (Oleaceae) show physiological and structural differences at the leaf level under severe water stress driven by drought and soil salinity. Leaf traits were measured in summer, at the height of the summer drought period, in male and hermaphrodite plants from two adjacent sites under contrasting soil salinity levels. Male plants from the saline site had significantly higher leaf proline content compared to males from the nonsaline site. By contrast, leaf proline levels were similarly low in hermaphrodite plants from both sites. On the other hand, hermaphrodite plants from the saline site had higher leaf stomatal frequency than hermaphrodites from the nonsaline site, whereas this parameter did not differ for male plants across sites. Such differences could be interpreted as the result of two different solutions to the same selective pressure in the androdioecious shrub P. angustifolia.     

The Comparative Osmoregulatory Ability of Two Water Beetle Genera Whose Species Span the Fresh-Hypersaline Gradient in Inland Waters (Coleoptera: Dytiscidae,Hydrophilidae)

A better knowledge of the physiological basis of salinity tolerance is essential to understanding the ecology and evolutionary history of organisms that have colonized inland saline waters. Coleoptera are amongst the most diverse macroinvertebrates in inland waters, including saline habitats; however, the osmoregulatory strategies they employ to deal with osmotic stress remain unexplored. Survival and haemolymph osmotic concentration at different salinities were examined in adults of eight aquatic beetle species which inhabit different parts of the fresh—hypersaline gradient. Studied species belong to two unrelated genera which have invaded saline waters independently from freshwater ancestors; Nebrioporus (Dytiscidae) and Enochrus (Hydrophilidae). Their osmoregulatory strategy (osmoconformity or osmoregulation) was identified and osmotic capacity (the osmotic gradient between the animal’s haemolymph and the external medium) was compared between species pairs co-habiting similar salinities in nature. We show that osmoregulatory capacity, rather than osmoconformity, has evolved independently in these different lineages. All species hyperegulated their haemolymph osmotic concentration in diluted waters; those living in fresh or low-salinity waters were unable to hyporegulate and survive in hyperosmotic media (> 340 mosmol kg^-1). In contrast, the species which inhabit the hypo-hypersaline habitats were effective hyporegulators, maintaining their haemolymph osmolality within narrow limits (ca. 300 mosmol kg^-1) across a wide range of external concentrations. The hypersaline species N. ceresyi and E. jesusarribasi tolerated conductivities up to 140 and 180 mS cm^-1, respectively, and maintained osmotic gradients over 3500 mosmol kg^-1, comparable to those of the most effective insect osmoregulators known to date. Syntopic species of both genera showed similar osmotic capacities and in general, osmotic responses correlated well with upper salinity levels occupied by individual species in nature. Therefore, osmoregulatory capacity may mediate habitat segregation amongst congeners across the salinity gradient.     

Aquatic plant dynamics of Waituna Lagoon, New Zealand: trade-offs in managing opening events of a Ramsar site

Coastal lagoons are at risk internationally due to impacts associated with human-induced land use change. The resilience of aquatic macrophytes in these systems is threatened by altered hydrological regimes, elevated nutrient loading, and increased dominance of nuisance species. We describe the aquatic plant dynamics of the Waituna Lagoon Ramsar Site, a 1,350?ha lagoon frequently opened to the sea for flood mitigation which is characterised by fluctuating water levels and salinity. The shallow lagoon supports a macrophyte community dominated by Ruppia megacarpa and R. polycarpa. Repeated survey of 48 sites across the lagoon during late summer in 2009, 2010 and 2011 were applied to describe aquatic plant composition and abundance. This period coincided with three opening events (winter 2008; winter 2009; spring 2010) when the lagoon switched from a predominantly fresh-brackish system to being influenced by tidal exchange and lower water levels. The lagoon experienced a period of 43?days open to the sea in 2008?C2009, 67?days in 2009?C2010 and 181?days in 2010?C2011, during which macrophytes were subject to saline conditions in excess of 10?ppt. We observed a decline in the occurrence of Ruppia from 2009 (69?% sites) to 2011 (23?% sites). The shift in productivity was associated with the duration of the open phase and the period plants were subject to saline conditions >20?ppt and low water levels. The resilience of the system is also at risk from increased algal-dominance due to the intensification of agricultural land use occurring in the Waituna Lagoon catchment. While lagoon opening events cause extreme changes in water depth and salinity that can limit macrophyte growth, they also provide a mechanism to reduce the effects of eutrophication. Understanding these trade-offs is pivotal in management decisions regarding the likely impact of opening events on the ecological character of coastal lagoons.     

The effect of inundation and salinity on the germination of seed banks from wetlands in South Australia

Three wetlands from the Upper South East of South Australia were chosen to investigate how a past history of drought (dry since 2002, 2004 and 2005) and salinity (2800 to >20,000 mg L⁻¹) influenced the response of the seed bank to two water regimes (drained and flooded) and four salinities (500, 1000, 3000 and 5000 mg L⁻¹). The maximum number of germinants (1270 ± 850 m⁻²) and species richness (7 ± 2.4) was greatest under the fresher drained treatment compared with the flooded more saline treatment under which there was no germination at one site. There were significant interactions between water regime and wetland previous history for two wetlands, but not the third which was the most saline and had experienced the longest drought. This indicated that the previous drought and salinity conditions experienced by a wetland affected seedling emergence but in the two less impacted wetlands the imposition of fresher drained conditions mitigated against these impacts. This suggests that if drought conditions continued with repeated exposure to elevated salinities the number of seeds and the species diversity of the seed banks would continue to decline.     

Succession of aquatic macrophytes in the Modern Yellow River Delta after 150 years of alluviation

This study evaluated the succession process of aquatic macrophytes after 150 years of alluviation in the Modern Yellow River Delta, China, and identified the roles of various environmental parameters that regulate vegetation succession. From 2007 to 2008, 214 quadrats were surveyed and 19 environmental parameters were measured, including elevation, plot distance from the seashore, 10 water parameters, and 7 soil parameters. Forty-six aquatic macrophytes belonging to 20 families and 34 genera were identified across the entire delta. Emergent and submerged plants were the most frequent species, accounting for 58.7 and 34.8 % of all species, respectively. Detrended canonical correspondence analysis showed that the presence of aquatic macrophytes in this delta was primarily regulated by water salinity, soil salinity, and distance from the seashore, followed by nutrient concentrations (e.g., NH₄ ⁺, total soil N and PO₄ ^? of water). Salinity-tolerant species (e.g., Ruppia maritima, Phragmites australis, and Typha angustifolia) tended to be widely distributed across the entire delta. In contrast, salinity-sensitive species (e.g., Ceratophyllum demersum, Hydrilla verticillata, and Potamogeton malaianus) tended to be distributed in areas at the early stages of succession, which were relatively distant from the shore. Moreover, this study also confirmed that species richness and diversity were negatively correlated with water and soil salinity, which in turn were negatively correlated with plot distance from the shore. These data indicate that the primary drivers of aquatic macrophyte succession in this delta are water and soil salinity. The information assimilated here is used to propose management practices for the protection of aquatic macrophytes in the Yellow River Delta.     

Ephemeral saline lakes on the Canadian prairies: their classification and management for emergent macrophyte growth

At two ephemeral saline lakes in Saskatchewan, changes in the physical and chemical features of water and sediments at various basin positions were monitored during a wet-dry cycle in 1978 and 1979. Water salinity fluctuated widely in response to changes in water volume and mass of solute in the water. When basins were dry, the soluble salt content of sediments 0–10 cm deep was higher than sediments 50–60 cm deep and sediments in the lake centre were more saline than at the shoreline. Upon reflooding, there was a large immediate decrease in sediment salinity at the 0–10 cm depth, such that this layer was less saline than sediments 50–60 cm deep. Sediments in the lake centre remained more saline than at the shoreline.Classification of lake salinity is necessary to assess the potential of a lake for emergent production. The large variances in ephemeral lake salinity due to water volume changes indicate that classification should be based upon the water volume-salinity cycle of these lakes rather than the salinity of any single water or sediment sample. Water management efforts to lower salinities, to improve these wetlands for emergent growth, should be aimed at reducing the salinity regime of the littoral zone. Flushing, dilution and drying and reflooding techniques are discussed as methods to decrease salinity.     

Effect of salinity on germination,seedling emergence,seedling growth and ion accumulation of a euhalophyte Suaeda salsa in an intertidal zone and on saline inland

The effect of salinity on germination, seedling emergence, seedling growth and ion accumulation of a euhalophyte Suaeda salsa L. in an intertidal zone and on saline inland were investigated. Brown seeds of S. salsa were heavier and better developed than black seeds in both the intertidal zone and on saline inland. The brown seeds/black seeds ratio for S. salsa in the intertidal zone was much higher than that for S. salsa on saline inland. More germinated seeds grew as seedlings under high salinity for S. salsa from the intertidal zone than S. salsa on saline inland; high salinity decreased the shoot length more severely for S. salsa from saline inland than for S. salsa from the intertidal zone; the seedling growth at a range of NaCl, measured either as shoot length or shoot dry weight, for S. salsa from the intertidal zone was lower than that of S. salsa from saline inland. In conclusion, for S. salsa from the intertidal zone there appears to be selection for slower growth and producing more brown seeds. The establishment of populations of S. salsa in different saline environments depends on the responses of seed germination, seedling emergence and seedling growth to salinity. These characteristics may determine the natural distributions of S. salsa populations in different saline environments.     

Treatment of domestic wastewater and production of commercial flowers in vertical and horizontal subsurface-flow constructed wetlands

In developing countries, the use of non-conventional plant species as emergent plants in constructed wetlands may add economic benefits besides treating wastewater. In this work, the use of four commercial-valuable ornamental species (Zantedeschia aethiopica, Strelitzia reginae, Anturium andreanum and Agapanthus africanus) was investigated in two types of subsurface wetlands for domestic wastewater treatment. Several water quality parameters were evaluated at the inlet and outlets of a pilot-scale system. Physical measurements were used to evaluate and compare the development of the ornamental plants under two patterns of flow in subsurface wetlands.The results for pollutant removal were significantly higher in the vertical subsurface-flow constructed wetlands (VFCW) for most pollutants. The average removals were more than 80% for BOD and COD; 50.6% for Org-N; 72.2% for NH₄⁺, 50% for Total-P and 96.9% for TC. Only two pollutants were removed in statistically higher percentages in the horizontal subsurface-flow constructed wetlands (HFCW) (NO₃^?, 47.7% and TSS, 82%). The pollutant removal efficiencies were similar to the results obtained in many studies with conventional macrophytes. Most ornamental plants survived the 12-month period of experimentation and their development depended on the type of constructed wetland they were planted. Z. aethiopica looked healthier and produced around 60 flowers in the HFCW. The other three species developed better in the VFCW, although A. andreanum died during the winter. S. reginae produced healthier flowers (and more) and bigger leaves and A. Agapanthus produced more leaves and more lasting flowers. This suggests that it is possible to produce commercial flowers in constructed wetlands without reducing the efficiency of the treatment system.     

Molecular characterization and the effect of salinity on cyanobacterial diversity in the rice fields of Eastern Uttar Pradesh, India

Background

Salinity is known to affect almost half of the world's irrigated lands, especially rice fields. Furthermore, cyanobacteria, one of the critical inhabitants of rice fields have been characterized at molecular level from many different geographical locations. This study, for the first time, has examined the molecular diversity of cyanobacteria inhabiting Indian rice fields which experience various levels of salinity.

Results

Ten physicochemical parameters were analyzed for samples collected from twenty experimental sites. Electrical conductivity data were used to classify the soils and to investigate relationship between soil salinity and cyanobacterial diversity. The cyanobacterial communities were analyzed using semi-nested 16S rRNA gene PCR and denaturing gradient gel electrophoresis. Out of 51 DGGE bands selected for sequencing only 31 which showed difference in sequences were subjected to further analysis. BLAST analysis revealed highest similarity for twenty nine of the sequences with cyanobacteria, and the other two to plant plastids. Clusters obtained based on morphological and molecular attributes of cyanobacteria were correlated to soil salinity. Among six different clades, clades 1, 2, 4 and 6 contained cyanobacteria inhabiting normal or low saline (having EC < 4.0 ds m^-1) to (high) saline soils (having EC > 4.0 ds m^-1), however, clade 5 represented the cyanobacteria inhabiting only saline soils. Whilst, clade 3 contained cyanobacteria from normal soils. The presence of DGGE band corresponding to Aulosira strains were present in large number of soil indicating its wide distribution over a range of salinities, as were Nostoc, Anabaena, and Hapalosiphon although to a lesser extent in the sites studied.

Conclusion

Low salinity favored the presence of heterocystous cyanobacteria, while very high salinity mainly supported the growth of non-heterocystous genera. High nitrogen content in the low salt soils is proposed to be a result of reduced ammonia volatilization compared to the high salt soils. Although many environmental factors could potentially determine the microbial community present in these multidimensional ecosystems, changes in the diversity of cyanobacteria in rice fields was correlated to salinity.