Aspects of population dynamics in Halimione portulacoides communities

Summary Studies on sample plots inHalimione portulacoides communities show that environmental disturbances, either natural or induced by man, start a sequence of partly overlapping density maxima inSuaeda maritima, Aster tripolium andPuccinellia maritima successively, before the originalHalimione community totally recovers. When succession time before recovering is long enough, there are tendencies in redundancy of this sequence stressing the unilinear character of the succession. Minor environmental impacts induce a longer time-lag period of theSuaeda density maximum, suggesting threshold values of these impacts for the species to maintain minimal population densities or to become locally extinct. This sequence of interim species starting after an environmental disturbance, suggests also a gradient character in various biological attributes, for instance in life-time, propagation, nutrient and genetic plasticity strategies. The mechanism described can therefore be interpreted as a complex of mostly well-adapted and well-integrated inherent species strategies capable of absorbing environmental shocks. It is suggested that in the salt-marsh ccosystem the pattern of spatial variation in densities and that of temporal variation in fluctuations of the three species populations under natural conditions reflect corresponding patterns of environmental disturbances in the vegetation taking into account a timelag associated with the magnitude of the impact concerned.Contribution to the Symposium on Plant species and plant communities held at Nijmegen, 11–12 November 1976, on the occasion of the 60th birthday of Professor Victor Westhoff.Nomenclature follows Heukels-van Ooststroom. Flora van Nederland, 18e druk, 1975. Wolters-Noodhoff, Groningen.The authors are greatly indebted to Dr K.F. Vaas (Yerseke) for reviewing the English text.Communication Nr. 160.     

Decomposition of Spartina anglica,Elytrigia pungens and Halimione portulacoides in a Dutch salt marsh in association with faunal and habitat influences

Decomposition of Spartina anglica, Elytrigia pungens and Halimione portulacoides was studied for 20.5 months in situ in two habitats on a salt marsh in The SW Netherlands. Litter bags of three different mesh sizes were used to exclude meio- and/or macrofauna. The middle-marsh habitat was flooded more frequently than the plant-debris habitat in the highest marsh zone. Decomposition of the three species followed an exponential pattern of decay: instantaneous decay rates varied from 0.0026 to 0.0054 per day. Decay rates were significantly influenced by habitat factors and fauna, while there was a significant interaction between plant species and habitat. In case of a significant meio- and/or macrofauna effect, this became noticeable 12–16 weeks after the start of decomposition and resulted in a difference of 5–10% ash-free dry weight remaining after 20.5 months. Nematodes were the dominant microfaunal group in the plant litter. Densities were influenced by habitat conditions but not by resource quality, season and meio- and/or macrofauna. Only initial C/N and C/P ratios were correlated with differences in decomposition rates between the plant species. During the later stages of decomposition N and P concentrations of the plant litter were higher in the plant-debris habitat than in the middle-marsh habitat, probably as a result of fluctuating detritivores densities. The course of the decomposition process differed per plant species and per habitat. The results of this study underline the importance of knowledge of long-term decomposition rates.     

Mineral composition of Halimione portulacoides (L.) Aellen leaves

Mineral composition ofHalimione portulacoides (L.) Aellen leaves was studied. The leaves accumulate salt, which is partly compensated by succulence. The ratio K/Na is less than 1. No distinct correlation between salt content in the soil and the mineral content at different stations could be found. Communication no. 148 of the Delta Institute for Hydrobiological Research, Yerseke, The Netherlands.     

The effect of the osmotic potential and specific ion concentration of the nutrient solution on the uptake and reduction of nitrate by barley seedlings

Summary Short-term absorption experiments were conducted with intact barley (Hordeum vulgare L.) seedlings to observe the effects of the osmotic potential (Ψ^π) and salt species on nitrate uptake andin vivo nitrate reduction. The experiments consisted of growing barley seedlings for 5 days in complete nutrient solutions salinized to (Ψ^π) levels of −0.6, −1.8, −3.0, −4.2, and −5.4 bars with NaCl, CaCl₂ or Na₂SO₄. After the absorption period, the seedlings were separated into shoots and roots, weighed, then analyzed for NO₃. The nutrient solutions were sampled for NO₃ analysis each day immediately before renewing the solutions. The accumulative loss of NO₃ from the solutions was considered to be uptake whereas NO₃ reduction was the difference between uptake and seedling content. Lowering the (Ψ^π) of the nutrient solutions resulted in decreased concentrations of NO₃ in the plant, little or no effect (except at the lowest (Ψ^π) level) on uptake, and increased nitrate reductase activity. Increased rates of NO₃ reduction were in particular associated with the Cl concentration of the nutrient solution.     

The phytosociology of British sea-cliff vegetation with special reference to the ecophysiology of some maritime cliff plants

The major factors thought to control the distribution of associations on the sea cliffs in Britain are discussed in relation to the zonation of cliff vegetation, and some experiments to investigate the effects of these factors are described.The seeds of the maritime cliff species are able to germinate in higher salinities than those of closely related inland species.Relative growth rates of maritime cliff species indicate stimulation at low salinities over non-saline conditions, and less reduction in growth at higher salinities than those of closely related inland species.Increasing salinity reduces both photosynthesis and dark respiration in Lavatera arborea. Mesophyll and stomatal resistances are increased while transpiration is reduced.The distribution of ions within Lavatera arborea grown at different salinities indicates differential accumulation between young leaves, old leaves and roots.Nomenclature follows Clapham, Tutin & Warburg (1962).     

不同缺氮营养水平对金色奥杜藻生长及光合生理的影响

采用了Φ6 cm柱状光生物反应器,在不同氮素营养条件(17.6 mmol/L N、8.8 mmol/L N、5.87 mmol/L N、0 mmol/L N)下通气培养硅藻金色奥杜藻[Odontella aurita(Bacillariophyceae;Centricae)],分析探讨藻细胞的光合生理及生长状况与氮素营养水平的关系。结果表明,不同氮素实验组藻细胞达到最大生长的时间明显差异,与对照组(17.6 mmol/L)相比,氮限制(5.87mmol/L N、8.8 mmol/L N)在培养的前期对金色奥杜藻的生长具有促进作用,氮饥饿(0 mmol/L)显著抑制藻细胞生长(P<0.05)。氮限制实验组藻细胞总碳水化合物的含量显著增加(P<0.05),而总蛋白含量明显下降(P<0.05)。藻细胞叶绿素a、c及总类胡萝卜素含量与培养液的氮素营养水平呈正相关。藻细胞最大光合放氧速率Pm随氮浓度下降而降低,呼吸速率Rd呈现相反趋势,PSⅡ最大光能转化效率(Fv/Fm)、实际光能转化效率(Yield)、潜在活性(Fv/Fo)以及相对电子传递效率(ETR)均随氮素限制而显著下降(P<0.05),说明藻细胞的表观光合生理状况与氮素营养水平直接相关。     

Two ecologically distinct subspecies ofHypochaeris radicata L.

Summary Uptake and assimilation of nitrate by two subspecies ofHypochaeris radicata L. were investigated under laboratory conditions as well as in the field.H. radicata ssp.radicata grows on relatively nitrogen-richer soils thanH. radicata ssp.ericetorum. Attempts were made to relate nitrate uptake and nitrate assimilation in the two subspecies to their different distribution in the field.No differences between the two subspecies with respect to nitrate uptake and nitrate assimilation were observed under laboratory conditions. In plants from the field intact tissue nitrate reductase was higher in ssp.radicata than in ssp.ericetorum. The nitrate reductase activity of both subspecies responded positively to nitrate addition.The significance of nitrate uptake capacity and the level of nitrate reductase for the distribution of plants in the field is here discussed.Grassland species research group, publ. no.15.     

Effects of NaCl on the nitrogen metabolism of the halophyteArthrocnemum fruticosum (L.) Moq., grown in a greenhouse

Summary Arthrocnemum fruticosum (L.)Moq., a halophyte from the shore of the Dead Sea in Jordan was grown in a greenhouse with nutrient solution supplemented with various concentrations of NaCl. It was shown that with increasing salinity the plants became more succulent, mainly due to an accumulation of sodium and water. Sodium was taken up into the roots in equal amounts to chloride, but in the shoots far more sodium than chloride was found, suggesting a control of these ions either in the excretion into the xylem, or in the uptake by the shoot out of the xylem. Ammonium and nitrate in the plants decreased with time on nutrient solution more or less independently of the salt concentration. However, more nitrate appeared again in the plants when they started flowering. After an initial period of adaptation the nitrate reductase activityin vivo was not inhibited by a salinity of up to 2%, but at higher NaCl concentrations a shift of nitrate reductase activity occurred from the roots to the shoots. This was consistent with earlier observations in the field. In the vegetative phase of the plants the nitrate reductase in the roots was influenced by the soil water potential, but in the shoot it was mainly dependent on the supply of nitrate from the roots. High NaCl concentrations delayed flower initiation. During flowering the nitrate reductase was involved in the re-allocation of nitrogenous compounds from the roots to the developing flowers, and it became effectively independent from salinity.     

Effects of temperature, salinity and irradiance on the growth of the red tide dinoflagellate Gyrodinium instriatum Freudenthal et Lee

The effects of temperature, salinity and irradiance on the growth of the red tide dinoflagellate Gyrodinium instriatum Freudenthal et Lee were examined in the laboratory. Exposed to 45 different combinations of temperature (10–30 °C) and salinity (0–40) under saturating irradiance, G. instriatum exhibited its maximum growth rate of 0.7 divisions/day at a combination of 25 °C and a salinity of 30. Optimum growth rates (>0.5 divisions/day) were observed at temperatures ranging from 20 to 30 °C and at salinities from 10 to 35. The organism could not grow at ≤10 °C. In addition, G. instriatum burst at a salinity of 0 at all temperatures, but grew at a salinity of 5 at temperatures between 20 and 25 °C. It is noteworthy that G. instriatum is a euryhaline organism that can live under extremely low salinity. Factorial analysis revealed that the contributions of temperature and salinity to its growth of the organism were almost equal. The irradiance at the light compensation point (I₀) was 10.6 μmol/(m² s) and the saturated irradiance for growth (I_s) was 70 μmol/(m² s), which was lower than I_s for several other harmful dinoflagellates (90–110 μmol/(m² s)).     

Comparison of the growth rates of dinitrogen fixing subterranean clover swards with those assimilating nitrate ions

Summary Subterranean clover plants were grown as swards (about 2000 plants/m²) under controlled conditions with N provided either by N₂-fixation (NO ₃ ^– withheld) or by assimilation of NO ₃ ^– (NO ₃ ^– supplied). Crop growth rates were measured by dry matter sampling over periods of up to 70 days at PPFD values of 400–1000 mole quanta/m²/s. When NO ₃ ^– was supplied from sowing the swards grew more rapidly than when the swards were not supplied with NO ₃ ^– and plants had to establish an N₂-fixing apparatus. When inter-plant competition was reduced within the sward, a difference in growth rate in favour of NO ₃ ^– -fed plants continued for at least 50 days. When however, a closed canopy was allowed to form, the NO ₃ ^– -fed swards had more dry weight than the N₂-fed swards at the time of canopy closure but thereafter the two swards grew at similar rates at light flux densities of above about 800 mole quanta/m²/s. At light flux densities of about 400 mole quanta/m²/s N₂-fed swards had a growth rate 70–80% of that of NO ₃ ^– -fed plants. NO ₃ ^– -fed plants had a higher organic N content than did N₂-fed plants under all conditions.     

Changes in morphological plasticity of Ulva prolifera under different environmental conditions: A laboratory experiment

The large-scale green tides, consisting mainly of Ulva prolifera, have invaded the coastal zones of western Yellow Sea each year since 2008, resulting in tremendous impacts on the local environment and economy. A large number of studies have been conducted to investigate the physiological traits of U. prolifera to explain its dominance in the green tides. However, little has been reported regarding the response of U. prolifera to changing environmental factors via morphological variation. In our experiments, we found remarkable morphological acclimation of U. prolifera to various temperature (20 and 25 °C) and salinity (10, 20, and 30) conditions. U. prolifera had more, but shorter branches when they were cultured at lower temperature and salinity conditions. To investigate the significance of these morphological variations in its acclimation to changes of environmental factors, physiological and biochemical traits of U. prolifera grown under different conditions were measured. Higher temperature increased the relative growth rate while salinity did not affect it. On the other hand, higher temperature did not enhance the net photosynthetic rate whilst lower salinity did. The increased net photosynthetic rate at lower salinity conditions could be attributed to more photosynthetic pigments—chlorophyll a, chlorophyll b, and carotenoids—in thalli due to there being more branches at lower salinity conditions. Increased numbers of branches and thus an increased intensity of thalli may be helpful to protect thalli from increased osmotic pressure caused by lower salinity, but it led to more shading. In order to capture enough light when being shaded, thalli of U. prolifera synthesized more photosynthetic pigments at lower salinity levels. In addition, higher temperature increased nitrate reductase activity and soluble protein content but variations in salinity did not impose any effect on them. Our results demonstrate conclusively that U. prolifera can acclimatize in the laboratory to the changes of environmental factors (salinity and temperature) by morphology-driven physiological and biochemical variation. We suggest that the morphological plasticity of U. prolifera may be an important factor for it to outcompete other algal species in a changing ocean.     

Interactive effects of triadimefon and salt stress on antioxidative status and ajmalicine accumulation in Catharanthus roseus

The ability of triadimefon (TDM), a triazole group of fungicide, to ameliorate salinity stress was studied in Catharanthus roseus (L.) G. Don. plants subjected to sodium chloride (NaCl) treatment. NaCl treatment at 80 mM level decreased overall growth of this plant and reduced the chlorophyll contents, protein, antioxidant enzymes such as peroxidase (POX), superoxide dismutase (SOD) and polyphenol oxidase (PPO). The root alkaloid ajmalicine got increased under salt treatment. When these stressed plants were treated with TDM at 15 mg l⁻¹ concentration minimized the inhibitory effects of NaCl stress by increasing the root, shoot growth and leaf area and increased dry weight (DW), chlorophyll, protein contents and the activities of antioxidant enzymes like POX, SOD and PPO, thereby paved the way to overcome the salinity injury. The quantity of ajmalicine was again increased with the TDM treatment when compared to both control and NaCl treated plants. From these results, it is proved that the fungicide TDM have great role in the enhancement of plant antioxidative enzymes and the enhanced scavenging of potentially harmful free radicals, as a mechanism of protecting plants against noxious oxidative stress from the environment and also in the enhancement of active principles.     

Pea responses to saline stress is affected by the source of nitrogen nutrition (ammonium or nitrate)

The effect of the source of nitrogen nutrition (ammonium or nitrate), onthe response of pea plants to a moderate saline stress (30 mMNaCl)was studied. Growth declined under saline stress but nitrate-fed plants wereless sensitive to salinity than ammonium-fed plants. This different sensitivitywas due mainly to a better maintenance of root growth in nitrate-fed plants.Organic nitrogen content decreased significantly in roots of ammonium-fedplants. Water relations changed slightly under saline stress leading to adecrease in stomatal conductance, which was correlated to a decline in carbonassimilation rates regardless of nitrogen source. Salinity affects the uptakeofseveral nutrients in a different way, depending on the nitrogen source. Thus,chloride was accumulated mainly in nitrate-fed plants, displacing nitrate,whereas sodium was accumulated mainly in ammonium-fed plants, especially inroots, displacing other cations such as ammonium and potassium. It is concludedthat the nitrogen source (ammonium or nitrate) is a major factor affecting pearesponses to saline stress, plants being more sensitive when ammonium is thesource used. The different sensitivity is discussed in terms of a competitionfor energy between nitrogen assimilation and sodium exclusion processes.     

Effects of salinity and cutting on the development of Phragmites australis

The effects of increased salinity and cutting the above ground biomass on the growth of Phragmites australis were evaluated by investigating four experimental reed stands grown in outdoor tanks. Two stands were treated with 30 salinity and the other two stands with freshwater; one stand of each treatment was cut to 20 cm during the second growing season. Growth conditions were observed until all the plants were dead at the end of the second year. The number of shoots emerged from the freshwater-treated stand was about 70% higher than that of the saltwater-treated stand. The number of shoots emerged from cut plant stands were markedly lower than uncut stands. The average shoot height was negatively affected by salinity and shoots that emerged after cutting further decreased in height. The average number of leaves on a shoot was not significantly affected by salinity, but reduced by cutting in both treatments. Leaf length, width and the distance between leaves were decreased by both salinity and cutting. In the freshwater-treated uncut stand more than 50% of the shoots formed panicles, but this proportion was reduced to 6% by salinity, to 15% by cutting, and to 0% by the combination of salinity and cutting. This study showed again that salinity reduces the growth of aboveground components. The growth, however, was most severely retarded by cutting combined with salinity, which has many implications for better management of P. australis stands.     

Salt tolerance of two differently drought-tolerant wheat genotypes during germination and early seedling growth

Summary Osmotic and specific ion effect are the most frequently mentioned mechanisms by which saline substrates reduce plant growth. However, the relative importance of osmotic and specific ion effect on plant growth seems to vary depending on the drought and/or salt tolerance of the plant under study. We studied the effects of several single salts of Na⁺ and Ca²⁺−NaCl, NaNO₃, Na₂SO₄, NaHCO₃, Na₂CO₃, and Ca(NO₃)₂—on the germination and root and coleoptile growth of two wheat (Triticum aestivum L.) cultivars, TAM W-101 and Sturdy, the former being more drought tolerant than the latter. The concentrations used were: 0, 0.02, 0.04, 0.08, 0.16, and 0.32 mol L⁻¹. Significant two- and three-way interactions were observed between cultivar, kind of salt, and salt concentration for germination, growth of coleoptile and root, and root/coleoptile ratio. Salts differed significantly (P<0.001) in their effect on seed germination, coleoptile and root growth of both cultivars. Germination of TAM W-101 seeds was consistently more tolerant than that of Sturdy to NaCl, CaCl₂, Ca(NO₃)₂, and NaHCO₃ salts at concentrations of 0.02, 0.04, 0.08, 0.16 mol L⁻¹. The osmotic potential, at which the germination of wheat seeds was reduced to 50% of that of the control, was different depending on the kind of salt used in the germination medium. NaCl at low concentrations (0.02 and 0.04 mol L⁻¹) stimulated the germination of both wheat cultivars. At concentrations of 0.02 to 0.16 mol L⁻¹, Ca²⁺ salts (CaCl₂ and Ca(NO₃)₂) were consistently more inhibitory than the respective Na⁺ salts (NaCl and NaNO₃) for germination of Sturdy. This did not consistently hold true for TAM W-101. Among the Na⁺ salts, NaCl was the least toxic and NaHCO₃ and Na₂CO₃ were the most toxic for seed germination. Root and coleoptile (in both wheat cultivars) differed in their response to salts. This differential response of coleoptile and root to each salt resulted in seedlings with a wide range of root/coleoptile ratios. For example, the root/coleoptile ratio of cultivar TAM W-101 changed from 2.09 (in the control) to 3.77, 3.19, 2.8, 2.44, 1.31, 0.32, and 0.0 when subjected to 0.08 mol L⁻¹ of Na₂SO₄, NaCl, CaCl₂, NaNO₃, Ca(NO₃)₂, NaHCO₃, and Na₂CO₃, respectively. Na₂CO₃ at 0.08 mol L⁻¹ inhibited root growth to such an extent that germinated wheat seeds contained coleoptile but no roots. The data indicate that, apart from the clear and more toxic effects of NaHCO₃ and Na₂CO₃ and lesser toxic effect of NaCl on germination and seedling growth, any toxicity-ranking of other salts done at a given concentration and for a given tissue growth may not hold true for other salt concentrations, other tissues and/or other cultivars. The more drought-tolerant TAM W-101, when compared to the less drought tolerant Sturdy, showed higher tolerance (at most concentrations) to NaCl, CaCl₂, Ca(NO₃)₂ and NaHCO₃ during its seed germination and to Na₂SO₄ and CaCl₂ for its root growth. This supports other reports that some drought-tolerant wheat cultivars are more tolerant to NaCl. In contrast, the coleoptile growth of drought-sensitive Sturdy was noticeably more tolerant to NaNO₃, Ca(NO₃)₂ and NaHCO₃ than that of drought-tolerant TAM W-101. Based on the above and the different root/coleoptile ratios observed in the presence of various salts, it is concluded that in these wheat cultivars: a) coleoptile and root tissues are differently sensitive to various salts, and b) at the germination stage, tolerance to certain salts is higher in the more drought-tolerant cultivar.     

Life strategy, ecophysiology and ecology of seaweeds in polar waters

Polar seaweeds are strongly adapted to the low temperatures of their environment, Antarctic species more strongly than Arctic species due to the longer cold water history of the Antarctic region. By reason of the strong isolation of the Southern Ocean the Antarctic marine flora is characterized by a high degree of endemism, whereas in the Arctic only few endemic species have been found so far. All polar species are strongly shade adapted and their phenology is finely tuned to the strong seasonal changes of the light conditions. The paper summarises the present knowledge of seaweeds from both polar regions with regard to the following topics: the history of seaweed research in polar regions; the environment of seaweeds in polar waters; biodiversity, biogeographical relationships and vertical distribution of Arctic and Antarctic seaweeds; life histories and physiological thallus anatomy; temperature demands and geographical distribution; light demands and depth zonation; the effect of salinity, temperature and desiccation on supra-and eulittoral seaweeds; seasonality of reproduction and the physiological characteristics of microscopic developmental stages; seasonal growth and photosynthesis; elemental and nutritional contents and chemical and physical defences against herbivory. We present evidence to show that specific characteristics and adaptations in polar seaweeds help to explain their ecological success under environmentally extreme conditions. In conclusion, as a perspective and guide for future research we draw attention to many remaining gaps in knowledge. Dedicated to Prof. Dr. Gunter O. Kirst and to Prof. Dr. Klaus Lüning on occasion of their retirement 28. Februar 2006 and 31. March 2006, respectively.     

Response to long- and short-term salinity in populations of the C4 nonhalophyte Andropogon glomeratus Walter B.S.P.

Summary This research was undertaken to investigate differences in salt tolerance under conditions in which salinity is increased gradually and maintained for long periods or increased rapidly and maintained for shorter periods. The responses of populations of a C₄ nonhalophytic grass, Andropogon glomeratus, to long- and short-term salinity were measured under controlled environment conditions. Additionally, plants from a salt marsh population and an inland population were transplanted into a salt marsh and their survival compared. The relative growth reductions in the salt marsh and the inland populations under long-term salinity were similar. Survival of seedlings of 4 populations inundated with full-strength seawater over a relatively short period indicated differential capacities to tolerate soil salinities imposed in a manner similar to tidal inundation in a salt marsh. The greater survival of plants from the marsh population transplanted into the salt marsh further indicated genetic differentiation between the populations. These results indicate that genetic differentiation to salt tolerance in A. glomeratus is better reflected by survival after shortterm salinity events, rather than growth inhibition due to long-term salinity imposed gradually.     

The role of nitrate in osmoregulation of Italian ryegrass

Summary The role of nitrate in osmotic control was studied with Italian ryegrass grown in a nutrient solution in a climate room. Quantum-flux density, osmotic potential of the nutrient solution and availability of nitrate and chloride were varied independently. Plants at high quantum flux density (650 mol m^–2 s^–1) had a lower osmotic potential, a higher carbohydrate concentration and a lower nitrate concentration than plants at low quantum flux density (310 mol m^–2 s^–1), the decrease in nitrate concentration was osmotically equivalent to the increase in carbohydrate concentration. When nitrate in the nutrient solution was partly replaced by chloride, the chloride taken up substituted an equivalent part of the nitrate in the plant. It is concluded that nitrate plays a role in osmoregulation of the plant and compensates for a shortage of other solutes.     

Effect of salinity on tissue architecture in expanding wheat leaves

Salinity greatly reduces the leaf cross-sectional area of wheat (Triticum aestivum L.) during its development, which may lead to variation in the architectural properties of growing leaves that would result in a change in leaf physiological functions. Our objective was to characterize the effect of salinity on the spatial distribution of the cross-sectional area and the anatomy of large and small veins of a growing wheat leaf. Spring wheat was grown in a growth chamber in soils with or without 120 mM NaCl. Leaf 4 in both treatments was harvested 2–3 days after its emergence and then cut into five transverse segments. Examination of the transverse sections revealed that salinity significantly reduced the cross-sectional area, width, and radii of both epidermal and mesophyll cells along the leaf axis. Reduction in the cross-sectional area and width occurred mainly at the leaf base, indicating that these reductions occur during the period of leaf initiation. The reduction in cross-sectional area was attributed to a decrease in the size of the vein segments and a reduced number of medium and small veins. The thickness of the leaf was also reduced under the 120 mM NaCl treatment. A greater intercellular air space in the large vein segments under saline conditions was also found. The approximately 35% reduction observed in the number of veins under saline conditions (mainly in the number of small veins) may suggest that salinity reduces the capacity for re-translocation of mineral nutrients and assimilates. The reduced area of protoxylem and metaxylem in midrib and large vein segments in growing tissues may be responsible for lower water deposition into the growth zone under saline conditions.     

Growth and survival of the invasive alga, <Emphasis Type="Italic">Caulerpa taxifolia</Emphasis>, in different salinities and temperatures: implications for coastal lake management

The alga Caulerpa taxifolia is an invasive pest species in many parts of the world and has recently become established in several estuaries in south eastern Australia. A major infestation has occurred in Lake Conjola, an intermittently open and closed coastal lagoon in southern NSW. Short term (1 week) laboratory experiments were carried out to investigate growth and survival of fragments of C. taxifolia collected from this outbreak, under a range of salinities (15–30 ppt) and water temperatures (15–30°C). Fronds, stolons and thalli of the alga all displayed similar responses. Many of the algal fragments doubled in size over the week and a maximum growth rate of 174 mm/week was recorded. Fragments showed good growth (> 20 mm/week) at salinities > 20 ppt and temperatures > 20°C. Almost total mortality occurred at salinities lower than 20 ppt and temperatures less than 20°C. Historical records of water quality demonstrate that prior to entrance manipulation in 2001, salinities in Lake Conjola had often dropped to below 17 ppt for extended periods (up to 2 years). This suggests that management of the alga may be improved if the lake was allowed to undergo its normal cycles of opening and closing to the ocean, and that entrance manipulation may be one factor that has influenced the success of this invasive species.