The annual cycle of growth rate and biomass change in Planktothrix spp. in Blelham Tarn, English Lake District

SUMMARY 1. The changes in the vertical distributions of red coloured Planktothrix rubescens and green P. agardhii filaments in Blelham Tarn, English Lake District, were related to vertical profiles of temperature and light attenuation and to continuous records of the surface irradiance and windspeed, from August 1999 to October 2000. 2. The potential growth rate of each organism was calculated from the irradiance and temperature at 0.5 m depths and hourly intervals throughout the year, using algorithms determined from growth rates in culture. The analyses indicated that there was sufficient irradiance for growth, integrated over the 24‐h cycle, at depths down to the metalimnion where the Planktothrix populations stratified in summer. The compensation depth for growth by P. rubescens reached a maximum of 9.3 m in spring and midsummer, and fell to a minimum of 1.6 m in midwinter; the corresponding values for P. agardhii were 7.9 and 0.5 m. 3. The mixed depth (z_m) exceeded the critical depth for growth (z_b) by P. rubescens (the condition preventing population increase) on only 3 days of the year; for P. agardhii, however, z_m exceeded z_b on 31 days, contributing to its faster decline. The stratified population of P. rubescens was the major cause of light attenuation during the summer of 2000, and resulted in competitive exclusion of P. agardhii. 4. The calculated growth rates integrated over the depth of the water column in Blelham Tarn equalled, or exceeded, the measured changes of the populations during periods when they were increasing, during summer and autumn. Close agreement between the two values was found for much of the year when allowance was made for dilution of the lake population by rainfall over the watershed. During periods of rapid decline, of P. agardhii in September 1999, P. rubescens in December 1999 and both in July–August 2000, additional losses (e.g. by chytrid parasitism and grazing) are invoked.     

Comparative effects of the quality and quantity of light and temperature on the growth of Planktothrix agardhii and P. rubescens1

The effects of temperature, light intensity, and quality on the growth of the cyanobacteria Planktothrix agardhii (Gomont) Anag. et Komárek and P. rubescens (Gomont) Anag. et Komárek were assessed in batch cultures. The relative competitiveness of the green‐pigmented P. agardhii and the red‐pigmented P. rubescens was evaluated in separate and mixed cultures, under different light intensities and qualities (green, red, and white), and at two different temperatures, chosen as representative of the natural conditions favoring the respective blooms of each species. In monocultures, the P. rubescens strain appeared to be particularly well adapted to low intensities of green light and displayed a strong photoinhibition under high irradiance levels. The P. agardhii strain appeared less specialized with regard to light quality and also less sensitive to photoinhibition at higher irradiances. In competition experiments, temperature (15°C vs. 25°C) was the most important parameter in determining relative fitness of the species and competitive success. At 15°C, P. rubescens appeared to be much more competitive than P. agardhii, while P. agardhii was more competitive at 25°C. Under low irradiance, however, the pigmentation of these strains was of primary importance in determining the outcomes of the competition experiments. On the basis of our experimental results and on field observations, we propose that the successful growth leading to the proliferation of these two differently pigmented strains may largely depend on the combined conditions of light and temperature. The two strains, being genetically close relatives, could therefore be considered as two ecotypes that are adapted to different light and temperature environments. Competition experiments showed that the combination of these parameters largely controls the success of one strain in comparison to the other.     

The daily integral of photosynthesis by Planktothrix rubescens during summer stratification and autumnal mixing in Lake Zürich

It has been suggested that the populations of planktonic cyanobacteria that occupy the metalimnion of stratified lakes during the summer months may be aestivating between the main periods of growth during entrainment in the epilimnion in spring and summer. We determined the vertical distribution of the biomass and daily integral of photosynthesis of the population of Planktothrix ( Oscillatoria ) rubescens in Lake Zürich for 136 d from July to November 1995. The population showed an 80-fold increase during the stratified period but it only doubled over the subsequent period of entrainment. During the first eight days, part of the increase was attributed to recruitment of filaments floating up from greater depths but all of the subsequent production could be accounted for by photoautotrophic growth. On sunny days the biomass-specific photosynthesis of this population reached some of the highest values over the whole period despite its depth (>13 m). On very cloudy days, however, primary productivity was very low and on 4 days, when the mean depth of the population exceeded 15 m, there was no net production. Over the whole period of the study, the accumulated photosynthetic production exceeded the increase in biomass of the population by a factor of 9·5. Although much of this production occurred during the period of entrainment only a small proportion was translated into growth of the population. It is concluded that the growth that takes place in the period of stratification in the metalimnion is essential to subsequent production.     

Experimental manipulations of the phytoplankton periodicity in large limnetic enclosures in Blelham Tarn,English Lake District

This paper reviews the results of experimental manipulations, carried out during the period 1977–1983, on the phytoplankton maintained in the limnetic enclosures at Blelham Tarn, English Lake District. Three categories of manipulations are considered.The effects of variation in the scale and frequency of phosphorus loading (range: 0.3 to 2.5 g P m^–2 a^–1) upon the mean phytoplankton biomass, its seasonal distribution and specific dominance are shown to conform to well-established patterns and relationships observed in natural lakes. Much of the seasonal variability in species dominance occurred independently of nutrient ratios, though carbon availability has been critical at times. Attempts to manipulate the rates of removal of phytoplankton by grazing have confirmed that they act selectively against certain smaller species only, that they alter the rate of successional change, rather than its direction, and that they have little lasting influence upon the total phytoplankton standing crop. Attempts to manipulate rates of sinking loss through artificial enlargement of the epilimnetic circulation also regulated the light-conditions experienced by suspended phytoplankton.Growth-rate relationships to an index of light exposure and to temperature fluctuation are also derived for several species and are related to morphological and physiological characters of the organisms concerned. These interpretations are briefly reviewed in relation to periodic cycles in natural lakes.     

The effect of lake fertilisation on the rotifers of Seathwaite Tarn,an acidified lake in the English Lake District

Seathwaite Tarn, in the English Lake District, was used as an experimental site to test the feasibility of increasing the pH of an acidified waterbody by adding a phosphorus-based fertiliser solution. The impact of this experiment on the planktonic rotifer community was assessed by monitoring for two years before treatment (1990–1991), and for a further two years once treatment had begun (1992–1993). The pH of the water rose by 0.5 pH units over the period of fertilisation, and the lake became very eutrophic. This had little effect on the species composition of the rotifer assemblage, which continued to reflect the acid, oligotrophic nature of the untreated lake. However, there were marked changes in the levels of abundance of most planktonic species. Population densities of Keratella serrulata and Trichocerca longiseta increased in early spring, compared to pre-treatment levels, apparently due to the rises in chlorophyll-a concentrations. In contrast, Polyarthra dolichoptera became very scarce after fertilisation began. The treatment seemed to have little effect on the population dynamics of the dominant openwater rotifer, Polyarthra remata. In 1993, very high densities of Bosmina coregoni (up to 250 × 10³ ind M^–3 ) developed in response to the eutrophication programme. This seemed to suppress the rotifer community in the summer months.     

Effects of temperature and pH on growth and photosynthesis of the thermophilic cyanobacterium Synechococcus lividus as measured by pulse-amplitude modulated fluorometry

In this study, the effects of five different temperatures and pH conditions on growth and photosynthetic performance of Synechococcus lividus Copeland from Taiwan were monitored in the field and the laboratory by using an underwater pulse‐amplitude modulated (Diving‐PAM) fluorometer. In the field, the optimal growth temperature of S. lividus was found to be 57°C. Such a finding was congruent with the growth rate in the laboratory culture, in which the optimal growth temperatures ranged from 45 to 60°C. In photosynthetic performance, the light‐saturated maximum relative electron transport rate (ETR_max) and the light‐limited slope (α^ETR) exhibited highest values at 50°C. At five different pH conditions, higher ETR_max and α^ETR were observed from pH 7 to 9. In addition, regression analysis demonstrated a significant positive relationship between the growth rate and the ETR_max values (R² = 0.9527), indicating that the growth of S. lividus was largely restricted to its photosynthetic performance. In conclusion, the photosynthetic performance and growth of the thermophilic cyanobacterium S. lividus were sensitive to fluctuations in temperature but not in pH. The present investigation offers a better understanding of the photosynthetic physiology.     

Marbled lungfish growth rates in Lake Baringo, Kenya, estimated by mark‐recapture

Mark‐recapture was used to quantify the relationship between body mass ( M _T) and individual growth rates of sub‐adult marbled lungfish Protopterus aethiopicus in Lake Baringo, Kenya. Specific growth rate (in mass) was found to be a well defined and decreasing function of M _T over the size range of recaptured fish. Growth trajectories based on this function indicated that Lake Baringo African lungfish reached maturity at an age of c . 3 years and had a low reproductive effort.     

Photosynthesis and growth rates of Laurencia brongniartii J. Agardh (Rhodophyta, Ceramiales) in preparation for cultivation

Laurencia brongniartii is usually found at depths below 4 m, but can be found in shallow subtidal areas in crevices and on the walls of a coral reef in Amami Oshima Island, Kagoshima Prefecture, Japan, where irradiances were significantly lower than those at similar depths in open water. In preparation for the possible cultivation of this species for its antibiotic compounds, the effects of temperature and irradiance on photosynthesis and growth were measured. Photosynthesis and growth rates of L. brongniartii explants were highest at 26 and 28 °C, which closely corresponded to temperatures found during August to late December when it was most abundant. The estimated maximum photosynthesis rate (P _max) was 4.41 mol photon m^–2 s^–1 at 26 °C and 4.07 mol photon m^–2 s^–1 at 28 °C. Saturating irradiance occurred at 95 mol photon m^–2 s^–1 at 26 °C and 65 mol photon m^–2 s^–1 at 28 °C. In contrast, growth experiments at 41.7 mol photon m^–2 s^–1 caused bleaching of explants and the maximum growth rate observed during the study was 3.02 ± 0.75% day^–1 at 28 °C and 25 mol photon m^–2 s^–1. The difference in the saturating irradiance for photosynthesis and the irradiance that caused bleaching in growth experiments suggests that long-term exposure to high irradiance was detrimental and should be addressed before the initiation of large scale cultivation.     

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.     

The application of ethephon (an ethylene releaser) increases growth, photosynthesis and nitrogen accumulation in mustard (Brassica juncea L.) under high nitrogen levels

Ethephon (2-chloroethyl phosphonic acid), an ethylene-releasing compound, influences growth and photosynthesis of mustard (Brassica juncea L. Czern & Coss.). We show the effect of nitrogen availability on ethylene evolution and how this affects growth, photosynthesis and nitrogen accumulation. Ethylene evolution in the control with low N (100 mg N kg(-1) soil) was two-times higher than with high N (200 mg N kg(-1) soil). The application of 100-400 microl x l(-1) ethephon post-flowering, i.e. 60 days after sowing, on plants receiving low or high N further increased ethylene evolution. Leaf area, relative growth rate (RGR), photosynthesis, leaf nitrate reductase (NR) activity and leaf N reached a maximum with application of 200 microl x l(-1) ethephon and high N. The results suggest that the application of ethephon influences growth, photosynthesis and N accumulation, depending on the amount of nitrogen in the soil.     

Supplemental manganese improves the relative growth, net assimilation and photosynthetic rates of salt-stressed barley

Previous results in our laboratory indicated that a reduced Mn concentration in the leaves of barley was highly correlated with the reduced relative growth and net assimilation rates of salt-stressed plants. If Mn deficiency limits the growth of salt-stressed barley, then increasing leaf Mn concentrations should increase growth. In the present study, the effect of supplemental Mn on the growth of salt-stressed barley ( Hordeum vulgare L. cv. CM 72) was tested to determine if a salinity-induced Mn deficiency was limiting growth. Plants were salinized with 125 mol m⁻³ NaCl and 9.6 mol m⁻³ CaCl₂. Supplemental Mn was applied in 2 ways: 1) by increasing the Mn concentration in the solution culture and 2) by spraying Mn solutions directly onto the leaves. Growth was markedly inhibited at this salinity level. Dry matter production was increased 100% in salt-stressed plants treated with supplemental Mn to about 32% of the level of nonsalinized controls. The optimum solution culture concentration was 2.0 mmol m⁻³, and the optimum concentration applied to the leaves was 5.0 mol m⁻³. Supplemental Mn did not affect the growth of control plants. Further experiments showed that supplemental Mn increased Mn concentrations and uptake to the shoot. Supplemental Mn increased the relative growth rate of salt-stressed plants and this increase was attributed to an increase in the net assimilation rate; there were no significant effects on the leaf area ratio. Supplemental Mn also increased the net photosynthetic rate of salt-stressed plants. The data support the hypothesis that salinity induced a Mn deficiency in the shoot, which partially reduced photosynthetic rates and growth.     

Carbohydrate partitioning, photosynthesis and growth in Lemna gibba G3.I. Effects of nitrogen Limitation

The growth rate of Lemna giba L. G3 was varied by limiting the supply of nitrogen (N) under otherwise constant condition. Two experimental approaches were used. 1) A series of suboptimally growing cultures were supplid daily with exponentially increasing doses on N. 2) Optimally growing cultures were transferred to a N-fre medium and cultivated in it for 10 days. Lveles of starch, sucrose, glucose, fructose, and systems. At RGR ranging from optimal to 50% of optimal caused decreased levels of soluble sugars, but increased lvels of starch.Starch accumulation showed a strong negative correlation with the CO² assimilation rate, indicating increased triose phosphate/inorganic phosphate (TP/Pⁱ) ratio in the chloroplast causing end product inhibition of photosyntheisis. The data indicat the quantitative rlationship betwen the photosynthetic activity and the carbon utilization rate influnces the activity of the sucrose synthesis pathway and thus the rate of the triose hosphate/Pⁱ exchange at the chloroplast membrane, which in turn regulates the activity of starch synthesis and the Calvin cycle.     

Carbohydrate partitioning, photosynthesis and growth in Lemna gibba G3. II. Effects of phosphorus limitation

The relationship between CO₂ assimilation rate, growth and partitioning of carbon among starch, sucrose, glucose and fructose were studied in phosphorus (P_i)-limited Lemna gibba L. G3. Two experimental models were used: 1) Cultures were grown at various stable, suboptimal rates regulated by the supply of P_i; 2) cultures growing at optimal rates were transferred to P_i-free medium. The response to a P_i deficiency can be divided into two phases. Phase I is characterized by hyperactivity of the sucrose synthesis pathway, leading to high levels of glucose and fructose. Phase II is characterized by starch accumulation associated with a decrease in the cytoplasmic pools of soluble sugars owing to inhibition of carbon export from the chloroplast. A strong negative correlation was found between the CO₂ assimilation rate and starch levels. No significant correlation was found between assimilation and ATP levels and decrease in relative growth rate did not significantly affect the adenylate energy charge (EC). The regulatory aspects of the partitioning of carbon among soluble sugars and starch as well as the negative correlation between carbohydrate levels and CO₂ assimilation at P_i-limited growth are discussed.     

龙须菜(Gracilaria lemaneiformis)的生长、光合作用及其对扇贝排泄氮磷的吸收

研究了不同温度、光照条件下大型藻类龙须菜(Gracilaria lemaneiformis)的生长和光合作用特性,及其对扇贝排泄氮、磷的吸收作用。结果表明温度与龙须菜的生长和光合作用显著相关,在本实验条件下,15~25℃都适宜龙须菜生长,其中20℃龙须菜具有较高的生长率(SGR),为2·8%/d;光合作用速率随温度升高和光照的增加而升高,30℃和120μmol/(m2·s)时最高,最大光合作用速率(Pmax)为5·0mg O2/(g dw·h)。龙须菜对扇贝排泄氮、磷有较强的吸收作用,其吸收率和去除效率与放养密度和养殖时间有关。对NH4-N和PO4-P的最大去除效率分别为83·7%和70·4%,最大吸收率分别为9·9μmol/(g ww·h)和4·3μmol/(g ww·h)。实验证明龙须菜生长温度范围和光照范围适合中国北方海区养殖,并且能有效吸收和去除扇贝排泄氮、磷,可以作为生物滤器与贝类及其他养殖动物进行综合养殖。     

Effects of salinity on growth, photosynthesis and respiration in a freshwater alga Rhizoclonium riparium (Chlorophyceae, Cladophorales)

A freshwater green alga, Rhizoclonium riparium (Roth) Harvey, was found to grow in diluted seawater with salinities (PSU) from 0.1 to 34.0 (0.1–34.0 S). It grew best at 13.6 S and least at 0.1 S which was the least salinity reported in its habitat. Net photosynthetic oxygen production of R. riparium rose with salinity up to 34.0. However, in the medium adjusted at pH 8.1. the net photosynthesis rose at low ranges of salinity and was almost at the same level in all ranges of salinities examined. The net photosynthesis was increased by the addition of bicarbonate in the medium. Respiratory oxygen consumption did not rise with the increase of external salinities from 0.1 to 34.0. The results indicate that R. riparium can grow by increasing net photosynthesis in diluted seawater in which the pH value is suitable for effective bicarbonate supply to photosynthesis.