Germination response and viability of an endangered tropical conifer Widdringtonia whytei seeds to temperature and light

The tropical conifer Widdringtonia whytei Rendle is an endangered species endemic to Mulanje Mountain in Malawi. A study was conducted for the first time under controlled conditions in order to assess the effects of temperature and light on germination and viability of W. whytei seeds. Seeds incubated at a constant temperature of 20 °C attained the highest cumulative germination percentage (100%) followed by 87% germination under fluctuating temperatures of 15 °C night/25 °C day. No seed germination occurred at temperatures below 15 °C. Seeds that failed to germinate at temperatures below 15 °C showed the highest (> 90%) viability compared to the seeds incubated at 25 °C (60%). Across temperature regimes, germination was significantly higher under light (44.7%) than dark (35.6%) conditions. It is concluded that temperature is one of the critical factors for germination of W. whytei seed. The ability of W. whytei seeds to germinate both in light and darkness implies that the species would unlikely form a persistent soil seed bank, an attribute which is common in species that survive in habitats frequently disturbed by fires.     

Temperature requirements for seed germination of Pereskia aculeata and Pereskia grandifolia

Pereskia aculeata and Pereskia grandifolia have been studied widely due to their high nutritional and therapeutic values. However, little is known about the biological requirements of their seeds for the various germination factors. Thus, this experiment aimed to evaluate the thermal effects on the germination of these species at the temperatures of 24 °C, 27 °C, 30 °C, 33 °C and 36 °C. After verification of the existence of differences in the performance of germination, a non-linear regression was carried out, relating the germination to temperature and identifying its point of maximum efficiency. We found that the lowest synchronization indexes of germination were observed close to 30 °C. The best germination response of the P. aculeata and P. grandifolia was observed at 30 °C and 33 °C, respectively, with greater germination strength and fewer days to attain 63.21% of germinations. The results obtained from the germination of P. aculeata and P. grandifolia can be described by the Weindull distribution model with three parameters, as proposed by Carneiro and Guedes (1992).     

Seed storage and germination in Kumara plicatilis,a tree aloe endemic to mountain fynbos in the Boland,south-western Cape,South Africa

Seed storage under appropriate conditions is a relatively inexpensive means of safeguarding plant genetic material for ex situ conservation. Post-storage germination trials are used to determine the viability of stored seeds, and hence the efficacy of the particular storage treatment. Kumara plicatilis (= Aloe plicatilis) is a tree aloe endemic to mountain fynbos in the Boland, south-western Cape. The viability and germination behaviour of K. plicatilis seeds were assessed for seeds stored for four and nine months at − 80 °C, 4 °C, 25 °C and under ambient conditions in a laboratory. Seeds were germinated under controlled conditions and germination rates and percentages determined. Ungerminated seeds were tested for viability using tetrazolium salt. Seed viability was not significantly reduced during storage. Seeds stored at − 80 °C for four and nine months exhibited the fastest germination rate overall (both 5.9 ± 0.3 weeks, mean ± S.E.), and slowest was for seeds stored under ambient conditions for four and nine months (both 7.8 ± 0.4 weeks). All seed lots showed similar percentage germination after four months of storage (78.0–90.4%). The highest percentage germination overall was for seeds stored at − 80 °C for four months (90.4%) and the lowest was for seeds kept at 4 °C and − 80 °C for nine months (39.2 and 39.6%, respectively). Respective percentage viability for ungerminated seeds in these two treatments was 82% and 87%, respectively, indicating the induction of secondary dormancy. Induced dormancy triggered by protracted cold temperatures may be an adaptation that enables seeds to survive prolonged extreme conditions that are unfavourable for germination. Further research on the long-term storage of aloe seeds would be beneficial for developing long-term seed storage and germination testing protocols for ex situ conservation.     

Differential protein expression for geothermal Agrostis scabra and turf-type Agrostis stolonifera differing in heat tolerance

Heat stress is a major factor limiting the growth of cool-season grasses in warm climatic regions by affecting many physiological processes, including protein metabolism. Protein degradation often occurs with increasing temperatures, but certain specific proteins such as heat shock proteins (HSPs) may be induced or enhanced in their expression under supraoptimal temperatures. The objectives of this study were to determine the critical temperature that causes protein induction or degradation in two Agrostis grass species differing in heat tolerance and to compare protein profiles between the two species under different temperature regimes. Plants of heat-tolerant Agrostis scabra and two cultivars of heat-sensitive Agrostis stolonifera (‘L-93’ and ‘Penncross’) were exposed to constant day/night temperatures of 20, 30, 35, 40, or 45 °C for 14 d. Leaf photochemical efficiency (Fv/Fm), chlorophyll and carotenoid contents, and soluble protein content declined with increasing temperatures. The decreases were the least severe for A. scabra, intermediate for ‘L-93’, and the most severe for ‘Penncross’, indicating interspecific and intraspecific variations in heat tolerance in Agrostis species. Protein degradation was observed at 30–45 °C in both cultivars of A. stolonifera, and at 40–45 °C in A. scabra.HSPs were induced or enhanced at 35–45 °C in ‘L-93’ and A. scabra, and at 40–45 °C in ‘Penncross’. Immunoblotting also revealed stronger expressions of HSP60 and HSP70 in A. scabra or ‘L-93’ than in ‘Penncross’ at 35–45 °C after 3 d. The results suggested the superior heat tolerance of Agrostis grass species and cultivars could be attributed to the early induction of HSPs, particularly small molecular weight (23 kDa), at a lower level of heat stress and the maintenance of protein thermostability, particularly high-molecular weight proteins (83 kDa and large units of Rubisco).     

Pre-incubation prior to semen processing and the subsequent effect on the quality of fresh-cooled and cryopreserved ram semen

For artificial insemination (AI) in the pig, semen is routinely maintained at room temperature for 2–4 h prior to extending—to reduce the cooling damage to sperm during cryopreservation. In the sheep industry, however, semen is diluted and cooled immediately after collection. This trial evaluated the effect of a 4 h pre-incubation period for semen at room temperature on the subsequent quality parameters of ram sperm prepared for AI. Immediately following collection, ram semen was divided in 2 aliquots—one was left undiluted for 4 h at room temperature (20 °C; pre-incubation) and the other (control) was diluted with an egg-yolk-based extender and either cooled to 5 °C (n = 8 different ejaculates) for short-term fresh conservation or cryopreserved (n = 6 different ejaculates). After 4 h at room temperature, the pre-incubated semen was then diluted and either cooled to 5 °C or cryopreserved, as was the control. Sperm motility, viability and chlortetracycline (CTC) pattern distribution of the pre-incubated semen were compared to the control. For fresh semen conserved at 5 °C, total sperm motility and the proportion of CTC pattern F sperm (referring to non-capacitated, non-acrosome reacted cells) were reduced by the 4 h incubation at room temperature, compared to the control. The effect of pre-incubation at room temperature was more evident in the cryopreserved semen in terms of total and progressive sperm motility, with the viability being reduced following pre-incubation. For the cryopreserved semen, the percentage of CTC pattern F sperm declined, while the pattern of AR sperm (referring to acrosome-reacted cells) increased, compared to the controls. In conclusion, pre-incubation of ram semen for 4 h at room temperature prior to preparation for AI is not beneficial to the subsequent functionality of the sperm. Furthermore, this pre-incubation period is more harmful to frozen-thawed than to fresh-cooled sperm.     

Germination characteristics of the grass weed Digitaria nuda (Schumach.)

The effect of various pre-treatments and their interaction with temperature on cumulative percentage and the rate of germination were evaluated for Digitaria nuda. Stored and fresh seeds were pre-treated with either 0.02 M KNO₃, soaked in water for 24 h (priming), sterilized with 0.5% NaOCl or heat treated at 60 °C. Seeds were germinated at constant temperatures of 25 and 30 °C and fluctuating temperature regimes of 25/10 and 30/15 °C. The effect of pre-chilling on germination of stored and fresh seed was evaluated at 30/15 °C, and seed emergence in two soil types at different burial depths (0, 0.5, 1, 2, 3, 4, 5 and 6 cm) was also determined. The pre-treatment of stored seed with KNO₃ resulted in the highest germination percentage (100%), whereas the pre-treatment of fresh seed with water for 24 h gave the best germination (99%), at constant temperatures of 25 and 30 °C. Pre-chilling of seed increased germination by more than 30%. Emergence from clay loam soil was greater compared with the emergence from sandy loam soil. Total seedling emergence decreased exponentially with increasing burial depths with only 5% of seed germinating from a burial depth of 6 cm. Results from this study showed that germination requirements are species specific and knowledge of factors influencing germination and emergence of grass weed seed can assist in predicting flushes in emergence allowing producers to implement control practices more effectively.     

Ecophysiological requirements on seed germination of a Mediterranean perennial grass (Stipa tenacissima L.) under controlled temperatures and water stress

Stipa tenacissima L. (alpha grass) steppes are one of the most representative ecosystems in arid Mediterranean ecosystems. On the one hand these steppes, which are perpetually exposed to climate and strong anthropogenic pressure, have undergone severe degradation. On the other hand, the ability of S. tenacissima to regenerate naturally is significantly reduced. In this study the germination response and seedling emergence of S. tenacissima are examined in relation to the main environmental factors (water stress and temperature) under laboratory-controlled conditions. The main aim of this paper was to investigate the influence of temperature over a temperature range (10 °C–30 °C) and water stress induced by the solutions of polyethylene glycol (PEG)-6000 (0 to − 1.6 MPa) for a period of 30 days, on the germination behavior of S. tenacissima seeds. The results showed that temperatures between 10° and 20 °C seem to be favorable for the germination of this species, with optimum temperatures among accessions found in 20 °C. When seeds were water-stressed, germination severely decreased at − 0.8 MPa, indicating that the accession resistance limits to the water stress, and was completely inhibited at − 1.6 MPa. Consequently, the final germination percentage (FGP) decreased and the mean time germination (MTG) increased. Based on the empirical data of the germination rate, we estimated that the parameters of the thermal time and hydrotime models showed different values in all accessions which proves the difference between accession adaptive capacities.     

The germination characteristics of Alexandrium minutum (Dinophyceae), a toxic dinoflagellate from the Fal estuary (UK)

The germination characteristics of Alexandrium minutum cysts from the Fal estuary were studied at different conditions of temperature (4–24 °C) and salinity (15–35‰) and in the dark and low light intensity (2 μmol^?2 s^?1). Sediment sub-samples were directly cultured and processed at the end of the experiment for counts of non-germinated cysts. A decrease in the number of cysts was interpreted as germination that was calculated by comparison of the number of cysts over time with that of initial counts. The 50% germination time (time at which 50% of the total initial number of cysts had germinated) was calculated for each condition. A. minutum did not germinate in the dark but it germinated under all other conditions studied. Highest germination occurred at salinities of 30 psu and 35 psu and temperatures from 8 °C to 24 °C (germination rate—expressed as the inverse of the 50% germination time: 1.1–1.2). Lowest germination occurred at 15 psu and 4 °C and 24 °C (germination rate: 3.9–3.8). However, little variation in germination rates occurred across the conditions studied. As these conditions represent those likely in the estuary it is probable that A. minutum cysts on the surface of the sediments represent a constant source of cells to the water column and sediment disturbance (revealing buried cysts) could rapidly inoculate the water column with vegetative cells. This data was used to develop a model for Alexandrium germination from coastal sediments.     

Role of calcium in alleviating effect of salinity on germination of Phragmites karka seeds

Phragmites karka (Retz.) Trin, ex. steud, a perennial reed with creeping rhizome from the family Poaceae, is distributed as pure population in brackish water swamps. Populations primarily propagate using ramets but also produce numerous seeds which form part of the seed bank after dispersal and are exposed to extremes of temperature, drought, and salinity stress. Seeds were germinated under a range of salinity (0, 100, 200, 300, 400, 500 mM NaCl) and temperature (10/20 °C, 15/25 °C, 20/30 °C, 25/35 °C, night/day) regimes in 12 h light:12 h dark photoperiod or in complete darkness with 0, 5, 10, 25 mM CaCl₂. Salinity, absence of light and high temperature (25/35 °C) reduced germination while calcium generally reversed this effect, more so at cooler temperature regimes. Calcareous soil around Karachi would help alleviate the salinity effect on the germination of P. karka and facilitate its survival.     

Effect of variable dew temperatures on infection of green foxtail by Pyricularia setariae,Drechslera gigantea,and Exserohilum rostratum

A thermogradient apparatus was used to investigate the effect of variable dew temperatures on infection of green foxtail by the indigenous pathogen Pyricularia setariae (Ps) and the exotic pathogens Drechslera gigantea (Dg), and Exserohilum rostratum (Er) from the southern USA that showed bioherbicide potential against several grassy weeds. This device is capable of creating multiple diurnal temperature cycles, mimicking daily temperature fluctuations that occur under field conditions. Seven temperature regimes, i.e., 15/10 °C, 20/5 °C, 20/15 °C, 25/10 °C, 25/20 °C, 30/15 °C, and 30/25 °C (maximum/minimum), were used with temperature cycling from maximum to minimum and then back up to maximum in a 24 h period. Ps and Dg were much more virulent than Er on green foxtail, resulting in higher levels of disease and weed control. Dg was little affected by the dew temperatures in terms of plant infection and was more efficacious than Ps under cooler dew temperatures (15/10 °C and 20/5 °C), causing twice as much disease. This greater amount of disease coincided with higher conidial germination, appressorial formation and infection-hypha frequency by Dg at the lower temperatures. The efficacy of Ps improved as dew temperature increased, accompanied by a higher percentage of germination and more frequent appressorial production. Dg caused severe disease 2 d after inoculation whereas Ps required 4 d to initiate disease symptoms. These observations suggest that Dg is a superior candidate than Ps for green foxtail control on the Canadian prairies.     

A novel organic solvent-stable alkaline protease from organic solvent–tolerant Bacillus licheniformis YP1A

An organic solvent-stable alkaline protease producing bacterium was isolated from the crude oil contaminant soil and identified as Bacillus licheniformis. The enzyme retained more than 95% of its initial activity after pre-incubation at 40 °C for 1 h in the presence of 50% (v/v) organic solvents such as DMSO, DMF, and cyclohexane. The protease was active in a broad range of pH from 8.0 to 12.0 with the optimum pH 9.5. The optimum temperature for this protease activity was 60 °C, and the enzyme remained active after incubation at 50–60 °C for 1 h. This organic solvent-stable protease could be used as a biocatalyst for organic solvent-based enzymatic synthesis.     

Response of in vitro pollen germination and pollen tube growth of almond (Prunus dulcis Mill.) to temperature,polyamines and polyamine synthesis inhibitor

Prunus dulcis L. ‘Mamaei’ is grown widely in souhtwest of Iran. It blooms in early spring when temperatures are still low. Based on our knowledge there are no reports in the literature regarding pollen behavior of this cultivar under specified condition. Thus, the possible factors for low germination percentage in this cultivar have not been reported. The effect of three different temperatures (10, 25, or 35 °C), polyamines (putrescine, spermidine, and spermine) and polyamine synthesis inhibitor, methylglyoxals-bis (guanyl-hydrazone) (MGBG) on in vitro pollen germination and pollen tube growth were investigated in P. dulcis L. ‘Mamaei’. All temperatures and chemicals significantly affected both pollen germination percentage and pollen tube growth. In general, different polyamines stimulated the pollen germination percentage compared to the control at all temperatures, but increasing the temperature, particularly to 35 °C, had demonstrated inhibitory effects on pollen germination. At a concentration of 0.05 mM putrescine and spermidine and 0.005 and 0.025 mM spermine revealed longer pollen tube growth than that of the control at 10 °C, while higher concentrations tended to inhibit pollen tube growth. At 25 °C, most of the treatments had an inhibitory effect on pollen tube growth except for 0.25 mM putrescine and 0.005 mM spermine, which slightly stimulated pollen tube growth. Pollen germination and pollen tube growth were inhibited by MGBG at all temperatures and in all concentrations.     

Effects of salt,alkali and salt–alkali mixed stresses on seed germination of the halophyte Salsola ferganica (Chenopodiaceae)

Salsola ferganica L. (Chenopodianceae) is an annual halophytic species. Experiments were carried out in laboratory to determine the effects of temperature, perianths and various types of salinity on seed germination and germination recovery. Seeds were germinated at 6 levels of temperature with perianths, plus perianths and removed perianths in complete darkness for 9 days. The germination responses of the seeds without perianths at 25 °C were determined over a wide range of NaCl, NaHCO₃ or NaCl–NaHCO₃ mixed stress for 13 days. Perianths seriously affected germination as a barrier for seed germination and the optimal temperature was at 25 °C. Highest germination percentage was obtained under control and seed germination was progressively inhibited with the increase of salinity concentration. The negative effect of NaHCO₃ at the same concentration on germination was stronger than that of NaCl and NaCl–NaHCO₃ mixed. When substrate salinity was removed, seeds exposed to a high NaCl concentration (400–800 mM), NaHCO₃ (50–200 mM) and NaCl–NaHCO₃ mixed (100–400 mM) germinated well. Final germination of Salsola ferganica seeds was significantly affected by types of salt at the low salinity (?200 mM) and with increased salinity it was influenced mainly by salinity concentration for various proportion of salt–alkali mixed stress.     

Evaluation of tomato cultivars to Helicoverpa armigera using two-sex life table parameters in laboratory

Helicoverpa armigera (Hübner) is one of the most important pests of a wide range of agricultural crops worldwide. Resistance of 10 tomato cultivars (‘Primoearly,’ ‘Riogrand,’ ‘CaljN3,’ ‘Kingstone,’ ‘Earlyurbana,’ ‘Petomech,’ ‘EarlyurbanaY,’ ‘Mobil,’ ‘Imprial’ and ‘Petoearly’) to H. armigera was evaluated under laboratory conditions at 25 ± 1 °C, 60 ± 5% RH and a photoperiod of 16:8 (L:D) hours using age-stage, two-sex life table parameters. The larval period ranged from 19.96 on ‘Riogrand’ to 24.58 days on ‘Imprial.’ The insects reared on ‘Imprial’ had the longest total preoviposition period (44.80 days) and those reared on ‘Riogrand’ had the shortest one (35.44 days). The longest adult longevity for female and male was observed on ‘EarlyurbanaY’ (14.40 days) and ‘Kingstone’ (15.00 days), respectively. Using age-stage, two-sex life table, the value of the net reproductive rate (R₀) varied from 7.8 on ‘Imprial’ to 186.9 offspring per individual on ‘Petomech.’ The lowest value of the intrinsic rate of increase (r) and finite rate of increase (λ) was on ‘Imprial’ (0.0410 and 1.0423 day^− 1, respectively) and the highest was on ‘Petomech’ (0.1274 and 1.1359 day^− 1, respectively). The mean generation time (T) on different cultivars varied from 39.9 to 48.2 days. The results revealed that ‘Petomech’ was the most susceptible (suitable) and ‘Imprial’ was the most resistant (unsuitable) cultivar to this pest among the tomato cultivars tested.     

Seed viability of five wild Saudi Arabian species by germination and X-ray tests

Our objective was to evaluate the usefulness of the germination vs. the X-ray test in determining the initial viability of seeds of five wild species (Moringa peregrina, Abrus precatorius, Arthrocnemum macrostachyum, Acacia ehrenbergiana and Acacia tortilis) from Saudi Arabia. Usually several days were required to determine the viability of all five species via germination tests. However, X-ray test will give immediate results on filled/viable seeds. Seeds of all species, except Acacia ehrenbergiana and Acacia tortilis showed high viability in both germination (96–72% at 25/15 °C, 94–70% at 35/25 °C) and X-ray (100–80%) test. Furthermore, there was a general agreement between the germination (19%, 14% at 25/15 °C and 17% and 12% at 35/25 °C) and X-ray (8%, 4%) tests in which seed viability of Acacia ehrenbergiana and Acacia tortilis was very low due to insect damaged embryo as shown in X-ray analysis. Seeds of Abruspreca torius have physical dormancy, which was broken by scarification in concentrated sulfuric acid (10 min), and they exhibited high viability in both the germination (83% at 25/15 °C and 81% at 35/25 °C) and X-ray (96%) tests. Most of the nongerminated seeds of the five species except those of Acacia ehrenbergiana and Acacia tortilis, were alive as judged by the tetrazolium test (TZ). Thus, for the five species examined, the X-ray test was proved to be a good and rapid predictor of seed viability.     

Determination of seed viability of eight wild Saudi Arabian species by germination and X-ray tests

Our purpose was to evaluate the usefulness of the germination vs. the X-ray test in determining the initial viability of seeds of eight wild species (Salvia spinosa, Salvia aegyptiaca, Ochradenus baccatus, Ochradenus arabicus, Suaeda aegyptiaca, Suaeda vermiculata, Prosopisfarcta and Panicumturgidum) from Saudi Arabia. Several days were required to determine viability of all eight species via germination tests, while immediate results on filled/viable seeds were obtained with the X-ray test. Seeds of all the species, except Sa.aegyptiaca, showed high viability in both the germination (98–70% at 25/15 °C, 93–66% at 35/25 °C) and X-ray (100–75%) test. Furthermore, there was general agreement between the germination (10% at 25/15 °C and 8% at 35/25 °C) and X-ray (5%) tests that seed viability of Sa.aegyptiaca was very low, and X-ray analysis revealed that this was due to poor embryo development. Seeds of P.farcta have physical dormancy, which was broken by scarification in concentrated sulfuric acid (10 min), and they exhibited high viability in both the germination (98% at 25/15 °C and 93% at 35/25 °C) and X-ray (98%) test. Most of the nongerminated seeds of the eight species except those of Sa.aegyptiaca were alive as judged by the tetrazolium test (TZ). Thus, for the eight species examined, the X-ray test was a good and rapid predictor of seed viability.     

Spontaneous whole body rotations and classical dance expertise: How shoulder–hip coordination influences supporting leg displacements

The link between supporting leg stability and individual trunk strategies used during spontaneous whole-body rotations was studied according to visual and kinesthetic imagery styles for classical dancers and untrained female participants. Shoulders–hip angles in the horizontal plane and supporting leg (SL) displacements were analyzed with three-dimensional kinematic at the beginning and end of the four turns, identified according to their SL (left vs. right) and turn direction (clockwise, CW vs. counterclockwise, CCW). To begin a turn in CCW on left SL, all the participants turned shoulders before hips (?25° angle), p < 0.01. Untrained participants yielded the reverse (+30° angle) in CW – their non-preferred turn - whereas dancers maintained their trunk en bloc. In the turn slow down, in their preferred direction all the participants adopted en bloc behavior to avoid imbalance. Dancers kept this pattern in CCW but untrained participants separated shoulders and hips, p < 0.01; on left SL (+20° angle) hips finished before shoulders and on right SL (?25° angle), shoulders finished before hips. Both mental imagery styles and spatial context link reduction of shoulder–hip angle and stability of SL. Daily expertise, not only dance training, facilitates the en bloc shoulder–hip coordination to maintain equilibrium.     

Nitrate removal in surface-flow constructed wetlands treating dilute agricultural runoff in the lower Yakima Basin,Washington

Constructed treatment wetlands (CTWs) have been used effectively to treat a range of wastewaters and non-point sources contaminated with nitrogen (N). But documented long-term case studies of CTWs treating dilute nitrate-dominated agricultural runoff are limited. This study presents an analysis of four years of water quality data for a 1.6-ha surface-flow CTW treating irrigation return flows in Yakima Basin in central Washington. The CTW consisted of a sedimentation basin followed by two surface-flow wetlands in parallel, each with three cells. Inflow typically contained 1–3 mg-N/L nitrate and <0.4 mg-N/L total Kjeldahl N (TKN). Hydraulic loading was fairly constant, ranging from around 125 cm/d in the sedimentation basin to 12 cm/d in the treatment wetlands. Concentration removal efficiencies for nitrate averaged 34% in the sedimentation basin and 90–93% in the treatment wetlands. Total N removal efficiencies averaged 21% and 57–63% in the sedimentation basin and treatment wetlands, respectively. Area-based first-order removal rate constants for nitrate in the wetlands averaged 142–149 m/yr. Areal removal rates for nitrate in treatment wetlands averaged 139–146 mg-N/m²/d. Outflow from the CTW typically contained <0.1 mg-N/L nitrate and <0.6 mg-N/L TKN. Rates of nitrate loss in wetlands were highly seasonal, generally peaking in the summer months (June–August). Nitrate loss rates also correlated significantly with water temperature (positively) and dissolved oxygen (negatively). Based on the modified Arrhenius relationship, θ for nitrate loss in the wetlands was 1.05–1.09. The CTW also significantly affected temperature and dissolved oxygen concentration in waters flowing through the system. On average, the sedimentation basin caused an increase in temperature (+1.7 °C) and dissolved oxygen (+1.5 mg/L); in contrast the wetlands caused a decrease in temperature (?1.6 °C) and dissolved oxygen (?5.0 mg/L). Results show that CTWs with surface-flow wetlands can be extremely effective at polishing dilute non-point sources, particularly in semi-arid environments where warm temperatures and low oxygen levels in treatment wetland water promote biological denitrification.     

Temperature-dependent physiological and biochemical responses of the marine medaka Oryzias melastigma with consideration of both low and high thermal extremes

This study aimed to investigate temperature effect on physiological and biochemical responses of the marine medaka Oryzias melastigma larvae. The fish were subjected to a stepwise temperature change at a rate of 1 °C/h increasing or decreasing from 25 °C (the control) to six target temperatures (12, 13, 15, 20, 28 and 32 °C) respectively, followed by a 7-day thermal acclimation at each target temperature. The fish were fed ad libitum during the experiment. The results showed that cumulative mortalities were significantly increased at low temperatures (12 and 13 °C) and at the highest temperature (32 °C). For the survivors, their growth profile closely followed the left-skewed ‘thermal performance curve’. Routine oxygen consumption rates of fish larvae were significantly elevated at 32 °C but suppressed at 13 and 15 °C (due to a high mortality, larvae from 12 °C were not examined). Levels of heat shock proteins and activities of malate dehydrogenase and lactate dehydrogenase were also measured in fish larvae exposed at 15, 25 and 32 °C. The activities of both enzymes were significantly increased at both 15 and 32 °C, where the fish larvae probably suffered from thermal discomfort and increased anaerobic components so as to compensate the mismatch of energy demand and supply at these thermal extremes. Coincidently, heat shock proteins were also up-regulated at both 15 and 32 °C, enabling cellular protection. Moreover, the critical thermal maxima and minima of fish larvae increased significantly with increasing acclimation temperature, implying that the fish could develop some degrees of thermal tolerance through temperature acclimation.