Impact of cadmium toxicity on leaf area,stomatal frequency,stomatal index and pigment content in mungbean seedlings

Effect of different concentrations of CdSO4 (10(-4) M, 5 x 10(-4) M and 10(-3) M) on leaf area, stomatal frequency, stomatal index and pigment content in 6 days old mungbean seedlings was studied under laboratory conditions. Except at 10(-4) M CdSO4, leaf area decreased with an increase in the concentration of CdSO4. Stomatal frequency on the leaf surface increased at 5 x 10(-4) M and 10(-3) M CdSO4 in comparison to untreated control. However, reverse was the case for stomatal index. Chlorophyll-a, chlorophyll-b, total chlorophyll, and chlorophyll a/b ratio were increased at 10(-4) M CdSO4, and decreased thereafter with an increase in the concentration of Cd2+. Possible reasons for the stimulatory effect at low concentrations and inhibitory effect with higher concentrations are discussed.     

不同形态磷对黑藻生长和生理特性的影响

研究了Hoagkand培养液中分别以磷酸二氢钾、焦磷酸钠、六偏磷酸钠、甘油磷酸钠、ATP-Na为磷源时黑藻的生长及生理活性变化.获得了不同形态磷培养黑藻的干重、根系生长以及叶绿素含量、光合、呼吸、磷含量等指标.研究结果表明,磷酸二氢钾对黑藻的生长及生理活性影响最显著,是黑藻吸收的最佳磷形态;有机磷不利于根系生长,叶绿素a/b较高;六偏磷酸钠和焦磷酸钠促进根系早发,光合生产力低于磷酸二氢钾,叶绿素a/b高于磷酸二氢钾试验组.ATP-Na试验组黑藻呼吸率最高,甘油磷酸钠试验组黑藻光合生产力最高.各实验组黑藻磷含量均增加,黑藻对各形态磷均能吸收利用.图5表4参24     

Studies on phytotoxic effect of aluminium on growth and some morphological parameters of Vigna radiata L. Wilczek

Aluminium toxicity is a major deterrent for plant growth in acid soils below pH 5.0. This study deals with effect of aluminium toxicity on growth of mungbean (Vigna radiata L. Wilczek) seedlings. Seed germination (in %) declined with increased content of Al2(SO4)3, while promotive effect was observed at very low dosage. Different concentrations of aluminum sulphate salt were applied to mungbean seeds. Measurement of aluminium content in mungbean leaves was done through atomic absorption spectrophotometer. Root length (root and hypocotyl length) and shoot length (shoot and epicotyl length) was measured at seven days old seedling stage. Different concentrations of Al2(SO4)3 were found to have significant effect both on shoot and root length. Leaf area, fresh and dry weight was significantly reduced. Increased stomatal frequency and trichome density with an increase in concentrations of Al2(S04)3 was observed through scanning electron microscope.     

Impact of copper on haematological profile of freshwater fish, Channa punctatus

The present study was to evaluate heavy metal toxicity stress symptoms in fish blood during long-term exposure of sublethal concentration of copper sulphate (CuSO4). The effects of copper on various heamatological parameters were evaluated exposing Indian fresh water fish, Channa punctatus to a sub-lethal concentration of copper sulphate (0.36 mg l(-1)) for different periods. Exposure of fish to copper showed a significant decrease in the haemoglobin (Hb) content from 10.73 to 6.60%, red blood cells (RBC) from 2.86 to 1.84 x 10(6)/mm3 and packed cell volume (PCV) from 31.00 to 23.33% at the end of 45th day as compared to control. Whereas the white blood cells (WBC) increased from 60.00 to 92.48 x10(3)/mm3, clotting time (CT) from 27.66 to 43.00 second, erythrocyte sedimentation rate from 5.0 to 13.66 mm/hr and mean corpuscular volume from 108.11 to 126.85 cmu, significantly, with increase in exposure periods. Although mean corpuscular haemoglobin concentration (MCHC) and mean corpuscular haemoglobin (MCH) values showed significant increase during 15 and 30 days exposures, both the values were found significantly increased at the end of the experimental period. The differential leucocytes count (DLC) showed a significant increase in the populations of lymphocytes and eosinophils, whereas neutrophils, monocytes and basophiles were found decreased after exposure to copper.     

Effects of calcium,strontium, and magnesium on the coccolithophorid Cricosphaera (Hymenomonas) carterae. II. Cell division

The effects of calcium-deficiency, magnesium-deficiency and strontium enrichment on cell division in the alga Cricosphaera (Hymenomonas) carterae have been studied. Cell growth was reduced at 10^-3 M Ca and was absent at 5x10^-4 M Ca and lower concentrations. The addition of Sr to Ca-deficient media enabled cells to divide, the effect increasing with Sr concentration. When 4.6x10^-4 M Sr was added to media containing 10^-4 M Ca, the rate of division and the final cell concentration were comparable to the control (10^-2 M Ca). Strontium was 20 times more effective than Ca. The rate of growth was also examined at various Mg concentrations. Cell division was absent, or nearly so, in Mg concentrations below 4.2x10^-5 M. Cell size increased progressively as the Mg concentration decreased; however, the lowest protein concentration was found in the absence of Mg. In media lacking Mg, cells exhibited changes in ultrastructure including rounding-up and apparent fragmentation of chloroplasts and an increase in vacuole size. Also, the number of mitochondria per cell section increased 2.9 times in the absence of Mg while the total cross-sectional area remained the same, indicating fragmentation.     

The effect of inhibitors of photosynthesis on zooxanthellae in corals and other marine invertebrates

The effect of the selective photosynthesis inhibitors Monuron (CMU), Diuron (DCMU) and methyl viologen on intact algal-marine invertebrate symbiotic associations was studied. CMU or DCMU (5x10^-4M) completely inhibited photosynthesis, both in intact branches, and in suspensions of isolated zooxanthellae from the reef-building coral Pocillopora damicornis. The inhibitory effect was totally reversible in 1 to 3 h after removal of the inhibitor. Similar inhibition of photosynthesis occurred in 8 other marine coelenterates symbiotic with zooxanthellae, and in 1 marine gastropod symbiotic with functional chloroplasts. Neither CMU nor DCMU appeared to affect behavior of the various hosts, such as swimming, phototaxis, phototropism, photoreception, tentacle contraction, ciliary beating and locomotion. Methyl viologen, however, was ineffective in inhibiting photosynthesis in intact P. damicornis at low concentrations, and lethal to the tissues at high concentrations. These observations indicate that CMU and DCMU are potential useful tools for investigation of symbiotic associations. DCMU (5x10^-4M) also reversibly inhibited light-enhanced calcification in P. damicornis. This strongly suggests that light-enhanced calcification is largely photosynthesis dependent, and probably not dependent on some other photobiological effect.Contribution No. 385, Hawaii Institute of Marine Biology, University of Hawaii     

计划烧除攀枝花苏铁林区地面覆盖物对苏铁生长和土壤理化性质的影响

选择攀枝花苏铁林下计划烧除试验后苏铁及其根系周围土壤(0~15 cm)为对象,研究火烧对攀枝花苏铁植株生长、叶片生理和苏铁根系周围土壤理化性质的影响,以期为区域攀枝花苏铁种群恢复和生态环境保护提供理论依据.结果表明:计划烧除区域苏铁成年树的株数及株高没有显著变化,新生叶片数目和幼苗株数相对未烧除区域显著增加,增幅分别达201.66%和317.7%;烧除区域苏铁植株新生叶片叶绿素a、叶绿素b、叶绿素a+b,可溶性糖、蛋白质含量,硝酸还原酶(NR)、谷氨酰胺合成酶(GS)活性,叶片碳(C)、氮(N)、磷(P)、钾(K)含量,C/N、N/P比与对照区域新生叶片相比无显著性差异,只有类胡萝卜素含量显著降低.计划烧除改变了苏铁根围土壤(0~15 cm)的理化性质,表现在烧除后的土壤含水量、pH值及总N、P、K含量显著降低;但是,火烧显著提高了土壤有机碳(TOC)、硝态氮(NO3--N)、铵态氮(NH4+-N)含量,微生物量C、N含量也略有升高;这说明火烧有利于增加苏铁林下土壤养分(N)的有效性,为烧除后苏铁快速恢复生长提供有利条件.     

外源Hg胁迫对3种烟草品种叶绿素含量和光合效应的影响

为研究不同浓度汞(Hg)对烟草光合作用的影响,选择福建省3个主栽烟草品种(翠碧1号、K326、云烟87)幼苗进行盆栽试验,设置0、1、2、4、8、16 mg·kg~(-1)共6个浓度组。结果表明:(1)3种烟草叶片叶绿素含量与对照比均无显著差异(P0.05),但F_v/F_m、F_v/F_o、PI_(ABS)随胁迫浓度增加均呈下降趋势,可见Hg胁迫下烟草叶绿素含量和光合强度没有必然的相关性。(2)在较高浓度(4 mg·kg~(-1))Hg胁迫下,OJIP曲线改变了形状,表明Hg胁迫对烟草叶片光合机构影响主要是PSⅡ及光系统反应中心受到损伤,光合电子传递过程受到抑制,这可能是烟草叶片光合效应显著下降的主要因素。(3)烟草叶片PSII单位反应中心比活性参数ABS/RC、TRo/RC、DIo/RC与胁迫浓度正相关,ETo/RC和RC/CSo与胁迫浓度呈负相关,在较高浓度Hg胁迫下烟草叶片通过耗散过剩的光能和提高多余能量消耗量来保护光合机构免受更大的伤害,表现出较强的自我调节能力。     

附着生物对沉水植物伊乐藻生长的研究

以沉水植物伊乐藻(Elodea nuttalii(Plant.)ST.John.)为研究对象,室内利用原位湖水进行培养,通过测定伊乐藻的生物量、叶绿素质量分数、光合作用速率等指标,研究了附着生物量的增加对沉水植物伊乐藻的影响。结果表明,随着附着生物处理量的增加,伊乐藻的生物量、叶绿素质量分数以及光合作用速率随之下降,50d后,各处理的生物量与对照相比分别减少了约5%~15%,叶绿素质量分数以及光合作用速率下降了20%~43%、10%~36%。同时也分析了丝状藻对沉水植物伊乐藻的遮阴作用,初步推测附着生物对沉水植物伊乐藻的影响可能是由于附着生物的遮荫作用。研究的结果为揭示富营养化湖泊沉水植被衰退的机理提供了理论依据。     

Photosynthesis and chlorophyll a fluorescence rhythms of marine phytoplankton

Circadian rhythms in photosynthesis were defined in field populations of phytoplankton. Measurements of carbon-dioxide fixation rates demonstrated that a diurnal periodicity of photosynthesis in samples incubated under natural light-dark (LD) cycles also were observed to continue in similar samples which had been photoadapted to constant dim light (LL) for 48 h. These changes in photosynthetic rates preceded sunset and sunrise, had daily amplitudes that ranged from 1.5 to 2.0, appeared to be independent of light-intensity, and displayed maxima about midday, while rates of dark fixation of carbon dioxide and the photosynthetic pigment content per cell were constant over the circadian cycle. Similar rhythmicity also was detected in room-temperature (22°C) chlorophyll a fluorescence yield, in both the obsence and presence of the photosynthesis inhibitor DCMU [3-(3,4-dichlorophenyl)-1, 1-dimethylurea]. However, the magnitude and timing of the fluorescence rhythm maxima seem to depend on wavelengths monitored and, in part, on the measuring technique used. Also, the circadian changes in the fluorescence intensity were abolished at low temperature (-60°C), and the shape of the emission spectra of chlorophyll fluorescence of cells in LD and LL did not change over time. The significance of the fluorescence rhythms with regard to chlorophyll a determinations and photosynthetic rates is discussed. It was concluded that there was sufficient similarity between circadian rhythms of photosynthesis in natural phytoplankton populations and in laboratory cultures of dinoflagellates to suggest that the mechanism of regulation may be the same for both of them.     

Ecotypic differentiation in the marine diatom Skeletonema costatum: influence of light intensity on the photosynthetic apparatus

Three genetically distinct clones of Skeletonema costatum (Grev.) Cleve were grown at 20°C under high (274 E m^-2 s^-1) and low (27 E m^-2 s^-1) light conditions and their photoadaptive photosynthetic responses compared. When all three clones were grown under low light, pigment analyses and fluorescence excitation spectra demonstrated that the accessory pigments, chlorophyll c and fucoxanthin, became more important in light-harvesting compared to chlorophyll a. Photosynthetic unit sizes increased for Photosystems I and II in low light, but photosynthesis vs irradiance characteristics were not reliable predictors of photosynthetic unit features. Fluorescence excitation spectra and photosynthesis vs irradiance (P-I) relationships indicated that changes in energy transfer occurred independent of changes in pigment content. Large increases in accessory pigment content were not accompanied by large increases in excitation from these pigments. Changes in energy transfer properties were as important as changes in PSU size in governing the photoadaptive responses of S. costatum. When the three clones were grown under identical conditions, each had a separate and distinct pattern of photoadaptation. Significant differences among clones were found for pigment ratios, photosynthetic unit sizes for Photosystems I and II and efficiency of energy transfer between pigments. These strikingly different photoadaptive strategies among clones may partially account for the great ecological success of the diatom species. This is the first quantitative investigation of the importance of both chlorophyll c and fucoxanthin to the adaptive responses of diatoms to light intensity, and represents the most complete characterization of the photoadaptive responses of a single species of marine phytoplankter to differences in light environment.     

镉对籽粒苋耐性生理及营养元素吸收积累的影响

初步阐明了镉对籽粒苋耐性生理及营养元素吸收积累的影响,为进一步揭示籽粒苋的镉耐性与镉富集机理奠定了基础。通过对生物量的监测,对叶绿素、蛋白质、游离氨基酸、大量元素及微量元素等的含量的测定,阐明镉胁迫对籽粒苋生长生理、抗胁迫耐性、营养元素吸收分配的影响。研究结果显示,镉胁迫对籽粒苋的生长抑制作用不明显,植株生物量随着镉浓度的提高而轻微降低。随着镉处理浓度的提高,叶绿素含量下降幅度显著;蛋白质和游离氨基酸含量变化幅度不明显;钾含量无大幅变化;镉、磷、钙、镁、锌、铁、锰、铜含量变化幅度较显著。镉、钾、磷、锰的迁移系数随着镉处理浓度的提高无显著变化;钙的迁移系数呈上升趋势;镁、锌、铁、铜的迁移系数均呈下降趋势。这些结果表明：镉胁迫降低籽粒苋叶绿素含量,抑制植株光合作用,继而抑制了植株的生长,但其程度不明显;镉胁迫条件启动活性氧防御机制;引起植株体内部分养分代谢紊乱。结论：低浓度镉处理条件下,籽粒苋受镉离子影响,抗氧化能力下降。在高浓度镉处理条件下,籽粒苋调节了营养元素的吸收和分配,启动了一系列活性氧防御机制,提高了抗胁迫能力。     

Algal chloroplasts in the protoplasm of three species of benthic foraminifera: taxonomic affinity,viability and persistence

The ultrastructure and pigment content of algal chloroplasts (derived from Bacillariophyceae or Chrysophyceae) are described from 3 benthic species of brackish-water foraminiferans.Elphidium williamsoni Haynes contains 4×10⁶ chloroplasts mg^-1, whereas the contents ofNonion germanicum (Ehrenberg) andE. excavatum (Terquem) are about 10% of this value. The two former contain chlorophyllsa andc and fucoxanthin, but these pigments were not detectable in the latter.E. williamsoni andN. germanicum had a net uptake of¹⁴C–HCO ₃ ^- , proportional to their content of chlorophyll and number of chloroplasts, increasing linearly up to approximately 10 Klux. At light saturation the former assimilates 2.3x10^-3 mg C mg^-1 h^-1 and the latter only about 20% of this value. Dark uptake was insignificant in all cases. Uptake could not be demonstrated inE. excavatum. The photosynthesis effected by these species is trivial in terms of the total benthic carbon fixation effected by the microflora. The chloroplasts survived longer in forminiferans kept in the dark than in light/dark adapted individuals. To keep a steady state population of chloroplasts under light/dark conditions,E. williamsoni must eat at least 65 chloroplasts individual^-1 h^-1, whereas the minimum consuption rate inN. germanicum is 20.     

Floristic and physiological differences between the shallow and the deep nanophytoplankton community in the euphotic zone of the open tropical Atlantic revealed by HPLC analysis of pigments

Suspended matter sampled in 1982 in the North Equatorial Current, in the open Atlantic to the west of West Africa, was analyzed by high performance liquid chromatography. The pigment fingerprint of samples taken in the surface mixed layer was dominated by zeaxanthin and chlorophyll a, in agreement with observed dominance of coccoid cyanobacteria. Near the bottom of the euphotic zone the fingerprint was more complicated, with a sharp transition at the depth of the deep chlorophyll maximum layer to dominance of chlorophyll b, 19-hexanoyloxyfucoxanthin and an unknown fucoxanthin derivative in the lower part of this layer; this fingerprint suggests dominance of eukaryotes (green algae, Prymnesiophyceae and Chrysophyceae) at depth. Up to 90% of the chl a was contained in particles smaller than 8 m, and in the surface mixed layer even more than 50% in particles smaller than 1 m. The high concentration of zeaxanthin relative to chl a near the surface suggests adaptation of the cyanobacteria to exposure to high irradiance. Evidence of this adaptation was the very high specific phytoplankton growth rate between sunrise and sunset (=0.16 h^-1), measured by recording ¹⁴C incorporation into organic carbon and into chl a carbon after isolation of the latter by HPLC. The high concentration of chl b relative to chl a at depth was possibly caused by shade-adapted green algae containing more chl b than chl a. The specific growth rate of the deep shade community was low (<0.04 h^-1), yet net primary production, calculated on the basis of chl a increase during incubation, was greatest at depth.     

Effects of light of altered spectral composition on coral zooxanthellae associations and on zooxanthellae in vitro

Pocillopora damicornis (Linnaeus) and Montipora verrucosa (Lamarck) were collected from Hawaiian reefs. In two experiments (September 1979-January 1980: ca. 4 mo; August-October 1980; ca. 2 mo), these reef corals were grown under sunlight passed through filters producing light fields of similar quantum flux but different spectral composition. In vitro cultures of symbiotic zooxanthellae (Symbiodinium microadriaticum Freudenthal) from M. verrucosa were cultured under similar conditions for 15 d. Blue or white light promoted more coral skeletal growth than green or red light. In both coral species, blue light increased the total amount of chlorophyll a of the coral-zooxanthellae association. In the perforate species, M. verrucosa, the pigment concentration was elevated by an increase in the density of zooxanthellae, but the pigment concentrations per algal cell remained unchanged; in the non-perforate species, P. damicornis, it appears that pigment concentration was elevated by an increase in pigment per algal cell, and not by an increase in density of zooxanthellae. The sunloving reef-flat coral P. damicornis did not grow as rapidly as the shade-species M. verrucosa at the low quantum flux (about 10% sunlight) provided by the experimental treatments. The in vitro cultures of zooxanthellae from M. verrucosa exhibited growth rates in light of altered spectral quality that correlated with the responses of the host coral species: blue and white light supported significantly greater growth than green light, and red light resulted in the lowest growth rate.Contribution No. 678 of the Hawaii Institute of Marine Biology     

Analysis of phytoplankton pigments by HPLC before,during and after mass occurrence of the microflagellate Corymbellus aureus during the spring bloom in the open northern North Sea in 1983

Daily observations in April and May 1983 near a subsurface drifter launched in the Fladen Grounds area of the North Sea revealed that a large crop of the microflagellate Corymbellus aureus Green, producing up to 3 g C m^-2 d^-1, succeeded the diatoms dominating during the earlier phase of the spring bloom. The concentration of fucoxanthin was highest during the first half of May, while pigment fingerprints of high-performance liquid chromatograms of suspended matter sampled during the second half of May were dominated by 19-hexanoyloxyfucoxanthin, the main carotenoid of C. aureus (0.8x10^-9 mg cell^-1). This colonial Prymnesiophycean was described for the first time less than 10 years ago and has nerver been reported to be present in the North Sea. After 16 May the C. aureus population rapidly lost its growth potential, but the peak of the bloom in terms of cell number was found several days later (up to 9x10⁶ cells per dm³ on 19 May). The population then started to decline; senescence was associated with decreasing pigment contents of cells. The low growth rate of copepods registered during the second half of May was probably related to the poor quality of C. aureus as copepod food: the concentration of a phaeophorbide a typically found in copepod fecal pellets was highest during the diatom phase of the spring bloom preceding the C. aureus bloom.     

Toxicity evaluation of a complex metal mixture to the softshell clam Mya arenaria

Adults of the softshell clam Mya arenaria were continuously subjected to a flowing raw seawater solution containing a mixture of salts of manganese, zinc, lead, nickel, copper, and cadmium. Final calculated concentrations, in g l^-1, of the toxicant solution were 7200 Mn, 2500 Zn, 70 Pb, 50 Ni, 50 Cu and 1 Cd; these concentrations approximated highest measured levels within surficial interstitial sediment waters from mid-Narragansett Bay, Rhode Island. M. arenaria were also subjected to a 20% solution, i.e., 1440 Mn, 500 Zn, 14 Pb, 10 Ni, 10 Cu, and 0.2 g l^-1 Cd. One study was conducted for 112 days in winter at 0° to 10°C and another for 16 days in summer at 16° to 22°C. In the winter study, all clams exposed to a 100% solution died between the 4th and 10th week; soft parts of survivors at 6 weeks contained about 19 times more Pb, 15 x more Zn, 12 x more Cu, 10 x more Mn, 3 x more Ni and 0.1 x more Cd than controls; relatively minor changes in whole body elemental content of Ca, Cr, Fe, K, Mg, Na, Sr, and V were observed. Clams exposed to a 20% solution during winter survived the 112 day study; at that time these contained about 5 x more Cu, 4 x more Mn, 3 x more Zn and about 2 x more Pb than controls; comparatively minor changes were observed in other elements examined. In the summer study, all M. arenaria subjected to the 100% solution died between 6 and 14 days; survivors from this group at 7 days contained about 25 x more Pb, 13 x more Cu, 11 x more Zn, 7 x more Mn, and 3 x more Ni than controls; other changes in elemental content were not as pronounced. Mortality in the 20% group during summer was slightly higher than controls during the 16 day study; at 14 days survivors from this group contained about 12 x more Mn, 7 x more Pb, 7 x more Zn, 4 x more Cu, and 3 x more Ni than controls. Survival and bioaccumulation patterns were not altered through feeding a supplemental diet of algae. The significance of these findings are discussed in terms of potential environmental perturbations, especially local dredging practices.     

Time-course of photoadaptation in the photosynthesis-irradiance relationship of a dinoflagellate exhibiting photosynthetic periodicity

Cultures of the marine dinoflagellate Glenodinium sp. were light-shifted and rates of photoadaptation determined by monitoring changes in cell volume, growth rate, pigmentation, parameters of the photosynthesisirradiance (P-I) curves and respiration. To approximate physiological conditions of field populations, cells were cultured on an alternating light-dark cycle of 12hL:12hD, which introduced a daily periodicity of photosynthesis. One result of the present study was to demonstrate how specific parameters of the P-I relationship influenced by periodicity of the light: dark cycle are distinguished from photosynthetic parameters influenced by changes in light level. Under steady-state conditions, rates of both light-saturated (P_max) and light-limited photosynthesis changed in unison over the day; these changes were not related to pigmentation, and displayed their maxima midday. This close relationship between P_max and the slope (a) of the cellular P-I curves in steadystate conditions was quickly adjusted when growth illumination was altered. Rates of light-limited photosynthesis were increased under low light conditions and the periodicity of cellular photosynthesis was maintained. The short-term responses of the P-I relationship to changing light level was different, depending on (1) whether the light shift was from high to low light or vice versa, and (2) whether the high light levels were sufficient to promote maximal photosynthesis rates. Major increases in the photosynthetic carotenoid peridinin, associated with a single type of light-harvesting chromo protein in the chloroplast, was observed immediately upon shifting high light cultures to low light conditions. Following pigment synthesis, significant increases in rates of light-limited photosynthesis were observed in about one-tenth the generation time, while cellular photosynthetic potential was unaffected. it is suggested that general results were consistent with suggested that general results were consistent with earlier reports that the major photoadaptive strategy of Glenodinium sp. is to alter photosynthetic unit (PSU) size. Photoadaptive response times to high light were light-dependent, but appeared to be shower than photoadaptive responses to low light. If light intensities were bright enough to maximize growth rates, photosynthetic response times were on the order of a generation period and pigmentation fell quickly as cells divided at a faster rate. If light-intensities were not sufficient to maximize growth rates, then pigment content did not decline, while rates of light-limited photosynthesis declined quickly. In all cases, photoadaptation was followed best by monitoring fast changes in half saturation constants for photosynthesis, rather than fluctuating changes in pigmentation. Results compared well with time-course phenomena reported for other groups of phytoplankton. Overall, results suggest phytoplankton can bring about photo-induced changes in photosynthesis very quickly and thus accommodate widely fluctuating light regimes over short periods of time.     

The impact of enhanced ammonium sulphate inputs exceeding critical load on calluna vulgaris /peat soil microcosms

Ammonium sulphate at six concentrations in simulated precipitation has been applied weekly over two years to Calluna vulgaris growing in peat soil. The nitrogen deposition treatments were chosen to embrace and exceed critical load. The growth and composition of the Calluna and the changes over time in the chemistry of the peat soil and its soil solution were monitored. In spite of significant increases in foliar nitrogen concentration in new shoots, especially in the first year, growth did not increase significantly in response to nitrogen treatment. Several factors could be contributing to the lack of significant growth response. (1) Increasing ammonium input significantly acidified the soil solution, which could adversely effect growth directly. (2) Foliar calcium concentration was reduced significantly in both years by the ammonium sulphate treatments, and more calcium was undoubtedly lost from the rooting zone at higher nitrogen inputs. (3) Foliar phosphate declined significantly between the first and second year, so lack of growth response might also reflect a phosphorus limitation. There was a distinctly visible darkening of the leaves in response to increasing ammonium applications, especially for the first year's growth, and the chlorophyll a and b concentrations in leaves from new growth at the three highest nitrogen treatments were significantly (at P <0.05) higher than those for the control. The pigment concentrations fell markedly by the end of the second season, and treatment effects were much less consistent. It is suggested that pigment analysis therefore probably has little diagnostic value for assessing damage from pollutant nitrogen effects.     

Action spectra and spectral quantum yield of photosynthesis in marine macroalgae with thin and thick thalli

Net photosynthesis at 10mol photons m^-2 s^-1 in each of 24 wavelengths was measured in absolute units by an O₂-electrode and corrected for dark respiration to construct action spectra for gross photosynthesis in nine species of algae, which included plants with thin and thick thalli from each of four major pigment groups. The photosynthesis of green and brown algae with thin thalli decreased in green light, but species with thick thalli from these two groups had action spectra which were almost flat, and matched the optical blackness of the thalli but did not reflect the pigment differences between the species. Among the red algae, on the other hand, there was little difference between the action spectra for thin and thick algae. Only wavelengths absorbed by the phycobilin pigments were effective in photosynthesis, even in species (e.g. Chondrus, Phyllophora) which absorbed all visible wavelengths strongly. Maximal quantum yields of 0.10 to 0.12 O₂ molecules per absorbed photon were recorded for thin green and brown algae, but thicker algae in these two groups had lower values. Red algae exhibited maximal values close to 0.10 O₂ molecules per absorbed photon, irrespective of thallus thickness or phycocyanin content, but the quantum yields of phycoerythrin-rich species in the 600 to 650 nm waveband were lower than those of phycocyanin-rich species.