The distribution of chlorophyll a in the eastern equatorial Pacific Ocean in boreal autumn

The distribution and size fractions of chlorophyll a (Chl a) concentration in the eastern equatorial Pacific Ocean in boreal autumn were investigated during October and November, 2011. Environmental factors, including hydrology and nutrients, that might affect the distribution and size composition were analyzed. A total of 18 stations including 11 CTD stations and 7 navigation stations were selected which stretch from the northwest coast of South America to the area of the central Pacific Ocean south of the Hawaiian Islands (2.77°S–13.02°N, 84.11–154.02°W). The studied area can be divided into two transects: the 6°N transect (124–148°W) and the154°W transect (10–13°N). Results showed that the surface Chl a concentration was higher in the east near the northwest coast of South America (>0.200 mg/m³) and lower in the west (0.100–0.200 mg/m³), and it presented a highly significant negative correlation with sea surface temperature (p < 0.001). There were some differences between the sectional distribution of Chl a concentration between the 6°N and 154°W transects. The high values of Chl a concentration occurred near the surface along the 6°N transect (0–75 m), while they were relatively deeper along the 154°W transect (50–100 m). Iron might be the factor that limited the growth of phytoplankton in the eastern equatorial Pacific Ocean. Picophytoplankton (Pico) was the dominant taxa in the surveyed area, particularly in the waters along the two transects (>70% of total Chl a). The Pico to total Chl a ratio was higher in the upper layer (>70%) than in the deeper layer.     

Effects of shade treatments on the photosynthetic capacity,chlorophyll fluorescence,and chlorophyll content of Tetrastigma hemsleyanum Diels et Gilg

Tetrastigma hemsleyanum Diels et Gilg was grown under full sunlight and moderate and high levels of shade for one month to evaluate its photosynthetic and chlorophyll fluorescence response to different light conditions. The results showed that T. hemsleyanum attained greatest leaf size and P_n when cultivated with 67% shade. Leaves of seedlings grown with 90% shade were the smallest. Leaf color of plants grown under full sunlight and 50% shade was yellowish-green. The P_n value increased rapidly as PPFD increased to 200 μmol m^?2 s^?1 and then increased slowly to a maximum, followed by a slow decrease as PPFD was increased to 1000 μmol m^?2 s^?1. P_n was highest for the 67% shade treatment and the LSP for this shade treatment was 600 μmol m^?2 s^?1. Full sunlight and 50% shade treatments resulted in significant reduction of ETR and qP and increased NPQ. Chl a, Chl b and total chlorophyll content increased and Chl a/b values decreased with increased shading. Results showed that light intensity greater than that of 50% shade depressed photosynthetic activity and T. hemsleyanum growth. Irradiance less than that of 75% shade limited carbon assimilation and led to decreased plant growth. Approximately 67% shade is suggested to be the optimum light irradiance condition for T. hemsleyanum cultivation.     

Differences in the photoacclimation and photoprotection exhibited by two species of the ciguatera causing dinoflagellate genus,Gambierdiscus

In culture, Gambierdiscus spp. have been shown to prefer irradiances that are relatively low (≤250 μmol photons m⁻² s⁻¹) versus those to which they are frequently exposed to in their natural environment (>500 μmol photons m⁻² s⁻¹). Although several behavioral strategies for coping with such irradiances have been suggested, it is unclear as to how these dinoflagellates do so on a physiological level. More specifically, how do long term exposures (30 days) affect cell size and cellular chlorophyll content, and what is the photosynthetic response to short term, high irradiance exposures (up to 1464 μmol photons m⁻² s⁻¹)? The results of this study reveal that cell size and chlorophyll content exhibited by G. carolinianus increased with acclimation to increasing photon flux density. Additionally, both G. carolinianus and G. silvae exhibited reduced photosynthetic efficiency when acclimated to increased photon flux density. Photosynthetic yield exhibited by G. silvae was greater than that for G. carolinianus across all acclimation irradiances. Although such differences were evident, both G. carolinianus and G. silvae appear to have adequate biochemical mechanisms to withstand exposure to irradiances exceeding 250 μmol photons m⁻² s⁻¹ for at least short periods of time following acclimation to irradiances of up to 150 μmol photons m⁻² s⁻¹.     

Variation of soil nutrients and particle size under different vegetation types in the Yellow River Delta

The Yellow River Delta wetland, located at the southern coast of Bohai Gulf, provides important ecosystem services such as flood control, water purification, biodiversity conservation, nutrient removal and carbon sequestration, shoreline stabilization, tourism attraction and wetland products maintains in the Yellow River Delta. This study assessed how agricultural activities in a reclamation wetland changed soil pH, soil electric conductivity, soil nutrient and soil particle size as compared to natural vegetation by using a combination of field experiments and lab analysis. The vegetation type included adjacent alfalfa field (Medicago sativa), cotton field (Gossypium spp.), Chinese tamarisk shrub (Tamarix chinensis), and reed marsh (Phragmites sage). The results indicated that the soil pH was higher (pH > 8) in alfalfa field and cotton field, and alfalfa field and reed marsh had significant function in reducing soil salt content, soil electric conductivity of alfalfa field at 0–30 cm were 140.38 ± 14.36, 114.48 ± 14.36, 125.30 ± 11.37 μs/cm. The effect of different vegetation types on soil nutrient was significant (P < 0.05). Soil organic matter at 0–10 cm in Chinese tamarisk shrub and reed marsh was 21.66 ± 3.82 g/kg and 16.51 ± 4.60 g/kg, which was higher than that of alfalfa field (10.47 ± 2.36 g/kg) and cotton field (9.82 ± 1.27 g/kg), but soil total nitrogen content in alfalfa field was the highest, which is significantly higher than that of cotton field, Chinese tamarisk shrub and reed marsh(P < 0.05), the content of soil total nitrogen at 0–10 cm and 10–20 cm was 7.67 ± 0.38 g/kg and 5.97 ± 0.51 g/kg, respectively, while the content of available P and available K was reversed. The difference of soil particle size between layers was not significant (P > 0.05), the sand content of Chinese tamarisk shrub soils in 0–10 cm was the highest, the next was alfalfa field and cotton field, and the content of silt and clay in reed marsh was higher than the others. The correlation and significant degree between soil particle size and soil nutrient was related with vegetation types, and soil organic matter was significantly positively correlated with soil silt and clay content on the alfalfa field. The results demonstrated that wetland cultivation was one of the most important factors influencing on the nutrient fate and reserves in soil, which could lead to rapid nutrient release and slow restoration through abandon cultivation. Consequently, compared with cotton field, alfalfa field is more favorable to sustainable management of wetland cultivation in the Yellow River Delta. It should be considered in wetland restoration projects planning.     

Identification and evaluation of nutrient limitation on periphyton growth in headwater streams in the Pawnee Nation,Oklahoma

The objective of the study was to identify nutrient impacts, if any, on stream periphyton growth in Black Bear Creek (north central Oklahoma) and its tributaries. Passive diffusion periphytometers were deployed at ten study sites within the Black Bear Creek basin to evaluate periphyton growth in response to nutrient enrichment. These sites were selected to represent a gradient of land uses, from predominantly agricultural to predominantly urban. Periphytometer treatments included phosphorus (P) (1.0 mg/L PO₄-P, n = 10), nitrogen (N) (10.0 mg/L NO₃-N, n = 10), N plus P (n = 10) and control (reverse osmosis-treated water, n = 10). Results indicated that average dissolved inorganic N (DIN, PQL = 0.04 mg/L) concentrations were significantly correlated (R² = 0.63, p < 0.01) with chlorophyll a production on the periphytometer control treatments in the Black Bear Creek basin. Periphytic growth was nutrient-limited (increased chlorophyll a was measured on nutrient-enriched growth media) at four of the ten sites sampled; two sites were limited by N and two sites were co-limited by both N and P. The lotic ecosystem trophic status index (LETSI), the ratio of C to N + P chlorophyll a, was calculated to compare treatment responses across sites. At nutrient-limited sites, LETSI was positively correlated to ambient DIN values (R² = 0.97, p < 0.01). However, some sites that were not nutrient-limited had ambient nutrient concentrations similar to sites with observed nutrient limitation, indicating other factors were limiting periphyton growth at those sites.     

Gas exchange acclimation to elevated CO2 in upper-sunlit and lower-shaded canopy leaves in relation to nitrogen acquisition and partitioning in wheat grown in field chambers

Growth at elevated CO₂ often decreases photosynthetic capacity (acclimation) and leaf N concentrations. Lower-shaded canopy leaves may undergo both CO₂ and shade acclimation. The relationship of acclimatory responses of flag and lower-shaded canopy leaves of wheat (Triticum aestivum L.) to the N content, and possible factors affecting N gain and distribution within the plant were investigated in a wheat crop growing in field chambers set at ambient (360 μmol mol⁻¹) and elevated (700 μmol mol⁻¹) CO₂, and with two amounts of N fertilizer (none and 70 kg ha⁻¹ applied on 30 April). Photosynthesis, stomatal conductance and transpiration at a common measurement CO₂, chlorophyll and Rubisco levels of upper-sunlit (flag) and lower-shaded canopy leaves were significantly lower in elevated relative to ambient CO₂-grown plants. Both whole shoot N and leaf N per unit area decreased at elevated CO₂, and leaf N declined with canopy position. Acclimatory responses to elevated CO₂ were enhanced in N-deficient plants. With N supply, the acclimatory responses were less pronounced in lower canopy leaves relative to the flag leaf. Additional N did not increase the fraction of shoot N allocated to the flag and penultimate leaves. The decrease in photosynthetic capacity in both upper-sunlit and lower-shaded leaves in elevated CO₂ was associated with a decrease in N contents in above-ground organs and with lower N partitioning to leaves. A single relationship of N per unit leaf area to the transpiration rate accounted for a significant fraction of the variation among sun-lit and shaded leaves, growth CO₂ level and N supply. We conclude that reduced stomatal conductance and transpiration can decrease plant N, leading to acclimation to CO₂ enrichment.     

Alterations in chlorophyll a fluorescence,pigment concentrations and lipid peroxidation to chilling temperature in coffee seedlings

Coffea arabica L. is considered to be sensitive to low temperatures throughout its life cycle. In some Brazilian regions, seedling production occurs under shade conditions and during the winter, with average temperatures of around 10 °C. The formation and functioning of the photosynthetic apparatus are strongly controlled by temperature. This study aimed to assess the changes that occurred in pigment contents, lipid peroxidation and variables of chlorophyll a fluorescence during the greening process of coffee seedlings submitted to chilling. Results indicate that saturation of the photosynthetic activity of coffee seedlings occurred before saturation of the accumulation of chloroplastid pigments. Pigment accumulation during the greening process is far beyond the metabolic needs for the maintenance of photosynthetic activity, more specifically of photosystem II. Coffee seedlings attained a quantum yield equivalent to that of the control with approximately half the chlorophyll a and b contents and around 40% of the carotenoid. Low temperature decreases the metabolism of seedlings, consequently reducing free radical production and lipid peroxidation. The chilling temperature (10 °C) used inhibited the accumulation of chloroplast pigments, in turn altering the capacity of the photosynthetic tissue of etiolated coffee seedlings to capture and transfer photon energy to the photosystem II reaction centre. These alterations were better demonstrated by O-J-I-P chlorophyll a fluorescence transients, rather than F_v/F_m and F_v/F₀ ratios.     

Physiological and isotopic signals in epilithic mosses for indicating anthropogenic sulfur on the urban–rural scale

The strength and source of anthropogenic sulfur (S) deposition is an important area of research in both environmental and ecological disciplines. Here S concentration, stable isotope (δ³⁴S) and photosynthetic pigments analyses were performed on epilithic mosses at Guiyang area (SW China) for investigating the distribution, origin and effect of urban-derived S at the urban–rural scale. Based on the variation of moss S, anthropogenic S was estimated to account for about 52% of total S in urban mosses and 35% in rural mosses within 30 km. The deposition of urban-derived S was biologically determined within 57 km from the urban center, but only 22% (about 24.4 × 10⁶ kg-S annually) reached over 30 km, with 78% (about 85.9 × 10⁶ kg-S) deposited within 30 km. δ³⁴S_moss signatures suggested the major source of anthropogenic S was still from coal combustion, and comparable δ³⁴S_moss values along the urban–rural transect suggested the inputs of urban-derived S into rural ecosystems. Unexpectedly, moss photosynthetic pigments did not show a decrease with S deposition, but express higher concentrations in the urban than in the rural. In contrast, correlations between moss photosynthetic pigments, and tissue nitrogen (N) and δ¹⁵N demonstrated a fertilizing effect of elevated N deposition on moss photosynthesis, which might buffer or offset the negative effect of S deposition on urban mosses. Collective evidences suggest that S% and δ³⁴S in epilithic mosses provided useful information for determining anthropogenic S deposition on the urban–rural scale, but moss photosynthetic pigments may not be applicable for reflecting S loading under high N deposition.     

Early responses of Bassia diffusa (Thunb.) Kuntze to submergence for different salinity treatments

Early responses of the salt marsh succulent Bassia diffusa (Thunb.) Kuntze to combined salinity and submergence were studied in a laboratory experiment aimed at determining the pattern of the response of photosynthetic pigments, membrane stability, oxalic acid and water relations to these stressors. Three key stages in the response were identified. A drop in chlorophyll a + b within 6 h (4.2 ± 0.2 to 2.4 ± 0.3 mg g^− 1 DM) with a corresponding increase in carotenoid concentration (0.6 ± 0.1 mg g^− 1 DM) indicated an immediate response to submergence. Oxalic acid concentration was highest on Day 4 (1.7 g g^− 1 DM) as opposed to control levels, indicative of its role in submergence tolerance, thus Day 4 may be the peak of positive acclimation. The third phase was marked by a sharp increase in electrolyte leakage to 47.5 ± 2.6% on Day 10, from 9.4 ± 1.4% on Day 7, with a corresponding decrease in total dissolved solutes between Days 7 and 10. Results suggest that oxalic acid accumulates under submergence possibly as a stabilising osmolyte. The threshold for tolerance of the species under submergence is 7 days with membrane damage thereafter. B. diffusa would not survive prolonged submergence (> 7 days) but could survive submergence of short duration (< 7 days) through continuous underwater photosynthesis, accumulation of osmolytes such as oxalic acid and carotenoid, and maintenance of relative water content and succulence within control levels. These data show that this upper intertidal salt marsh plant would be sensitive to prolonged inundation as a result of sea level rise or due to estuary mouth closure and a subsequent rise in water level.     

Decomposition of Phragmites australis rhizome in a shallow lake

Decomposition of Phragmites australis (Cav. Trin ex Steudel) rhizome was studied at Lake Fertő/Neusiedler See using the litter bag technique. Samples were analysed for rhizome dry mass, fibre (cellulose, hemicellulose, lignin) and nutrient content (C, N, P and S), litter-associated fungal biomass, potential microbial respiration (electron transport activity: ETS) and cellulolitic bacteria. The mass loss of decomposing rhizome was rapid in the initial period and only 13.6% of the dry mass remained at the end of the experiment during 953 days. Substantial quantities of C, N, S and P were lost during 99 days; only 18% C, 19% N, 14% S and 6.4% of the P remained after 953 days. Hemicellulose degraded more rapidly than the other fibres whilst the lignin had the slowest rate of decomposition. Bacteria were found to be the primary colonizers of plant detritus, which was followed by fungal growth. An antagonistic relationship was observed between bacteria and fungi. Fungal biomass as determined by ergosterol concentrations ranged between 4.1 and 420 μg g⁻¹ and peaked every year in September. The number of cellulolitic bacteria varied from 0 to 22 MPN g⁻¹ with higher values in summer. The ETS-activity ranged between 0.1 and 1.6 mg O₂ g⁻¹ h⁻¹. The changes in ETS-activity varied almost in parallel with the in situ temperature of the lake water.     

Evaluation of total and non-fatty ether extract in feeds and cattle feces using two analytical methods

The objective of this study was to evaluate ether extract (EE) concentrations, pigments, and wax in forages (n = 14), concentrates (n = 23), and cattle feces (n = 100) using extraction methods recommended by Association of Official Analytical Chemists (AOAC; method 920.39) and American Oil Chemist's Society (AOCS; method Am 5-04). The EE contents were compared by adjusting a linear regression model for each sample type. For the feces and forage samples, the EE contents produced by the AOCS method were greater (P<0.05) compared to those obtained using the AOAC method. No differences between methods were observed in EE content of concentrates (P>0.05). Concentration of vegetable pigments and wax were evaluated by using analysis for variance. Vegetable pigments were lower (P<0.05) in the post-extraction residues using the AOCS method, than the AOAC method, indicating greater participation of vegetable pigments in the EE. No differences were observed between the methods in wax concentration of the post-extraction residues (P>0.05). The quantification method of the EE content that is recommended by AOCS is not suggested for analyses of forage and feces of ruminants because it possibly increases the removal of non-fatty material, mostly pigments, in comparison to the method recommended by AOAC.     

Diel activities of antioxidant enzymes,photosynthetic pigments and malondialdehyde content in stationary-phase cells of Tetraselmis gracilis (Prasinophyceae)

The activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX), as well as photosynthetic pigment contents and free malondialdehyde (MDA), were determined in senescent batch cultures of Tetraselmis gracilis (Kylin) Butcher, under a cyclic light regime. A 2.6-fold increase in SOD activity (from 53 to 137 U mg⁻¹ protein) was observed in the light phase, contrasting with a 9-fold increase in CAT (from 1 to 9 μmol H₂O₂ min⁻¹ mg⁻¹ protein) and a 1.7-fold increase in APX (from 3 to 5 μmol ascorbate min⁻¹ mg⁻¹ protein) activities, both enzymes peaking in the dark phase. The β-carotene and lycopene content did not vary significantly with the light–dark cycle. The Chl a, Chl b, lutein, zeaxanthin, violaxanthin and neoxanthin pigments exhibited the highest values in the first half (3–6 h) of the light phase, followed by a declining trend and a plateau or a slight increase 3 h from the beginning of the dark phase onwards. The highest values for prasinoxanthin were observed in the second half of the dark phase and the first half of the light phase. None of the pigments displayed any discernible cyclic trend. The possibility of the xanthophyll cycle occurring during senescence is discussed in light of the high value (∼0.9) obtained for the zeaxanthin/(zeaxanthin + violaxanthin) ratio. The free MDA content was enhanced during the experimental period, which may be an indicator of oxidative stress in aging cell cultures. Our results indicated the occurrence of an imbalance between the production of reactive oxygen species and the antioxidant defense in stationary T. gracilis cells.     

Salt effects on β-glucosidase: pH-profile narrowing

Salts inhibit the activity of sweet almond β-glucosidase. For cations (Cl⁻ salts) the effectiveness follows the series: Cu⁺², Fe⁺² > Zn⁺² > Li⁺ > Ca⁺² > Mg⁺² > Cs⁺ > NH₄⁺ > Rb⁺ > K⁺ > Na⁺ and for anions (Na⁺ salts) the series is: I⁻ > ClO₄⁻ > ⁻SCN > Br⁻ ≈ NO₃⁻ > Cl⁻ ≈ ⁻OAc > F⁻ ≈ SO₄^− 2. The activity of the enzyme, like that of most glycohydrolases, depends on a deprotonated carboxylate (nucleophile) and a protonated carboxylic acid for optimal activity. The resulting pH-profile of k_cat/K_m for the β-glucosidase-catalyzed hydrolysis of p-nitrophenyl glucoside is characterized by a width at half height that is strongly sensitive to the nature and concentration of the salt. Most of the inhibition is due to a shift in the enzymic pK_as and not to an effect on the pH-independent second-order rate constant, (k_cat/K_m)^lim. For example, as the NaCl concentration is increased from 0.01 M to 1.0 M the apparent pK_a1 increases (from 3.7 to 4.9) and the apparent pK_a2 decreases (from 7.2 to 5.9). With p-nitrophenyl glucoside, the value of the pH-independent (k_cat/K_m)^lim (= 9 × 10⁴ M^− 1 s^− 1) is reduced by less than 4% as the NaCl concentration is increased. There is a similar shift in the pK_as when the LiCl concentration is increased to 1.0 M. The results of these salt-induced pK_a shifts rule out a significant contribution of reverse protonation to the catalytic efficiency of the enzyme. At low salt concentration, the fraction of the catalytically active monoprotonated enzyme in the reverse protonated form (i.e., proton on the group with a pK_a of 3.7 and dissociated from the group with a pK_a of 7.2) is very small (≈ 0.03%). At higher salt concentrations, where the two pK_as become closer, the fraction of the monoprotonated enzyme in the reverse protonated form increases over 300-fold. However, there is no increase in the intrinsic reactivity, (k_cat/K_m)^lim, of the monoprotonated species. For other enzymes which may show such salt-induced pK_a shifts, this provides a convenient test for the role of reverse protonation.     

Allelopathic interactions between the macroalga Hizikia fusiformis (Harvey) and the harmful blooms-forming dinoflagellate Karenia mikimotoi

The effects of algal blooms on seaweeds have been rarely studied, although harmful algal blooms (HABs) are now normally regarded as worldwide incidents. In the present study, the effects of dense Karenia mikimotoi cells on the growth and photosynthesis of Hizikia fusiformis, a common and commercially cultivated macroalga in coastal waters of the East China Sea (ECS), were studied to understand the possible consequences when the mariculture encountered a dense harmful algal bloom. Furthermore, the counteraction of the latter on the growth and photosynthetic activities of K. mikimotoi was determined to evaluate the contribution of H. fusiformis commercial cultivation to environmental improvements. The results showed that the chlorophyll a (Chl a) contents, maximal photochemical efficiency (F_v/F_m) and relative electron transfer rate (rETR) of gas vesicles (specialized leaves), adult and young receptacles of H. fusiformis were all significantly (P < 0.05) inhibited compared with the mono-cultured ones. When compared with mono-cultured H. fusiformis (without K. mikimotoi), the Chl a contents in gas vesicles, adult and young receptacles decreased by 20.6%, 17.6% and 33.2% within 2 weeks. Correspondingly, the F_v/F_m decreased by 7.9%, 37.4% and 43.7%; the apparent photosynthetic efficiency (α) decreased by 9.4%, 47.1% and 48.3%; and rETR decreased by 19.5%, 52.6% and 68.2%, respectively. The Chl a concentration of the mono-cultured K. mikimotoi (without H. fusiformis) increased to 2247.97 μg l⁻¹ from 958.11 μg l⁻¹ within 14 d. Those of the co-cultivated ones (with H. fusiformis), however, increased to 1591.31 μg l⁻¹ on the 8th day and then decreased rapidly to 254.99 (±37.73) μg l⁻¹ after the next 6 days. Furthermore, compared with the mono-cultured K. mikimotoi cells, the F_v/F_m, α and rETR_max of co-cultivated ones decreased by 9.4%, 36.3% and 30.6%, respectively. The results indicated that the mature sporophytes of H. fusiformis were resistant to dense K. mikimotoi blooms and this resistance was organ-dependent as: gas vesicle > adult receptacles > young receptacles. On the other hand, commercial mariculture of H. fusiformis demonstrated the potential of preventing the occurrence of algal blooms.     

Impact of in vitro CO2 enrichment and sugar deprivation on acclimatory responses of Phalaenopsis plantlets to ex vitro conditions

We assessed the effect of growth at either 400 μmol mol^?1 (ambient) or 1000 μmol mol^?1 (elevated) CO₂ and 0 g L^?1 (deprivation) or 30 g L^?1 (supplementation) sugar on morphological traits, photosynthetic attributes and intrinsic elements of the CAM pathway using the CAM orchid Phalaenopsis ‘Amaglade’. The growth of shoot (retarded) and root (induced) was differently affected by CO₂ enrichment and mixotrophic regime (+sugar). The Fv/Fm ratio was 14% more in CO₂-enriched treatment than at ambient level during in vitro growth. At elevated level of CO₂ and sugar treatment, the content of Chl(a + b), Chl a/b and Chl/Car was enhanced while carotenoid content remained unaltered. During in vitro growth, gas-exchange analysis indicated that increased uptake of CO₂ accorded with the increased rate of transpiration and unchanged stomatal conductance at elevated level of CO₂ under both photo- and mixotrophic growth condition. At elevated level of CO₂ and sugar deprivation, activities of Rubisco (26.4%) and PEPC (74.5%) was up-regulated. Among metabolites, the content of sucrose and starch was always higher under CO₂ enrichment during both in vitro and ex vitro growth. Our results indicate that plantlets grown under CO₂ enrichment developed completely viable photosynthetic apparatus ready to be efficiently transferred to ex vitro condition that has far-reaching implications in micropropagation of Phalaenopsis.     

Parietin in the tolerant lichen Xanthoria parietina (L.) Th. Fr. increases protection of Trebouxia photobionts from cadmium excess

Secondary metabolites of lichens can be involved in production of chelates with heavy metals. We hypothesized that parietin plays important role in protection of photobiont cells in Xanthoria parietina from an excess of cadmium ions. Two types of X. parietina lichen thalli, natural with presence of secondary metabolite parietin (p+) as well as without parietin (p−) were exposed to different doses of cadmium (up to 300 μmol g⁻¹ dw). Based on determination of the total and intracellular Cd-accumulation, ergosterol and thiobarbituric acid reactive substances (TBARS) content did not show statistically significant differences in the response of both types of thalli (p+ and p−). However, a stronger toxic effect of the highest Cd-dose on photosynthetic pigment content and chlorophyll a fluorescence was observed in the parietin-depleted thalli. The protective role of parietin against Cd excess was better supported and concluded from the differences observed in the production of non-protein thiol compounds (cysteine, glutathione and phytochelatins) involved in Cd detoxification. In the p+ thalli Cys content was stable but GSH content slightly decreased in the studied Cd range, while in the p− thalli these compounds were completely absent at high Cd doses. At Cd doses higher than 37.5 μmol Cd g⁻¹ dw, toxic to both types of X. parietina thalli, Cys and GSH contents were significantly higher in p+ than in p− thalli. Also, the photobiont partner in the p+ thalli was better protected of the metal exposition, and able to produce phytochelatins (PCs) over the whole range of metal, while in the p− thalli the production was completely inhibited at 75 μmol Cd g⁻¹ dw and higher concentrations, together with the inhibition of cysteine (Cys) and reduced glutathione (GSH) production. The obtained results indicate that the parietin layer is a natural barrier decreasing Cd access to algal cells in X. parietina. Comparison of PCs production appeared to be the most sensitive marker for estimation of Cd availability to photobiont in the symbiotic system.     

Comparative assessment of single and joint effects of diuron and Irgarol 1051 on Arctic and temperate microalgae using chlorophyll a fluorescence imaging

Ship groundings and ice-breakers can cause pollution of the polar environment with antifouling biocides such as diuron and Irgarol 1051. The present study used pulse amplitude modulated fluorometry to compare single and joint toxicities of diuron and Irgarol 1051 on two freshwater taxa of microalgae (Chlorella and Chlamydomonas) originating from Arctic and temperate regions. 30 min acute toxicity tests using chlorophyll a (Chl a) fluorescence revealed that Arctic strains of microalgae were more sensitive to herbicides than their temperate counterparts. Diuron and Irgarol 1051 had equal toxicities in the Arctic species, while Irgarol 1051 was more toxic (EC₅₀ = 5.55–14.70 μg L⁻¹) than diuron (EC₅₀ = 12.90–>40 μg L⁻¹) in the temperate species. Toxicity assessment of various mixtures of diuron and Irgarol 1051 revealed antagonistic, additive, and synergistic effects. Our data suggest that herbicides can adversely affect photosynthesis in Arctic microalgae at relatively low levels, and their impact can increase under complex mixture conditions.     

Plant photosynthesis and its influence on removal efficiencies in constructed wetlands

The photosynthetic characteristics of several wetland plants and their influence on oxygen-evolving activities and disposal efficiencies of horizontal flow subsurface constructed wetlands were compared. The results indicated that the photosynthetic rate of wetlands plants was highly correlated with light intensity and temperature. The photosynthetic characteristics of wetlands species can affect their ability to provide oxygen, and this ultimately influences their disposal efficiencies. Observations indicated that the ability of wetland plants to provide oxygen and remove pollutants decreases in the following order: Phragmites > Canna > Camellia > Dracaena.     

Partial protection of photosynthetic apparatus from UV-B-induced damage by UV-A radiation

Alteration in the photosynthetic apparatus of clusterbean (Cyamopsis tetraganoloba) cotyledons owing to UV-B irradiation in the absence or presence of UV-A radiation (UV-A + UV-B) during steady phase of its growth has been studied. UV-B radiation induces a decline in the photosynthetic pigments content and O₂ evolution along with a modification in the absorption spectra of chloroplasts. UV-A + UV-B irradiation moderately reverses these changes. The partial restoration of F_V/F_M value and other fluorescence transient parameters in UV-A + UV-B treated sample compared to that of UV-B treated one suggest that UV-A helps in developing a protective pathway against UV-B-induced impairment. UV-B-mediated alteration in S state transition of Mn cluster associated with oxygen evolving complex, as appeared from TL glow curves, is retrieved by UV-A radiation and Car is considered to negotiate against UV-B-induced damage of photosynthetic apparatus.     

Sex-specific light acclimation of Chara canescens (Charophyta)

Bisexual populations of the charophyte Chara canescens (Desv. et Loisel. in Loisel., 1810) containing male and female individuals are rarely found. Two experiments were carried out to study whether male and female algae from the same site exhibit different physiological capacities, especially with respect to light acclimation.Algae from two different shore levels and from laboratory cultures acclimated to six irradiance conditions (35–500 μmol photons m⁻² s⁻¹) were compared. Field measurements showed that both female and male algae of C. canescens are able to acclimate to daily changes in solar irradiance. The quantum yield of Photosystem II (PSII) decreased with increasing irradiance in the morning and increased with decreasing irradiance in the afternoon. Growth experiments showed increasing growth rates from 35 μmol photons m⁻² s⁻¹ (∼7 mg FW) up to 500 μmol photons m⁻² s⁻¹ (∼27 mg FW) in female and male C. canescens. The irradiance saturation point for photosynthesis (E_k) was about 140 μmol m⁻² s⁻¹ for both sexes within the whole range of acclimation irradiances. The maximum photosynthesis rate at saturating irradiances (P_max) of male algae was highest at E_k, whereas P_max of female algae was highest at 500 μmol photons m⁻² s⁻¹. The photosynthetic efficiency in the light-limited range (α) increased in female C. canescens and decreased in male C. canescens. The ratio of the non-photochemical quenching parameter (NPQ) to the relative electron transport rates rETR_(MT) increased in both sexes with irradiance, but showed a steeper increase in male than in female algae. Pigment analysis showed similar acclimation pattern for male and female C. canescens. Chl a/Chl b ratios of both sexes were constant over the whole range of E_g, whereas Chl a/carotenoid ratios in male and female C. canescens decreased from 70 μmol photons m⁻² s⁻¹ upwards. Pigment analysis pointed out that the carotenes α-, β- and γ-carotene were more prominent in male than in female algae.Our results indicate that female C. canescens are more efficient in light acclimation than male algae from the same site. Nevertheless, further investigations of bisexual C. canescens populations resolving CO₂-uptake mechanisms and/or genetic differences are needed.