Photoinhibition and recovery of the kelp Laminaria saccharina at optimal and superoptimal temperatures

Effects of high irradiance on photosynthetic characteristics were examined in sporophytes of the kelp Laminaria saccharina Lamour. from 1992 to 1994. Exposure to high irradiance (700 mol photons m^-2s^-1) for 1 h at optimal temperature (12°C) caused a 40 to 60% decline in photosynthetic efficiency (alpha), quantum yield, and the ratio of variable to maximum chlorophyll fluorescence (F_v/F_m), an indicator of Photosystem II efficiency. Although the photoinhibition effects were partly attributable to protective mechanisms, a concurrent increase in minimal fluorescence (F_o) indicated damage to Photosystem II reaction centers. The magnitude of photoinhibition was proportional to irradiance and duration; however, F_v/F_m was significantly reduced after exposure to irradiances as low as 40 to 50 mol photons m^-2s^-1 for 1 h, or to 700 mol photons m^-2s^-1 for only 5 min. In contrast, photosynthetic capacity (P_max) was affected only at much higher irradiance. Superoptimal temperatures up to 24°C did not exacerbate high-light effects. At 25°C, however, alpha and P_max were more susceptible to photoinhibition than at lower temperatures. Recovery from photoinhibition was examined by following F_v/F_m and F_o for 24 h after exposure to high light. Recovery of F_v/F_m was fastest during the first 1 to 3 h, and slowed or ceased after 6 to 12 h, while recovery of F_o was relatively constant over 12 h. Dithiothreitol, which blocks formation of energy-dissipating xanthophylls, reduced both the initial rate and extent of recovery. Chloramphenicol, which blocks chloroplast-encoded protein synthesis, had little effect on initial rates of recovery, but stopped recovery after 3 h. Thus, L. saccharina appears to rely on the xanthophyll cycle to protect the photosynthetic apparatus, and reversal of this protective mechanism causes the rapid initial recovery in F_v/F_m. Longterm recovery depends on repair of damaged reaction centers. Both the rate and extent of recovery were temperature-dependent. The initial rate was higher at 18 to 22°C than at 12°C, but the extent of recovery over 24 h declined with increasing temperature. High temperatures, therefore, appear to enhance protective mechanisms, but disrupt repair processes. L. saccharina from Long Island Sound, an ecotype adapted to low light and high temperature, showed slightly but consistently greater effects of photoinhibition than plants from the Atlantic coast of Maine, but exhibited faster recovery at superoptimal temperatures.     

Caribbean mangroves and seagrass beds as daytime feeding habitats for juvenile French grunts, Haemulon flavolineatum

Caribbean seagrass beds are important feeding habitats for so-called nocturnally active zoobenthivorous fish, but the extent to which these fishes use mangroves and seagrass beds as feeding habitats during daytime remains unclear. We hypothesised three feeding strategies: (1) fishes feed opportunistically in mangroves or seagrass beds throughout the day and feed predominantly in seagrass beds during night-time; (2) fishes start feeding in mangroves or seagrass beds during daytime just prior to nocturnal feeding in seagrass beds; (3) after nocturnal feeding in seagrass beds, fishes complete feeding in mangroves or seagrass beds during the morning. We studied the effect of habitat type, fish size, social mode and time of day on resting and feeding behaviour of large juvenile (5–10 cm) and sub-adult (10–15 cm) Haemulon flavolineatum in mangroves and seagrass beds during daytime. Sub-adults occurred in mangroves only, spent most time on resting, and showed rare opportunistic feeding events (concordant with strategy 1), regardless of their social mode (solitary or schooling). In contrast, large juveniles were present in both habitat types and solitary fishes mainly foraged, while schooling fishes mainly rested. Exceptions were small juveniles (±5 cm) in seagrass beds which foraged intensively while schooling. Large juveniles showed more feeding activity in seagrass beds than in mangroves. In both habitat types, they showed benthic feeding, whereas pelagic feeding was observed almost exclusively in the seagrass beds. In both habitat types, their feeding activity was highest during 8:00–10:30 hours (concordant with strategy 3), and for seagrass fishes, it was also high during 17:30–18:30 hours (concordant with strategy 2). The study shows that both mangroves and seagrass beds provide daytime feeding habitats for some life-stages of H. flavolineatum, which is generally considered a nocturnal feeder.     

Metals in feathers of sooty tern, white tern, gray-backed tern, and brown noddy from islands in the North Pacific

Levels of heavy metals are usuallyhigher in adult than young birds because they eatlarger, more contaminated prey, or because they havehad longer to accumulate metals in their tissues.Further, levels of contaminants are usually less inbirds nesting on remote, offshore islands than inbirds breeding closer to mainland areas that areurbanized and industrialized. We examined the featherlevels of arsenic, cadmium, chromium, lead, manganese,mercury, and selenium in adult sooty terns (Sterna fuscata), gray-backed terns (Sterna lunata), and brown noddy (Anous stolidus, and adult and young white terns (Gygis alba, fromMidway Atoll, and in adult and young sooty terns andadult brown noddy from Manana Island, Hawaii (chicksof other terns were not available). We tested andrejected the null hypotheses that metal levels are notsignificantly different among species, ages, andlocations. Despite their small size, adult white ternshad the highest levels of lead, arsenic and tin. Brownnoddies had the highest levels of cadmium, chromium,manganese, and selenium. Sooty and white terns had thehighest levels of mercury. Sooty tern adults hadsignificantly higher levels of cadmium, mercury, andselenium than young, while young had significantlyhigher levels of arsenic and manganese. White ternadults had significantly higher levels of selenium andtin than young, while young had higher levels ofcadmium and mercury than adults. Except for mercury,there were significant inter-location differenceswithin species in all heavy metals. Contrary toexpectation, where the differences were great, metalsgenerally were higher in the feathers of terns andnoddies from Midway than from Manana.     

Slow eyelid closure as a measure of driver drowsiness and its relationship to performance

Objective: Slow eyelid closure is recognized as an indicator of sleepiness in sleep-deprived individuals, although automated ocular devices are not well validated. This study aimed to determine whether changes in eyelid closure are evident following acute sleep deprivation as assessed by an automated device and how ocular parameters relate to performance after sleep deprivation.

Methods: Twelve healthy professional drivers (45.58 ± 10.93 years) completed 2 randomized sessions: After a normal night of sleep and after 24 h of total sleep deprivation. Slow eye closure (PERCLOS) was measured while drivers performed a simulated driving task.

Results: Following sleep deprivation, drivers displayed significantly more eyelid closure (P < .05), greater variation in lane position (P < .01) and more attentional lapses (P < .05) compared to after normal sleep. PERCLOS was moderately associated with variability in both vigilance performance (r = 0.68, P < .05) and variation in lane position on the driving task (r = 0.61, P < .05).

Conclusions: Automated ocular measurement appears to be an effective means of detecting impairment due to sleep loss in the laboratory.     

Introducing urine-enriched biochar-based fertilizer for vegetable production: acceptability and results from rural Bangladesh

Improved agricultural practices that increase yields and preserve soils are critical to addressing food insecurity and undernutrition among smallholder farmer families. Urine-enriched biochar has been shown to be an accessible and effective fertilization option in various subtropical countries; however, it is new to Bangladesh. To better understand attitudes and experiences preparing and using urine-enriched biochar fertilizer, mixed-methods research was undertaken among smallholder farmers in northeastern Bangladesh in 2016/2017. In-depth interviews were conducted with 25 respondents who had compared the production of crops grown with biochar-based fertilizer to usual practice. In addition, in areas where trainings on biochar-based fertilization had been offered, 845 farmers were asked about their experience through a quantitative survey. Interview results indicated that cow urine-enriched biochar was favored over human urine because cow urine was perceived as clean and socially acceptable, whereas human urine was considered impure and disgusting. Respondents praised biochar-based fertilizer because it increased yields, cost little, was convenient to prepare with readily available natural materials, produced tastier crops, and allowed families to share their larger yields which in turn enhanced social and financial capital. Comparative field trials indicated a 60% yield benefit in both cabbage and kohlrabi crops. Challenges included uneven access to ingredients, with some respondents having difficulty procuring cow urine and biomass feedstock. The low social, health, and financial risk of adoption and the perceived benefits motivated farmers to produce and apply biochar-based fertilizer in their gardens, demonstrating strong potential for scale-up of this technology in Bangladesh.

     

Wool-waste as organic nutrient source for container-grown plants

A container experiment was conducted to test the hypothesis that uncomposted wool wastes could be used as nutrient source and growth medium constituent for container-grown plants. The treatments were: (1) rate of wool-waste application (0 or unamended control, 20, 40, 80, and 120 g of wool per 8-in. pot), (2) growth medium constituents [(2.1) wool plus perlite, (2.2) wool plus peat, and (2.3) wool plus peat plus perlite], and (3) plant species (basil and Swiss chard). A single addition of 20, 40, 80, or 120 g of wool-waste to Swiss chard (Beta vulgaris L.) and basil (Ocimum basilicum L.) in pots with growth medium provided four harvests of Swiss chard and five harvests of basil. Total basil yield from the five harvests was 1.6–5 times greater than the total yield from the unamended control, while total Swiss chard yield from the four harvests was 2–5 times greater relative to the respective unamended control. The addition of wool-waste to the growth medium increased Swiss chard and basil tissue N, and NO₃–N and NH₄–N in growth medium relative to the unamended control. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) microanalysis of wool fibers sampled at the end of the experiments indicated various levels of decomposition, with some fibers retaining their original surface structure. Furthermore, most of the wool fibers’ surfaces contained significant concentrations of S and much less N, P, or K. SEM/EDX revealed that some plant roots grow directly on wool-waste fibers suggesting either (1) root directional growth towards sites with greater nutrient concentration and/or (2) a possible role for roots or root exudates in wool decomposition. Results from this study suggest that uncomposted wool wastes can be used as soil amendment, growth medium constituent, and nutrient source for container-grown plants.     

Quantification of activated carbon contents in soils and sediments using chemothermal and wet oxidation methods

Activated carbon (AC) strongly sorbs organic pollutants and can be used for remediation of soils and sediments. A method for AC quantification is essential to monitor AC (re)distribution. Since AC is black carbon (BC), two methods for BC quantification were tested for AC mixed in different soils and sediments: i) chemothermal oxidation (CTO) at a range of temperatures and ii) wet-chemical oxidation with a potassium dichromate/sulfuric acid solution. For three soils, the amount of AC was accurately determined by CTO at 375 °C. For two sediments, however, much of the AC disappeared during combustion at 375 °C, which could probably be explained by catalytic effects by sediment constituents. CTO at lower temperatures (325-350 °C) was a feasible alternative for one of the sediments. Wet oxidation effectively functioned for AC quantification in sediments, with almost complete AC recovery (81-92%) and low remaining amounts of native organic carbon (5-16%).     

Microbial diversity and dynamics during methane production from municipal solid waste

The objectives of this study were to characterize development of bacterial and archaeal populations during biodegradation of municipal solid waste (MSW) and to link specific methanogens to methane generation. Experiments were conducted in three 0.61-m-diameter by 0.90-m-tall laboratory reactors to simulate MSW bioreactor landfills. Pyrosequencing of 16S rRNA genes was used to characterize microbial communities in both leachate and solid waste. Microbial assemblages in effluent leachate were similar between reactors during peak methane generation. Specific groups within the Bacteroidetes and Thermatogae phyla were present in all samples and were particularly abundant during peak methane generation. Microbial communities were not similar in leachate and solid fractions assayed at the end of reactor operation; solid waste contained a more abundant bacterial community of cellulose-degrading organisms (e.g., Firmicutes). Specific methanogen populations were assessed using quantitative polymerase chain reaction. Methanomicrobiales, Methanosarcinaceae, and Methanobacteriales were the predominant methanogens in all reactors, with Methanomicrobiales consistently the most abundant. Methanogen growth phases coincided with accelerated methane production, and cumulative methane yield increased with increasing total methanogen abundance. The difference in methanogen populations and corresponding methane yield is attributed to different initial cellulose and hemicellulose contents of the MSW. Higher initial cellulose and hemicellulose contents supported growth of larger methanogen populations that resulted in higher methane yield.