Short-term Laboratory Experiments Research Articles

Long-term mineral transformation of Ca-rich oil shale ash waste

Power generation and other industries using solid fossil fuels like coal, lignite, oil shale and peat are responsible for producing large quantities of solid residues that are often chemically reactive and/or unstable and are disposed in holding ponds and deposition sites. Stability and long-term behaviour of such deposits are typically studied in short-term laboratory experiments that cannot describe nor predict long-term changes taking place in these materials. Here, we study long-term (>40 years) transformations, in highly alkaline conditions, of the Ca-rich ash deposit in Estonia composed of oil shale processing residues from the Eesti power plant. Detailed mineralogical, chemical and micromorphological analyses using X-ray diffraction, X-ray fluorescence, 29Si nuclear magnetic resonance, scanning electron microscopy and other methods were applied in order to identify the composition of the waste with a focus on formation and transformation of semicrystalline phases in the deposit. The results show progressive formation of calcium-silicate-hydrate (C-S-H) type phase at the expense of silicate minerals and amorphous glass phases with increasing depth and age of the sediments, from about 25% in the upper part of the depository to over 60% in the oldest-deepest part. This demonstrates that over time the high alkalinity of the ash is responsible for initiating natural alkali-activation. The formation of C-S-H-type phases increases the mechanical strength of the sediment and ensures long-term stability of waste deposits. These findings may encourage the use of these ashes in binder or other construction material production or as construction aggregates.

Reduced carbon use efficiency and increased microbial turnover with soil warming.

Global soil carbon (C) stocks are expected to decline with warming, and changes in microbial processes are key to this projection. However, warming responses of critical microbial parameters such as carbon use efficiency (CUE) and biomass turnover (rB) are not well understood. Here, we determine these parameters using a probabilistic inversion approach that integrates a microbial-enzyme model with 22years of carbon cycling measurements at Harvard Forest. We find that increasing temperature reduces CUE but increases rB, and that two decades of soil warming increases the temperature sensitivities of CUE and rB. These temperature sensitivities, which are derived from decades-long field observations, contrast with values obtained from short-term laboratory experiments. We also show that long-term soil C flux and pool changes in response to warming are more dependent on the temperature sensitivity of CUE than that of rB. Using the inversion-derived parameters, we project that chronic soil warming at Harvard Forest over six decades will result in soil C gain of <1.0% on average (1st and 3rd quartiles: 3.0% loss and 10.5% gain) in the surface mineral horizon. Our results demonstrate that estimates of temperature sensitivity of microbial CUE and rB can be obtained and evaluated rigorously by integrating multidecadal datasets. This approach can potentially be applied in broader spatiotemporal scales to improve long-term projections of soil C feedbacks to climate warming.

Self-efficacy and emotional intelligence

PurposeThis study aims to examine empirically the effect of emotional intelligence of the team, as calculated by the average of all team members’ individual emotional intelligence measurements, on the cohesiveness of the team, and the effect of the perception of self-efficacy of the team members on the relationship between emotional intelligence and team cohesion. Finally, certain financial indicators were analyzed to evaluate team performance.Design/methodology/approachThis study used quasi-experimental design. Participated in the experiment a total of 146 students (35 teams) who were senior business major students in the mid-sized university in the USA. In the experiment, the participants played a business simulation game over an eight-year simulated time frame. After the final round of the simulation game, the variables of emotional intelligence, self-efficacy and team cohesion were measured using the survey questionnaire and team performance and participation data were collected from the business simulation game. In the support of the quantitative data analysis, the current study also collected and analyzed qualitative data comments on other group members’ contribution to the group task.FindingsResults indicated that team cohesion was highest when team members demonstrated greater emotional intelligence. Self-efficacy also had a positive influence on team cohesion. High self-efficacy was found to be an important mediator of the relationship between emotional intelligence and team cohesion. High emotional intelligence promoted the development of self-efficacy, resulting in increased team cohesion. Increased team cohesion resulted in improved team performance and participation.Research limitations/implicationsThe current study has several limitations. First, the sample is mostly business major students in the mid-sized university in the USA. There is a limitation in generalizing the findings into other populations. Second, this study accessed information on 35 teams comprising a total of 146 students. While the number of students and teams is sufficient for a study, more data would improve the robustness of the results. Third, this study collected and analyzed cross-sectional data, so there is the possibility for the reversed causal relationship in the findings. Although the authors concluded that team cohesion had a positive impact on team performance and participation, they also found the reverse relationship from the additional analysis. Fourth, the validity of the construct for emotional intelligence has some detractors, mainly because of the subjective nature of the measurement that tends to overlap existing personality measures and the objective measurement which involves a consensual scoring method with poor reliability.Practical implicationsThis paper implies practical strategies to manage teams and team members for enhanced team productivity. Teams are critical resources within companies. This study demonstrates that high team cohesion leads to better team performance. As team cohesion is important for team performance, the authors found that two antecedents for team cohesion are emotional intelligence and self-efficacy within team members. Therefore, it is important for managers to hire and select team members with high levels of emotional intelligence and self-efficacy. Managers can train employees to internalize increased levels of these traits.Originality/valueThe current study demonstrated that self-efficacy mediated emotional intelligence and team cohesion during a research project lasting one semester. There have been few studies examining the mediating effect of self-efficacy on the relationship between emotional intelligence and team cohesion. In particular, unlike many other studies that use short-term laboratory experiments, the duration of this study could provide enough time to more thoroughly develop cohesion among members. The current study collected both quantitative and qualitative data. In addition to the quantitative data analysis, the analysis of qualitative data reinforced the findings of the quantitative data analysis.

Sustaining efficient production of aqueous iron during repeated operation of Fe(0)-electrocoagulation

Iron-electrocoagulation is a promising contaminant (e.g. arsenic) removal technology that is based on electrochemical Fe(II) production from steel electrodes and subsequent transport of Fe(II) to the bulk solution, where contaminant removal occurs. Although Fe-electrocoagulation systems have been shown to effectively remove contaminants in extended field trials, the efficiency of field systems can be lower than in laboratory studies. One hypothesis for this disparity is that the Faradaic efficiency of short-term laboratory experiments is higher than field systems operated over extended periods. The Faradaic efficiency is a pivotal performance indicator that we define as the measured Fe dosage normalized by the theoretical Fe dosage calculated by Faraday's law. In this work, we investigated the Faradaic efficiency in laboratory experiments for up to 35 operating cycles (>2 months) with varied Fe(0) anode purity, charge dosage rate, and electrolyte composition. Our results showed that the Faradaic efficiency decreased continuously during repeated operation under typical field conditions (charge dosage rate = 4 C/L/min, synthetic groundwater) regardless of the Fe(0) anode purity, leading to a Faradaic efficiency ≈ 0.6 after 2 months. By contrast, increasing the charge dosage rate to ≥15 C/L/min produced a Faradaic efficiency >0.85 over the entire experiment for both Fe(0) anode purities. Electrolyte solutions free of oxyanions also resulted in sustained Faradaic efficiency >0.85, regardless of the charge dosage rate. Our results confirm a previously proposed relationship between low Faradaic efficiency and the formation of macroscopic electrode surface layers, which consist of Fe (oxyhydr)oxides on the anode and a mixture of Fe (oxyhydr)oxides and calcite on the cathode. Based on these results, we discuss potential strategies to maintain a high Faradaic efficiency during Fe-electrocoagulation field treatment.

Ocean acidification increases iodine accumulation in kelp-based coastal food webs.

Kelp are main iodine accumulators in the ocean, and their growth and photosynthesis are likely to benefit from elevated seawater CO2 levels due to ocean acidification. However, there are currently no data on the effects of ocean acidification on iodine metabolism in kelp. As key primary producers in coastal ecosystems worldwide, any change in their iodine metabolism caused by climate change will potentially have important consequences for global geochemical cycles of iodine, including iodine levels of coastal food webs that underpin the nutrition of billions of humans around the world. Here, we found that elevated pCO2 enhanced growth and increased iodine accumulation not only in the model kelp Saccharina japonica using both short-term laboratory experiment and long-term in situ mesocosms, but also in several other edible and ecologically significant seaweeds using long-term in situ mesocosms. Transcriptomic and proteomic analysis of S.japonica revealed that most vanadium-dependent haloperoxidase genes involved in iodine efflux during oxidative stress are down-regulated under increasing pCO2 , suggesting that ocean acidification alleviates oxidative stress in kelp, which might contribute to their enhanced growth. When consumed by abalone (Haliotis discus), elevated iodine concentrations in S.japonica caused increased iodine accumulation in abalone, accompanied by reduced synthesis of thyroid hormones. Thus, our results suggest that kelp will benefit from ocean acidification by a reduction in environmental stress however; iodine levels, in kelp-based coastal food webs will increase, with potential impacts on biogeochemical cycles of iodine in coastal ecosystems.

Grazing and growth rate of a cyclopoid copepod fed with a phytoplankton diet constituted by a filamentous cyanobacterium

Many tropical freshwaters experience persistent cyanobacterial blooms throughout the year. However, to date, most of the cyanobacteria–zooplankton interaction studies focused on temperate regions using large generalist grazers, which rarely coexist with cyanobacteria. Here a short-term (3 h) laboratory experiment was conducted to examine the grazing rate of Thermocyclops decipiens exposed to different combinations of phytoplankton (T1 = 100% Nitzschia-0% Cylindrospermopsis, T2 = 75% Nitzschia-25% Cylindrospermopsis, T3 = 50% Nitzschia-50% Cylindrospermopsis, T4 = 25% Nitzschia-75% Cylindrospermopsis and T5 = 0% Nitzschia-100% Cylindrospermopsis). In addition, an 8-day experiment was performed to determine the effect of the diet treatments on Thermocyclops survivorship and growth. The total biomass of phytoplankton in treatments with higher proportion of Nitzschia (i.e., T1 and T2) showed abrupt decline (i.e., down to 61% and 71%, respectively) over time when compared to other treatments. While Thermocyclops largely excluded Cylindrospermopsis when Nitzschia is abundant, they were capable of shortening the longer filaments of Cylindrospermopsis into significantly smaller fragments and ingesting them when provided as a sole food. This, however, negatively influenced their survivorship and growth. Our results generally suggest that dominantly occurring selective grazers in tropical and warmer-temperate lakes may shift the phytoplankton community composition to favor cyanobacteria by grazing on the alternative food source, at least before the cyanobacteria becomes dominant.

Effects of Cd, Cu, Zn and their combined action on microbial biomass and bacterial community structure

Heavy metal pollution can decrease the soil microbial biomass and significantly alter microbial community structure. In this study, a long-term field experiment (5 years) and short-term laboratory experiment (40 d) were employed to evaluate the effects of heavy metals (Cd, Cu, Zn), and their combinations at different concentrations, on the soil microbial biomass and the bacterial community. The ranges of heavy metal concentration in the long-term and short-term experiments were similar, with concentration ranges of Cd, Cu and Zn of about 0.3–1.5, 100–500, and 150–300 mg kg−1, respectively. Microbial biomass decreased with increasing soil heavy metal concentrations in both the long-term and short-term experiments. The interaction between soil physicochemical factors (pH, TN, TC) and heavy metals (Cd, Cu, Zn) played a major role in change in the bacterial community in long-term polluted soil. In the laboratory experiment, although each heavy metal had an adverse effect on the microbial biomass and community structure, Cu appeared to have a greater role in the changes compared to Cd and Zn. However, the synergistic effects of the heavy metals were greater than those of the single metals and the synergistic effect between Cu and Cd was greater than that of Cu and Zn.

Sensitivity of peatland litter decomposition to changes in temperature and rainfall

Changes to climate are projected over the next 50 years for many peatland areas. As decomposition of peat-forming vegetation is likely to be intrinsically linked to these changes in climate, a clear understanding of climate-peat dynamics is required. There is concern that increased temperature and decreased precipitation could increase the rate of decomposition and put the carbon sink status of many peatlands at risk, yet few studies have examined the impact of both climatic factors together. To better understand the sensitivity of peatland decomposition to changes in both temperature and precipitation and their interaction, we conducted a short-term laboratory experiment in which plant litters and peat soil were incubated, in isolation, in a factorial design. Treatments simulated baseline and projected climate averages derived from the latest UK climate change projections (UKCP09) for Exmoor, a climatically marginal peatland in SW England. Regular carbon dioxide flux measurements were made throughout the simulation, as well as total mass loss and total dissolved organic carbon (DOC) leached. The largest effect on carbon loss in this multifactor experiment was from substrate, with Sphagnum/peat releasing significantly less C in total during the experiment than dwarf shrubs/graminoids. Climate effects were substrate specific, with the drier rainfall treatment increasing the DOC leaching from Calluna, but decreasing it from Sphagnum. Partitioning between CO2 and DOC was also affected by climate, but only for the peat and Sphagnum samples, where the future climate scenarios (warmer and drier) resulted in a greater proportion of C lost in gaseous form. These results suggest that indirect effects of climate through changes in species composition in peatlands could ultimately turn out to be more important for litter decomposition than direct effects of climate change from increased temperatures and decreased rainfall.

On the tolerance of charophytes to high-nitrate concentrations

ABSTRACTCurrently a debate exists about whether the reduced growth of macrophytes with increased nitrogen loading in shallow ecosystems is determined by ecological or physiological factors. To discover whether nitrate in the water is detrimental per se to charophytes, we subjected Chara hispida and Chara vulgaris specimens, collected from two habitats greatly differing in nitrate concentrations (1.5 and 10 mg NO3-N/L, annual means), to a wide nitrate range (0.5–50 mg NO3-N/L) in two experiments (with free-floating specimens using nitrate as the sole N source, and with planted specimens, with other N sources in sediment). Charophytes grew both unplanted and planted in all treatments, and growth reductions occurred at the highest concentration in all cases. Some charophyte responses when faced with nitrate increases were different depending on (i) the species and (ii) population origin. Under the most realistic situation, the growth of both planted C. vulgaris populations was higher than that of C. hispida populations. C. vulgaris specimens from the nitrate-rich waterbody adapted best to the highest nitrate concentrations when they grew floating. Despite charophytes being vital and growing under high-nitrate concentrations in short-term laboratory experiments, such a situation in the environment may eventually not be sustainable, since ecological factors act in the field.

Feeding, survival, and reproduction of two populations of Eurytemora (Copepoda) exposed to local toxic cyanobacteria

Studying the responses of crustacean zooplankton to harmful algal blooms is important for understanding changes in lower food webs following eutrophication in the Laurentian Great Lakes and other regions around the world. Here we examine responses to toxic cyanobacteria by crustacean copepods of the genus Eurytemora from eutrophic coastal regions of Lake Michigan (Green Bay) and the Baltic Sea (Gulf of Finland). We measured grazing, survivorship, reproduction, and juvenile (nauplius) size in short-term laboratory experiments. Females were incubated with representative non-toxic food and mixtures of non-toxic food with either cyanobacteria or cyanobacteria filtrate. Eurytemora from both locations were affected negatively by cyanobacteria filtrates, even with non-toxic food available. Eurytemora carolleeae from Green Bay exhibited reduced grazing rates when exposed to filtrates, but this effect was not observed when animals were fed the cyanobacteria and filtrate along with non-toxic food. Eurytemora sp. from the Baltic Sea given filtrates and non-toxic food also exhibited decreased grazing rates, as well as decreased adult survival and nauplius size. Similarly, when cyanobacterial cells were included along with filtrate and non-toxic food these effects were not observed. Our results also demonstrated a significant trade-off between offspring quantity and quality for both groups of animals, being more pronounced when food quality was manipulated by the presence of cyanobacterial cells. These findings further our knowledge of how a widely distributed group like Eurytemora may respond in the face of changing local selection pressures from natural and anthropogenic stressors.

Field study of the long-term release of block copolymers from fouling-release coatings

Abstract The addition of block copolymers (i.e. oils) is a common technique to enhance the biofouling-resistance properties of poly(dimethylsiloxane) (PDMS)-based fouling-release coatings. These copolymers diffuse from the bulk to the surface of the coating, thus modifying the properties of the surface and providing fouling-resistance properties. Upon release, dissolution or degradation of copolymer molecules at the surface, new molecules can diffuse from the bulk of the coating and cover the surface. Therefore, the long-term performance of these coatings is dependent on the stability and release rate of copolymer molecules from the surface. A method was developed to quantify the concentration of PDMS-based block copolymers from fouling-release coatings. About 300 experimental coatings exposed to seawater for up to 5.2 years were included in the analysis. The results showed that the loss of copolymer (in % on a weight basis) is significantly higher in warm waters, while the initial copolymer concentration in the coating does not have any effect for copolymer concentrations between 1 and 7 wt%. In short-term exposure, it was found that loss of copolymer was much higher in coatings containing small amounts of an organic biocide (copper pyrithione). Conversely, biocide-containing coatings displayed larger copolymer retention values in long-term experiments. Opposite results were obtained for biocide-free coatings, suggesting that the addition of the organic biocide alters the release profile of copolymers from fouling-release coatings. Finally, the potential of long-term field-studies is discussed, as compared to short-term laboratory experiments usually performed within fouling-release coatings studies.

Effects of olive pomace amendment on soil enzyme activities

Agricultural soils generally have a low content of organic matter, which affects soil fertility and hence crop yields. The use of olive pomace as an organic amendment could enhance soil properties due to its high content of organic matter and exchangeable cations as well as its extensive availability. However, little is known about the potentially detrimental effects of salts and high content of phenolic substances that might occur over time with the use of pomace amendment in agricultural soils. Similarly, its impact on microbial communities and enzyme activities is largely unknown. To ascertain these effects, we tested the response of soil enzyme activities (β-glucosidase, urease, acid phosphomonoesterase and dehydrogenase) starting from a long-term (8-year) previously amended soil and a control (non-amended) soil and exposing these soils to a short-term (12-week) laboratory experiment. We also focused on soil organic matter and mineral N, on relating enzymatic data to bacterial and fungal biomasses, and on an index for soil functional quality based on enzyme activities (AI3). Our results show that organic matter, enzyme activities and the soil quality index were improved by long-term treatment with olive pomace, contrasting with scant effects from short-term laboratory incubation. In spite of its high content in salts and phenolic substances, no detectable negative impact emerged from the use of this amendment. Overall, olive pomace clearly increased soil organic matter and improved soil biological activity and quality, without any detectable negative effects.

Child differential sensitivity to parental self-efficacy improvement

This study investigates the hypothesis of a child differential sensitivity to parenting improvement. One hundred and fourteen parents of preschoolers participated in two parenting micro-trials aiming to increase parental self-efficacy in view of improving child behavior. The first micro-trial took place in a short-term laboratory experiment; the other was an eight-week parenting group intervention, both focusing on altering parental cognition. Differential effects of parental self-efficacy improvement on child’s positive and negative behaviors, depending on child temperament, were compared at post-test between control and experimental groups. Both observation and questionnaires were used to measure child behavior as well as regression and Regions of Significance analyses. Child differential sensitivity was found both in the laboratory experiment and in the parenting intervention for the temperamental trait of negative emotionality but not for the temperamental trait of activity. However, this sensitivity was in an unexpected direction. Highly emotional children benefited less from this parental cognitive improvement than children low on emotionality. These results may be explained by the specific cognitive nature of these two parenting micro-trials.

Branches and plates of the morphologically plastic coral Porites rus are insensitive to ocean acidification and warming

This study tested the hypothesis that intraspecific morphological plasticity within a scleractinian coral elicits differential responses to elevated PCO2 and temperature. In Mo'orea, French Polynesia, two short-term laboratory experiments (21 and 14days) were conducted to test the effects of PCO2 (400 vs. 700μatm), and PCO2 (400 vs 1000 μatm) combined with temperature (27.0 vs. 29.8°C), on branches and plates of Porites rus. Experiments employed two irradiances (~1000 vs 200μmolphotonsm−2s−1), which characterized the microenvironments on the shallow fringing reefs where branching and plating morphologies are common, respectively. Calcification of both morphologies was insensitive to PCO2, as well as the combined effects of elevated PCO2 and temperature. Mean calcification rates were faster in high light than in low light for both morphologies, and biomass was greater in plates than branches in all treatments. Together, our results suggest P. rus is robust to increased PCO2 and high temperature within the constraints of the treatments applied. Morphological plasticity in this species does not mediate physiological resistance to low pH and high temperature.

Effect of barley straw biochar application on greenhouse gas emissions from upland soil for Chinese cabbage cultivation in short-term laboratory experiments

Chinese cabbage was cultivated in upland soil with the addition of biochar in order to investigate the potential for reduction of greenhouse gas emissions. Barley straw biochar (BSB) was introduced in a Wagner pot (1/5000a) in amounts of 0 (BSB0, control), 100 (BSB100), 300 (BSB300), and 500 (BSB500) kg 10a-1. After the addition of BSB into the upland soil, carbon dioxide (CO2) emission increased while methane (CH4) and nitrous oxide (N2O) emissions decreased. The highest CO2 flux was measured for the BSB500 sample, (84.6 g m-2) followed by BSB300, BSB100, and BSB0 in decreasing order. Relative to those of control, the total CH4 flux and N2O flux for the BSB500 treatment were lower by 31.6% and 26.1%, respectively. The global warming potential (GWP) of the treatment without biochar was 281.4 g CO2 m-2 and those for treatments with biochar were in the range from 194.1 to 224.9 g CO2 m-2. Therefore, introducing BSB into upland soil to cultivate Chinese cabbages can reduce the global warming potential.

Ocean acidification and marine microorganisms: responses and consequences

Summary Ocean acidification (OA) is one of the global issues caused by rising atmospheric CO 2 . The rising pCO 2 and resulting pH decrease has altered ocean carbonate chemistry. Microbes are key components of marine environments involved in nutrient cycles and carbon flow in marine ecosystems. However, these marine microbes and the microbial processes are sensitive to ocean pH shift. Thus, OA affects the microbial diversity, primary productivity and trace gases emission in oceans. Apart from that, it can also manipulate the microbial activities such as quorum sensing, extracellular enzyme activity and nitrogen cycling. Short-term laboratory experiments, mesocosm studies and changing marine diversity scenarios have illustrated undesirable effects of OA on marine microorganisms and ecosystems. However, from the microbial perspective, the current understanding on effect of OA is based mainly on limited experimental studies. It is challenging to predict response of marine microbes based on such experiments for this complex process. To study the response of marine microbes towards OA, multiple approaches should be implemented by using functional genomics, new generation microscopy, small-scale interaction among organisms and/or between organic matter and organisms. This review focuses on the response of marine microorganisms to OA and the experimental approaches to investigate the effect of changing ocean carbonate chemistry on microbial mediated processes.

Characterisation of soil irrigated with pulp and paper mill wastewater for variation in physico-chemical, biological and enzymatic properties

Treated wastewater has attracted worldwide attention for its disposal on land; since it is eco-friendly, cost-effective, helps in irrigation of crops and ground water recharge. The study reported here highlights the disposal of treated pulp and paper mill wastewater through well designed land treatment method i.e., high rate transpiration system (HRTS). The HRTS is based on the well controlled hydraulic loading of treated wastewater in land using ridges and furrows. Long term field irrigation experiments (20 years) and short term laboratory experiment (three-seasons) were carried out to evaluate the effect of treated wastewater irrigation on soil physiochemical and microbiological properties. Seasonal variation affected both microbial count and enzyme activity significantly (P < 0.03) with peak value in autumn and trough in winter. Soil enzyme activities indicated significant positive correlation with the number of microbial population in all the seasons of study. Different microbial population and enzyme activities indicated significant positive correlation with percent organic carbon irrespective of soil types.

Short-term effects of phosphorus addition and pH rise on bacterial utilization and biodegradation of dissolved organic carbon (DOC) from boreal mires

Natural mires and forested peatlands are known to be very significant sources of dissolved organic carbon (DOC) to aquatic ecosystems. Peatland management operations (e.g., forestry operations, restoration of drained mires and peat mining) and extreme hydrological events may increase the DOC runoff. We hypothesized that an increase in phosphorus (P) leaching, together with near-neutral conditions in recipient lakes will accelerate decomposition of DOC that originates from acidic, nutrient-poor mire waters. The efficiency of DOC utilization was evaluated by measuring microbial respiration and bacterial production (BP) in short-term laboratory experiments with runoff waters from six boreal mire sites. Mere inorganic phosphorus (PO4-P) addition did not affect the rate of respiration or the proportion of decayed DOC. However, in the nutrient-poor bog waters, P addition slightly promoted BP and bacterial growth efficiency (BGE). In contrast, the elevation of pH alone, and the elevation of pH and PO4-P level together, caused a significant increase in respiration and in the proportion of decayed DOC, but did not affect net BP. Elevated pH alone, however, depressed BGE when compared to that under the combined elevation of pH and PO4-P. These results suggest that the increased P availability, e.g., after mire restoration, would slightly benefit bacterial net growth in P-limited waters. However, in near-neutral recipient lakes, the increased microbial decomposition of mire-originated DOC contributes more to carbon dioxide (CO2) supersaturation than potentially supporting detritus-based food chains.

Effects of UVB radiation exposure from the molecular to the organism level in macrophytes from shallow Mediterranean habitats

The available data on the effects of UVB radiation (UVBR) are scarce for submerged macrophytes, particularly charophytes. We studied the effects of UVBR on Chara baltica, Chara hispida, Chara vulgaris, Nitella hyalina and Myriophyllum spicatum, collected from shallow Mediterranean waterbodies. In a short-term laboratory experiment, we subjected these species to three different UVBR treatments corresponding to daily biologically effective integrated doses of 0, 1 and 6kJm−2. The analysed response variables were DNA damage, UV-absorbing compounds (both the methanol-soluble–SUVACs- and, for the first time in charophytes, the methanol-insoluble cell wall-bound fraction–WUVACs-), the stoichiometric composition, photosynthetic pigments, metabolic and growth rates and morphological architecture. UVBR induced harmful effects on DNA in all species, but M. spicatum appeared to be the most sensitive. The observed DNA damage only appeared to be UVB-dose dependent for C. vulgaris. The charophytes produced higher WUVACs levels and the angiosperm higher SUVACs levels. Higher chlorophyll and carotenoid concentrations were detected in the presence of UVBR, but their ratio was not modified by the applied treatments. The Chl a/b ratio decreased under UVBR in two charophyte species, whereas it increased in the angiosperm, which also exhibited a greater photosynthetic response. Relative growth rates were negatively influenced by UVBR, although the degree of this influence depending on the dose was different among species. UVBR modified growth patterns, particularly in those species exhibiting apical growth. We observed more species-specific differences than commonalities in the effects of and responses to UVBR across the investigated species.

Effects of temperature change and tree species composition on N2O and NO emissions in acidic forest soils of subtropical China

Tree species and temperature change arising from seasonal variation or global warming are two important factors influencing N2O and NO emissions from forest soils. However, few studies have examined the effects of temperatures (5–35°C) on the emissions of forest soil N2O and NO in typical subtropical region. A short-term laboratory experiment was carried out to investigate the influence of temperature changes (5–35°C) on soil N2O and NO emissions under aerobic conditions in two contrasting (broad-leaved and coniferous) subtropical acidic forest types in China. The results showed that the temporal pattern of N2O and NO emissions between the three lower temperatures (5°C, 15°C, and 25°C) and 35°C was significantly different for both broad-leaved and coniferous forest soils. The effects of temperature on soil N2O and NO emission rates varied between broad-leaved and coniferous forest soils. Both N2O and NO emissions increased exponentially with an increase in temperature in the broad-leaved forest soil. However, N2O and NO emissions in the coniferous forest soil were not sensitive to temperature change between 5°C and 25°C. N2O and NO emission rates were significantly higher in the broad-leaved forest soil as compared with the coniferous forest soil at all incubation temperatures except 5°C. These results suggest that the broad-leaved forest could contribute more N2O and NO emissions than the coniferous forest for most of the year in the subtropical region of China.