Environmental controls of diatom species in northeast Pacific sediments

Non-linear, unimodal techniques are suitable for estimation of environmental properties in the northeast (NE) Pacific based on fossil diatom taxa (species and/or species groups) found in modern (core-top) sediments. Canonical Correspondence Analysis (CCA), a constrained ordination technique, discerned best-fit relationships among two multivariate datasets (the floral and the environmental) and thus yielded insight into the environmental variables that best explain the species variance within diatom populations. Based on these insights, we developed predictive functions for annual Primary Productivity (PP) and seasonal range of sea Sea-Surface Temperature using unimodal models and cross validation techniques. Estimates of annual PP (r²_jack = 0.92; RMSEP = 91.94 gC/m²/y) explained the highest percentage of variance in the core-top diatom record (22.1%).     

Effects of two contrasting hemiparasitic plant species on biomass production and nitrogen availability

Hemiparasitic plants can substantially change plant community structure; the drainage of host resources has a direct negative effect on host biomass and, as a consequence, promotes non-host biomass production (parasitism pathway); on the other hand, hemiparasitic litter inputs can enhance nutrient cycling which may have an indirect positive effect on both host and non-host biomass production (litter pathway). We evaluated the net effect of both pathways on total shoot biomass (with and without the hemiparasite) and shoot biomass of graminoids, forbs and ericaceous shrubs using a removal experiment in three sites infested with the annual Rhinanthus angustifolius, and three sites infested with the biennial Pedicularis sylvatica. We addressed the potential importance of litter effects by determination of litter quantity and quality, as well as modeling N release during decomposition. In the second year after removing the hemiparasites, total plant biomass at Rhinanthus sites was 24 % higher in weeded plots than in control plots, while weeding had no significant effect at Pedicularis sites. The increase in total biomass following Rhinanthus removal was mainly due to a higher biomass of graminoids. The amount of litter produced by Rhinanthus was only half of that produced by Pedicularis; N contents were similar. The amount of N in the litter was 9 and 30 % of the amount removed by mowing for Rhinanthus and Pedicularis sites, respectively. Within 2 months, about 45 % of the N in both hemiparasitic litter types was released by decomposition. Our results suggest that in addition to the suppression of host biomass due to parasitism, positive litter feedbacks on host and non-host biomass—via an increase in nutrient availability—also affect plant community structure. We propose that, depending on the particular hemiparasite and/or site conditions, these positive litter feedbacks on shoot biomass can compensate for the negative effect of parasitism.     

Effects of fundamental nutrient stresses on the lipid accumulation profiles in two diatom species Thalassiosira weissflogii and Chaetoceros muelleri

Bioprocess and Biosystems Engineering - Microalgae are considered as attractive feedstocks for biofuel production nowadays because of their high lipid contents and easy cultivation. In the present...     

Effect of different CO2 concentrations on biomass,pigment content,and lipid production of the marine diatom Thalassiosira pseudonana

The marine diatom Thalassiosira pseudonana grown under air (0.04% CO₂) and 1 and 5% CO₂ concentrations was evaluated to determine its potential for CO₂ mitigation coupled with biodiesel production. Results indicated that the diatom cultures grown at 1 and 5% CO₂ showed higher growth rates (1.14 and 1.29 div day⁻¹, respectively) and biomass productivities (44 and 48 mg_AFDWL⁻¹ day⁻¹) than air grown cultures (with 1.13 div day⁻¹ and 26 mg_AFDWL⁻¹ day⁻¹). The increase of CO₂ resulted in higher cell volume and pigment content per cell of T. pseudonana. Interestingly, lipid content doubled when air was enriched with 1–5% CO₂. Moreover, the analysis of the fatty acid composition of T. pseudonana revealed the predominance of monounsaturated acids (palmitoleic-16:1 and oleic-18:1) and a decrease of the saturated myristic acid-14:0 and polyunsaturated fatty acids under high CO₂ levels. These results suggested that T. pseudonana seems to be an ideal candidate for biodiesel production using flue gases.

     

Environmental controls on growth and lipid content for the freshwater diatom, Fragilaria capucina: A candidate for biofuel production

The use of microalgae for biofuel production has the potential to reduce fossil fuel consumption. Ideal candidate species of microalgae for bio-oil production need both relatively high growth rates and lipid content. Here, we report on the effects of temperature, nutrients (N, Si), and salinity on growth rates and lipid content of the common freshwater diatom, Fragilaria capucina (Desm), isolated from western Lake Erie. At low NaCl salinity, growth rate increased rapidly from 10 to 20°C, and then further increased slowly from 20 to 30°C, with a maximum specific growth rate of 0.61?day^?1. Growth rate declined with increasing salinity (e.g., reduced by ca. 50 and 100% at 137 and 274?mmol?L^?1 NaCl, respectively), and increased with increased N and Si concentration until ca. 100?μmol?L^?1 for each (with >85% of maximum growth rate at 10?μmol?L^?1). Lipid content (% total lipid per dry mass) in nutrient-replete cultures was 14% and (1) increased to >30% at low N and, especially, low Si; (2) was lower at 30°C vs. 20 or 10°C; and (3) decreased with salinity. Thus, F. capucina accumulates lipid to high levels even under N, Si, and temperature levels that permit a high growth rate for this species, and hence, this species is a candidate for use in biofuel production.     

Effect of ultraviolet-B radiation on biomass production,lipid peroxidation,reactive oxygen species,and antioxidants in Withania somnifera

The present study was aimed at understanding the effects of long term supplemental UV-B (3.6 kJ m^?2 d^?1) on biomass production, accumulation of reactive oxygen species, lipid peroxidation, and enzymatic antioxidants in leaves and roots of Withania somnifera (an indigenous medicinal plant). Under the UV-B treatment, a reduction in biomass and an increased malondialdehyde content (a characteristic of lipid peroxidation) were observed in both the shoots and roots. Amongst ROS, H₂O₂ content increased under UV-B in the leaves, whereas it decreased in the roots, and superoxide radical production rate decreased in both the plant parts. The activities of all enzymatic antioxidants tested (ascorbate peroxidase, catalase, glutathione reductase, peroxidase, polyphenol oxidase, and superoxide dismutase) increased under the UV-B treatment, the increase being greater in the roots.     

Dynamics of biomass partitioning in two competing meadow plant species

The optimal allocation theory predicts that growth is allocated between the shoot and the roots so that the uptake of the most limiting resource is increased. Allocation is dynamic due to resource depletion, interaction with competitors, and the allometry of growth. We assessed the effects of intra- and inter-specific competition on growth and resource allocation of the meadow species Ranunculus acris and Agrostis capillaris, grown in environments with high (+) or low (−) availability of light (L) and nutrients (N). We took samples twice a week over the 7 weeks experiment, to follow the changes in root-to-shoot ratios in plants of different sizes, and carried out a larger scale harvest at the end of the experiment. Of all the tested factors, availability of nutrients had the largest effect on the growth rate and shoot-to-root allocation in both species, although both competition and light had significant effects as well. The highest root-to-shoot ratios were measured from the L+N− treatment, and the lowest from the L−N+ treatment, as predicted by the optimal allocation theory. Competition changed resource allocation, but not always toward acquiring the resource that is most limiting to growth. We thus conclude that the greatest variation in shoot-to-root allocation was due to the resource availability and the effects of competition were small, probably due to low density of plants in the experiment.     

Trophic control of grassland production and biomass by pathogens

Current theories of trophic regulation of ecosystem net primary production and plant biomass incorporate herbivores, but not plant pathogens. Obstacles to the incorporation of pathogens include a lack of data on pathogen effects on primary production, especially outside agricultural and forest ecosystems, and an apparent inability to quantify pathogen biomass. Here, I report the results of an experiment factorially excluding foliar fungal pathogens and insect herbivores from an intact grassland ecosystem. At peak in control plots, 8.9% of community leaf area was infected by pathogens. Disease reduction treatment dramatically increased root production and biomass by increasing leaf longevity and photosynthetic capacity. In contrast, herbivory reduction had no detectable effects at the ecosystem or leaf scale. Additionally, biomass of foliar fungal pathogens in the ecosystem was comparable with that of insect herbivores. These results identify pathogens as potential regulators of ecosystem processes and promote the incorporation of pathogens into trophic theory.     

Plasmids in diatom species.

We have discovered plasmids in 5 of 18 diatom species surveyed. In several species, more than one type of plasmid is present. Several of the plasmids show similarity by hybridization previously characterized plasmids in Cylindrotheca fusiformis (J. D. Jacobs et al., unpublished data). Additionally, there is similarity between the plasmids found in C. fusiformis and chloroplast DNA in three diatom species. These results add to the evidence that the plasmids have features of mobile genetic elements.     

Two-stage heterotrophic and phototrophic culture strategy for algal biomass and lipid production

A two-stage heterotrophic and phototrophic culture strategy for algal biomass and lipid production was studied, wherein high density heterotrophic cultures of Chlorellasorokiniana serve as seed for subsequent phototrophic growth. The data showed growth rate, cell density and productivity of heterotrophic C.sorokiniana were 3.0, 3.3 and 7.4 times higher than phototrophic counterpart, respectively. Hetero- and phototrophic algal seeds had similar biomass/lipid production and fatty acid profile when inoculated into phototrophic culture system. To expand the application, food waste and wastewater were tested as feedstock for heterotrophic growth, and supported cell growth successfully. These results demonstrated the advantages of using heterotrophic algae cells as seeds for open algae culture system. Additionally, high inoculation rate of heterotrophic algal seed can be utilized as an effective method for contamination control. This two-stage heterotrophic phototrophic process is promising to provide a more efficient way for large scale production of algal biomass and biofuels.     

Environmental and endogenous control of diapause inTrichogramma species

The 1st feature revealed typical for diapause phenomena inTrichogramma species is the interaction of environmental conditions in both parental and filial generations in induction of diapause in the latter. Lowered temperature during larval development is the ultimate factor evoking diapause in pronymphs but the norm of this thermal reaction is not fixed but varies depending on photoperiod and temperature in the previous generation due to maternal influence. Short day and in some cases high temperature in parental generation enhance tendency to diapause in the progeny. Unlike maternal influence the development to filial generation itself is not (or almost is not) governed by its own photoperiodic reaction. The 2nd typical feature revealed is the occurrence of endogenous process running in the sequence of generations and causing changes in the diapause tendency and underlying reaction norms even under constant rearing conditions.      

Multivariate control of plant species richness and community biomass in blackland prairie

Recent studies have shown that patterns of plant species richness and community biomass are best understood in a multivariate context. The objective of this study was to develop and evaluate a multivariate hypothesis about how herbaceous biomass and richness relate to gradients in soil conditions and woody plant cover in blackland prairies. Structural equation modeling was used to investigate how soil characteristics and shade by scattered Juniperus virginiana trees relate to standing biomass and species richness in 99 0.25 m² quadrats collected in eastern Mississippi, USA. Analysis proceeded in two stages. In the first stage, we evaluated the hypothesis that correlations among soil parameters could be represented by two underlying (latent) soil factors, mineral content and organic content. In the second stage, we evaluated the hypothesis that richness and biomass were related to (1) soil properties, (2) tree canopy extent, and (3) each other (i.e. reciprocal effects between richness and biomass). With some modification to the details of the original model, it was found that soil properties could be represented as two latent variables. In the overall model, 51% and 53% of the observed variation in richness and biomass were explained. The order of importance for variables explaining variations in richness was (1) soil organic content, (2) soil mineral content, (3) community biomass, and (4) tree canopy extent. The order of importance for variables explaining biomass was (1) tree canopy and (2) soil organic content, with neither soil mineral content nor species richness explaining significant variation in biomass. Based on these findings, we conclude that variations in richness are uniquely related to both variations in soil conditions and variations in herbaceous biomass. We further conclude that there is no evidence in these data for effects of species richness on biomass.     

Serial optimization of biomass production using microalga Nannochloris oculata and corresponding lipid biosynthesis

As energy and environment have become urgent issues, there has been increasing needs to develop alternative energy source, such as microalgal bio-fuel. In this study, we investigated the growth and lipid contents of microalgae Nannochloris oculata under various environmental conditions for biodiesel production. Our results indicated that biomass productivities of N. oculata were correlated with increasing nitrogen concentrations up to 37.5 ppm. High irradiance using 230-250 μmol/m(2) led to higher biomass yields than low irradiance of 160-180 μmol/m(2). Biomass productivities increased further by manipulating surface to volume ratio (S/V), which in turn enhanced light penetration. Finally, optimal biomass productivities (1.04 g/l day) could be achieved by the supplementation of yeast extract. Lipid contents and fatty acid profiles of N. oculata were affected by the different growth conditions. Lipid contents of N. oculata decreased as nitrogen concentration increased. Lower temperature (15 °C) resulted in higher lipid content than higher temperature (25 °C). Fatty acid profiles of N. oculata indicated that palmitic acid (C16:0) and linoleic acid (C18:2) were the two most abundant fatty acids, but the supplementation of yeast extract increased linolenic acid (C18:3) content. Our results suggested the feasibility of N. oculata for the biodiesel production.     

Meristem activity and biomass production as response mechanisms in two forest herbs

Actaea spicata and Geranium sylvaticum are deciduous rosette herbs, frequently coexisting in nutrient-rich forests of boreal Sweden. A. spicata is restricted to this habitat whereas G. sylvaticum has a wider ecological amplitude. To explore the different distributions of these species we studied the growth mechanisms by which they responded to nutrient and light supply. Plants raised from seeds were grown under four combinations of light and nutrient supplies and growth was followed for 20 weeks. Growth responses were measured as biomass accumulation and meristem activity, i.e. leaf development by shoot meristems. Biomass accumulation and meristem activity were affected by nutrient and light treatments. However, A. spicata responded more to nutrients, whereas G. sylvaticum responded more to light, and low resource supply shortened the time during which shoot meristems of A. spicata developed leaves without a corresponding effect on biomass accumulation. In G. sylvaticum, the periods of leaf development and biomass accumulation were the same, but a relationship between high development rates and peak allocation of biomass to shoot meristems indicated a storage function of these during leaf development. We conclude that the inflexible growth of A. spicata, mainly affected by nutrient supply, makes it less competitive in open habitats and restricts it to shaded, nutrient-rich habitats. G. sylvaticum should be more successful in habitats subjected to unpredictable disturbances, due to a flexible growth morphology and a dynamic function of meristems that buffers against variation in nutrient supply and facilitates positive light responses. Meristematic data should be included in interspecific comparisons on growth responses to different resource supplies. Unless species have the same growth mechanism, it is not satisfactory to study biomass-related traits alone, as internal constraints concerning plant development might confuse the interpretation.     

Grazer control and nutrient limitation of phytoplankton biomass in two Australian reservoirs

1. Grazer and nutrient controls of phytoplankton biomass were tested on two reservoirs of different productivity to assess the potential for zooplankton grazing to affect chlorophyll/phosphorus regression models under Australian conditions. Experiments with zooplankton and nutrients manipulated in enclosures, laboratory feeding trials, and the analysis of in-lake plankton time series were performed. 2. Enclosures with water from the more productive Lake Hume (chlorophyll a = 3–17.5 μg l^–1), revealed significant zooplankton effects on chlorophyll a in 3/6, phosphorus limitation in 4/6 and nitrogen limitation in 1/6 of experiments conducted throughout the year. Enclosures with water from the less productive Lake Dartmouth (chlorophyll a = 0.8–3.5 μg l^–1), revealed significant zooplankton effects in 5/6, phosphorus limitation in 5/6 and nitrogen limitation in 2/6 of experiments. 3. While Lake Hume enclosure manipulations of the biomass of cladocerans (Daphnia and Diaphanosoma) and large copepods (Boeckella) had negative effects, small copepods (Mesocyclops and Calamoecia) could have positive effects on chlorophyll a. 4. In Lake Hume, total phytoplankton biovolume was negatively correlated with cladoceran biomass, positively with copepod biomass and was uncorrelated with total crustacean biomass. In Lake Dartmouth, total phytoplankton biovolume was negatively correlated with cladoceran biomass, copepod biomass and total crustacean biomass. 5. In both reservoirs, temporal variation in the biomass of Daphnia carinata alone could explain more than 50% of the observed variance in total phytoplankton biovolume. 6. During a period of low phytoplankton biovolume in Lake Hume in spring–summer 1993–94, a conservative estimate of cladoceran community grazing reached a maximum of 0.80 day^–1, suggesting that Cladocera made an important contribution to the development of the observed clear-water phase. 7. Enclosure experiments predicted significant grazing when the Cladocera/Phytoplankton biomass ratio was greater than 0.1; this threshold was consistently exceeded during clear water phase in Lake Hume. 8. Crustacean length had a significant effect on individual grazing rates in bottle experiments, with large Daphnia having highest rates. In both reservoirs, mean crustacean length was negatively correlated with phytoplankton biovolume. The observed upper limit of its variation was nearly twice as high compared to other world lakes.