Percentage Of Biomass Research Articles

Patterns of relative magnitudes of soil energy channels and their relationships with environmental factors in different ecosystems in Romania.

The percentage compositions of soil herbivorous, bacterivorous and fungivorous nematodes in forests, grasslands and scrubs in Romania was analysed. Percentages of nematode abundance, biomass and metabolic footprint methods were used to evaluate the patterns and relative size of herbivory, bacterial- and fungal-mediated channels in organic and mineral soil horizons. Patterns and magnitudes of herbivore, bacterivore and fungivore energy pathways differed for a given ecosystem type and soil depth according to the method used. The relevance of herbivore energy channel increased with soil depth due to higher contribution of root-feeders. Ectoparasites, sedentary parasites and epidermal cell and root hair feeders were the most important contributors to the total biomass and metabolic footprints of herbivores. Metabolic footprint method revealed the general dominance of bacterial-based energy channel in all five types of ecosystems. The influence of altitude and climatic factors on percentages of abundance, biomass and metabolic footprints of herbivores, bacterivores and fungivores decreased with soil depth, whereas the influence of humus content, cation-exchange capacity and base saturation increased. Vegetation, altitude, climate and soil physico-chemical characteristics are important factors that influenced the abundance, biomass and metabolic footprints of herbivores, bacterivores and fungivores.

Maize and pea germination and seedling growth responses to compost generated from biowaste of selected invasive alien plant species

Plant biowaste of alien species represents a potential resource for compost production. This study investigated the seed and seedling responses of maize and pea to composts generated from the biowaste of four invasive species in eThekwini, South Africa: Acacia podalyriifolia, Hedychium gardnerianum, Litsea glutinosa, and Tithonia diversifolia. Except for a 40% concentration of T. diversifolia, leachates of the biowaste from the four species had no marked effects on germination. In seedling growth studies, Berea Red soil (control) was supplemented with composts produced using combinations of the four species (A. podalyriifolia + T. diversifolia [T1], A. podalyriifolia + H. gardnerianum [T2], L. glutinosa + T. diversifolia [T3], and L. glutinosa + H. gardnerianum [T4]), and a commercial compost (T5). Carbon and nitrogen levels of the biowaste composts were higher than the control, while their associated C/N ratios were low enough to encourage microbial growth, facilitate rapid decomposition, and support plant growth. A comparison of percentage seedling production, growth rate, and biomass production between the commercial compost and alien biowaste treatments revealed all parameters to be statistically comparable among T5, T1, and T3 for maize, and between T5 and T1 for pea. These superior biowaste composts did not enhance growth relative to the commercial compost, but supported growth to the same extent. However, N and P levels in T1 and T3 were lower than the commercial compost and appear to have altered biomass allocation patterns in both species relative to the commercial compost. The results suggest that there is potential to use invasive alien plant biowaste to improve soil for agricultural purposes.

Patterns of selectiveness in the Amazonian freshwater fisheries: implications for management

Tropical fisheries, which are considered multi-species, may show selectiveness. We analyzed the degree of selectivity of fish catches in 46 sites along the Amazon basin through the percentage of biomass corresponding to the most caught fish species. Amazonian fisheries were considered moderately selective, as 54% of the sites directed more than a quarter of fishing effort to one fish species and in 87% of the sites more than half the fishing effort was directed to five fish species. Commercial fisheries were more selective than subsistence fisheries. Eleven fish species (nine of them migratory) have received more fishing pressure in the studied Amazonian regions and the catch composition differed among regions. We thus recommend that fisheries management in the Amazon basin should distribute fishing effort among more fish species; incorporate the particularities of commercial and subsistence fisheries; evaluate fishing effects on ecosystem services; and consider the biological characteristics of preferred fish.

Prediction of high-temperature rapid combustion behaviour of woody biomass particles

Biomass energy is becoming a promising option to reduce CO2 emissions, due to its renewability and carbon neutrality. Normally, biomass has high moisture and volatile contents, and thus its combustion behaviour is significantly different from that of coal, resulting in difficulties for large percentage biomass co-firing in coal-fired boilers. The biomass combustion behaviour at high temperatures and high heating rates is evaluated based on an updated single particle combustion model, considering the particle size changes and temperature gradients inside particle. And also the apparent kinetics determined by high temperature and high heating rate tests is employed to predict accurate biomass devolatilization and combustion performances. The time-scales of heating up, drying, devolatilization, and char oxidation at varying temperatures, oxygen concentrations, and particle sizes are studied. In addition, the uncertainties of swelling coefficient and heat fractions of volatile combustion absorbed by solid on the devolatilization time and total combustion time are discussed. And the characterised devolatilization time and total combustion time are finally employed to predict the biomass combustion behaviour. At the last, a biomass combustion/co-firing approach is recommended to achieve a better combustion performance towards large biomass substitution ratios in existing coal-fired boilers.

Evaluating the influence of diet‐related variables on breeding performance and home range behaviour of a top predator

AbstractDiet composition is linked to reproductive performance directly or indirectly by other life‐history traits, including home range behaviour. The relationships between prey abundance, diet and individual fitness have often been explored. However, these relationships are complex and difficult to disentangle, especially in vertebrate top predators. Here, we present the results of a long‐term study using multi‐model inference procedures to elucidate the influence of diet‐related variables on breeding parameters and home range behaviour of a top predator, the eagle owl Bubo bubo. Superpredation, diet diversity, rat biomass and rabbit mean weight were the most important variables when analysing reproductive parameters, suggesting that less diverse diets with greater rabbit biomass percentage may benefit reproductive performance, whereas rat biomass percentage is apparently associated with greater variation of breeding success. Earlier laying dates seem to be associated with the consumption, on average, of smaller rabbits. On the other hand, edge density was the most relevant factor determining the variation in home range behaviour, with individual characteristics, such as age and sex, also being important. Although the relative importance of the diet‐related variables was generally low, mean weight of alternative prey, diet diversity and rabbit biomass also helped to explain home range parameters. In an optimal foraging context, centred on the abundance of the main prey species, our results suggest that when rabbits are less available eagle owls may increase home range size in order to obtain alternative prey, increasing at the same time their dietary diversity, which may also require higher movement speed.

Patterns of reproductive traits of fucoid species in core and marginal populations

Fucoid macroalgae are important primary producers and habitat modifiers on North Atlantic intertidal rocky shores. With decreasing latitude, western European fucoid populations display reduced levels of abundance, biomass and recruitment, while experiencing higher levels of physical environmental stress during summer months. We hypothesized that such reduction in the south is accompanied by a detectable decline in fucoid reproductive capacity. To test this hypothesis, morphological and reproductive traits of core (Welsh) and marginal (Portuguese) populations of two common fucoid species, Fucus vesiculosus and F. spiralis (Ochrophyta, Fucales), were examined. Morphological measurements showed that for a given thallus length, both fucoid species had smaller thallus volume and lower biomass in the southerly marginal part of the range. Significantly lower biomass of reproductive tissue of F. vesiculosus and a smaller number of receptacles per individual on specimens of both species indicate that levels of reproductive output are probably lower in southern populations. Despite the differences in reproductive traits observed between regions, reproductive effort (measured as the percentage of total dry biomass represented by reproductive tissue) of both species remained similar, as algae from both regions made similar investments in reproduction. The results indicate that stressful conditions reduced growth and number of receptacles of both species and amount of reproductive biomass of F. vesiculosus in the south but do not seem to change the way these algal species invest their energy. The decline in mass and reproductive biomass of specimens from southern shores found in this study, when combined with the lower abundance of adults and lower recruitment levels previously observed, is a strong indication of fucoid populations with lower levels of propagule output. This is an important factor when considering responses of these populations to a changing environment.

Trends and composition of trawl bycatch and its implications on tropical fishing grounds off Goa, India

Trawl bycatch is a globally recognized issue with intensified effects in tropical waters affecting both the ecosystem function and biodiversity, as well as causing physical damage and habitat loss. The present study envisages temporal variations of bycatch with regard to the species and their biological interactions based on data obtained from commercial single-day bottom trawlers operating off Goa, west coast of India. The data revealed that bycatch constituted about 68% of the trawl catch, the remaining being target species (shrimp, flat fishes, sciaenids, squids and crabs). Approximately 89% of the species discarded into the sea comprised of juveniles of target and trash species, suggesting a major share of non-target species, leading to species loss. Out of 196 taxa observed in the trawl catch, 174 constituted bycatch with a significantly high percentage of biomass. Abundance of discarded bycatch species (crustaceans, echinoderms, teleosts) displayed distinct peaks during pre-monsoon whereas molluscs, crustaceans and teleosts dominated during post-monsoon. A conspicuous increase in abundance of molluscs during post-monsoon (October, 2012) and echinoderms during pre-monsoon (April, 2011 and April, 2013) is largely attributed to the recruitment process. Cluster analysis identified different clusters during pre-monsoon and post-monsoon season corresponding to their recruitment patterns and diverse species assemblages. Principal Component Analysis performed using three environmental parameters accounted for 84% (five components) and 86% (four components) of variance during pre-monsoon and post-monsoon, respectively. Regression analysis indicated a significant linear relationship between total catch and bycatch (R2=0.89), and between bycatch and discarded catch (R2=0.94).

Microbial community shifts 2.6 years after top dressing of Miscanthus biochar, hydrochar and feedstock on a temperate grassland site

Within the last decades, considerable knowledge has been gained on the impacts of carbonaceous soil additives such as hydrochar (or HTC) and biochar (or pyrochar) on plant growth and various soil properties. However, still little is known about the effects of hydrochar and biochar on soil microorganisms, especially from field studies. Microorganisms are closely linked to nutrient dynamics in soil and therefore are tightly linked to soil fertility. As a consequence, possible changes in the microbial community structure due to HTC/biochar soil application may lead to considerable changes in soil nutrient dynamics. To gain insights into HTC/biochar associated long-term effects on microorganisms, soil samples were taken from a grassland field study 2.6 years (31 months) after its initiation (April 2011), where Miscanthus × giganteus feedstock, HTC and biochar, each mixed with pig slurry had been applied as top-dressing in a randomized block design, next to a slurry-only control (n = 4, 16 plots). The samples were analyzed for microbial activity and biomass by substrate induced respiration (SIR). Bacterial and fungal fractions in soil microbial biomass (SMB) were determined using the inhibitors streptomycin and cycloheximide respectively. Total SMB in biochar-amended soils was significantly higher compared to all other treatments; fungal biomass was significantly higher compared to feedstock and control treatments. The percentage of bacterial biomass was higher in the feedstock and HTC amended soil, as compared to the control. Additionally, HTC exhibited a significantly higher percentage of fungal biomass compared to the feedstock treatment, indicating a microbial community shift. While the uncarbonized feedstock material depleted both total SMB and especially fungi, HTC and biochar did not trigger any adverse long-term effects on SMB. Rather, the observed biochar-induced stimulation of SMB may improve soil aggregation and increase the soil organic carbon content in the long term.

Second-generation sustainability: Application of the distributed activation energy model to the pyrolysis of locally sourced biomass–coal blends for use in co-firing scenarios

While first generation biofuels paved the way for a vision of a renewable energy future, their competition for arable land limited widespread applicability. Second generation fuels, made from a variety of carbonaceous wastes, are considerably more “sustainable” in a land competition sense, but require a higher degree of processing to extract energy. Here we extend the idea of second-generation sustainability by investigating blends of coal and biomasses found within 20miles of coal-fired power stations in the Northeast United States for use in co-firing scenarios that would limit long-range transport of biomass. A commercial high volatile bituminous Pennsylvanian coal was blended at 90, 80, and 50wt% with one of three biomasses: feed corn stover from a local farm, brewer’s spent grains from Redhook Brewery, or cocoa shells from the Lindt chocolate factory. The Distributed Activation Energy Model was applied to analyze the pyrolysis kinetics of the solid fuels and blends, yielding activation energies as a function of mass fraction conversion ranging from 304 to 522kJ/mol for coal, 164 to 304kJ/mol for the biomasses, and 218 to 530kJ/mol for the coal–biomass blends. Overall, the peak reaction rates and temperatures for the primarily biomass decomposition stages were linearly correlated with the percent biomass in the blend. Such an additive scheme did not represent the blends’ kinetics, instead over-predicting the activation energies. Synergy was noted between the fuels, in that the biomass does appear to be promoting the devolatilization of the coal at lower temperatures.

Effect of Low Temperature and Wheat Winter-Hardiness on Survival of Puccinia striiformis f. sp. tritici under Controlled Conditions.

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most important diseases of wheat worldwide. Understanding the survival of Pst during the overwintering period is critical for predicting Pst epidemics in the spring. Real-time quantitative PCR (qPCR) methods quantifying Pst DNA and RNA (cDNA) were developed and compared for the ability to quantify viable Pst in leaf tissues. Both qPCR of DNA and RNA can provide reliable measurement of viable Pst in plant tissues prior to the late sporulation stage for which qPCR of DNA gave a much higher estimate of fungal biomass than qPCR of RNA. The percentage of Pst biomass that was viable in detached and attached leaves under low temperatures decreased over time. Pst survived longer on attached leaves than on detached leaves. The survival of Pst in cultivars with strong winter-hardiness at 0°C and -5°C was greater than those with weak winter-hardiness. However, such differences in Pst survival among cultivars were negligible at -10, -15 and -20°C. Results indicated that Pst mycelia inside green leaves can also be killed by low temperatures rather than through death of green leaves under low temperatures. The relationship of Pst survival in attached leaves with temperature and winter-hardiness was well described by logistic models. Further field evaluation is necessary to assess whether inclusion of other factors such as moisture and snow cover could improve the model performance in predicting Pst overwintering potential, and hence the epidemic in spring.

A Novel Delivery System for the Root Symbiotic Fungus, Sebacina vermifera, and Consequent Biomass Enhancement of Low Lignin COMT Switchgrass Lines

Sebacina vermifera (MAFF-305830) is a mycorrhizal fungus originally isolated from the roots of orchids that we have previously shown to be tremendously beneficial in enhancing biomass yield and drought tolerance in switchgrass, an important bioenergy crop for cellulosic ethanol production in the United States. Towards this end, we have developed a bentonite clay particle-based delivery system for mass production and dissemination of S. vermifera for large-scale field trials. A greenhouse-based experiment was conducted to evaluate this novel delivery method for biomass enhancement of wild type and transgenic, low lignin (COMT down-regulated) switchgrass lines compared to an efficient in vitro colonization method. S. vermifera colonization enhanced plant biomass regardless of delivery method, although the percentage of fungal biomass in planta increased with the clay-based delivery system. Further, we found that release of some clay minerals in solution was enhanced in the presence of S. vermifera, while others were seemingly reduced. Intriguingly, the presence of S. vermifera has little or no impact on cell wall composition, including lignification. This research is the first report documenting the development of a bentonite clay particle-based delivery system for mass production of any symbiotic microbe and suggests that S. vermifera can be packaged with a mineral composite and effectively delivered to a target host plant.

Bed-to-surface heat transfer in conical spouted beds of biomass–sand mixtures

The effects of superficial gas velocity, bed composition and other operating parameters on bed hydrodynamics and bed-to-surface heat transfer were investigated the influence of bed height and gas velocity sawdust, sand and 30–70, 40–60 and 50–50 mixtures of biomass and sand in a conical spouted bed. Experiments were performed at minimum spouting velocity and 10 and 20% above this. At each superficial velocity, experiments were conducted at three heights, 0.1, 0.2 and 0.3m above the inlet. A specially designed heat transfer probe measured the bed-to-surface heat transfer coefficient. The heat transfer coefficient increased from the wall to the spout, and also was observed to increase with increasing percentage of biomass in the blend. The experimental results are compared with published results, showing good agreement with the influence of height of the bed and gas velocity.

A food web modeling analysis of a Midwestern, USA eutrophic lake dominated by non-native Common Carp and Zebra Mussels

Food web modeling is recognized as fundamental to understanding the complexities of aquatic systems. Ecopath is the most common mass-balance model used to represent food webs and quantify trophic interactions among groups. We constructed annual Ecopath models for four consecutive years during the first half-decade of a zebra mussel invasion in shallow, eutrophic Clear Lake, Iowa, USA, to evaluate changes in relative biomass and total system consumption among food web groups, evaluate food web impacts of non-native common carp and zebra mussels on food web groups, and to interpret food web impacts in light of on-going lake restoration. Total living biomass increased each year of the study; the majority of the increase due to a doubling in planktonic blue green algae, but several other taxa also increased including a more than two-order of magnitude increase in zebra mussels. Common carp accounted for the largest percentage of total fish biomass throughout the study even with on-going harvest. Chironomids, common carp, and zebra mussels were the top-three ranking consumer groups. Non-native common carp and zebra mussels accounted for an average of 42% of the total system consumption. Despite the relatively high biomass densities of common carp and zebra mussel, food web impacts was minimal due to excessive benthic and primary production in this eutrophic system. Consumption occurring via benthic pathways dominated system consumption in Clear Lake throughout our study, supporting the argument that benthic food webs are significant in shallow, eutrophic lake ecosystems and must be considered if ecosystem-level understanding is to be obtained.

High production of β-glucosidase from a marine Aspergillus niger immobilized on towel gourd vegetable sponges

Abstract To produce β-glucosidase by consecutive batch fermentation, a marine Aspergillus niger was immobilized on a natural carrier, towel gourd vegetable sponges. The immobilized mycelia were 0.15 g/g carrier with the immobilized biomass percentage of over 95%. The immobilized mycelia possessed the long durability (22.5 days). The maximum production occurred 1.5 day earlier by the immobilized mycelia than by the free mycelia. β-Glucosidase production of five consecutive batches was over 110 U/mL. At high salinity, the activity and stability of β-glucosidase from the marine A. niger increased remarkable. Immobilizing the marine A. niger on the novel natural carrier achieved the efficient production of β-glucosidase.

Carbon footprint of sawn timber products of Castanea sativa Mill. in the north of Spain

Sweet chestnut is the most abundant native tree species in Asturias (Northern Spain). This hardwood timber is used in construction for both structural and non-structural purposes, and is processed into a wide variety of products, those based on sawn timber being the most common and having better national and international markets. The study presents the carbon footprint of sawn timber products of chestnut forests in Asturias calculated according to PAS 2050, and evaluates the potential for its reduction and options for achieving this. System boundaries were established according to a cradle-to-gate approach, based on primary data from the largest representative of the sawn timber industry in the region, over a one-year period. A sensitivity analysis was carried out taking into account the influence of the origin of the wood (distribution routes of the raw material) and the efficiency of the sawmill as calculated by the Lumber Recovery Factor. The distribution of emissions in the life cycle stages showed that the total emissions of 1 m3 of air dried sawn timber products was significantly lower (95.2 kg CO2e per 1 m3) than 1 m3 of kiln dried sawn timber product (383.7 kg CO2e per 1 m3), as a result of the lower energy consumption of the former process. The hotspots in the life cycles of these wood products were identified. The greater emissions from kiln dried sawn timber were made in the sawmill processing and in the case of air dried sawn timber the important contribution to overall emissions was made by the haulage from forest to sawmill. The greatest opportunities for improvements in terms of emission reduction were located in the sawmill stage of the process, where emissions can be reduced significantly depending on the choice of drying system, and through the use of local suppliers. Other actions that could influence the reduction of emissions are: decreasing the reliance on the co-generation motor system; increasing the percentage of biomass burned during the drying process; and using the waste wood currently left in the forest in the biomass boiler. A great positive of this study is that the methodology presented can serve as a blueprint for determining the carbon footprint of other types of sawn timber products, and the information generated can be used in future studies related to the carbon footprint of other wood-based products. Future work will enhance the model to incorporate the carbon footprint of the end of life emissions of these sawn timber products in order to establish the full cradle-to-grave life cycle.

The life history and seasonal cycle of the ant, Pheidole morrisi Forel, as revealed by wax casting

The dimorphic ant, Pheidole morrisi Forel, is the most common ant of the longleaf pine flatwoods ecosystem of northern Florida and occurs throughout the eastern USA. Although ecologically significant, its life history, and annual cycle have been little investigated. The effects of colony size and the annual cycle were described by collecting the full range of colony sizes during each of five seasonal phases (n = 40 total). Nests were cast in wax to capture and census all colony members, and to determine their vertical distribution within the nest. Colony sizes ranged from 800 to 49,000 ants, larger than previous literature reports. Colonies invested in worker production during the spring and fall and reduced worker production as they produced alates in the summer. Colonies over 3000 workers were able to produce alates, but the number was not related to colony size. Vertical distribution of nest volume was strongly top heavy, with the greatest proportion of the nest volume near the surface. The mean weight of majors was about four times that of minors. The mean percentage of total workers that were major workers (11 % by number, 30 % by weight) did not change significantly as colonies grew, but varied with season. Production of major pupae was highest in spring, so that the percentage of colony biomass represented by majors increased from about 27 % in spring to 38 % in late summer. The overall density of the ants was highest in medium-sized colonies, lowest in small colonies, and moderate in large colonies. Broadly, the colony moved lower in the nest from summer to winter and higher from winter to summer. The seasonal vertical distribution of ants suggested that the ants responded to temperature, but not crowding. Temperatures in the nest varied from 12 to 17 °C in the winter to 23–33 °C in the late summer. Broods were nearly always found in the warmest regions. The distribution of callow workers was strongly correlated with that of the brood. The results are discussed in light of the utility of the wax-casting method and the nature of the data needed to describe and understand the superorganism.

Effects of Preconditioning Through Mycorrhizal Inoculation on the Control of Melon Root Rot and Vine Decline Caused by Monosporascus cannonballus

AbstractThe use of inoculum of arbuscular mycorrhizal fungi (AMF) in nursery represents a promising field in horticulture because of its known benefits in terms of plant growth and bioprotection. The present work was undertaken to determine the effect of mycorrhizal inoculation with Rhizophagus irregularis in a nursery medium on the containment of melon root rot and vine decline (MRRVD) caused by the soil‐borne pathogen Monosporascus cannonballus. The percentage of mycorrhization, biomass and yield following mycorrhizal inoculation were also evaluated. Biocontrol activity was assessed in greenhouse pot experiments upon artificial inoculation of M. cannonballus and in a two‐season field experiment under production conditions in an unheated greenhouse with a history of MRRVD. On the basis of the mycorrhization parameters, the interaction appeared to be established within 30 days after inoculation. The total shoot growth in the mycorrhized plants was significantly higher when compared to the control, while the root growth was unaffected. Upon artificial inoculation of M. cannonballus, mycorrhization provided complete protection against the pathogen. Greenhouse experiments under production conditions during spring cropping season showed that pretransplanting inoculation with R. irregularis significantly decreased the severity of the disease. Also, the average fruit weight of mycorrhized plants was significantly higher than the untreated control. Nevertheless, in summer crop, the bioprotection activity of AMF failed. Present results indicate that the use of AMF in a nursery setting can contribute to the prevention of the onset of this problematic soil‐borne disease within a sustainable and integrated soil‐borne disease management.

RobOKoD: microbial strain design for (over)production of target compounds.

Sustainable production of target compounds such as biofuels and high-value chemicals for pharmaceutical, agrochemical, and chemical industries is becoming an increasing priority given their current dependency upon diminishing petrochemical resources. Designing these strains is difficult, with current methods focusing primarily on knocking-out genes, dismissing other vital steps of strain design including the overexpression and dampening of genes. The design predictions from current methods also do not translate well-into successful strains in the laboratory. Here, we introduce RobOKoD (Robust, Overexpression, Knockout and Dampening), a method for predicting strain designs for overproduction of targets. The method uses flux variability analysis to profile each reaction within the system under differing production percentages of target-compound and biomass. Using these profiles, reactions are identified as potential knockout, overexpression, or dampening targets. The identified reactions are ranked according to their suitability, providing flexibility in strain design for users. The software was tested by designing a butanol-producing Escherichia coli strain, and was compared against the popular OptKnock and RobustKnock methods. RobOKoD shows favorable design predictions, when predictions from these methods are compared to a successful butanol-producing experimentally-validated strain. Overall RobOKoD provides users with rankings of predicted beneficial genetic interventions with which to support optimized strain design.

The effect of Herbicides on Residual Effects of Atrazine under Conservation Agriculture

An experiment was set up to evaluate the residual effect of atrazine in cowpea production under conservation agriculture. The trial was superimposed on a previous herbicide trial of a maize crop in 2012/2013 season. The experiment was laid out in a randomized complete block design with three replicates and four treatments as follows; 1. control (manual weeding), 2. Atrazine (3.6 litres/ha), 3. Atrazine (3.6 litres/ha) + glyphosate (2.5 litres/ha) and 4. Atrazine (3.6 litres/ha) + glyphosate (2.5 litres/ha) + metolachlor (1 litre/ha). Herbicide treatment was carried out at planting time and manual weeding at 10 cm weed height. Data collected include: germination percentage, weed counts and weed biomass, cowpea biomass, pod length and cowpea yield. The herbicidal treatments showed a significant effect (p 0.05) effects were recorded on percentage germination, weed counts and weed biomass as well as on cowpea biomass. Tank mixing of two or more herbicides is recommended when using atrazine to reduce residual effect and further research is recommended under different soil types with different climatic conditions.

Sodium accumulation contributes to salt stress tolerance in lettuce cultivars

Increasing soil salinity of irrigated agricultural areas represents a major environmental stress factor that impairs the production of many salt-sensitive crop plants. Different lettuce cultivars were studied for identification of more tolerant ones, based on physiological properties. Five selected lettuce cultivars were grown hydroponically, salt stress was induced by 50 mM and 100 mM of NaCl. The cultivars exhibited differential reduction in shoot fresh weight. The highest sodium and free proline accumulation in the shoot of the most tolerant cultivar, associated with a moderate decrease of the root hydraulic conductance and of the leaf stomatal conductance, can be related to a better defense mechanism against osmotic stress. Salt exposure increased the potassium and calcium ion content of the xylem sap, which may be important for an efficient osmotic adjustment needed to support leaf expansion. The fact that the highest amount of Na+ was found in the shoot of the most tolerant cultivar, and the lowest in the most sensitive one, reflects that in lettuce Na+ exclusion is not a main strategy for salt tolerance. Lettuce is a good example for the case in which salinity tolerance is related not to exclusion, but to inclusion of sodium ions in the shoot system. For salt tolerant varieties the marketable yield has a higher dry biomass percentage, leaves of plants grown under high salinity are crispier, darker green and have a slight salty taste.