A simple inhibition coefficient for quantifying potency of biocontrol agents against plant-pathogenic fungi

Microbial interactions depend on a range of biotic and environmental variables, and are both dynamic and unpredictable. For some purposes, and under defined conditions, it is nevertheless imperative to evaluate the inhibitory efficacy of microbes, such as those with potential as biocontrol agents. We selected six, phylogenetically diverse microbes to determine their ability to inhibit the ascomycete Fusarium
coeruleum, a soil-dwelling pathogen of potato tubers that causes the storage disease dry rot. Interaction assays, where colony development was quantified (for both fungal pathogen and potential control agents), were therefore carried out on solid media. The key parameters that contributed to, and were indicative of, inhibitory efficacy were identified as: fungal growth-rates (i) prior to contact with the biocontrol
agent and (ii) if/once contact with the biocontrol agent was established (i.e. in the zone of mixed
culture), and (iii) the ultimate distance traveled by the fungal mycelium. It was clear that there was no correlation between zones of fungal inhibition and the overall reduction in the extent of fungal colony development. An inhibition coefficient was devised which incorporated the potential contributions of distal inhibition of fungal growth-rate; prevention of mycelium development in the vicinity of the biocontrol
agent; and ability to inhibit plant-pathogen growth-rate in the zone of mixed culture (in a ratio of 2:2:1). The values derived were 84.2 for Bacillus subtilis (QST 713), 74.0 for Bacillus sp. (JC12GB42), 30.7 for Pichia anomala (J121), 19.3 for Pantoea agglomerans (JC12GB34), 13.9 for Pantoea sp. (S09:T:12), and
21.9 (indicating a promotion of fungal growth) for bacterial strain (JC12GB54). This inhibition coefficient, with a theoretical maximum of 100, was consistent with the extent of F. coeruleum-colony development (i.e. area, in cm2) and assays of these biocontrol agents carried out previously against Fusarium
spp., and other fungi. These findings are discussed in relation to the dynamics and inherent complexity of natural ecosystems, and the need to adapt models for use under specific sets of conditions.

Process simulation of co-firing torrefied biomass in a 220 MWe coal-fired power plant

Torrefaction based co-firing in a pulverized coal boiler has been proposed for large percentage of biomass co-firing. A 220 MWe pulverized coal-power plant is simulated using Aspen Plus for full understanding the impacts of an additional torrefaction unit on the efficiency of the whole power plant, the studied process includes biomass drying, biomass torrefaction, mill systems, biomass/coal devolatilization and combustion, heat exchanges and power generation. Palm kernel shells (PKS) were torrefied at same residence time but 4 different temperatures, to prepare 4 torrefied biomasses with different degrees of torrefaction. During biomass torrefaction processes, the mass loss properties and released gaseous components have been studied. In addition, process simulations at varying torrefaction degrees and biomass co-firing ratios have been carried out to understand the properties of CO₂ emission and electricity efficiency in the studied torrefaction based co-firing power plant. According to the experimental results, the mole fractions of CO ₂ and CO account for 69-91% and 4-27% in torrefied gases. The predicted results also showed that the electrical efficiency reduced when increasing either torrefaction temperature or substitution ratio of biomass. A deep torrefaction may not be recommended, because the power saved from biomass grinding is less than the heat consumed by the extra torrefaction process, depending on the heat sources. 

Conserved histidine of metal transporter AtNRAMP1 is crucial for optimal plant growth under manganese deficiency at chilling temperatures

Manganese (Mn) is an essential nutrient required for plant growth, in particular in the process of photosynthesis. Plant performance is influenced by various environmental stresses including contrasting temperatures, light or nutrient deficiencies. The molecular responses of plants exposed to such stress factors in combination are largely unknown. 

Screening of 108 Arabidopsis thaliana (Arabidopsis) accessions for reduced photosynthetic performance at chilling temperatures was performed and one accession (Hog) was isolated. Using genetic and molecular approaches, the molecular basis of this particular response to temperature (GxE interaction) was identified. 

Hog showed an induction of a severe leaf chlorosis and impaired growth after transfer to lower temperatures. We demonstrated that this response was dependent on the nutrient content of the soil. Genetic mapping and complementation identified NRAMP1 as the causal gene. Chlorotic phenotype was associated with a histidine to tyrosine (H239Y) substitution in the allele of Hog NRAMP1. This led to lethality when Hog seedlings were directly grown at 4 degrees C. 

Chemical complementation and hydroponic culture experiments showed that Mn deficiency was the major cause of this GxE interaction. For the first time, the NRAMP-specific highly conserved histidine was shown to be crucial for plant performance.

Milling plant and soil material in plastic tubes over-estimates carbon and under-estimates nitrogen concentrations

Milling of plant and soil material in plastic tubes, such as microcentrifuge tubes, over-estimates carbon (C) and under-estimates nitrogen (N) concentrations due to the introduction of polypropylene into milled samples, as identified using Fourier-transform infra-red spectroscopy.

This study compares C and N concentrations of roots and soil milled in microcentrifuge tubes versus stainless steel containers, demonstrating that a longer milling time, greater milling intensity, smaller sample size and inclusion of abrasive sample material all increase polypropylene contamination from plastic tubes leading to overestimation of C concentrations by up to 8 % (0.08 g g(-1)).

Erroneous estimations of C and N, and other analytes, must be assumed after milling in plastic tubes and milling methods should be adapted to minimise such error.

Effect of heating vermiculites on extractability of phosphorus and some essential plant micronutrients

The study assessed the effect of heating vermiculites on extractability of phosphorus, iron, zinc and manganese with respect to their potential agricultural use. Of these elements, phosphorus was from apatite and monazite that occur as accessory minerals in vermiculites. Vermiculites were heated at 15-800 degrees C and digested by acetic acid for extracting phosphorus and diethylene triamine pentaacetic acid (DTPA) for extracting zinc, iron and manganese. Phosphorus in the extract was analysed by a flow injection method while zinc, iron and manganese were measured by atomic absorption spectrometry. The results showed that heating vermiculites to 400 C enhanced extractability of phosphorus from apatite and monazite to a level of 335 mg kg(-1). Further heating to 800 degrees C reduced extractable phosphorus to less than 75 mg kg(-1). Maximum extractable zinc, iron and manganese found were 2.7, 19.1 and 22.9 mg kg(-1), respectively, values that are beneficial and tolerable by most plants. Thus, it was concluded that heating vermiculites to

Plant community assembly at small scales: spatial versus environmental factors in a central European grassland

Dispersal limitation and environmental conditions are crucial drivers of plant species distribution and establishment. As these factors operate at different spatial scales, we asked: Do the environmental factors known to determine community assembly at broad scales operate at fine scales (few meters)? How much do these factors account for community variation at fine scales? In which way do biotic and abiotic interactions drive changes in species composition? We surveyed the plant community within a dry grassland along a very steep gradient of soil characteristics like pH and nutrients. We used a spatially explicit sampling design, based on three replicated macroplots of 15x15, 12x12 and 12x12 meters in extent. Soil samples were taken to quantify several soil properties (carbon, nitrogen, plant available phosphorus, pH, water content and dehydrogenase activity as a proxy for overall microbial activity). We performed variance partitioning to assess the effect of these variables on plant composition and statistically controlled for spatial autocorrelation via eigenvector mapping. We also applied null model analysis to test for non-random patterns in species co-occurrence using randomization schemes that account for patterns expected under species interactions. At a fine spatial scale, environmental factors explained 18% of variation when controlling for spatial autocorrelation in the distribution of plant species, whereas purely spatial processes accounted for 14% variation. Null model analysis showed that species spatially segregated in a non-random way and these spatial patterns could be due to a combination of environmental filtering and biotic interactions. Our grassland study suggests that environmental factors found to be directly relevant in broad scale studies are present also at small scales, but are supplemented by spatial processes and more direct interactions like competition.

Holocene landscape intervention and plant food production strategies in island and mainland Southeast Asia

In the areas adjacent to the drowned Pleistocene continent of Sunda – present-day Mainland and Island SE Asia – the Austronesian Hypothesis of a diaspora of rice cultivators from Taiwan ∼4200 years ago has often been linked with the start of farming. Mounting evidence suggests that these developments should not be conflated and that alternative explanations should be considered, including indigenous inception of complex patterns of plant food production and early exchange of plants, animals, technology and genes. We review evidence for widespread forest disturbance in the Early Holocene which may accompany the beginnings of complex food-production. Although often insubstantial, evidence for incipient and developing management of rainforest vegetation and of developing complex relationships with plants is present, and early enough to suggest that during the Early to mid-Holocene this vast region was marked by different approaches to plant food production. The trajectory of the increasingly complex relationships between people and their food organisms was strongly locally contingent and in many cases did not result in the development of agricultural systems that were recognisable as such at the time of early European encounters. Diverse resource management economies in the Sunda and neighbouring regions appear to have accompanied rather than replaced a reliance on hunting and gathering. This, together with evidence for Early Holocene interaction between these neighbours, gives cause for us to question some authors continued adherence to a singular narrative of the Austronesian Hypothesis and the ‘Neolithisation’ of this part of the world. It also leads us to suggest that the forests of this vast region are, to an extent, a cultural artefact.

Ecological dynamics of extinct species in empty habitat networks. 2. The role of host plant dynamics

This paper explores the relative effects of host plant dynamics and butterfly-related parameters on butterfly persistence. It considers an empty habitat network where a rare butterfly (Cupido minimus) became extinct in 1939 in part of its historical range in north Wales, UK. Surviving populations of the butterfly in southern Britain were visited to assess use of its host plant (Anthyllis vulneraria) in order to calibrate habitat suitability and carrying capacity in the empty network in north Wales. These data were used to deduce that only a portion ( similar to 19%) of the host plant network from north Wales was likely to be highly suitable for oviposition. Nonetheless, roughly 65,460 eggs (3273 adult equivalents) could be expected to be laid in north Wales, were the empty network to be populated at the same levels as observed on comparable plants in surviving populations elsewhere. Simulated metapopulations of C. minimus in the empty network revealed that time to extinction and patch occupancy were significantly influenced by carrying capacity, butterfly mean dispersal distance and environmental stochasticity, although for most reasonable parameter values, the model system persisted. Simulation outputs differed greatly when host plant dynamics was incorporated into the modelled butterfly dynamics. Cupido minimus usually went extinct when host plant were at low densities. In these simulations host plant dynamics appeared to be the most important determinant of the butterfly's regional extirpation. Modelling the outcome of a reintroduction programme to C. minimus variation at high quality locations, revealed that 65% of systems survived at least 100 years. Given the current amount of resources of the north Wales landscape, the persistence of C. minimus under a realistic reintroduction programme has a good chance of being successful, if carried out in conjunction with a host plant management programme.

Mechanisms of plant resistance to metal and metalloid ions and potential biotechnological applications

Metal and metalloid resistances in plant species and genotypes/accessions are becoming increasingly better understood at the molecular and physiological level. Much of the recent focus into metal resistances has been on hyperaccumulators as these are excellent systems to study resistances due to their very abnormal metal(loid) physiology and because of their biotechnological potential. Advances into the mechanistic basis of metal(loid) resistances have been made through the investigation of metal(loid) transporters, the construction of mutants with altered metal(loid) transport and metabolism, a better understanding of the genetic basis of resistance and hyperaccumulation and investigations into the role of metal(loid) ion chelators. This review highlights these recent advances. © Springer 2005.

Arsenic uptake and metabolism in arsenic resistant and nonresistant plant species

Elevation of arsenic levels in soils causes considerable concern with respect to plant uptake and subsequent entry into wildlife and human food chains, Arsenic speciation in the environment is complex, existing in both inorganic and organic forms, with interconversion between species regulated by biotic and abiotic processes. To understand and manage the risks posed by soil arsenic it is essential to know how arsenic is taken up by the roots and metabolized within plants. Some plant species exhibit phenotypic variation in response to arsenic species, which helps us to understand the toxicity of arsenic and the way in which plants have evolved arsenic resistances. This knowledge, for example, could be used produce plant cultivars that are more arsenic resistant or that have reduced arsenic uptake. This review synthesizes current knowledge on arsenic uptake, metabolism and toxicity for arsenic resistant and nonresistant plants, including the recently discovered phenomenon of arsenic hyperaccumulation in certain fern species. The reasons why plants accumulate and metabolize arsenic are considered in an evolutionary context. © New Phytologist.