Nitrification,denitrification, and related functional genes under elevated CO2: A meta-analysis in terrestrial ecosystems

Global change may have profound effects on soil nitrogen (N) cycling that can induce positive feedback to climate change through increased nitrous oxide (N₂O) emissions mediated by nitrification and denitrification. We conducted a meta-analysis of the effects of elevated CO₂ on nitrification and denitrification based on 879 observations from 58 publications and 46 independent elevated CO₂ experiments in terrestrial ecosystems. We investigated the effects of elevated CO₂ alone or combined with elevated temperature, increased precipitation, drought, and N addition. We assessed the response to elevated CO₂ of gross and potential nitrification, potential denitrification, and abundances of related functional genes (archaeal amoA, bacterial amoA, nirK, nirS, and nosZ). Elevated CO₂ increased potential nitrification (+28%) and the abundance of bacterial amoA functional gene (+62%) in cropland ecosystems. Elevated CO₂ increased potential denitrification when combined with N addition and higher precipitation (+116%). Elevated CO₂ also increased the abundance of nirK (+25%) and nirS (+27%) functional genes in terrestrial ecosystems and of nosZ (+32%) functional gene in cropland ecosystems. The increase in the abundance of nosZ under elevated CO₂ was larger at elevated temperature and high N (+62%). Four out of 14 two-way interactions tested between elevated CO₂ and elevated temperature, elevated CO₂ and increased precipitation, and elevated CO₂ and N addition were marginally significant and mostly synergistic. The effects of elevated CO₂ on potential nitrification and abundances of bacterial amoA and nirS functional genes increased with mean annual temperature and mean annual precipitation. Our meta-analysis thus suggests that warming and increased precipitation in large areas of the world could reinforce positive responses of nitrification and denitrification to elevated CO₂ and urges the need for more investigations in the tropical zone and on interactive effects among multiple global change factors, as we may largely underestimate the effects of global change on soil N₂O emissions.     

Normania,an endemic Macaronesian genus distinct fromSolanum (Solanaceae)

Morphological data and results from scanning electron microscopy of seeds and pollen show thatNormania Lowe [syn.Solanum L. subg.Potatoe (G. Don)D'Arcy sect.Normania (Lowe)Bitter] (Solanaceae: Solaneae) should be considered as a distinct genus fromSolanum L. It has two species, one restricted to the island of Madeira [Normania triphylla (Lowe)Lowe] and the other to Tenerife and Gran Canaria [Normania nava (Webb & Berthel.)Franc.-Ort. & R. N. Lester]. These species are extremely rare and had not been found for about 100 years, untilN. nava was rediscovered in two different localities in Tenerife in 1973 and 1982.Normania triphylla was reported in two different places from northern Madeira in 1991. Both species have the highest conservation priority in the Macaronesian region.     

Comparison of dispersal ability between the green leafhoppers,Nephotettix virescens andN. cincticeps (hemiptera: Cicadellidae) by tethered flight

Dispersal propensity of green leafhoppers was compared between a tropical species, Nephotettix virescens, and a temperate species, N. cincticeps. The flight ability was measured with tethered flight technique under laboratory conditions (25°C, 16L-8D). The pre-flight period was shorter and the flight duration was longer in N. virescens than in N. cincticeps in both sexes. No significant correlations were found between the flight activity and morphometric characters for either of the two species. The results suggested that dispersal propensity of N. virescens is higher than that of N. cincticeps.     

Antibiotic production by strains of Gliocladium virens and its relation to the biocontrol of cotton seedling diseases

Strains of the fungal antagonist Gliocladium virens were separated into two distinct groups on the basis of secondary metabolite production in vitro. Strains of the ‘P’ group produced the antibiotics gliovirin and heptelidic acid but not the antibiotic gliotoxin and its companion, dimethylgliotoxin. Strains of the ‘Q’ group produced gliotoxin and dimethylgliotoxin but not gliovirin or heptelidic acid. Strains from both groups produced the antibiotic viridin and phytotoxin viridiol. Gliovirin was very inhibitory to Pythium ultimum but had no activity against Rhizoctonia solani, and strains that produce it were more effective seed treatment biocontrol agents of disease incited by P. ultimum. Conversely, gliotoxin was more active against R. solani than against P. ultimum, and strains that produced it were more effective seed treatments for controlling disease incited by R. solani. These results indicate that the antibiotic profiles of strains should be considered when screening strains for biocontrol efficacy, and that it may be necessary to treat seeds with a combination of strains in order to broaden the disease control spectrum.     

First chemical synthesis of a scorpion alpha-toxin affecting sodium channels: the Aah I toxin of Androctonus australis hector.

Aah I is a 63-residue alpha-toxin isolated from the venom of the Buthidae scorpion Androctonus australis hector, which is considered to be the most dangerous species. We report here the first chemical synthesis of Aah I by the solid-phase method, using a Fmoc strategy. The synthetic toxin I (sAah I) was renatured in DMSO-Tris buffer, purified and subjected to thorough analysis and comparison with the natural toxin. The sAah I showed physico-chemical (CD spectrum, molecular mass, HPLC elution), biochemical (amino-acid composition, sequence), immunochemical and pharmacological properties similar to those of the natural toxin. The synthetic toxin was recognized by a conformation-dependent monoclonal anti-Aah I antibody, with an IC50 value close to that for the natural toxin. Following intracerebroventricular injection, the synthetic and the natural toxins were similarly lethal to mice. In voltage-clamp experiments, Na(v) 1.2 sodium channel inactivation was inhibited by the application of sAah I or of the natural toxin in a similar way. This work describes a simple protocol for the chemical synthesis of a scorpion alpha-toxin, making it possible to produce structural analogues in time.     

Toxicity of parathion-methyl to cells, akinetes and heterocysts of the cyanobacterium Cylindrospermum, sp. and the probit analysis of toxicity

The toxicity of a commercial formulation of the insecticide parathion‐methyl to the N2‐fixing filamentous cyanobacterium (blue‐green alga) Cylindrospermum, sp. was studied. A concentration of parathion‐methyl of 0.5 ppm caused growth increase in liquid growth media. The minimum inhibitory concentration of parathion‐methyl for both types (N₂, fixing and nitrate supplemented) of liquid and solid media was 1.0 ppm. LC₅₀ values were: 4.4 ppm (liquid, N₂, fixing), 5.5 ppm (liquid, nitrate supplemented), 3.3 ppm (agar, N₂‐fixing) and 4.0 ppm (agar, nitrate supplemented). LC100 values for N₂‐fixing liquid and both types of agar media were 10.0 ppm, while for the liquid nitrate supplemented medium the LC₁₀₀ was 12.0 ppm. Both akinete (spore) formation and germination were inhibited below the highest permissive concentration of 8.0 ppm, with the insecticide incorporated in the agar media. In soil, the LC50 and LC100 values for parathion‐methyl were 13.6 and 30 ppm, respectively. Both the dehydrogenase activity of heterocysts (monitored by 2,3,5‐triphenyl tetrazolium chloride reduction) and the nitrogen concentration of cultures (estimated by the micro‐Kjeldahl method) were affected by the insecticide, but the latter (N₂‐fixation) was more sensitive. The Kruskal‐Wallis H test on the numbers of vegetative cells in the filaments revealed that the insecticide significantly affected the division of vegetative cells. The cyanobacterium could detoxify the growth medium containing high levels (30 and 40 ppm) of the insecticide in short‐term exposures at the expense of cell viability.     

Effects of plant nutrition on the balance of insect relevant cardenolides and glucosinolates in Erysimum cheiranthoides

The possible effects of environmental stress on plant chemistry that are important to herbivorous insects were examined by growing a wild crucifer, Erysimum cheiranthoides, under different nutrient regimes. Oviposition by the cabbage butterfly, Pieris rapae, is thought to be affected by the balance of glucosinolates (stimulants) and cardenolides (deterrents) at the surface of leaves. E. cheiranthoides seedlings were provided with three levels of nitrogen and two levels of sulfur for a period of 15 days before analysis of semiochemicals in whole leaf tissue and at the surface of the foliage. The ratio of cardenolides to glucosinolates in the plants at elevated C/N ratios followed the carbon/nutrient balance hypothesis. However, a high nitrogen supply enhanced biomass production to the extent that concentrations of secondary compounds were unchanged or reduced. The concentration of glucosinolates (glucoiberin and glucocheirolin) at the surface was positively related to whole tissue levels. However, cardenolide (erysimoside and erychroside) concentrations, which were highest in leaf tissue of nitrogen-deficient plants, had the lowest surface levels on foliage of these plants. Possible reasons for differential expression of cardenolides and glucosinolates in a plant as a result of nutrient deficiency are discussed.     

Belowground positive and negative feedbacks on CO2 growth enhancement

In this paper we present a conceptual model of integrated plant-soil interactions which illustrates the importance of identifying the primary belowground feedbacks, both positive and negative, which can simultaneously affect plant growth responses to elevated CO₂. The primary negative feedbacks share the common feature of reducing the amount of nutrients available to plants. These negative feedbacks include increased litter C/N ratios, and therefore reduced mineralization rates, increased immobilization of available nutrients by a larger soil microbial pool, and increased storage of nutrients in plant biomass and detritus due to increases in net primary productivity (NPP). Most of the primary positive feedbacks share the common feature of being plant mediated feedbacks, the only exception being Zak et al.'s hypothesis that increased microbial biomass will be accompanied by increased mineralization rates. Plant nutrient uptake may be increased through alterations in root architecture, physiology, or mycorrhizal symbioses. Further, the increased C/N ratios of plant tissue mean that a given level of NPP can be achieved with a smaller supply of nitrogen.Identification of the net plant-soil feedbacks to enhanced productivity with elevated CO₂ are a critical first step for any ecosystem. It is necessary, however, that we first identify how universally applicable the results are from one study of one ecosystem before ecosystem models incorporate this information. The effect of elevated CO₂ on plant growth (including NPP, tissue quality, root architecture, mycorrhizal symbioses) can vary greatly for different species and environmental conditions. Therefore it is reasonable to expect that different ecosystems will show different patterns of interacting positive and negative feedbacks within the plant-soil system. This inter-ecosystem variability in the potential for long-term growth responses to rising CO₂ levels implies that we need to parameterize mechanistic models of the impact of elevated CO₂ on ecosystem productivity using a detailed understanding of each ecosystem of interest.