Aboveground nutrient components of Eucalyptus camaldulensis and E. grandis in semiarid Brazil under the nature and the mycorrhizal inoculation conditions

A study was conducted to evaluate the aboveground biomass, nutrient content and the percentages of mycorrhizal colonization in Eucalyptus camaldulensis and Eucalyptus grand＆ plantations in the semiarid region （ 15° 09′ S 43° 49′ W） in the north of the State of Minas Gerais in Brazil. Results show that the total above-ground biomass （dry matter） was 33.6 Mg.ha^-1 for E. camaldulensis and 53.1 Mg·ha^-1 for E. grandis. The biomass of the stem wood, leaves, branches, and stein bark for E. camaldulens accounted for 64.4%, 19.6%, 15.4%, and 0.6% of the total biomass, respectively （Table 2）; meanwhile a similar partition of the total above-ground biomass was also found for E. grand＆. The dry matter of leaves and branches of E. camaldulensis accounted for 35% of total biomass, and the contents of N, P, K, Ca, Mg, and S in leaves and branches accounted for 15.5%, 0.7%, 12.3%, 22.6%, 1.9%, and 1.4% of those in total above-ground biomass, respectively. In the trunk （bark and wood）, nutrient accumulation in general was lower. Nutrient content of E. grand＆ presented little variation compared with that orE. camaJd^llensis. Wood localized in superior parts of trunk presented a higher concentration of P and bark contained significant amounts of nutrients, especially in E. grand＆. This indicated that leaving vegetal waste is of importance on the site in reducing the loss of tree productivity in this semi-arid region. The two species showed mycotrophy.

The Role of Red Algae in Abrupt Appearance of Animals in the Early Cambrian on Siberian Platform

Calcified rock-forming marine filamented benthic micro- and macrophytes of Dzhelindia Kolosov, 1970 (Figure 1(а)) and Chaptchaica Kolosov, 1975 (Figure 1(b)) genera, thrived in Neoproterozoic (1000-541 million years ago) Siberia together with cyanobacteria. Their belonging to Rhodophyta is well-grounded. These and other Neoproterozoic rodofits, as well as Epiphyton Bornemann 1886 (Figure 1(c)) and other Early Cambrian (541-513 million years ago) benthic algae, oxygenating floor of epicontinental sea basin, formed conditions, favorable for the animals. In combination with other biotic, and such abiotic factors as: equatorial position and tectonic feature of Siberian platform;volcanism;transgression of the sea;diversity of ecologic niches, these conditions were prerequisites of skeleton and shell acquisition by Early Cambrian animals, and as a consequence, accelerated morphologic evolution, increased diversity of taxons of different groups of animals.

Strigolactones are a new-defined class of plant hormones which inhibit shoot branching and mediate the interaction of plant-AM fungi and plant-parasitic weeds

Because plants are sessile organisms,the ability to adapt to a wide range of environmental conditions is critical for their survival.As a consequence,plants use hormones to regulate growth,mitigate biotic and abiotic stresses,and to communicate with other organisms.Many plant hormones function plei-otropically in vivo,and often work in tandem with other hormones that are chemically distinct.A newly-defined class of plant hormones,the strigolactones,cooperate with auxins and cytokinins to control shoot branching and the outgrowth of lateral buds.Strigolactones were originally identified as compounds that stimulated the germination of parasitic plant seeds,and were also demonstrated to induce hyphal branching in arbuscular mycorrhizal(AM) fungi.AM fungi form symbioses with higher plant roots and mainly facilitate the absorption of phosphate from the soil.Conforming to the classical definition of a plant hormone,strigolactones are produced in the roots and translocated to the shoots where they inhibit shoot outgrowth and branching.The biosynthesis of this class of compounds is regulated by soil nutrient availability,i.e.the plant will increase its production of strigolactones when the soil phosphate concentration is limited,and decrease production when phosphates are in ample supply.Strigolactones that affect plant shoot branching,AM fungal hyphal branching,and seed germination in parasitic plants facilitate chemical synthesis of similar compounds to control these and other biological processes by exogenous application.

Influence of"protective"symbionts throughout the different steps of an aphid-parasitoid interaction

Microbial associates are widespread in insects,some conferring a protection to their hosts against natural enemies like parasitoids.These protective symbionts may affect the infection success of the parasitoid by modifying behavioral defenses of their hosts,the development success of the parasitoid by conferring a resistance against it or by altering life-history traits of the emerging parasitoids.Here,we assessed the effects of different protective bacterial symbionts on the entire sequence of the host-parasitoid interaction(i.e.,from parasitoid attack to offspring emergence)between the pea aphid,Acyrthosiphon pisum,and its main parasitoid,Aphidius ervi and their impacts on the life-history traits of the emerging parasitoids.To test whether symbiont-mediated phenotypes were general or specific to particular aphid-symbiont associations,we considered several aphid lineages,each harboring a different strain of either Hamiltonella defensa or Regiella insecticola,two protective symbionts commonly found in aphids.We found that symbiont species and strains had a weak effect on the ability of aphids to defend themselves against the parasitic wasps during the attack and a strong effect on aphid resistance against parasitoid development.While parasitism resistance was mainly determined by symbionts,their effects on host defensive behaviors varied from one aphid-symbiont association to another.Also,the symbiotic status of the aphid individuals had no impact on the attack rate of the parasitic wasps,the parasitoid emergence rate from parasitized aphids nor the life-history traits of the emerging parasitoids.Overall,no correlations between symbiont effects on the different stages of the host-parasitoid interaction was observed,suggesting no trade-offs or positive associations between symbiont-mediated phenotypes.Our study highlights the need to consider various sequences of the host-parasitoid interaction to better assess the outcomes of protective symbioses and understand the ecological and evolutionary dynamics of insect-symbiont associations.

Extremotolerant fungi from alpine rock lichens and their phylogenetic relationships

Fungi other than the lichen mycobiont frequently co-occur within lichen thalli and on the same rock in harsh environments.In these situations dark-pigmented mycelial structures are commonly observed on lichen thalli,where they persist under the same stressful conditions as their hosts.Here we used a comprehensive sampling of lichen-associated fungi from an alpine habitat to assess their phylogenetic relationships with fungi previously known from other niches.The multilocus phylogenetic analyses suggest that most of the 248 isolates belong to the Chaetothyriomycetes and Dothideomycetes,while a minor fraction represents Sordariomycetes and Leotiomycetes.As many lichens also were infected by phenotypically distinct lichenicolous fungi of diverse lineages,it remains difficult to assess whether the culture isolates represent these fungi or are from additional cryptic,extremotolerant fungi within the thalli.Some of these strains represent yet undescribed lineages within Chaethothyriomycetes and Dothideomycetes,whereas other strains belong to genera of fungi,that are known as lichen colonizers,plant and human pathogens,rock-inhabiting fungi,parasites and saprotrophs.The symbiotic structures of the lichen thalli appear to be a shared habitat of phylogenetically diverse stress-tolerant fungi,which potentially benefit from the lichen niche in otherwise hostile habitats.