Carbon allocation in ectomycorrhizal plants at limited and optimal N supply: an attempt at unraveling conflicting theories

With regard to mycorrhiza, conflicting theories try to explain how the balance between fungal demand for carbohydrates and the plant’s needs for nutrients varies, resulting in conflicting predictions. In order to evaluate current concepts, we investigated some metabolic parameters, which are indicative for plant carbon allocation in response to mycorrhization at limited and optimal N supply. Pinus pinaster seedlings were inoculated with living or dead (control) cultures of Pisolithus tinctorius, supplied with ammonium at 4 (limiting) or 7% d⁻¹ (non-limiting) N relative addition rate (RAR_N), and followed development for 29 days. Mycorrhizal colonization of roots was quantified by the determination of ergosterol. A series of enzymes (sucrose and trehalose metabolism, anaplerosis) and metabolites (soluble carbohydrate, including trehalose; fructose 2,6 bisphosphate, free amino acids) relevant in the C/N exchange between symbionts, and in the carbon allocation and sink strength within the plant were assayed for 2-day-intervals for up to 14 days, and at 5-day-intervals for the rest of the experiment. The first 10 days reflected the establishment of mycorrhizal interaction, and the carbon allocation to the root was higher in M plants independent of N supply. Following this period, carbon allocation became N-related, higher at low, and lower at high N supply. The belowground C investment of M plants was dependent on N availability, but not on N gain. Finally, increased belowground C allocation was accompanied by a shift from plant to fungal metabolism.     

Searching for bioindicators of forest fragmentation: passerine birds in the Atlantic forest of southeastern Brazil

Aiming to evaluate the potential of Passerine birds as bioindicators of forest fragmentation, we studied the avifauna in the mountain region of the state of Rio de Janeiro by mist-netting between 2001 and 2005. We sampled six sites, including four small fragments (from 4 to 64 ha) in an agricultural area (Teresópolis), one second-growth forest (440 ha - Miguel Pereira) and a continuous forest (10,600 ha, Serra dos Org?os National Park - SONP). Indicator Species analysis and a Monte Carlo test were run to detect associations between species and sites, considering at least 30% of perfect indication and a significant value for the statistical test, only considering species with at least 10 captures. A total of 30 Passerine birds were sampled, and due to their association to the largest area (SONP), we considered Sclerurus scansor, Mionectes rufiventris, Chiroxiphia caudata and Habia rubica as the best indicators for this area. Five species were more captured not by chance in the 440 ha second-growth: Conopophaga melanops, Myiobius barbatus, Myrmeciza loricata, Philydor atricapillus and Schiffornis virescens and no species were related to any small fragment. This analysis has identified specialized Passerine species in many aspects (foraging substract, needs for nesting, rarity status), and it can be a valuable tool for detecting possible bioindicators.     

Vertical movement and time allocation of a freshwater pulmonate snail

The paper presents an analysis of locomotion and location in a vertical water column of 10Biomphalaria glabrata, under constant conditions of light, temperature, and food availability. Individual snails varied in distance traveled, and in the percentage of time spent in different areas of the water column. Distance covered ranged from 53 cm to 100 cm h^–1 . Approximately 21% of locomotion was observed to be passive (floating up or sinking down). Snails spent approximately 58% of the time in the bottom section, 35% in the top section and only 7% in the middle region. The study provides baseline data that can be used to compare further studies ofBiomphalaria glabrata as various conditions are altered.     

Microsatellite markers for <Emphasis Type="Italic">Caesalpinia echinata</Emphasis> Lam. (Brazilwood), a tree that named a country

Caesalpinia echinata, commonly known as Pau-brasil (Brazilwood), the famous tree that named Brazil is native to the Atlantic forest. Men extensively exploited it ever since discovery and colonial times due to its value as a source of red dye. As a consequence, Brazilwood is a threatened species with populations reduced to small forest fragments. Ten polymorphic microsatellite loci were developed from an enriched genomic library. Using fluorescently-labeled primers, a total of 83 alleles were found after analyzing a sample of 44 trees. These high genetic information content markers should allow detailed investigations of mating systems, gene flow, population structure and paternity in natural populations.     

Plant colonization in a gravel mine revegetated with Stylosanthes spp. in a Neotropical savanna

Tree establishment on degraded sites has failed in many tropical areas due to invasive plants and competition with herbs. The cultivation of plants that are capable of maintaining a site can avoid the dominance of invasive species. Some native species of the genus Stylosanthes (family Fabaceae) have been reported to effectively block invasive plants off ecosystems that are under restoration in Brazil. The aim of this study was therefore to evaluate the influence of perennial Stylosanthes spp. on plant colonization in a rehabilitated gravel mine in the Brazilian savanna region. Half of the mining area was sown with a mixture of three perennial Styloshantes species (treatment), while half of it remained unsown (control). The line intercept method was used to sample recruited plants within the mine after five years of site rehabilitation. Results showed that 31 plant species recruited in the gravel mine: 27 in the area sown with Stylosanthes spp. and 17 in the control area. Native species contributed for 47 % of the importance value index (IVI) in the treated area and 26 % in the control area. Two invasive exotic grasses made up 31 % of the plant community IVI in the treated area and 59 % in the control area. Perennial Stylosanthes spp. were supposed to block the development of incoming plants, but their presence actually allowed the area to be colonized by 1.6-fold more plant species than the control area. Ultimately, the area covered with Stylosanthes spp. evolved into a plant community that was more diverse and less dominated by exotic species than the control area.     

Chromosomal and electric signal diversity in three sympatric electric knifefish species (Gymnotus, Gymnotidae) from the Central Amazon Floodplain

We describe chromosomal and electric signal diversity in three sympatric species of Gymnotus (Gymnotidae) fish from the Central Amazon Floodplain. Gymnotus arapaima presents a karyotype of 2n = 44 (24 m-sm + 20st-a), G. mamiraua 2n = 54 (42 m-sm + 12st-a), and G. jonasi 2n = 52 (12 m-sm + 40st-a). No evidence for a chromosomal sexual system was observed in two species for which both males and females were analyzed (G. mamiraua and G. arapaima). In all three species the constitutive heterochromatin is located primarily in pericentromeric regions, but also at some other sites. G. arapaima and G. mamiraua exhibit simple nucleolar organizing regions (NORs) on short arms of chromosome pairs 19 and 24, respectively. Gymnotus jonasi exhibits a multiple interstitial NOR on the long arm of pairs 9 and 10, and on the short arm of pair 11. G. arapaima and G. mamiraua exhibit several additional similarities in their karyotypic formulas—reflecting the phylogenetic proximity of these species within a G. carapo group clade (based on molecular phylogenetic evidence). The chromosomal differences among these three sympatric species imply complete post-zygotic reproductive isolation. A prominent pattern of partitioning of the peak power frequency of the electric organ discharge of these three species indicates pre-zygotic reproductive isolation of mate attraction signals. We conclude by discussing the evolutionary events that may have promoted signal divergence and reproductive isolation in Gymnotus of the Central Amazon, and the role that chromosomal rearrangements may place in diversification.     

Comparative evaluation of different preservation methods for cyanobacterial strains

Maintaining pure cultures using preservation methods is of high importance for biotechnological purposes. However, preservation does not necessarily guarantee the genetic stability of these cultures. Therefore, preservation methods are currently needed to assure viability as well as genetic, physiological, and morphological integrity across storage periods. In this study, preservation of five isolates from the microalgae and cyanobacteria collection of the Plant Biology Department, Federal University of Viçosa, Minas Gerais, Brazil was investigated via monthly analyses of cell viability, biomass recovery, and contaminant concentrations over a period of 120 days. Lyophilization was adequate for both heterocystous cyanobacteria and other strains that were able to differentiate hormogones or to synthesize thick layers of exopolysaccharides. Lyophilization was also able to maintain cultures with low levels of contaminants. Dimethyl sulfoxide was relatively efficient, though some of the strains were susceptible to its cytotoxic effects. Our results demonstrated that cryopreservation with glycerol was the most efficient method. The ability to routinely preserve cyanobacterial strains reduces costs associated with maintaining large culture collections and reduces the risks of losing particular strains or species through contamination and genetic drift. The results obtained in this study are therefore discussed in the context of the efficiency of the methods and the current need to develop suitable methods for maintenance of cyanobacterial collections.