Gas exchange and photosynthesis of Eucalyptus camaldulensis seedlings inoculated with different ectomycorrhizal symbionts

Eucalyptus camaldulensis Dehnh. seedlings inoculated with Pisolithus tinctorius (Pers.) Coker & Couch and Thelephora terrestris Ehrl. per Fr. were grown in well watered soil (_s –0.03 MPa) or subjected to a long-term soil water stress of up to –1.0 MPa over 13-week period in a glasshouse. After 13 weeks, all seedling containers were watered to field capacity and then water was withheld from the E. camaldulensis seedlings to induce a short-term drought. Diurnal measurements of seedling photosynthesis rate (A), leaf stomatal conductance (g) and leaf water potential (_p) were completed before, during, and after the short term drought. Although they were growing in an equal soil volume, photosynthesis rate (A), leaf stomatal conductance and leaf water potential (_p) of larger seedlings with P. tinctorius ectomycorrhizae were similar to those of smaller seedlings colonized with T. terrestris during the short-term drought period. Seedlings inoculated with Pisolithus tinctorius maintained higher photosynthesis rates over the course of the short-term drought. Thus, P. tinctorius ectomycorrhizae appear to be more efficient than those of T. terrestris in assisting seedlings to maintain gas exchange and photosynthesis under limited soil moisture conditions.     

The importance of initial seed size in wheat plant response to salinity

Large initial seed size frequently confers distinct advantages on cereal crops in terms of seedling vigor, hardiness, improved stand establishment, and higher productivity. This study was conducted to determine if these advantages inherent in the plants grown from large seeds persist when the crop is subjected to salinity stress. Two hard red spring wheat cultivars, Yecora Rojo and Anza were grown in greenhouse sand cultures from seed of two size classes that differed in weight by a factor of 2. The cultures were irrigated four times daily with complete nutrient solutions to which NaCl and CaCl₂ (2:1 molar ratio) were added to achieve osmotic potentials of –0.05. –0.55, and –0.70 MPa with electrical conductivities of 1.8, 12.8, and 15.8 dS m^-1, respectively. In response to both salinity and small initial seed size, the following plant characteristics decreased: leaf appearance rate, blade area, tillers per plant, spikelets per spike and seeds per spike. Plants grown from large seeds out-yielded those from small seeds by 8, 37, and 27% for Yecora Rojo and by 15, 30, and 23% for Anza at osmotic potentials of –0.05, –0.55 and –0.70 MPa, respectively. Compared to the corresponding nonsaline controls, the yield of Yecora Rojo grown at –0.55 MPa was 51% for the plants from large seed and 35% from the small seeds. For Anza salinized at –0.55 MPa, these values were 49 and 40%, respectively. Exploitation of the benefits derived from large initial seed size may be a cost-effective management strategy for improving wheat productivity in salt-affected areas.     

Evidence that both Ca(2+)-specific sites of skeletal muscle TnC are required for full activity

To investigate the role of the Ca2(+)-specific (I and II) sites of fast skeletal muscle troponin C (TnC) in the regulation of contraction, we have produced two TnC mutants which have lost the ability to bind Ca2+ at either site I (VG1) or at site II (VG2). Both mutants were able to partially restore force to TnC-depleted skinned muscle fibers (approximately 25% for VG1 and approximately 50% for VG2). In contrast, bovine cardiac TnC (BCTnC), which like VG1 binds Ca2+ only at site II, could fully reactivate the contraction of TnC-depleted fibers. Higher concentrations of both mutants were required to restore force to the TnC-depleted fibers than with wild type TnC (WTnC) or BCTnC. VG1 and VG2 substituted fibers could not bind additional WTnC, indicating that all of the TnC-binding sites were saturated with the mutant TnC's. The Ca2+ concentration required for force activation was much higher for VG1 and VG2 substituted fibers than for WTnC or BCTnC substituted fibers. Also, the steepness of force activation was much less in VG1 and VG2 versus WTnC and BCTnC substituted fibers. These results suggest cooperative interactions between sites I and II in WTnC. In contrast, BCTnC has essentially the same apparent Ca2+ affinity and steepness of force activation as does WTnC. Thus, cardiac TnC must have structural differences from WTnC which compensate for the lack of site I, while in WTnC, both Ca2(+)-specific sites are probably crucial for full functional activity.     

Egg load influences search intensity,host selectivity,and clutch size inBattus philenor butterflies

Numerous studies have documented the influence of environmental factors such as host plant species and host quality on the oviposition behavior of female insects. This paper shows that an internal physiological factor, the number of mature eggs a female carries (egg load), correlates with host selectivity and clutch size in unmanipulated natural populations of the pipevine swallowtail butterfly, Battus philenor.In addition, search intensity and host selectivity differed among females whose egg loads were manipulated experimentally before they were released and followed in the field. Females with many eggs searched more intensely for hosts and were less selective when they encountered them.     

Structure and conformation in solution of the parallel-stranded hybrid α-d(CGCAATTCGC)·β-d(GCGTTAAGCG) by high-resolution 2D NMR

Summary The unnatural duplex oligonucleotide -d(CGCAATTCGC)·-d(GCGTTAAGCG) was analyzed by high-resolution NMR methods. All of the exchangeable imino and nonexchangeable protons of the duplex were assigned. Detection of all 10 of the exchangeable imino protons confirms that a parallel, unsymmetrical duplex is formed. The thermal stability of the parallel duplex is similar to the analogous antiparallel - duplex. The right handedness of the helix is confirmed by inter-residue [H8/H6-H1] and [H8/H6-H2] NOEs to the 5-neighbor in the -strand and [H8/H6-H1] NOEs to the 3-neighbor in the -strand. Intra-residue and inter-residue distances between base protons and deoxyribose protons in both strands were determined using the isolated spin-pair approximation for NOESY cross peaks acquired with mixing times 50 ms or less. The NOE data are consistent with a B-form geometry adopted by the / hybrid decamer.     

Biodiversity and ecology of flower-associated actinomycetes in different flowering stages of <Emphasis Type="Italic">Protea repens</Emphasis>

Actinomycete bacteria have previously been reported from reproductive structures (infructescences) of Protea (sugarbush/suikerbos) species, a niche dominated by fungi in the genera Knoxdaviesia and Sporothrix. It is probable that these taxa have symbiotic interactions, but a lack of knowledge regarding their diversity and general ecology precludes their study. We determined the diversity of actinomycetes within Protea repens inflorescence buds, open inflorescences, young and mature infructescences, and leaf litter surrounding these trees. Since the P. repens habitat is fire-prone, we also considered the potential of these bacteria to recolonise infructescences after fire. Actinomycetes were largely absent from flower buds and inflorescences but were consistently present in young and mature infructescences. Two Streptomyces spp. were the most consistent taxa recovered, one of which was also routinely isolated from leaf litter. Lower colonisation rates were evident in samples from a recently burnt site. One of the most consistent taxa isolated from older trees in the unburnt site was absent from this site. Our findings show that P. repens has a distinct community of actinomycetes dominated by a few species. These communities change over time and infructescence developmental stage, season and the age of the host population. Mature infructescences appear to be important sources of inoculum for some of the actinomycetes, seemingly disrupted by fire. Increased fire frequency limiting maturation of P. repens infructescences could thus impact future actinomycete colonisation in the landscape. Streptomyces spp. are likely to share this niche with the ophiostomatoid fungi, which merits further study regarding their interactions and mode of transfer.     

Distribution of greenhouse gases in hyper-arid and arid areas of northern Chile and the contribution of the high altitude wetland microbiome (Salar de Huasco,Chile)

Northern Chile harbors different bioclimatic zones including hyper-arid and arid ecosystems and hotspots of microbial life, such as high altitude wetlands, which may contribute differentially to greenhouse gases (GHG) such as carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). In this study, we explored ground level GHG distribution and the potential role of a wetland situated at 3800 m.a.s.l, and characterized by high solar radiation <?1600 W m^?2, extreme temperature ranges (?12 to 24 °C) and wind stress (<?17 m s^?1). The water source of the wetland is mainly groundwater springs, which generates streams and ponds surrounded by peatlands. These sites support a rich microbial aquatic life including diverse bacteria and archaea communities, which transiently form more complex structures, such as microbial mats. In this study, GHG were measured in the water and above ground level air at the wetland site and along an elevation gradient in different bioclimatic areas from arid to hyper-arid zones. The microbiome from the water and sediments was described by high-throughput sequencing 16S rRNA and rDNA genes. The results indicate that GHG at ground level were variable along the elevation gradient potentially associated with different bioclimatic zones, reaching high values at the high Andean steppe and variable but lower values in the Atacama Desert and at the wetland. The water areas of the wetland presented high concentrations of CH₄ and CO₂, particularly at the spring areas and in air bubbles below microbial mats. The microbial community was rich (>?40 phyla), including archaea and bacteria potentially active in the different matrices studied (water, sediments and mats). Functional microbial groups associated with GHG recycling were detected at low frequency, i.e., <?2.5% of total sequences. Our results indicate that hyper-arid and arid areas of northern Chile are sites of GHG exchange associated with various bioclimatic zones and particularly in aquatic areas of the wetland where this ecosystem could represent a net sink of N₂O and a source for CH₄ and CO₂.     

Pathogeography: leveraging the biogeography of human infectious diseases for global health management

Biogeography is an implicit and fundamental component of almost every dimension of modern biology, from natural selection and speciation to invasive species and biodiversity management. However, biogeography has rarely been integrated into human or veterinary medicine nor routinely leveraged for global health management. Here we review the theory and application of biogeography to the research and management of human infectious diseases, an integration we refer to as ‘pathogeography’. Pathogeography represents a promising framework for understanding and decomposing the spatial distributions, diversity patterns and emergence risks of human infectious diseases into interpretable components of dynamic socio‐ecological systems. Analytical tools from biogeography are already helping to improve our understanding of individual infectious disease distributions and the processes that shape them in space and time. At higher levels of organization, biogeographical studies of diseases are rarer but increasing, improving our ability to describe and explain patterns that emerge at the level of disease communities (e.g. co‐occurrence, diversity patterns, biogeographic regionalisation). Even in a highly globalized world most human infectious diseases remain constrained in their geographic distributions by ecological barriers to the dispersal or establishment of their causal pathogens, reservoir hosts and/or vectors. These same processes underpin the spatial arrangement of other taxa, such as mammalian biodiversity, providing a strong empirical ‘prior’ with which to assess the potential distributions of infectious diseases when data on their occurrence is unavailable or limited. In the absence of quality data, generalized biogeographic patterns could provide the earliest (and in some cases the only) insights into the potential distributions of many poorly known or emerging, or as‐yet‐unknown, infectious disease risks. Encouraging more community ecologists and biogeographers to collaborate with health professionals (and vice versa) has the potential to improve our understanding of infectious disease systems and identify novel management strategies to improve local, global and planetary health.     

Alien plants have greater impact than habitat fragmentation on native insect flower visitation networks

Aim

Habitat fragmentation and alien species are among the leading causes of biodiversity loss. In an attempt to reduce the impact of forestry on natural systems, networks of natural corridors and patches of natural habitat are often maintained within the afforested matrix, yet these can be subject to degradation by invasion of non‐native species. Both habitat fragmentation and alien invasive species disrupt the complex interaction networks typical of native communities. This study examines whether an invasive plant and/or the fragmented nature of the forestry landscape influences natural flower visitation networks (FVNs), flower–visitor abundance and richness or flower/visitor species composition.

Location

The species rich and diverse grasslands in the KwaZulu‐Natal Midlands, South Africa is under threat from transformation, particularly by commercial forestry plantations, restricting much of the remaining untransformed grasslands into remnant grassland patches (RGPs). Remaining patches are under additional threat from the invasive Rubus cuneifolius Pursh (bramble). Sites were established in RGPs and in a nearby protected area (PA), with and without brambles present for both areas.

Results

Flower abundance and flower area of native plant species were greater within RGP than in PA, but only in the absence of R. cuneifolius. Flower–visitor assemblages differed between invaded and uninvaded sites and also differed between PA and RGP sites. Both areas lost specialist flower–visitor species in the presence of brambles. Network modularity was greatly reduced by the presence of bramble, indicating a reduction in complexity and organization. The structure of FVNs was otherwise unaffected by presence of bramble or being located in RGPs or the PA.

Main conclusions

The RPGs contribute to regional biodiversity conservation through additional compositional diversity and intact FVNs. Rubus cuneifolius reduces ecological complexity of both RGPs and PAs, however, and its removal must be prioritized to conserve FVNs.