Are variations of direct and indirect plant interactions along a climatic gradient dependent on species’ strategies? An experiment on tree seedlings

Investigating how interactions among plants depend on environmental conditions is key to understand and predict plant communities’ response to climate change. However, while many studies have shown how direct interactions change along climatic gradients, indirect interactions have received far less attention. In this study, we aim at contributing to a more complete understanding of how biotic interactions are modulated by climatic conditions. We investigated both direct and indirect effects of adult tree canopy and ground vegetation on seedling growth and survival in five tree species in the French Alps. To explore the effect of environmental conditions, the experiment was carried out at 10 sites along a climatic gradient closely related to temperature. While seedling growth was little affected by direct and indirect interactions, seedling survival showed significant patterns across multiple species. Ground vegetation had a strong direct competitive effect on seedling survival under warmer conditions. This effect decreased or shifted to facilitation at lower temperatures. While the confidence intervals were wider for the effect of adult canopy, it displayed the same pattern. The monitoring of micro‐environmental conditions revealed that competition by ground vegetation in warmer sites could be related to reduced water availability; and weak facilitation by adult canopy in colder sites to protection against frost. For a cold‐intolerant and shade‐tolerant species (Fagus sylvatica), adult canopy indirectly facilitated seedling survival by suppressing ground vegetation at high temperature sites. The other more cold tolerant species did not show this indirect effect (Pinus uncinata, Larix decidua and Abies alba). Our results support the widely observed pattern of stronger direct competition in more productive climates. However, for shade tolerant species, the effect of direct competition may be buffered by tree canopies reducing the competition of ground vegetation, resulting in an opposite trend for indirect interactions across the climatic gradient.     

Demographic controls of aboveground forest biomass across North America

Ecologists have limited understanding of how geographic variation in forest biomass arises from differences in growth and mortality at continental to global scales. Using forest inventories from across North America, we partitioned continental‐scale variation in biomass growth and mortality rates of 49 tree species groups into (1) species‐independent spatial effects and (2) inherent differences in demographic performance among species. Spatial factors that were separable from species composition explained 83% and 51% of the respective variation in growth and mortality. Moderate additional variation in mortality (26%) was attributable to differences in species composition. Age‐dependent biomass models showed that variation in forest biomass can be explained primarily by spatial gradients in growth that were unrelated to species composition. Species‐dependent patterns of mortality explained additional variation in biomass, with forests supporting less biomass when dominated by species that are highly susceptible to competition (e.g. Populus spp.) or to biotic disturbances (e.g. Abies balsamea).     

Mapping and analysis of a spatiotemporal H3K27ac and gene expression spectrum in pigs

Science China Life Sciences - The limited knowledge of genomic noncoding and regulatory regions has restricted our ability to decipher the genetic mechanisms underlying complex traits in pigs. In...     

The cold-inducible RNA-binding protein migrates from the nucleus to cytoplasmic stress granules by a methylation-dependent mechanism and acts as a translational repressor

The cold-inducible RNA-binding protein (CIRP) is a nuclear 18-kDa protein consisting of an amino-terminal RNA Recognition Motif (RRM) and a carboxyl-terminal domain containing several RGG motifs. First characterized for its overexpression upon cold shock, CIRP is also induced by stresses such as UV irradiation and hypoxia. Here, we investigated the expression as well as the subcellular localization of CIRP in response to other stress conditions. We demonstrate that oxidative stress leads to the migration of CIRP to stress granules (SGs) without alteration of expression. Stress granules are dynamic cytoplasmic foci at which stalled translation initiation complexes accumulate in cells subjected to environmental stress. Relocalization of CIRP into SGs also occurs upon other cytoplasmic stresses (osmotic pressure or heat shock) as well as in response to stresses of the endoplasmic reticulum. CIRP migration into SGs is independent from TIA-1 which has been previously reported to be a general mediator of SG formation, thereby suggesting the existence of multiple pathways leading to SG formation. Moreover, deletion mutants revealed that both RGG and RRM domains can independently promote CIRP migration into SGs. However, the methylation of arginine residues in the RGG domain is necessary for CIRP to exit the nucleus to be further recruited into SGs. By RNA-tethering experiments, we also show that CIRP down-regulates mRNA translation and that this activity is carried by the carboxyl-terminal RG-enriched domain. Altogether, our findings further reveal the diversity of mechanisms by which CIRP is regulated by environmental stresses and provide new insights into CIRP cytoplasmic function.     

Differential expression of sarcoplasmic proteins in four heterogeneous ovine skeletal muscles

Fiber-type distribution is known to vary widely within and between muscles according to differences in muscle functions. 2-DE and MALDI-MS were used to investigate the molecular basis of muscle fiber type-related variability. We compared four lamb skeletal muscles with heterogeneous fiber-type composition that are relatively rich in fast-twitch fiber types, i.e., the semimembranosus, vastus medialis, longissimus dorsi, and tensor fasciae latae (TL). Our results clearly showed that none of the glycolytic metabolism enzymes detected, including TL which was most strongly glycolytic, made intermuscular differentiation possible. Muscle differentiation was based on the differential expression of proteins involved in oxidative metabolism, including not only citric acid cycle enzymes but also other classes of proteins with functions related to oxidative metabolism, oxidative stress, and probably to higher protein turnover. Detected proteins were involved in transport (carbonate dehydratase, myoglobin, fatty acid-binding protein), repair of misfolding damage (heat shock protein (HSP) 60 kDa, HSP-27 kDa, alpha-crystallin beta subunit, DJ1, stress-induced phosphoprotein), detoxification or degradation of impaired proteins (GST-Pi, aldehyde dehydrogenase, peroxiredoxin, ubiquitin), and protein synthesis (tRNA-synthetase). The fractionating method led to the detection of proteins involved in different functions related to oxidative metabolism that have not previously been shown concomitancy.     

The ends of a continuum: genetic and temperature-dependent sex determination in reptiles

Two prevailing paradigms explain the diversity of sex-determining modes in reptiles. Many researchers, particularly those who study reptiles, consider genetic and environmental sex-determining mechanisms to be fundamentally different, and that one can be demonstrated experimentally to the exclusion of the other. Other researchers, principally those who take a broader taxonomic perspective, argue that no clear boundaries exist between them. Indeed, we argue that genetic and environmental sex determination in reptiles should be seen as a continuum of states represented by species whose sex is determined primarily by genotype, species where genetic and environmental mechanisms coexist and interact in lesser or greater measure to bring about sex phenotypes, and species where sex is determined primarily by environment. To do otherwise limits the scope of investigations into the transition between the two and reduces opportunities to use studies of reptiles to advance understanding of vertebrate sex determination generally.     

Synthesis of novel d-glucuronic acid fatty esters using Candida antarctica lipase in tert-butanol

Glucuronic acid n-alkyl esters, a novel class of promising biosurfactants and their corresponding glucose esters with the same side-chain length, were synthesized by direct esterification in a non-aqueous phase (tert-butanol) using an immobilized lipase.     

Change in plasma cortisol and metabolites during the attendance period ashore in fasting lactating subantarctic fur seals

Lactating fur seals (Arctocephalus tropicalis) alternate foraging trips at sea and pup attendance periods ashore. During the onshore nursing periods, lactating females do not have access to food and meet both their own metabolic requirements and milk production from their body reserve. Blood and milk samples were collected from females captured soon after their arrival ashore from a foraging trip and before their departure. Milk lipid but not milk protein content was positively related to the body condition index (BCI) of the female. During the 4-day attendance period ashore, females lost body mass, and plasma cortisol levels increased, whereas plasma urea concentration decreased and beta-hydroxybutyrate (beta-OHB) remained unchanged. The increase in cortisol level took place while blood urea concentration decreased and beta-OHB remained at a low level suggesting that it was independent from the transition from phase II to phase III that is indicative of the depletion of lipid body store as described in penguins. Thus, our results suggest that the increase in cortisol level in relation to decreasing BCI may either contribute to the mobilization of protein stores to ensure milk production when easily mobilized stores are used and/or could act as a re-feeding signal which is triggered well before females have depleted their body store.     

Plant parasite control and soil fauna diversity

The use of pesticides to control plant parasites and diseases has generated serious problems of public health and environmental quality, leading to the promotion of alternative Integrated Pest Management strategies that tend to rely more on natural processes and the active participation of farmers as observers and experimenters in their own fields. We present three case studies that point at different options provided by locally available populations of soil organisms, the maintenance of diverse populations of pests or increased resistance of plants to pest attacks by their interactions with earthworms and other useful soil organisms. These examples demonstrate the diversity of options offered by the non-planned agro-ecosystem diversity in pest control and the need to identify management options that maintain this biodiversity.