Role of carbon allocation efficiency in the temperature dependence of autotroph growth rate

To predict how plant growth rate will respond to temperature requires understanding how temperature drives the underlying metabolic rates. Although past studies have considered the temperature dependences of photosynthesis and respiration rates underlying growth, they have largely overlooked the temperature dependence of carbon allocation efficiency. By combining a mathematical model that links exponential growth rate of a population of photosynthetic cells to photosynthesis, respiration, and carbon allocation; to an experiment on a freshwater alga; and to a database covering a wide range of taxa, we show that allocation efficiency is crucial for predicting how growth rates will respond to temperature change across aquatic and terrestrial autotrophs, at both short and long (evolutionary) timescales

Phase appearance or disappearance in two-phase flows

This paper is devoted to the treatment of specific numerical problems which appear when phase appearance or disappearance occurs in models of two-phase flows. Such models have crucial importance in many industrial areas such as nuclear power plant safety studies. In this paper, two outstanding problems are identified: first, the loss of hyperbolicity of the system when a phase appears or disappears and second, the lack of positivity of standard shock capturing schemes such as the Roe scheme. After an asymptotic study of the model, this paper proposes accurate and robust numerical methods adapted to the simulation of phase appearance or disappearance. Polynomial solvers are developed to avoid the use of eigenvectors which are needed in usual shock capturing schemes, and a method based on an adaptive numerical diffusion is designed to treat the positivity problems. An alternate method, based on the use of the hyperbolic tangent function instead of a polynomial, is also considered. Numerical results are presented which demonstrate the efficiency of the proposed solutions

Review of Available Data for Validation of Nuresim Two-Phase CFD Software Applied to CHF Investigations

The NURESIM Project of the 6th European Framework Program initiated the development of a new-generation common European Standard Software Platform for nuclear reactor simulation. The thermal-hydraulic subproject aims at improving the understanding and the predictive capabilities of the simulation tools for key two-phase flow thermal-hydraulic processes such as the critical heat flux (CHF). As part of a multi-scale analysis of reactor thermal-hydraulics, a two-phase CFD tool is developed to allow zooming on local processes. Current industrial methods for CHF mainly use the sub-channel analysis and empirical CHF correlations based on large scale experiments having the real geometry of a reactor assembly. Two-phase CFD is used here for understanding some boiling flow processes, for helping new fuel assembly design, and for developing better CHF predictions in both PWR and BWR. This paper presents a review of experimental data which can be used for validation of the two-phase CFD application to CHF investigations. The phenomenology of DNB and Dry-Out are detailed identifying all basic flow processes which require a specific modeling in CFD tool. The resulting modeling program of work is given and the current state-of-the-art of the modeling within the NURESIM project is presented

Presence of a resident species aids invader evolution

Interactions between phytoplankton species shape their physiological and evolutionary responses. Yet, studies addressing the evolutionary responses of phytoplankton in changing environments often lack an explicit element of biotic interactions. Here, we ask (1) how the presence of a locally adapted phytoplankton species will affect an invading phytoplankton species' evolutionary response to a physiologically challenging environment; (2) whether this response is conserved across environments varying in quality; and (3) which traits are associated with being a successful invader under climate change scenarios. In a conceptual first step to disentangle these broad questions, we experimentally evolved populations of fresh‐ and seawater phytoplankton in a novel salinity (the freshwater green algae Chlamydomonas in salt water, and the marine Ostreococcus in freshwater), either as mono‐cultures (colonizers) or as co‐cultures (invaders: invading a novel salinity occupied by a resident species, for example, Chlamydomonas invading salt water occupied by resident Ostreococcus) for 200 generations. We superimposed a temperature treatment (control (22°C), mild warming (26°C), drastic warming (32°C), and fluctuating (22°C/32°C) warming) as a representative aspect of climate change with the potential to ameliorate or deteriorate existing environmental conditions. Invaders had systematically lower extinction rates and evolved overall higher growth rates, as well as broader salinity and temperature preferences than colonizers. The invading species' evolutionary responses differed from those of colonizers in a replicable way across environments of differing quality. The evolution of small cell size and high reactive oxygen species tolerance may explain the invaders' higher fitness under the scenarios tested here.British Ecological Society http://dx.doi.org/10.13039/501100000409https://doi.org/10.5281/zenodo.688404

Influence of plant fraction, soil and plant species on the microbiota: a multi-kingdom comparison

Plant roots influence the soil microbiota via physical interaction, secretion and plant immunity. However, it is unclear whether the root fraction or soil is more important in determining the structure of the prokaryotic or eukaryotic community and whether this varies between plant species. Furthermore, the leaf (phyllosphere) and root microbiota have a large overlap, however it is unclear whether this results from colonization of the phyllosphere by the root microbiota. Soil, rhizosphere, rhizoplane and root endosphere prokaryotic, eukaryotic and fungal-specific microbiota of four plant species were analyzed with high-throughput sequencing. The strength of factors controlling microbiota structure was determined using PERMANOVA statistics. The origin of the phyllosphere microbiota was investigated with a soil swap experiment. Global microbial kingdom analysis conducted simultaneously on multiple plants, show that cereals, legumes and Brassicaceae establish similar prokaryotic and similar eukaryotic communities inside and on the root surface. While the bacterial microbiota are recruited from the surrounding soil, its profile is influenced by the root itself more so than by soil or plant species. However, by contrast, the fungal microbiota are most strongly influenced by soil. This was observed in two different soils and for all plant species examined. Microbiota structure is established within two weeks of plant growth in soil and remains stable thereafter. A reciprocal soil swap experiment shows that the phyllosphere is colonized from the soil in which the plant is grown

Metabolic traits predict the effects of warming on phytoplankton competition

Understanding how changes in temperature affect interspecific competition is critical for predicting changes in ecological communities with global warming. Here, we develop a theoretical model that links interspecific differences in the temperature dependence of resource acquisition and growth to the outcome of pairwise competition in phytoplankton. We parameterised our model with these metabolic traits derived from six species of freshwater phytoplankton and tested its ability to predict the outcome of competition in all pairwise combinations of the species in a factorial experiment, manipulating temperature and nutrient availability. The model correctly predicted the outcome of competition in 72% of the pairwise experiments, with competitive advantage determined by difference in thermal sensitivity of growth rates of the two species. These results demonstrate that metabolic traits play a key role in determining how changes in temperature influence interspecific competition and lay the foundation for mechanistically predicting the effects of warming in complex, multi‐species communities

Abrupt declines in marine phytoplankton production driven by warming and biodiversity loss in a microcosm experiment

This is the author accepted manuscript. The final version is availab;e from Wiley via the DOI in this recordRising sea surface temperatures are expected to lead to the loss of phytoplankton biodiversity. However, we currently understand very little about the interactions between warming, loss of phytoplankton diversity and its impact on the oceans' primary production. We experimentally manipulated the species richness of marine phytoplankton communities under a range of warming scenarios, and found that ecosystem production declined more abruptly with species loss in communities exposed to higher temperatures. Species contributing positively to ecosystem production in the warmed treatments were those that had the highest optimal temperatures for photosynthesis, implying that the synergistic impacts of warming and biodiversity loss on ecosystem functioning were mediated by thermal trait variability. As species were lost from the communities, the probability of taxa remaining that could tolerate warming diminished, resulting in abrupt declines in ecosystem production. Our results highlight the potential for synergistic effects of warming and biodiversity loss on marine primary production.Leverhulme TrustNatural Environment Research Council (NERC)European Commissio