Developmental plasticity of Brachypodium distachyon (L.) P. Beauv. in response to P-solubilizing bacteria inoculation

Introduction. Mineral phosphorus (P) fertilizers should be sparingly used to slow down the depletion of rock phosphate, a finite and non-renewable resource. Plants cope with stresses in their environment and heterogeneous soil conditions by adjusting their phenotype, what defines the phenotypic plasticity. The use of fertilizers in agriculture could be reduced by integrating plastic root system traits into crop breeding strategies. Bacterial bioinoculants are also considered as an interesting strategy to increase the nutrient use efficiency of plants and reach desired phenotypes. This project studied the impact of inoculation of the model plant Brachypodium distachyon with P solubilizing bacteria on the plant phosphorus use efficiency, focusing on enhancement of phosphorus bioavailability and modulation of the root system plasticity. Materials and methods. The first step of this project consisted in the characterization of the response of B. distachyon to inorganic P deficiency, in order to define levels of inorganic P resulting in contrasted plant phenotypes. Then the ability of selected bacterial strains to solubilize poorly available P forms (tricalcium phosphate and hydroxyapatite) was quantified. Finally, based on the results of the previous steps, the response of B. distachyon to contrasted P supplies and inoculation with P-solubilizing bacteria was studied by focusing on the plant developmental plasticity and P use efficiency. Allometry analyses were performed to study plasticity in the biomass allocation pattern and persistent homology analyses were conducted to detect differences in root system morphology. Results. A plastic response in B. distachyon biomass allocation pattern was observed, by prioritizing root over shoot development under poorly soluble P conditions. All the bacterial strains were able to solubilize tricalcium phosphate and hydroxyapatite in the solubilization test. However, inoculation of the plants with bacteria reduced the shoot productivity. On the other hand, the root system development was maintained. Both P condition and inoculation with bacteria impacted the root system morphology. P use efficiency in B. distachyon was not improved by the modulation of its developmental plasticity induced by the bacteria. Conclusion. The results support the hypothesis that P-solubilizing bacteria can modulate the plastic response of B. distachyon in response to limited P condition. The methods used to study the plant plasticity were useful and should be considered as potential tools to investigate the effects of bioinoculants on plant nutrient use efficiency. The experimental system can greatly impact plant-bacteria interaction. Experimental conditions as close as possible to agronomic ones are recommended to work with bacterial bioinoculants

Plasticité developpementale de Brachypodium distachyon en réponse à la déficience en phosphore: modulation par inoculation de bactéries solubilisatrices du phosphate

peer reviewedMineral phosphorus (P) fertilisers must be used wisely in order to preserve rock phosphate, a limited and non-renewable resource. The use of bio-inoculants to improve soil nutrient availability and trigger an efficient plant response to nutrient deficiency is one potential strategy in the attempt to decrease P inputs in agriculture. An in vitro co-cultivation system was used to study the response of Brachypodium distachyon to contrasted P supplies (soluble and poorly soluble forms of P) and inoculation with P solubilizing bacteria. Brachypodium's responses to P conditions and inoculation with bacteria were studied in terms of developmental plasticity and P use efficiency. Brachypodium showed plasticity in its biomass allocation pattern in response to variable P conditions, specifically by prioritizing root development over shoot productivity under poorly soluble P conditions. Despite the ability of the bacteria to solubilize P, shoot productivity was depressed in plants inoculated with bacteria, although the root system development was maintained. The negative impact of bacteria on biomass production in Brachypodium might be attributed to inadequate C supply to bacteria, an increased competition for P between both organisms under P-limiting conditions, or an accumulation of toxic bacterial metabolites in our cultivation system. Both P and inoculation treatments impacted root system morphology. The modulation of Brachypodium’s developmental response to P supplies by P solubilizing bacteria did not lead to improved P use efficiency. Our results support the hypothesis that plastic responses of Brachypodium cultivated under P-limited conditions are modulated by P solubilizing bacteria. The considered experimental context impacts plant–bacteria interactions. Choosing experimental conditions as close as possible to real ones is important in the selection of P solubilizing bacteria. Both persistent homology and allometric analyses proved to be useful tools that should be considered when studying the impact of bio-inoculants on plant development in response to varying nutritional context

Taking Language out of the Equation: The Assessment of Basic Math Competence Without Language

While numerical skills are fundamental in modern societies, some estimated 5–7% of children suffer from mathematical learning difficulties (MLD) that need to be assessed early to ensure successful remediation. Universally employable diagnostic tools are yet lacking, as current test batteries for basic mathematics assessment are based on verbal instructions. However, prior research has shown that performance in mathematics assessment is often dependent on the testee's proficiency in the language of instruction which might lead to unfair bias in test scores. Furthermore, language-dependent assessment tools produce results that are not easily comparable across countries. Here we present results of a study that aims to develop tasks allowing to test for basic math competence without relying on verbal instructions or task content. We implemented video and animation-based task instructions on touchscreen devices that require no verbal explanation. We administered these experimental tasks to two samples of children attending the first grade of primary school. One group completed the tasks with verbal instructions while another group received video instructions showing a person successfully completing the task. We assessed task comprehension and usability aspects both directly and indirectly. Our results suggest that the non-verbal instructions were generally well understood as the absence of explicit verbal instructions did not influence task performance. Thus we found that it is possible to assess basic math competence without verbal instructions. It also appeared that in some cases a single word in a verbal instruction can lead to the failure of a task that is successfully completed with non-verbal instruction. However, special care must be taken during task design because on rare occasions non-verbal video instructions fail to convey task instructions as clearly as spoken language and thus the latter do not provide a panacea to non-verbal assessment. Nevertheless, our findings provide an encouraging proof of concept for the further development of non-verbal assessment tools for basic math competence

Triggering root system plasticity in a changing environment with bacterial bioinoculants – Focus on plant P nutrition

peer reviewedTo improve the sustainability of agricultural systems, an efficient use of resources such as phosphorus (P) nutrients is necessary. To reach this goal, the development of more resilient crop varieties able to cope with heterogeneous soil conditions in space and time is a promising strategy. Plants face many stresses in their natural environment and can respond to them by adjusting their phenotype (phenotypic plasticity). Integrating plastic root system traits into breeding strategies may help reach acceptable yields in low-input systems by enhancing water and nutrient uptake, thus reducing resource inputs in conventional farming systems. Bacterial bioinoculants, also considered to be a class of biostimulants, have shown great potential to increase the nutrient use efficiency of plants through diverse strategies including the modulation of root system plasticity. However, the study of plant plasticity can be challenging, particularly regarding the root system. This paper aims to encourage the integration of bioinoculants into the study of root system plasticity in response to P deficiency. We first focus on the plasticity of root architectural traits in a P-limiting context and on how bioinoculants can modulate root system plasticity and enhance P use efficiency. Then, important methodological points of attention to consider for the study of root system plasticity are highlighted

Development of an ex-vitro system allowing plant-bacteria interactions through VOCs in the context of water stress

Water stress is one of the major environmental factors limiting the crop productivity . Plant stress responses are very complex and drought tolerance may be linked to the presence of specific microorganisms in the rhizosphere. Indeed, some plant growth promoting bacteria (PGPR) strains have been found to improve plant growth under abiotic stresses. Among the many mechanisms by which those PGPR can support plant growth, the emission of volatile organic compounds (VOCs) and their biological impact are still under study. The aim of this work is to evaluate the interaction between the model grass Brachypodium distachyon (Bd21) and two strains of PGPR. The impact of volatile emission on Bd21 growth was studied using an ex-vitro cocultivation system without physical contact between plant and bacteria during 10 days. This peculiar system was developed to assess bacterial VOCs impacts on plants under realistic growth and stress conditions. In parallel, the response of Bd21 seedlings to water deficit induced by polyethylene glycol 6000 (PEG 6000) was studied to establish contrasted growth conditions regarding water availabilit