Understanding the partitioning and concentration of trace elements in the plant organs of some food crops: influence of the plant allometry and of the growth stage

246 p.This PhD Thesis has been carried out as a co-tutelle between the UPV/EHU and the University of Bordeaux, in the framework of the Cross-Border Euroregional Campus of International Excellence IdEx Bordeaux ¿ Euskampus. The work is focused on the accumulation of essential and non-essential elements, paying special attention to the edible part of the plants, in terms of food safety and human health. This Thesis work has been divided in two main parts: The first one is related to a field experiment performed in open-air plots, where Swiss chards and tomato plants were grown from seedlings to maturity in natural soil during five months, using organic or conventional agricultural practices. Plants were harvested at six different growth stages and the total concentrations of 27 elements were measured in all plant organs. The objective was to study the partitioning of the elements between the plant organs, depending on the plant age and on the cultivation practice. The second part of the Thesis is devoted to the understanding and modelling of the partitioning of Cd in sunflowers at the reproductive stages. Sunflowers were grown in a nutrient solution at low Cd availability consistent with that found in the field, from germination to maturity. During the reproductive period, five samplings were carried out to investigate the partitioning of the total Cd between plant organs and the origin of the Cd allocated to seeds (root uptake vs. remobilization from other plant organs). A the flower bud and grain filling stages, the partitioning of the Cd recently taken up between the different plant organs was followed and modelled by exposing several plants for three days to a 111Cd enriched nutrient solution. The roles of the transpiration and of the plant allometry were specially investigated

Response of Horticultural Soil Microbiota to Different Fertilization Practices

Environmentally friendly agricultural production necessitates manipulation of microbe–plant interactions, requiring a better understanding of how farming practices influence soil microbiota. We studied the effect of conventional and organic treatment on soil bacterial richness, composition, and predicted functional potential. 16S rRNA sequencing was applied to soils from adjacent plots receiving either a synthetic or organic fertilizer, where two crops were grown within treatment, homogenizing for differences in soil properties, crop, and climate. Conventional fertilizer was associated with a decrease in soil pH, an accumulation of Ag, Mn, As, Fe, Co, Cd, and Ni; and an enrichment of ammonia oxidizers and xenobiotic compound degraders (e.g., Candidatus Nitrososphaera, Nitrospira, Bacillus, Pseudomonas). Soils receiving organic fertilization were enriched in Ti (crop biostimulant), N, and C cycling bacteria (denitrifiers, e.g., Azoarcus, Anaerolinea; methylotrophs, e.g., Methylocaldum, Methanosarcina), and disease-suppression (e.g., Myxococcales). Some predicted functions, such as glutathione metabolism, were slightly, but significantly enriched after a one-time manure application, suggesting the enhancement of sulfur regulation, nitrogen-fixing, and defense of environmental stressors. The study highlights that even a single application of organic fertilization is enough to originate a rapid shift in soil prokaryotes, responding to the differential substrate availability by promoting soil health, similar to recurrent applications.This work was supported by the Earth Microbiome Project; the METAMAHA project funded by the Basque Government’s Department of Industry, Trade, and Tourism (SAIOTEK program; S-PE13UN130); and IT1014-16 and IT1213-19 Consolidated Research Group Projects

Understanding the partitioning and concentration of trace elements in the plant organs of some food crops : influence of the plant allometry and of the growth stage

Le travail est axé sur l'accumulation d'éléments chimiques essentiels et non essentiels avec une attention particulière pour les parties des consommées, en lien avec la qualité sanitaire des produits alimentaires. Le travail de thèse est divisé en deux grandes parties. La première porte sur une expérimentation en plein champ où des plantes de blettes et de tomates ont été cultivées du stade plantules jusqu'à la maturité pendant 5 mois avec des pratiques agricoles conventionnelles ou biologiques. Les plantes ont été récoltées à 6 stades différents de croissance et nous avons déterminé la concentration des organes végétaux pour 27 éléments chimiques. L'objectif était d'étudier la répartition des éléments entre les organes en fonction de l'âge de la plante et des pratiques culturales.La seconde partie de la thèse a été consacrée à la compréhension et à la modélisation de la répartition du cadmium (Cd) chez le tournesol aux stades reproducteurs. Des plantes ont été cultivées du stade plantule jusqu'à la maturité, en solution nutritive avec une faible concentration en Cd cohérente avec les expositions aux champs. Durant la phase reproductive, cinq échantillonnages ont été effectués pour comprendre la répartition du Cd entre les organes ainsi que l'origine du Cd des graines (prélèvement racinaire versus remobilisation à partir d'autres organes). Au stade du bouton floral et pendant le remplissage des graines, le devenir du Cd récemment absorbé par les racines a été suivi et modélisé par traçage isotopique avec du 111Cd. Les rôles de la transpiration et de l'allométrie entre organes ont été plus particulièrement examinés.This work is focuded on the accumulation of essential and non-essential elements, paying a special attention to the dible part of the plants, in terms of food safety and human health. The thesis work has been divided in two main parts. The first one is related to a field expeiment performed in open-air plots, where Swiss chards and tomato plants were grown from seedlings to maturity in a natural soil during five months, using organic or conventional agricultural practices. Plants were harvested at six different growth satges and the total concentrations of 27 elements were measured in all plants organs. The objective was to study the partitioning of elements between the plant organs, depending on the plant age on the cultivation practice. The second part of the thesis is devoted to the understanding and modelling of the partitioning of cadmium (Cd) in sunflowers at the reproductive stages. Sunflowers wre grown in nutrient solution at low Cd availability consistent with thaht found in the field, from germination toi maturity. During the reproductive period, five samplings were carried out to investigate the partitioning of the total Cd between plant organs and the origin of the Cd allocated to seeds (root uptake vs; remobilization from other plant organs). At the flower bud and grain filling stages, the partitioning of the Cd recently taken up between the different plant organs was followed and modelled by exposing several plants for the three days to a 111Cd enriched nutrient solution. The roles of the transpiration and of the plant allometry were specially investigated