Phosphorus (P) in durum wheat grains after anthesis originates from either the external P source or the internal remobilization of P from different plant organs. The supply of P and its use by the plant are important factors that can affect the contribution of each source to grain P nutrition. Thus, this experiment aimed to quantify the origin of P in grains of durum wheat plants with different P nutritional status. Wheat plants were grown from juvenile stages to maturity in complete nutrient solutions with either high (0.125 mM) or low (0.025 mM) P concentrations in greenhouse conditions. Phosphorus in nutrient solutions was spiked by introducing ³²P after anthesis to quantify the external P uptake and its partitioning within plant organs (spikelets, leaves, stems, roots, and post-anthesis tillers) and grains. Phosphorus use efficiency in durum wheat plants was also determined. The low and high P supply resulted in two highly different plant nutritional P status. Plants with low P status remobilized most of their stored P in all organs and allocated more than 72% of post-anthesis P uptake to grain P nutrition, whereas in the high P plants this was only 56%. Enhanced remobilization of P and the efficient allocation of newly acquired P to grains were crucial for durum wheat grain P nutrition grown under low P supply. The remobilization of P represented 81% of grain P in low P plants while it represented 65% for high P plants. Organs that contributed the most to P remobilization in low P plants were spikelets (43%) and leaves (35%). The post-anthesis tiller development was reduced in low P plants suggesting a preferential allocation of P to grains under this treatment. We concluded that P loading into grains in durum wheat is mainly derived from the remobilization of internal P sources stored before anthesis, even at high external P supply during grain filling.

Agricultural residues are generated during the production and processing of agricultural crops. Under modern date palm plantation practices, field operations generate huge quantities of residues, which are discarded with little valorization. The date palm agro-industry produces significant amounts of waste. The accumulation of these residues can cause ecological damage to the oasis ecosystems. There is a lack of comprehensive data on long-term research studies that aim to assess the impact of date palm waste management practices. Composting and/or pyrolysis of date palm residues showed benefits for improving soil physical and chemical properties, particularly in sandy soils. This claim holds particular significance for arid and semi-arid regions, which are characterized by low fertility and are susceptible to soil degradation, accentuated by ongoing climate change. This review summarizes the existing literature concerning the valorization of date palm residues with regards to compost and pyrolysis processes, as well as the impact of their application on soil quality. Further research is required to assess the effects of using date palm residues for better soil amendment management. Research should focus on composting and biochar technologies for date palm residues and their application in arid and semi-arid regions to combat soil erosion and degradation. Increasing the beneficial uses of date palm residues could lead to sustainable and economic growth in dry areas.

Post-anthesis phosphorus (P) uptake and the remobilization of the previously acquired P are the principal sources of grain P nutrition in wheat. However, how the acquired P reaches the grains and its partitioning at the whole plant level remain poorly understood. Here, the temporal dynamics of the newly acquired P in durum wheat organs and its allocation to grain were examined using pulse-chase ${}^{32}$P-labeling experiments at 5 and 14 days after anthesis. Durum wheat plants were grown hydroponically under high and low P supplies. Each labeling experiment lasted for 24 h. Plants were harvested 24, 48, and 96 h after labeling. Low and high P treatments significantly affected the allocation of the newly acquired P at the whole plant level. Three days (96 h) after the first ${}^{32}$P-labeling, 8% and 4% of the newly acquired P from exogenous solution were allocated to grains, 73% and 55% to the remainder aboveground organs, and 19% and 41% to the roots at low and high P supplies, respectively. Three days after the second labeling, the corresponding values were 48% and 20% in grains, 44% and 53% in the remainder aboveground organs, and 8% and 27% in roots at low and high P supplies, respectively. These results reveal that the dynamics of P allocation to grain was faster in plants grown under low P supply than under high supply. However, the obtained results also indicate that the origin of P accumulated in durum wheat grains was mainly from P remobilization with little contribution from post-anthesis P uptake. The present study emphasizes the role of vegetative organs as temporary storage of P taken up during the grain filling period before its final allocation to grains.

Une des pistes pour gérer durablement le phosphore (P) dans les agrosystèmes consiste à diminuer les exportations répétées du P avec les récoltes. La teneur en P des produits récoltés, en particulier les grains, est alors un paramètre clé dans la gestion du cycle du P dans les agrosystèmes. Au cours de la période postfloraison, l’accumulation du P dans les grains dépend de l’absorption post-floraison et de la remobilisation du P des organes végétatifs. Cependant les processus écophysiologiques qui régissent le remplissage des grains en P et la contribution des deux sources sont encore mal connus. Les objectifs de cette thèse étaient de mieux comprendre les processus impliqués dans le remplissage des grains en P et de déterminer la contribution de la remobilisation et de l’absorption post-floraison au P des grains chez le blé dur (Triticum turgidum. L). Trois expérimentations ont été réalisées en conditions contrôlées avec un système de culture hydroponique permettant de contrôler l’offre en P. D’abord, les effets de la privation en P pendant la période post-floraison sur la remobilisation et les teneurs en P des grains ont été analysés chez deux cultivars de blé dur. Ensuite, l’utilisation du traçage isotopique du P exogène a permis d’étudier la dynamique fine du P durant la période post-floraison et son transport aux grains. Les résultats obtenus montrent que la croissance des grains n’est pas limitée par l’offre en P pendant la période post-floraison si les plantes sont suffisamment alimentées en P pendant la phase végétative. En effet, la privation en P appliquées à partir de la floraison n’a pas eu d’effet négatif sur le rendement et sur la qualité des grains, malgré la diminution significative dans la teneur en P des grains. Nous avons également montré que les flux de remobilisation augmentent en conditions de limitation en P. Le marquage au 32P de la floraison à la maturité a permis de montrer que la remobilisation du P représente 81 % du P des grains pour les plantes cultivées avec un faible niveau en P tandis qu’elle représente 65 % pour les plantes cultivées avec un niveau élevé en P. Les deux marquages successifs au 32P au cours du développement des grains révèlent que le P absorbé par les racines pendant la période post-floraison n’est pas directement alloué aux grains via le xylème. Enfin, ce travail ouvre de nouvelles perspectives pour améliorer l’efficience d’utilisation du P en limitant les exportations répétées de P et ses conséquences environnementales et sur la qualité nutritionnelle des grains.