Improving crop quality: investigations on soil selenium and zinc transfer and bioavailability

Doctor of PhilosophyDepartment of AgronomyGanga M. HettiarachchiManagement of beneficial and/or essential trace elements, such as Se and Zn, is challenging, and it is complicated by the fact that the margin of safety between the levels that will cause dietary deficiency, and those that result in toxicity, is narrow. This research focused on the ability of the plant system to pretreat wastewaters rich in potentially toxic trace elements and nutrients and enhancing phytoavailability of Zn in Zn-deficient calcareous soils. Plant systems may possess a significant capacity to remediate marginal waters through several phytoremediation processes, including uptake, accumulation, and assisting with biotransformation of inorganic and organic compounds. The aim of the first study was to determine the ability of the halophyte, salicornia europaea, to grow in wastewater or brackish waters and to remove excess trace elements, nutrients, and salts in these highly saline wastewaters. Greenhouse and growth chamber studies were conducted to examine the ability of salicornia europaea to grow and remediate marginal waters. Salicornia europaea showed the ability to remove excess trace elements (Se and B) and salts (Na), indicating salicornia europaea has the potential to be used for precleaning the highly saline wastewaters. Enhanced biomass showed that it can also produce valuable stock for biofuel and bio-based products from marginal waters. Agronomic biofortification is an effective way to increase micronutrient concentrations in grain crops. Formation of dissolved micronutrient-organic C complexations can enhance the solubility of micronutrients. The aims of the second study were to investigate the effectiveness of various Zn sources (organic and inorganic) with and without organic C-based fertilizer co-additives on biofortification of wheat with Zn in a mildly-calcareous soil and to determine distribution (stems/leaves, whole grain, bran and flour) and bioavailability of Zn in different plant parts (bran and flour). A greenhouse experiment was conducted to study wheat grown under different Zn sources. Application of Zn significantly increased grain yield, grain Zn concentration, and Zn bioavailability in white flour. Less soluble ZnO showed more promising results compared to soluble ZnSO4. Co-additives did not improve the soil Zn extractability or the Zn uptake by wheat. Understanding the interactions and speciation of Zn is very important to gain more insights into the fate of added Zn in calcareous soil and also for the efficient management of soil for optimum crop production and environmental conservation. The objectives of the third study were to investigate and understand differences in mobility, extractability, and fractionation of Zn from different sources of granular and liquid Zn, with and without co-additives, in two mildly calcareous soils. A 5-wk long incubation study allowed for spatial evaluation of Zn fate and transport in two soils. Diffusion of Zn was limited to a 0 to 7.5 mm section for all treatments with or without co-additives. The energy dispersive X-ray analysis results were in agreement and revealed that the remaining Zn-incorporated monoammonium phosphate granules, after incubation in soil, contained significant amounts of P and Zn. This study also showed that the liquid Zn sources with no P were better than the co-granulated Zn-P fertilizers

Overview of the use of biochar from main cereals to stimulate plant growth

The total global food demand is expected to increase up to 50% between 2010 and 2050; hence, there is a clear need to increase plant productivity with little or no damage to the environment. In this respect, biochar is a carbon-rich material derived from the pyrolysis of organic matter at high temperatures with a limited oxygen supply, with different physicochemical characteristics that depend on the feedstock and pyrolysis conditions. When used as a soil amendment, it has shown many positive environmental effects such as carbon sequestration, reduction of greenhouse gas emissions, and soil improvement. Biochar application has also shown huge benefits when applied to agri-systems, among them, the improvement of plant growth either in optimal conditions or under abiotic or biotic stress. Several mechanisms, such as enhancing the soil microbial diversity and thus increasing soil nutrient-cycling functions, improving soil physicochemical properties, stimulating the microbial colonization, or increasing soil P, K, or N content, have been described to exert these positive effects on plant growth, either alone or in combination with other resources. In addition, it can also improve the plant antioxidant defenses, an evident advantage for plant growth under stress conditions. Although agricultural residues are generated from a wide variety of crops, cereals account for more than half of the world¿s harvested area. Yet, in this review, we will focus on biochar obtained from residues of the most common and relevant cereal crops in terms of global production (rice, wheat, maize, and barley) and in their use as recycled residues to stimulate plant growth. The harvesting and processing of these crops generate a vast number and variety of residues that could be locally recycled into valuable products such as biochar, reducing the waste management problem and accomplishing the circular economy premise. However, very scarce literature focused on the use of biochar from a crop to improve its own growth is available. Herein, we present an overview of the literature focused on this topic, compiling most of the studies and discussing the urgent need to deepen into the molecular mechanisms and pathways involved in the beneficial effects of biochar on plant productivity.This work was supported by the Spanish Government (PID2019-105924RB-I00 MCIN/AEI/10.13039/501100011033 and RED2018-102407-T) and the Castilla-La Mancha Government (SBPLY/17/180501/000287 and SBPLY/21/ 180501/000033) to CE. The laboratory received support from UCLM intramural funds, and ÁM-G was recipient of a PhD grant from Fundación Tatiana Pérez de Guzmán el Bueno. EU FEDER funds complemented all the grants

Ascophyllum nodosum-Based Biostimulants: Sustainable Applications in Agriculture for the Stimulation of Plant Growth, Stress Tolerance, and Disease Management

Abiotic and biotic stresses limit the growth and productivity of plants. In the current global scenario, in order to meet the requirements of the ever-increasing world population, chemical pesticides and synthetic fertilizers are used to boost agricultural production. These harmful chemicals pose a serious threat to the health of humans, animals, plants, and the entire biosphere. To minimize the agricultural chemical footprint, extracts of Ascophyllum nodosum (ANE) have been explored for their ability to improve plant growth and agricultural productivity. The scientific literature reviewed in this article attempts to explain how certain bioactive compounds present in extracts aid to improve plant tolerances to abiotic and/or biotic stresses, plant growth promotion, and their effects on root/microbe interactions. These reports have highlighted the use of various seaweed extracts in improving nutrient use efficiency in treated plants. These studies include investigations of physiological, biochemical, and molecular mechanisms as evidenced using model plants. However, the various modes of action of A. nodosum extracts have not been previously reviewed. The information presented in this review depicts the multiple, beneficial effects of A. nodosum-based biostimulant extracts on plant growth and their defense responses and suggests new opportunities for further applications for marked benefits in production and quality in the agriculture and horticultural sectors

Breeding for microbiome-mediated disease resistance

Plant-associated microbial communities play a crucial role for the expression of various plant traits including disease resistance. Increasing evidence suggests that host genotype influences the composition and function of certain microbial key groups, which, in turn, effects how the plant reacts to environmental stresses. Several studies indicate that modern plant breeding may have selected against plant traits essential for hosting and supporting beneficial microbes. However, they also highlight the presence of an exploitable genetic base for the regulation of the rhizosphere microbiota. We illustrate the concept of breeding for microbial symbioses with pea (Pisum sativum L.). Firstly, genotypic variation for the efficiency of a mycorrhizal symbiosis is shown, as measured by an estimation of the plant benefit per symbiotic unit. Secondly, we extend the view towards the wider fungal community using ITS amplicon sequencing. Two pea genotypes with contrasting resistance levels against pathogen complexes are investigated to provide information on the functional diversity of the rhizosphere microbiome in a naturally infested agricultural soil. In the near future, microbial hubs and diversity indices will be linked with root exudation in order to elucidate the plant’s capacity to influence the microbial composition leading to disease susceptibility or resistance. Current and future research activities of our group aim to make use of plant-microbiome interactions to develop advanced screening tools for breeders for an improved expression and stability of important plant traits