Impacts of Oak Mulch Amendments on Rhizosphere Microbiome of Citrus Trees Grown in Florida Flatwood Soils.

Rhizosphere interactions are an understudied component of citrus production. This is even more important in Florida flatwood soils, which pose significant challenges in achieving sustainable and effective fruit production due to low natural fertility and organic matter. Citrus growers apply soil amendments, including oak mulch, to ameliorate their soil conditions. Thus, the aim of this research was to evaluate the effects of oak mulch on citrus nutrient uptake, soil characteristics, and rhizosphere composition. The plant material consisted of 'Valencia' sweet orange (Citrus × sinensis) trees grafted on 'US-812' (C. reticulata × C. trifoliata) rootstock. The experiment consisted of two treatments, which included trees treated with oak mulch (300 kg of mulch per plot) and a control. The soil and leaf nutrient contents, soil pH, cation exchange capacity, moisture, temperature, and rhizosphere bacterial compositions were examined over the course of one year (spring and fall 2021). During the spring samplings, the citrus trees treated with oak mulch resulted in significantly greater soil Zn and Mn contents, greater soil moisture, and greater rhizosphere bacterial diversity compared to the control, while during the fall samplings, only a greater soil moisture content was observed in the treated trees. The soil Zn and Mn content detected during the spring samplings correlated with the significant increases in the diversity of the rhizosphere bacterial community composition. Similarly, the reduced rates of leaching and evaporation (at the soil surface) of oak mulch applied to Florida sandy soils likely played a large role in the significant increase in moisture and nutrient retention.

Divergent effects of cerium oxide nanoparticles alone and in combination with cadmium on nutrient acquisition and the growth of maize (Zea mays).

Introduction: The increasing use of cerium nanoparticles (CeO2-NPs) has made their influx in agroecosystems imminent through air and soil deposition or untreated wastewater irrigation. Another major pollutant associated with anthropogenic activities is Cd, which has adverse effects on plants, animals, and humans. The major source of the influx of Cd and Ce metals in the human food chain is contaminated food, making it an alarming issue; thus, there is a need to understand the factors that can reduce the potential damage of these heavy metals. Methods: The present investigation was conducted to evaluate the effect of CeO2-10-nm-NPs and Cd (alone and in combination) on Zea mays growth. A pot experiment (in sand) was conducted to check the effect of 0, 200, 400, 600, 1,000, and 2,000 mg of CeO2-10 nm-NPs/kg-1 dry sand alone and in combination with 0 and 0.5 mg Cd/kg-1 dry sand on maize seedlings grown in a partially controlled greenhouse environment, making a total of 12 treatments applied in four replicates under a factorial design. Maize seedling biomass, shoot and root growth, nutrient content, and root anatomy were measured. Results and discussion: The NPs were toxic to plant biomass (shoot and root dry weight), and growth at 2,000 ppm was the most toxic in Cd-0 sets. For Cd-0.5 sets, NPs applied at 1,000 ppm somewhat reverted Cd toxicity compared with the contaminated control (CC). Additionally, CeO2-NPs affected Cd translocation, and variable Ce uptake was observed in the presence of Cd compared with non-Cd applied sets. Furthermore, CeO2-NPs partially controlled the elemental content of roots and shoots (micronutrients such as B, Mn, Ni, Cu, Zn, Mo, and Fe and the elements Co and Si) and affected root anatomy.

Grapefruit Root and Rhizosphere Responses to Varying Planting Densities, Fertilizer Concentrations and Application Methods.

Huanglongbing (HLB) disease has caused a severe decline in citrus production globally over the past decade. There is a need for improved nutrient regimens to better manage the productivity of HLB-affected trees, as current guidelines are based on healthy trees. The aim of this study was to evaluate the effects of different fertilizer application methods and rates with different planting densities on HLB-affected citrus root and soil health. Plant material consisted of 'Ray Ruby' (Citrus × paradisi) grapefruit trees grafted on 'Kuharske' citrange (Citrus × sinensis × Citrus trifoliata). The study consisted of 4 foliar fertilizer treatments, which included 0×, 1.5×, 3× and 6× the University of Florida Institute of Food and Agriculture (UF/IFAS) recommended guidelines for B, Mn and Zn. Additionally, 2 ground-applied fertilizer treatments were used, specifically controlled-release fertilizer (CRF1): 12-3-14 + B, Fe, Mn and Zn micronutrients at 1× UF/IFAS recommendation, and (CRF2): 12-3-14 + 2× Mg + 3× B, Fe, Mn and Zn micronutrients, with micronutrients applied as sulfur-coated products. The planting densities implemented were low (300 trees ha-1), medium (440 trees ha-1) and high (975 trees ha-1). The CRF fertilizer resulted in greater soil nutrient concentrations through all of the time sampling points, with significant differences in soil Zn and Mn. Grapefruit treated with ground-applied CRF2 and 3× foliar fertilizers resulted in the greatest bacterial alpha and beta diversity in the rhizosphere. Significantly greater abundances of Rhizobiales and Vicinamibacterales were found in the grapefruit rhizosphere of trees treated with 0× UF/IFAS foliar fertilizer compared to higher doses of foliar fertilizers.

Influence of ionic cerium and cerium oxide nanoparticles on Zea mays seedlings grown with and without cadmium.

Cerium (Ce4+) and cerium oxide nanoparticles (CeO2-NPs) have diversified reported effects on plants. Once dispersed in the environment their fate is not well understood, especially in co-existence with other pollutants like cadmium (Cd). The effect of co-application of Ce and Cd are reported in various studies, but the role of Ce source (ionic or bulk) and nanoparticle size is still unknown in cereal plants like maize (Zea mays). To better understand the synergistic effects of Ce and Cd, 500 mg kg-1 Ce coming from ionic (Ce4+ as CeSO4) and CeO2 nano sources (10 nm, 50 nm, and 100 nm) alone and in combination with 0.5 mg Cd kg-1 sand were applied to maize seedlings. Growth, physiology, root structure, anatomy, and ionic homeostasis in maize were measured. The results revealed that Ce4+ resulted in overall decrease in seedling growth, biomass and resulted in higher heavy metal (in control sets) and Cd (in Cd spiked sets) uptake in maize seedlings' root and shoot. The effects of CeO2-NPs were found to be dependent on particle size; in fact, under Cd-0 (non-Cd spiked sets) CeO2-100 nm showed beneficial effects compared to the control. While under co-application with Cd, CeO2-50 nm showed net beneficial effects on maize seedling growth parameters. The Ce alone, and in combination with Cd, altered the root suberin barrier formation. Both ionic and nano Ce sources alone and in co-existence with Cd behaved differently for tissue elemental concentrations (Ce, Cd, micronutrients like B, Mn, Ni, Cu, Zn, Mo, Fe and elements Co, Si) suggesting a strong influence of Cd-Ce coexistence on the element's uptake and translocation in maize.

Root-Shoot Nutrient Dynamics of Huanglongbing-Affected Grapefruit Trees.

With huanglongbing (HLB) causing a reduction in fine root mass early in disease progression, HLB-affected trees have lower nutrient uptake capability. Questions regarding the uptake efficiency of certain fertilizer application methods have been raised. Therefore, the goals of this study are to determine if nutrient management methods impact nutrient translocation and identify where in the tree nutrients are translocated. Destructive nutrient and biomass analysis were conducted on field grown HLB-affected grapefruit trees (Citrus × paradisi) grafted on 'sour orange' (Citrus × aurantium) rootstock under different fertilizer application methods. Fertilizer was applied in the form of either 100% soluble granular fertilizer, controlled release fertilizer (CRF), or liquid fertilizer. After three years, the entire tree was removed from the grove, dissected into eight different components (feeder roots, lateral roots, structural roots, trunk, primary branches, secondary branches, twigs, and leaves), weighed, and then analyzed for nutrient contents. Overall, application methods showed differences in nutrient allocation in leaf, twig, and feeder root; however, no consistent pattern was observed. Additionally, leaf, twig, and feeder roots had higher amount of nutrients compared to the other tree components. This study showed that fertilization methods do impact nutrient contents in different components of HLB-affected trees. Further research should be conducted on the impact of different fertilizer application methods and rates on HLB-affected trees.