Showing their mettle: extraradical mycelia of arbuscular mycorrhizae form a metal filter to improve host Al tolerance and P nutrition.

BACKGROUND: New evidence has shown that arbuscular mycorrhizal (AM) fungi can contribute to the aluminum (Al3+ ) tolerance of host plants growing in acidic soils with phytotoxic levels of Al3+ . The aim of this study was to investigate the role of AM fungi isolated from naturally occurring Al3+ acidic soils in conferring host tolerance to Al3+ toxicity in three wheat cultivars differing in Al3+ sensitivity. The experiment was conducted in a soilless substrate (vermiculite/perlite, 2:1 v/v) using two Al3+ -tolerant wheat genotypes and one Al3+ -sensitive wheat genotype. The wheat was colonized with a consortium of AM fungi isolated from an Andisol, with or without Al3+ at a concentration of 200 µmol L-1 . RESULTS: The response of wheat to Al3+ in the medium was dependent on both the plant genotype and AM colonization. The benefits of the AM fungi to the wheat cultivars included an increased P concentration and relatively low Al3+ accumulation in the plants. This was achieved through two mechanisms. First, the metal-chelating capacity of the AM fungi was clear in two of the cultivars ('Tukan' and 'Porfiado'), in which the enhanced extraradical mycelium development was able to retain Al3+ in the glomalin and hyphae. Second, the increased AM-induced acid phosphatase activity in the rhizosphere of the other cultivar ('Atlas 66') increased host nutrition possibly by hyphae-mediated nutrient uptake and glomalin-related soil protein. CONCLUSION: The results suggest that the role of AM fungi in cultivar-specific Al3+ detoxification can be achieved by increased extraradical mycelial filters and enhanced bioavailability of P in the host rhizosphere. © 2019 Society of Chemical Industry.

Hazelnut and Walnut Nutshell Features as Emerging Added-Value Byproducts of the Nut Industry: A Review.

The hard-shelled seed industry plays an important role in the global agricultural economy. In fact, only considering hazelnut and walnut, the global nut supply is over 5.6 tons. As a result considerable amounts are produced year by year, burnt or discarded as waste, bypassing a potential source of valuable compounds or features. This review deals with the recent scientific literature on their chemical composition as well as functional applications as an approach to sustain the utilization of the main byproduct derived from industry. Indeed, nutshells have received great interest due to their lignin, antioxidant, physical and mechanical features. It was found that these properties vary among cultivars and localities of plantation, influencing physical and structural features. The inconsistencies regarding the above-mentioned properties of nutshells lead to exploring the status of hazelnut and walnut shell applications in sustainable bio-economy chains. In fact, in terms of potential applications, the state of the art links their use to the construction industry and the manufacture of materials, such as resin or plastic composites, particleboards or construction panels, or vital infrastructure and as a filler in cement pavements. However, their current use continues bypassing their great antioxidant potential and their interesting chemical and mechanical features.

Antioxidants in Shell and Nut Yield Components after Ca, Mg and K Preharvest Spraying on Hazelnut Plantations in Southern Chile.

To determine the effects of pre-harvest calcium (Ca), magnesium (Mg) and potassium (K) spraying on the antioxidant activity and capacity of hazelnut (Corylus avellana L.) shells, as an approach to sustain the utilization of the main residue derived from this industry, four commercial hazelnut (Tonda di Giffoni) orchards located in Southern Chile (Cunco, Gorbea, Perquenco and Radal), during the 2018/19 season were sprayed three times with five combinations of Ca (300 and 600 mg L-1), Mg (300 and 600 mg L-1) and K (300 and 600 mg L-1). Yield components were determined in harvested whole nuts, whereas Ca, Mg and K concentrations, as well as total phenolic compounds, free radical scavenging antioxidant activity, and oxygen radical absorbance capacity, were determined in shells. All spray treatments with both Ca, Mg and K combinations showed a significant interaction between locality and treatment (L × T) on increased stabilized nut yield (kg ha-1) in comparison with the control treatments, whereas nut quality was differentially affected by treatment and orchard locality, thus confirming a significant L × T relationship regarding nut length and kernel yield. However, locality showed a major effect on kernels and shells. A significant relationship was determined between locality and the Ca, Mg and K spraying (L × T) concerning antioxidant compounds such as phenolics, whose amounts exceeded those of the control treatments by three times. Antioxidant capacity and activity in shells showed a significant L × T relationship, and nutshells collected from Cunco showed remarkably (3-4 times) higher levels of these factors than the other evaluated localities. Interactions between spray treatment and orchard location were responsible for the different values obtained in the experiments, confirming the influence of the environment on the efficacy of the treatments. Finally, these shells are worth further study as an interesting residue of the hazelnut industry due to their nutritional and antioxidant properties.

Salt Stress in Plants and Mitigation Approaches.

Salinization of soils and freshwater resources by natural processes and/or human activities has become an increasing issue that affects environmental services and socioeconomic relations. In addition, salinization jeopardizes agroecosystems, inducing salt stress in most cultivated plants (nutrient deficiency, pH and oxidative stress, biomass reduction), and directly affects the quality and quantity of food production. Depending on the type of salt/stress (alkaline or pH-neutral), specific approaches and solutions should be applied to ameliorate the situation on-site. Various agro-hydrotechnical (soil and water conservation, reduced tillage, mulching, rainwater harvesting, irrigation and drainage, control of seawater intrusion), biological (agroforestry, multi-cropping, cultivation of salt-resistant species, bacterial inoculation, promotion of mycorrhiza, grafting with salt-resistant rootstocks), chemical (application of organic and mineral amendments, phytohormones), bio-ecological (breeding, desalination, application of nano-based products, seed biopriming), and/or institutional solutions (salinity monitoring, integrated national and regional strategies) are very effective against salinity/salt stress and numerous other constraints. Advances in computer science (artificial intelligence, machine learning) provide rapid predictions of salinization processes from the field to the global scale, under numerous scenarios, including climate change. Thus, these results represent a comprehensive outcome and tool for a multidisciplinary approach to protect and control salinization, minimizing damages caused by salt stress.

Combined Spraying of Boron and Zinc During Fruit Set and Premature Stage Improves Yield and Fruit Quality of European Hazelnut cv. Tonda di Giffoni.

Boron (B) and zinc (Zn) are essential micronutrients of plant nutrition programs in orchards for securing the crop quality and yield. Although orchard supplementation with B and Zn is a common practice to overcome deficiencies or maintain their optimal levels, the efficiency of combined B and Zn spraying in relation to European hazelnut (Corylus avellana L.) phenological stage has not been investigated so far. Leaf and kernel mineral and functional traits were studied in cultivar Tonda di Giffoni after B and Zn spraying in four phenological stages. During the 2016/2017 season, 9-year-old trees were sprayed with B (0, 800, and 1,600 mg L-1) and Zn (0, 400, and 800 mg L-1) under three treatments: B0+Zn0, B800+Zn400, and B1600+Zn800 implemented in three spring application programs scheduled from October to December (P1: four times, P2: early two times, and P3: late two times). B and Zn treatments in P1 and P3 led to higher Zn concentration both in leaves and in kernels compared with non-sprayed trees. Stabilized nut production increased 2.5-fold under B800+Zn400 in all three programs. Kernel/nut ratio improved in both B+Zn treatments in P1 and P3, while the percentage of blank nuts was reduced compared with B0+Zn0. Increased radical scavenging activity in B+Zn-treated kernels and leaves was not attributed to the accumulation of phenolics in P3 compared with B0+Zn0, whereas B and Zn spraying reduced the level of lipid peroxidation in both studied organs. According to the results, combined B and Zn should be sprayed at the end of spring (P3) on hazelnut plantations in temperate areas such as Southern Chile, whereas early applications (P2) showed an irregularity in nut production and functional traits in nuts. Moderate and partialized rates of B and Zn and the time of implementation contribute to improving the quantitative and qualitative features crucial for future sustainable hazelnut production.

Synthesis of calcium borate nanoparticles and its use as a potential foliar fertilizer in lettuce (Lactuca sativa) and zucchini (Cucurbita pepo).

This study was carried out to evaluate the effects of foliar sprays containing boron (B) nano-fertilizer (NF) on the growth and physiology of lettuce (Lactuca sativa) and zucchini (Cucurbita pepo). Plants were grown under greenhouse conditions for 60 days on a modified Hoagland solution with the presence and absence of boron (+B or -B). A synthesized B-NF foliar spray and a commercial B foliar fertilizer (Bortrac™ 150, BT) was applied at a concentration of 30 mg B L-1 at 10-d intervals throughout the experiment. The B-NF treatment increased the growth of lettuce 2.7- and 1.9-fold for shoots and roots, respectively, with an average production of lettuce biomass by ~58%. Similarly, the NF increased the growth of zucchini by 18 and 66% compared with Control-B (the absence of B), and 13 and 36% compared with BT, both for shoots and roots, respectively. Nevertheless, NF + B mostly decreased lettuce growth with symptoms of B toxicity in leaves. In lettuce, addition of B did not affect concentrations of phenols; however, in zucchini, Control-B induced a higher production of phenolic compounds possibly related to B deficiency. The B addition in lettuce reduced the DPPH activity by 32 and 21% in NF and BT, respectively, compared to Control-B. These responses were similar in zucchini; however, the effect of B was product of its presence in mineral solution rather than due the foliar product applied. This suggests that a NF-based delivery system for B may be highly effective at boosting plant productivity on B-limited soils.

Biogeochemistry of soil organic matter in agroecosystems & environmental implications.

The biogeochemistry of soil organic matter (SOM), as a highly complex and dynamic soil property, is of vital importance for the health and ecological functioning of ecosystems, including managed and natural ones. Dominantly composed of carbon (C), SOM functions in global C cycling, including C sequestration and emission (e.g. soil respiration). Mediterranean agroecosystems especially, due to favourable climate conditions for mineralisation of SOM, are expected to go through enhanced SOM decomposition (i.e. C emission) under the ongoing global warming and related climatic change and variability (frequent heat waves, fires and extreme water disturbances). The relatively stable (humified) SOM components, especially in the organically-enriched topsoil layers, due to their specific physical chemistry (strongly charged interface) may have a significant role in biogeochemistry of charged (in)organic nutrients and/or contaminants such as toxic metal ions and persistent organic pollutants. The recent studies show that some natural vulnerabilities of Mediterranean regions (such as high risk of the erosion-driven processes) can increase movement of some hazardous pedospheric constituents (e.g. pesticides) to water bodies and/or into the air, thus influencing the whole ecosystem health. A majority of recent surveys confirm depletion of SOM and spatially variable distribution of metal contamination in the Mediterranean topsoils. Using the advanced geochemical prediction approaches in combination with the relevant soil databases, we characterised organo-mineral and organo-metal complexation and its effect on speciation and sorption of trace metals in karstified Mediterranean agroecosystems. Metal biogeochemistry was found to vary markedly under relatively constant pedosphere conditions, depending on organo-mineral soil components and pH, which may significantly impact metal mobility/availability in the soil-plant continuum. The knowledge of the SOM spatial distribution and dynamics and its interactions with other pedovariables is essential for sustainable management of SOM and control of contaminant mobility to avoid degradation processes in (agro)ecosystems.