Biostimulants from food processing by-products: agronomic, quality and metabolic impacts on organic tomato (Solanum lycopersicum L.).

BACKGROUND: Biostimulants have recently gained increased attention due to their multiple benefits for sustainable agriculture. In this study, three food processing by-products - fennel processing residues (FPR), lemon processing residues (LPR) and brewer's spent grain (BSG) - were investigated as potential sources of biostimulants. Their aqueous extracts as individual and associated applications were assessed for their effects on agronomic, quality and metabolic performance of organic tomato in comparison to extract of humic substances (HS) and untreated control (CTRL). RESULTS: Only FPR extracts stimulated shoot growth and tomato dry matter content, whereas all candidates improved tomato yield. FPR and BSG increased fruit mineral content and BSG-FPR-LPR in combination enhanced titratable acidity. FPR-treated fruits had also 20% more vitamin C than CTRL, and higher phenol content was obtained in those of BSG-LPR. Fruit metabolomic profile showed the tendency of all extracts, except BSG-LPR, to increase tomato citric acid and to decrease ß-glucose and methanol concentrations. The analysis revealed accordingly the indispensable role of FPR in combined applications for inducing an HS-like response in fruits. CONCLUSION: The results were indicative of the biostimulant activity of these extracts and demonstrated them, particularly FPR, as promising candidates for enhancing plant productivity and fruit quality. © 2017 Society of Chemical Industry.

Olive mill waste biochar: a promising soil amendment for metal immobilization in contaminated soils.

The potential use of biochar from olive mill waste for in situ remediation of metal contaminated soils was evaluated. Biochar was mixed with metal contaminated soil originating from the vicinity of an old zinc smelter. Soil-biochar mixtures were equilibrated for 30 and 90 days. At these time points, Ca(NO3)2 exchangeable metals were determined, and effects of the biochar amendment on soil toxicity were investigated using plants, bacteria, and earthworms. Bean (Phaseolus vulgaris) growth, metal content, antioxidative enzymes activities, and soluble protein contents were determined. Furthermore, effects on soil microbial communities (activity, diversity, richness) were examined using Biolog ECOplates. After 120 days of soil-biochar equilibration, effects on weight and reproduction of Eisenia foetida were evaluated. With increasing biochar application rate and equilibration period, Ca(NO3)2 exchangeable metals decreased, and growth of bean plants improved; leaf metal contents reduced, the activities of antioxidative stress enzymes decreased, and soluble protein contents increased. Soil microbial activity, richness, and diversity were augmented. Earthworm mortality lowered, and their growth and reproduction showed increasing trends.

Evaluation of Atriplex halimus, Medicago lupulina and Portulaca oleracea for phytoremediation of Ni, Pb, and Zn.

Suitable plant species are able to accumulate heavy metals and to produce biomass useful for non-food purposes. In this study, three endemic Mediterranean plant species, Atriplex halimus, Portulaca oleracea and Medicago lupulina were grown hydroponically to assess their potential use in phytoremediation and biomass production. The experiment was carried out in a growth chamber using half strength Hoagland's solutions separately spiked with 5 concentrations of Pb and Zn (5, 10, 25, 50, and 100 mg L(-1)), and 3 concentrations of Ni (1, 2 and 5 mg L(-1)). Shoot and root biomass were determined and analyzed for their metals contents. A. halimus and M. lupulina gave high shoot biomass with relatively low metal translocation to the above ground parts. Metals uptake was a function of both metals and plant species. It is worth noting that M. lupulina was the only tested plant able to grow in treatment Pb50 and to accumulate significant amount of metal in roots. Plant metal uptake efficiency ranked as follows: A. halimus > M. lupulina > P. oleracea. Due to its high biomass production and the relatively high roots metal contents, A. halimus and M. lupulina could be successfully used in phytoremediation, and in phytostabilization, in particular.

Effect of compost and manure amendments on zinc soil speciation, plant content, and translocation in an artificially contaminated soil.

The addition of organic matter in soil can modify the bioavailability of heavy metals. A greenhouse pot experiment was carried out using an edible plant species Eruca vesicaria L. Cavalieri grown on an artificially contaminated soil with Zn (665 mg kg(-1)). In this study, the effect of compost at 20 t ha(-1) (C20) and at 60 t ha(-1) (C60), manure at 10 t ha(-1) (M10) and at 30 t ha(-1) (M30), and chemical fertilizers (NPK) on Zn fate in a soil-plant system was evaluated. At the end of the experiment, the main growth parameters and Zn content in plants were determined. In addition, Zn speciation in the soil was assessed using the original Community Bureau of Reference sequential extraction and diethylene triamine pentaacetic acid extraction. Zinc, though an essential element for plant growth, caused toxicity effects in plants grown on control and manure treatments, while in the compost treatments, plants showed no visual toxicity symptoms. The concentrations of Zn in roots were similar for all treatments, while significant differences were observed for shoots. In fact, in the compost treatments, plants showed the lowest Zn concentration in shoots. Zinc speciation seems not to be affected by the applied treatments. Indeed, Zn plant content and translocation to shoots seems to be affected. Compost amendments significantly reduced Zn content and translocation in comparison to other treatments.

Zinc distribution and speciation within rocket plants (Eruca vesicaria L. Cavalieri) grown on a polluted soil amended with compost as determined by XRF microtomography and micro-XANES.

Zinc distribution and speciation within different organs (root, petiole, and leaf) of the edible plant Eruca vesicaria L. Cavalieri were determined using synchrotron microbeam X-ray techniques (XRF microtomography and mu-XANES) for plants grown in polluted soil with or without compost amendment. Data on soil derived from different extraction procedures and using mu-XANES analyses on rhizospheric soil indicated that compost amendment did not significantly influence the Zn speciation and availability in soil. However, major differences were observed within the plants. Plants grown in the presence of compost were able to partly block zinc immediately outside the root endodermis in the form of zinc-phytate, while a smaller Zn fraction was allowed to xylem transport as zinc-citrate. In the leaves, zinc was largely excluded from leaf cells, and about approximately 50% was in the form of phosphate precipitates, and the other 50% was complexed by cysteine and histidine residues. The reported data provide new information concerning the mechanisms of zinc tolerance in E. vesicaria L. Cavalieri, a very common edible plant in Mediterranean regions, and on the role of compost in influencing the molecular strategies involved in zinc uptake and detoxification.