Effects of marine sediment as agricultural substrate on soil microbial diversity: an amplicon sequencing study.

BACKGROUND: The soil microbiota has a direct impact on plant development and other metabolic systems, such as the degradation of organic matter and the availability of microelements and metabolites. In the context of agricultural soils, microbial activity is crucial for maintaining soil health and productivity. Thus, the present study aimed to identify, characterize, and quantify the microbial communities of four types of substrates with varying proportions of marine port sediment used for cultivating lemons. By investigating microbial diversity and relative abundance, the work aimed to highlight the importance of soil microbial communities in agriculture when alternative culture media was used. RESULTS: The composition and structure of the sampled microbial communities were assessed through the amplification and sequencing of the V3-V4 variable regions of the 16 S rRNA gene The results revealed a diverse microbial community composition in all substrate samples, with a total of 41 phyla, 113 classes, 266 orders, 405 families, 715 genera, and 1513 species identified. Among these, Proteobacteria, Bacteroidota, Planctomycetota, Patescibacteria, Chloroflexi, Actinobacteriota, Acidobacteriota, Verrucomicrobiota, and Gemmatimonadota accounted for over 90% of the bacterial reads, indicating their dominance in the substrates. CONCLUSIONS: The impact of the substrate origin on the diversity and relative abundace of the microbiota was confirmed. The higher content of beneficial bacterial communities for plant development identified in peat could explain why is considered an ideal agricultural substrate. Development of "beneficial for plants" bacterial communities in alternative agricultural substrates, regardless of the edaphic characteristics, opens the possibility of studying the forced and specific inoculation of these culture media aiming to be agriculturally ideals.

Metabolomic Approach to Study the 'Purple Queen' Pomegranate Cultivar Response to Alternative Culture Media and Phenological Stages.

The increasingly evident threat of depletion of world peat bogs is encouraging the search for and study of alternative agricultural substrates that can fully or partially replace peat, guaranteeing food supply (quality and quantity). On the other hand, the identification of the potential for the reuse of waste from relevant economic activities has increased in recent years, mainly motivated by the change to a sustainable circular economy, as is the case of port sediments. Taking into account that significant volumes of dredged port sediments are generated annually so that ports can maintain their economic activity, it is necessary to find objective, sustainable and safe reuse alternatives. In this sense, the objective of this study was to study the response of the "Purple Queen" pomegranate when grown with dredged port sediment. For this, the fruit production (kg), number of fruits (fruits tree-1), fruit weight (g), and seed yield (%) aiming to verify the correct tree development were evaluated. In addition, a 1H-NMR foliar metabolomic study for the three most relevant phenological phases was performed (flowering, fruit development, and post-harvest) to identify metabolic changes in trees. In total, 29 metabolites were identified; among them, 11 were amino acids, 6 organic acids, 5 sugars, and 7 secondary metabolites. The good agronomical development of the trees and fruits indicated the potential for using the dredged sediment as an agricultural substrate. On the other hand, the results revealed that the greatest variability in the metabolomic study occurred between the phenological phases and a lower variability is explained by the substrates used.

Life Cycle Assessment (LCA) of Substrate Mixes Containing Port Sediments for Sustainable 'Verna' Lemon Production.

The increase in maritime trade and its global economic importance have forced port management actors to carry out the periodic dredging of their sediments to maintain an adequate depth for the passage of large ships to maintain their operation and competitiveness. During the dredging process, large volumes of port sediment are generated. Dredged port sediment is currently considered a waste material and its disposal is regulated. Finding ways to safely reuse port sediments is necessary for sustainable development. In this study, a life cycle assessment (LCA) methodology was applied to identify the environmental impact of port sediments when used as a culture medium for lemon trees. A total of 90 lemon trees (Citrus limon L. Burm var 'Verna') were used in the trial. The trees were grown under controlled conditions using three substrates, with different portions of peat and port sediment (25%, 50%, and 75%) to identify the real impacts of the culture media on the growth process. The LCA was calculated and analyzed according to the ISO 14040:2006 standard, using the SimaPro v. 9.3 software (PRé Sustainability B.V, Amersfoort, The Netherlands). The functional unit defined for the three-culture media was 1 kg of lemons. The LCA results showed a significant increase in the environmental impact of lemon cultivation proportional to port sediment content (75%), due to the decrease in fruit production caused by the sediment. However, the least impact was identified for the culture medium at 50% peat and 50% port sediment. The greatest impacts were more related to crop management rather than the port sediment content. The results showed that the use of the port sediment, mixed with other substrates as an agricultural medium amendment, is a viable option for lemon growers.

Physico-Chemical Attributes of Lemon Fruits as Affected by Growing Substrate and Rootstock.

Due to its high content of bioactive compounds, the lemon is considered one of the most relevant species around the world. Its great economic importance is motivated, in addition to its fresh consumption, by its applications in the medical, pharmaceutical, and food industries, etc. However, the chemical and nutritional composition of lemon is not constant and can be influenced by external factors such as variety, weather conditions, crop management, etc. Determining the compositional variations of the fruit, essential to defining its potential use, was the main objective of this study. The physicochemical characteristics of the 'Verna' lemon were studied as a function of two controlled variables, the growing substrate and the rootstock. For this, 90 lemon trees were cultivated in three rootstocks and three different culture media. Lemon trees cultivated with 50% sediment/peat mix substrate presented a higher total production (590 lemons and 90.53 kg) while this production was 80% lower on trees cultivated with 75% marine sediment. Citrus macrophylla and Citrus aurantium/Citrus sinensis rootstocks showed a significantly higher production than the Citrus aurantium. All the fruits presented a predominantly yellow color appropriate for the market (0 < CI < +5). Nutritional and chemical parameters were consistent with data reported for the 'Verna' clones. All the obtained lemons were suitable for marketing and consumption both in fresh and processed forms. The results indicated the limited influence that the studied variables have on the quality parameters of lemon fruits, but they also could confirm the potential of marine sediment as a culture substrate.

Potential of dredged bioremediated marine sediment for strawberry cultivation.

For the maintenance of the economic activity of the ports, it is necessary to dredge the marine sediments in order to guarantee their depth. These sediments, considered by European legislation as residues, present relevant limitations of use and generate environmental and economic problems concerning their final disposal. In this context, the present work aims to identify the phytoremediated dredged sediments potential as an alternative to the traditional substrate (peat) in horticultural growing through two-years controlled strawberry cultivation. The growing media mixes used were: (1) 100% peat (Pt) as a control substrate; (2) 100% dredged remediated sediment (DRS); (3) 50% each (Pt-DRS). The dredged sediment, plant drainage and strawberry plant parts (leaves, stems, roots, and fruits) were analyzed to mineral elements, heavy metal contents, and pesticide residues (polycyclic aromatic hydrocarbons, polychlorinated biphenyls and specific fumigants) during the experimental period. Only seven (Mn, Fe, Zn, Mo, Al, Mn and Ni) of the twenty-two metals and two (nitrates and fluorene) of the six hundred-thirteen pesticides analyzed were detected in the strawberry fruits. In all the cases, values detected were under the Spanish and European legal limit. The suitability of strawberry fruits for fresh and/or processed consumption with no risk was confirmed. Based on the results, can be affirmed that the dredged remediated sediment can be used as a culture substrate, alone or mixed with other substrates. Additional researches should be carried out to confirm the sediment characteristics and compare with other substrates to improve the physical and chemical properties.