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The use of Mediterranean euryhaline fish and halophytes in aquaponics presents a sustainable and alternative approach to food production. The present study investigates the effect of compensatory growth on sea bass (Dicentrarchus labrax) and Baltic prawn (Palaemon adspersus) co-cultivated with the halophytic glasswort (Salicornia europaea). Three autonomous systems were established, each containing forty-five sea bass, nine Baltic prawns, and eight glasswort plants, with different feeding regimes for each treatment: (i) daily feeding (treatment A), (ii) three days of feeding per week followed by four days of fasting (treatment B), and (iii) feeding for seven days followed by seven days of fasting (treatment C). The growth performance of the fish was significantly higher in treatment B. Conversely, the feed conversion ratio (FCR) was notably higher in treatment A. As for the prawns, their final body weight and length were similar across all treatments. The glasswort plants also demonstrated significantly improved growth in treatment B. These results indicate that the incorporation of feeding and fasting cycles can be an effective feed management strategy for polyculture aquaponic systems. Additionally, food deprivation had a positive impact on the growth performance of both glasswort and prawns. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the effect of starvation and refeeding on the growth and food intake of gilthead seabream (Sparus aurata) and seabass (Dicentrarchus labrax) and on the growth and nitrogen uptake of glasswort (Salicornia europaea) in a polyculture aquaponic system under 12 ppt salinity for 75 days. Nine small-scale autonomous aquaponic systems were used, each containing 10 gilthead seabreams (average weight of 6.33 ± 0.73 g and average length of 5.73 ± 0.72 cm) and 10 seabasses (5.82 ± 0.77 g and 6.35 ± 0.45 cm), as well as five glasswort plants. Three fish feeding treatments were performed, a control (A), in which fish were fed daily until satiation, and two fasting treatments for 4 (B) and 7 days (C). Fish growth performance was significantly lower (p < 0.05) in the C treatment for both species compared to treatments A and B. Food consumption (FC) and feed conversion ratio (FCR) were significantly higher (p < 0.05) in treatment C. Glasswort growth performance was significantly higher in treatment C (p < 0.05). The results showed that the 4-day food-deprived fish were similar to the control fish by achieving partial compensatory growth. The more extended fasting period (7 days) resulted in significantly lower growth performance. The lipid and nitrogen retention levels in both species were significantly lower in food-deprived fish than in the control fish both before and during compensatory growth. The results suggest that a feeding schedule involving starvation–refeeding cycles is a promising feed management option for these species in polyculture aquaponic systems. The effect of food deprivation was also significantly beneficial (p < 0.05) for the growth performance of glasswort compared to the control treatment. [ABSTRACT FROM AUTHOR]

Zero-discharge and low-input aquaponics systems are a promising alternative to the intensive agricultural and aquacultural production systems currently used, ensuring high environmental sustainability. However, new approaches and management practices are needed to increase their productivity to reach the yields of classic production systems. In this context, the present study investigated for the first time the potential of two biostimulants to improve lettuce performance in aquaponics, whether coupled or decoupled, with hydroponics serving as a control. A comprehensive evaluation was conducted to assess the plant functional (focusing on the photosynthetic process evaluation) and growth responses at the whole-plant level. In addition, the nutritional state of the leaves was determined and metabolomic analysis was performed at the cellular level, the latter also for the first time in aquaponics research. The results demonstrated the limitations that coupled aquaponics poses in relation to lettuce growth, function and metabolism, which were already obvious from the 12th day of the experiment. Indicatively, the plants grown under coupled aquaponics exhibited a notable decrease in the leaf fresh weight, potassium content and nitrogen content, with reductions of 80%, 60%, and 30%, respectively, in comparison to the hydroponics control. However, the combined physiological and metabolomic data indicate that these plants down-regulate processes and metabolism to acclimate to low nutrient levels in lettuce leaves rather than experiencing damage. The application of biostimulants did not significantly optimize the plants' performance, though one of them appeared to be effective in improving some aspects of the photochemical efficiency. The decoupled and hydroponics systems resulted in similarly high yields and efficiency in terms of plant function, without any marked contribution from the biostimulants. We conclude that the decoupled aquaponics system has been successful in achieving yields comparable to those of hydroponics, with lower chemical inputs. Future studies should focus on examining other biostimulants in this system to further improve its performance while maintaining its environmental benefits within a circular economy framework. [ABSTRACT FROM AUTHOR]

In soil with extremely high contents of Cd (101.87), Pb (26,526.44), and Zn (17,652.63 mg kg−1), we aimed to test the phytostabilization capacity of purslane (Portulaca oleracea) with the use of various soil improvers, both organic (biochar, compost, insect frass) and inorganic (lime and zeolite). Thus, in a 60-day pot experiment, we amended this heavily contaminated soil with the five materials at two rates, 2% and 4%, resulting in 11 treatments (control plus five materials × two rates) replicated 10 times. We found that soil extractions of Cd with DTPA (diethylenetriaminepentaacetic acid) were not affected by any of the amendments, as there was no recorded significant reduction in soil Cd. In the case of Pb, there were even significant increases in its extractability with added biochar, and so was the case for compost at 4%. The reason may be the formation of organometallic complexes with organic substances of low molecular weight eluted by the organic amendments. Similarly, Zn extractability increased significantly compared to the control in the compost and frass treatments. As for purslane shoots, Cd decreased from 61 μg kg−1 fresh weight (FW) at control to 39 at biochar 4%, but the reduction was non-significant. As for Pb, it decreased with biochar but not significantly, while it exhibited a significant decrease in all other treatments. However, in all cases the content of Pb in purslane was well above the European regulation limit of 0.100 mg kg−1 FW (fresh weight) for vegetables and fresh herbs, while Cd fell below the regulation limit of 50 μg kg−1 FW at biochar 4%, compost 4%, and frass 2% and 4% (with control being 62.5 μg kg−1 FW). We conclude that in heavily contaminated soils, although biochar, along with compost and frass, was not entirely unsuccessful, the tested amendments did not reduce satisfactorily toxic elements to sufficiently low levels both in soil and in the test plant (here, purslane) in order to achieve phytostabilization. However, further research is necessary to identify exact mechanisms and to elucidate the role of different biochars. [ABSTRACT FROM AUTHOR]

A novel type of heliotropic leaf movement is presented for Capparis spinosa L., a summer perennial shrub of Mediterranean and arid ecosystems. In contrast to plants that demonstrate uniform diaheliotropic and/or paraheliotropic movement for all their foliage, the alternate leaves of C. spinosa follow different movement patterns according to their stem azimuth and the side of the stem that they come from (cluster). Additionally, leaf movement for each cluster may not be uniform throughout the day, showing diaheliotropic characteristics during half of the day and paraheliotropic characteristics during the rest of the day. In an attempt to reveal the adaptive significance of this differential movement pattern, the following hypotheses were tested: (i) increase of the intercepted solar radiation and photosynthesis, (ii) avoidance of photoinhibitory conditions, (iii) amelioration of water-use efficiency and (iv) adjustment of the leaf temperature microenvironment. No evidence was found in support of the first two hypotheses. A slight difference toward a better water use was found for the moving compared with immobilized leaves, in combination with a better cooling effect. [ABSTRACT FROM AUTHOR]