NUTRIENT DELIVERY AND WATER MANAGEMENT FOR PRODUCING LETTUCE (Lactuca sativa L.)FOR BIOREGENERATIVE LIFE SUPPORT SYSTEMS

Space farming for fresh food production is a key requirement for the success of long duration space missions through self-sufficiency and human life sustainment (physical and psychological well-being) in space colonies. Plant production contributes to atmosphere revitalizing, water purification and waste product recycling as well. However, several obstacles have to be overleaped including abnormal environmental conditions, space energy and resources limitations. Therefore choosing the appropriate cultivar is as important as the species selection, since such choice can influence the obtained fresh biomass, water use efficiency (WUE), growing cycle duration, qualitative features and more importantly quality conservation after harvest. So far, several studies have suggested various crop species highlighting the varied response to environmental constraints in a genotype and cultivar dependent manner. The aim of the present study was to evaluate six lettuce cultivars belonging to different groups and with different leaf colors under low and optimal light intensity in order to identify the most promising genotypes for incorporation in controlled life support systems. Then two differently pigmented butterhead Lactuca sativa L. (red and green Salanova) were chosen and assessed in term of morphometric, mineral, bioactive compounds and physiological parameters. Through precise control of the nutrient solution (NS), closed soilless systems effectuate targeted manipulation of plant secondary metabolites that constitute health-promoting components of human daily diet. An NFT system in a controlled-environement growth chamber was presently employed to grow these cultivars for 19 day, under optimal light and to assess the effect of NS macronutrient-based concentration, proportion (Ca/Mg/K) and biofortification (Iron and Selenium) effect on the bioactive profile of red and green-pigmented Salanova. In this study, morphometric analysis, mineral composition, antioxidant activitiy, phenolic acids and carotenoids content where studied for all treatments: (i) full, half- and quarter-strength corresponding to EC 1.5, 0.75 and 0.5 dS m-1 , (ii) Macrocations proportions, (iii) four Fe concentrations in the nutrient solution (0.015 control, 0.5, 1.0 or 2.0 mM Fe) and (iv) six Se concentrations (0, 8, 16, 24, 32, 40 μM as sodium selenite). Baby Romaine plants had a better agronomic performance than the rest of the tested cultivars under low light intensity conditions, indicating a more efficient light harvesting mechanism. As for intrinsic water use efficiency (WUEi), it was the highest for baby Romaine and red oak leaf cultivars, regardless of light regime. Chicoric acid was the major detected compound, followed by chlorogenic, caffeoyl-tartaric and caffeoyl-meso-tartaric acids. The major phenolic compound (chicoric acid) and total phenolic acids were not affected by light intensity, whereas the rest of the detected phenolic compounds showed a varied response to light intensity. Regarding cultivars response, red oak leaf was mostly affected by low light intensity showing the highest content in chicoric acid and consequently in total phenolic acids content, while under optimal light conditions red Salanova exhibited the highest phenolic profile. The main detected pigments were β-cryptoxanthin and violaxanthin + neoxanthin, followed by lutein and β-carotene. All the target carotenoids decreased significantly under low light intensity, with red Salanova having a distinct profile of carotenoids. Red Salanova registered a biomass of 130 g at harvesting (19 DAT), 22.1 % bigger than green Salanova, with a water uptake of 1.42 L during the full growing cycle and a WUE of 91.9 g L-1, 13.8 % higher than the green cultivar. The latter had accumulated more P, K, Ca, Mg and 37.2 % more nitrate than red Salanova that in its turn had higher relative water content, leaf total and osmotic potential and higher SPAD index. Red Salanova as well exhibited at harvest around two-fold greater lipophilic antioxidant activity and total phenols, and around six-fold greater ascorbic acid. On the other hand the half-strength nutrient solution reduced fresh yield of both cultivars by 14%, however, moderate nutrient stress (half-strength NS) boosted red Salanova concentrations of ascorbate, chlorogenic, chicoric, caffeoyl-meso-tartaric and total phenolic acids, and anthocyanins by 266%, 199%, 124%, 251%, 162% and 380%, respectively compared to control full-strength NS. Moreover, red Salanova plants treated with elevated Mg (Solution of high proportion of Mg) contained higher amounts of pigments. Chicoric and chlorogenic acid were the main phenolic compounds in SMg, and SCa and SMg red Salanova plants, respectively. As for the biofortification, thhe percentage of yield reduction in comparison to the control treatment was 5.7%, 13.5% and 25.3% at 0.5, 1.0 and 2.0 mM Fe, respectively. Irrespective of the cultivars, the addition of 1.0 mM and especially 2 mM Fe in the nutrient solution induced an increase in the Fe concentration of lettuce leaves by 20.5% and 53.7%, respectively. No significant effects of Fe application on phenolic acids and carotenoid profiles were observed in green Salanova. However, increasing Fe concentration in the nutrient solution to 0.5 mM triggered a spike in chlorogenic acid and total phenolics in red Salanova lettuce by 110.1% and 29.1% compared to the control treatment, respectively; moreover, increased accumulation of caffeoyl meso tartaric phenolic acid by 31.4% at 1.0 mM Fe and of carotenoids violaxanthin, neoxanthin and β-carotene by 37.0% at 2.0 mM Fe were also observed in red Salanova compared to the control (0.015 mM Fe) treatment. Whereas, leaf selenium content increased significantly with Se application in both cultivars, in particular, the red leaf lettuce accumulated 57% more Se than the green one. Regardless the cultivar, the addition of 16 μM Se in the nutrient solution improved the content of all detected phenolic acids, and at the same dose in red Salanova, a substantial increase in anthocyanins content (184%) was also recorded. In conclusion, cultivation of mixed lettuce cultivars is the most possible scenario for space farming where some cultivars could provide adequate amounts of fresh biomass while others could contribute to covering daily diet requirements in nutrients and health beneficial compounds. Moreover, the high phenolics and ascorbic acid contents of red Salanova represent natural sources of antioxidants to enrich human diet, and more convenient agronomic requirements make it an appropriate cultivar candidate for bio-regenerative life support systems, plus a nutritional eustress constitute effective means to increase phytochemical content and optimize year-round production of lettuce in closed soilless systems. In conclusion, nutrient solution management and biofortification could be used as an effective cultural practice to increase bioactive properties and quality of hydroponically grown lettuce

An appraisal of urine derivatives integrated in the nitrogen and phosphorus inputs of a lettuce soilless cultivation system

Reinforcing and optimizing sustainable food production is an urgent contemporary issue. The depletion of natural mineral resources is a key problem that is addressed by recycling mined potassium and phosphorus, and nitrogen, whose production depends on very high energy input. A closed-loop approach of fertilizer use asserts the necessity for efficient management and practices of organic waste rich in minerals. Human-derived urine is an underutilized yet excellent source for nitrogen fertilizer, and, in this study, processed urine fertilizer was applied to greenhouse soilless cultivation of lettuce (Lactuca sativa L.) cv. Grand Rapids. Biomass increase, biometric parameters, soil plant analysis development (SPAD) index, minerals, and organic acids content of lettuce were analyzed. From eight different urine fertilizer products generated, K-struvite, urine precipitate-CaO, and the liquid electrodialysis (ED) concentrate supported the growth of lettuce similar to that of commercial mineral fertilizer. ED concentrate application led to the accumulation of potassium (+17.2%), calcium (+82.9%), malate (+185.3%), citrate (+114.4%), and isocitrate (+185.7%); K-struvite augmented the accumulation of magnesium (+44.9%); and urine precipitate-CaO induced the highest accumulation of calcium (+100.5%) when compared to the control, which is an added value when supplemented in daily diet. The results underlined the potential of nitrogen- and phosphate-rich human urine as a sustainable source for the fertilization of lettuce in soilless systems

Mars Regolith Simulant Ameliorated by Compost as In Situ Cultivation Substrate Improves Lettuce Growth and Nutritional Aspects

Heavy payloads in future shuttle journeys to Mars present limiting factors, making self-sustenance essential for future colonies. Therefore, in situ resources utilization (ISRU) is the path to successful and feasible space voyages. This research frames the concept of planting leafy vegetables on Mars regolith simulant, ameliorating this substrate’s fertility by the addition of organic residues produced in situ. For this purpose, two butterhead lettuce (Lactuca sativa L. var. capitata) cultivars (green and red Salanova®) were chosen to be cultivated in four dierent mixtures of MMS-1 Mojave Mars simulant:compost (0:100, 30:70, 70:30 and 100:0; v:v) in a phytotron open gas exchange growth chamber. The impact of compost rate on both crop performance and the nutritive value of green- and red-pigmented cultivars was assessed. The 30:70 mixture proved to be optimal in terms of crop performance, photosynthetic activity, intrinsic water use eciency and quality traits of lettuce. In particular, red Salanova® showed the best performance in terms of these quality traits, registering 32% more phenolic content in comparison to 100% simulant. Nonetheless, the 70:30 mixture represents a more realistic scenario when taking into consideration the sustainable use of compost as a limited resource in space farming, while still accepting a slight significant decline in yield and quality in comparison to the 30:70 mixture

Morpho-Anatomical, Physiological, and Mineral Composition Responses Induced by a Vegetal-Based Biostimulant at Three Rates of Foliar Application in Greenhouse Lettuce

A promising strategy for sustainably increasing the quality and yield of horticultural products is the use of natural plant biostimulants. In this work, through a greenhouse experiment, we evaluated the effect of a legume-derived biostimulant at three dose treatments (0.0 control, 2.5 mL L−1, and 5.0 mL L−1) on the yield performance, nutrients traits, leaf anatomical traits, gas exchanges, and carbon photosynthetic assimilation of greenhouse lettuce. The lettuce plants were foliar sprayed every 7 days for 5 weeks. The application of plant biostimulant, at both lower and higher dosages, increased the nutrient use efficiency, root dry weight, and leaf area. However, it is noteworthy that the 5.0 mL L−1 dose enhanced photosynthetic activity in the early phase of growth (15 DAT), thus supplying carbon skeletons useful for increasing the number of leaves and their efficiency (higher SPAD), and for boosting nutrient uptake (P, S, and K) and transport to leaves, while the 2.5 mL L−1 dose exerted specific effects on roots, increasing their dimension and enabling them to better use nitrate and Ca. A higher dose of biostimulant application might find its way in shorter growing cycle, thus presenting new horizons for new lines of research in baby leaves production

Can Seaweed Extract Improve Yield and Quality of Brewing Barley Subjected to Different Levels of Nitrogen Fertilization?

Barley is the primary matrix for malting process of beer production. Farmers count on increasing cultivation inputs, especially nitrogen fertilization, in order to reach a higher yield. Nevertheless, an overuse of nitrogen, besides causing environmental damages, can determine a deterioration of quality traits of malting barley, in particular an increase in grains protein content, which should range between 10 and 11% as required by the mating industry. Over two successive years, barley was grown under 4 different nitrogen (N) doses—0 kg N ha−1—N0; 20 kg N ha−1—N20; 40 kg N ha−1—N40 and 60 kg N ha−1—N60, and subject to a biostimulant treatment (Ecklonia maxima seaweed extract). Barley yield and growth parameters increased with nitrogen and seaweed application. N40 was already sufficient in the second year to reach the plateau of the highest production. Biostimulant application increased 17.9% the nitrogen use efficiency, 15.7% the biomass production, and 17.0% the yield with respect to untreated plants. Our results indicate that a significant reduction in nitrogen is possible and desirable, combined with the application of a plant-based biostimulant like seaweed extract, which determines an improvement in nitrogen use efficiency, assuring a higher production and lower fertilization inputs

Application of Trichoderma harzianum, 6-pentyl-α-pyrone and Plant Biopolymer Formulations Modulate Plant Metabolism and Fruit Quality of Plum Tomatoes

Many Trichoderma are successfully used to improve agriculture productivity due to their capacity for biocontrol and to stimulate plant growth and tolerance to abiotic stress. This research elucidates the effect of applications with Trichoderma harzianum strain T22 (T22), or biopolymer (BP) alone or in combination (BP + T22 or BP + 6-pentyl-α-pyrone (6PP); a Trichoderma secondary metabolite) on the crop performance, nutritional and functional quality of greenhouse tomato (Solanum lycopersicum L. cultivar Pixel). T22 elicited significant increases in total yield (+40.1%) compared to untreated tomato. The content of lycopene, an important antioxidant compound in tomatoes, significantly increased upon treatment with T22 (+ 49%), BP + T22 (+ 40%) and BP + 6PP (+ 52%) compared to the control. T22 treatments significantly increased the content of asparagine (+37%), GABA (+87%) and MEA (+102%) over the control; whereas BP alone strongly increased GABA (+105%) and MEA (+85%). The synthesis of these compounds implies that tomato plants are able to reuse the photorespiratory amino acids and ammonium for producing useful metabolites and reduce the pressure of photorespiration on plant metabolism, thus optimizing photosynthesis and growth. Finally, these metabolites exert many beneficial effects for human health, thus enhancing the premium quality of plum tomatoes

Genotype and Successive Harvests Interaction Affects Phenolic Acids and Aroma Profile of Genovese Basil for Pesto Sauce Production

Basil (Ocimum basilicum L.) is an essential ingredient of the Mediterranean cuisine due to its distinctive aroma. Genovese basil leaves are used to prepare "pesto", a condiment that has always caught the interest of consumers and producers. Usually, basil for industrial processing is harvested more than once to extract a higher yield. However, successive cuts can affect quality traits that play a crucial role in defining the product's final sensory profile. This research was aimed to evaluate the impact of cut on the quantitative and qualitative properties of three Genovese basil cultivars (Aroma 2, Eleonora and Italiano Classico) grown in an open field. Nitrate content, phenolic acids and aromatic profile were determined by ion chromatography (IC), high-performance liquid chromatography (HPLC), and gas chromatography coupled to a mass spectrometer (GC/MS) analysis, respectively. The second harvest increased fresh biomass and total phenolic acids content by 172% and 413%, respectively, with Italiano Classico recording the highest values. The combination of second-cut Aroma 2 yielded the lowest nitrate (473.8 mg kg-1 of fresh weight) and Eugenol (2.4%) levels. In the second harvest, Eleonora showed an increase in eugenol and trans-α-bergamotene of 75.3% and 48.2%, respectively; whereas, eucalyptol and β-cis-ocimene decreased by 34.4% and 51.6%, respectively. Although successive harvests may increase basil yield and quality overall, the cultivar-dependent response to successive cuts needs to be accounted for in order to accomplish standardization of industrial "pesto" sauce

Protein Hydrolysate Combined with Hydroponics Divergently Modifies Growth and Shuffles Pigments and Free Amino Acids of Carrot and Dill Microgreens

Microgreens are the new sophisticated commodity in horticulture that boost the human diet with bioactive metabolites and garnish it with colors and tastes. Microgreens thrive well when cultivated in soilless systems, of which closed-loop soilless systems combined with biostimulant application can provide a sustainable, innovative method of growing microgreens. Daucus carota L. and Anethum graveolens L. microgreens were grown in greenhouse conditions implementing a floating raft system combined with a protein hydrolysate of leguminous origin as root application (0.3 mL L−1 nutrient solution). Growth, colorimetric parameters, macronutrients, chlorophylls, carotenoids, carbohydrates, free amino acids, and soluble proteins were assessed. The use of a protein hydrolysate in the nutrient solution engendered an increase in anthocyanins (+461.7%) and total phenols (+12.4%) in carrot, while in dill, the fresh yield (+13.5%) and ascorbic acid (+17.2%) increased. In both species, soluble proteins and total free amino acids increased by 20.6% and 18.5%, respectively. The floating raft system proved to be promising for microgreens and can ease the application of biostimulants through root application. Future research should also investigate the yield and nutritional parameter responses of other species of microgreens with the aim of large-scale sustainable production

Assessment of yield and nitrate content of wild rocket grown under salinity and subjected to biostimulant application

Soil secondary salinity due to irrigation is a condition that frequently occurs in Mediterranean areas, and negatively affects crop growth and yield. Biostimulants are proven to alleviate the detrimental effect of salinity on plant growth and production. Four increasing saline concentration levels of water irrigation reaching 6.0 dS m-1 (Electrical Conductivity - EC) were combined with foliar biostimulant treatments (tropical plants and a protein hydrolysate) in pots containing wild rocket. The combined effect of experimental factors improved the SPAD index with greater increases in the EC4 and EC6 plants (+9 and +12% compared to untreated, respectively) but also caused an increase in nitrate content (+48%, on average, compared to the untreated control) without exceeding the EC legal threshold. Overall, for the other parameters analyzed, the response of wild rocket both to application of both salinity and biostimulant was consistent with previous studies. Our results show that biostimulant effectiveness in alleviating the detrimental effect of salinity was not evident for all parameters analyzed. In addition, harvest time affected most parameters, showing the important role of growing conditions in modulating plant response to salinity stress when biostimulants are applied. Plant response thus seems to depend on biostimulant application (type, dose, timing), growing conditions, and genetic traits