با همکاری انجمن علمی منظر ایران
نوع مقاله : مقالات پژوهشی
نویسندگان
1 فارغ التحصیل ارشد دانشگاه زنجان
2 استاد - گروه علوم باغبانی، دانشکده کشاورزی، دانشگاه زنجان، شهر زنجان، ایران
3 استادیار - گروه علوم باغبانی ، دانشکده کشاورزی، دانشگاه زنجان، شهر زنجان، ایران
4 دانشیار - گروه علوم باغبانی، دانشکده کشاورزی، دانشگاه زنجان، شهر زنجان، ایران
کلیدواژهها
عنوان مقاله English
نویسندگان English
Introduction
Vertical farming has emerged as a transformative agricultural strategy, designed to meet the escalating demands for sustainable food production in an era of rapid global urbanization and climate change. By capitalizing on vertical space, this innovative system offers a compelling solution to the critical challenges of diminishing arable land and water scarcity, enabling substantial increases in crop yield per unit area. Lettuce (Lactuca sativa L.), with its short growth cycle, compact morphology, and high commercial value as a fresh salad green, is widely regarded as an exemplary crop for cultivation in such controlled-environment systems. However, a significant technical challenge inherent to vertical farming is the development of pronounced environmental gradients within the cultivation structure. Key factors, particularly light intensity and air temperature, often vary considerably between the top and bottom levels. These non-uniform conditions create distinct microclimates that can differentially influence plant physiology, leading to inconsistencies in growth, development, and the accumulation of important phytochemicals. Consequently, achieving uniform, high-quality, and high-yielding production requires precise optimization of the cultivation environment. Two of the most critical and manageable factors in this regard are the vertical positioning of plants (cultivation height) and the selection of genetically suitable cultivars. Different heights within a system experience unique combinations of light and temperature, which can either promote or hinder growth and metabolic processes. Simultaneously, different lettuce cultivars possess inherent genetic traits that determine their response to these two factors, influencing their potential for biomass production or synthesis of quality-related compounds such as antioxidants. Therefore, understanding the individual and interactive effects of cultivation height and cultivar is fundamental to optimizing vertical farming protocols. This research was specifically conducted to address this knowledge gap, aiming to systematically quantify how different vertical cultivation heights influence the agronomic performance and nutritional quality of two distinct and commercially important lettuce cultivars: the green-leaf Lollo Bionda and the red-leaf Lollo Rossa.
Materials and Methods
This study was conducted in a research greenhouse using a vertical hydroponic tower system. A split-plot design in a randomized complete block design with four replications was applied. The main plot factor included three cultivation height levels: 40–70 cm (Low), 115–145 cm (Medium), and 190–220 cm (High). The sub-plot factor comprised two lettuce cultivars: Lollo Bionda (green-leaf) and Lollo Rossa (red-leaf). Plants were grown in a coarse perlite substrate with a recirculating Hoagland nutrient solution. Environmental parameters (light intensity and temperature) were monitored across heights. At harvest, quantitative traits (leaf number, plant height, leaf area index, and yield per unit area) and qualitative traits (total chlorophyll, anthocyanin, total phenols, and nitrate content) were measured using standard analytical methods.
Results and Discussion
The experimental results provided clear evidence of the significant influence exerted by both cultivation height and genetic cultivar.Cultivation height had a profound impact on growth and yield parameters. The intermediate height level (Level 2: 115–145 cm) consistently yielded the best performance, producing plants with the highest values for leaf number (17.6 leaves per plant), plant height (24.3 cm), leaf area index, and consequently, the maximum fresh yield per unit area (659.9 g m⁻²). This optimal outcome suggests that Level 2 provided a balanced microclimate, avoiding the light limitation prevalent at the lower level and mitigating the potential combined stress of excessive light and elevated temperature at the highest level. A strong and independent main effect of cultivar was also highly evident. Lollo Bionda demonstrated superior vegetative growth, achieving significantly higher values for leaf number (20.6), plant height (24.9 cm), LAI (0.15), and plot-level fresh yield (793.3 g m⁻²), highlighting its genetic predisposition for high biomass production in controlled environments. In a notable contrast, Lollo Rossa excelled in the accumulation of specific secondary metabolites and compounds related to quality. It exhibited significantly higher concentrations of anthocyanin (0.66 µmol g⁻¹ FW), total phenolic compounds (1.14 mg g⁻¹), and nitrate. Importantly, a statistically significant interaction between cultivation height and cultivar was detected for these quality traits. The most pronounced accumulation of health-promoting compounds occurred specifically in Lollo Rossa plants grown at the highest level (Level 3). In this specific treatment, anthocyanin content reached 0.83 µmol g⁻¹ FW and total phenolics reached 1.15 µg mL⁻¹. This indicates that the environmental conditions at the top of the tower, characterized by higher light and temperature, acted as a mild abiotic elicitor, stimulating the plant's phenylpropanoid biosynthetic pathway associated with defense and antioxidant production. Similarly, nitrate concentration peaked in Lollo Rossa at Level 3 (1075 µg g⁻¹ DW), a common physiological response often linked to the inhibition of the nitrate reductase enzyme activity under warmer conditions, leading to disrupted assimilation and tissue accumulation. Total chlorophyll content was predominantly determined by cultivar, with Lollo Bionda containing significantly more (0.71 mg g⁻¹ FW) than Lollo Rossa. From a systemic productivity perspective, a key agronomic result was the total harvestable yield from the vertical system, which reached 1.76 kg of fresh lettuce per square meter of floor area. This figure notably surpasses the standard yield range reported for conventional, single-layer horizontal hydroponic or soil-based lettuce production (1.1–1.5 kg m⁻²), providing tangible evidence of the enhanced spatial efficiency achievable through vertical farming.
Conclusion
This study confirms that vertical farming effectively increases lettuce production density. Optimal results require science-based management, with the intermediate height (115–145 cm) identified as best for growth and yield. Cultivar selection should align with production goals: Lollo Bionda for higher biomass yield, and Lollo Rossa for enhanced nutritional quality and color, though nitrate levels must be monitored at higher tiers. The interaction between height and cultivar supports precision management. These findings offer a practical framework for optimizing vertical farming systems. Future research should focus on advanced climate control and broader cultivar screening.
کلیدواژهها English
