Regulatory effects of laser irradiation on greenhouse-grown strawberry productivity

【Objective】Facility cultivation is one of the primary modes for strawberry cultivation. However, the shading effect of glass, shading nets, and plastic films limits the yield and economic benefits of greenhouse- grown strawberries due to reduced light intensity. Supplementing with artificial light sources like Light Emitting Diode (LED) is an effective strategy to address low-light conditions. Previous LED supplementation has predominantly used long-term high-intensity modes, leading to increased energy consumption and economic costs. Laser technology amplifies light through stimulated emission but has safety limitations in horticultural settings, particularly with short-term high-intensity helium-neon lasers due to their high energy output. Semiconductor lasers, characterized by high photoelectric conversion efficiency, offer potential energy savings. In this study, the semiconductor lasers were utilized to investigate the regulatory effects of long-term low-intensity laser modes on strawberry yield in facility cultivation, aiming to provide new insights into addressing issues such as limited yield due to low light and high energy consumption of supplemental lighting.【Methods】In this study, the facility cultivated Hongyan strawberries served as materials and soil cultivation experiments were carried out in plastic greenhouses. From the strawberry seedling stage to maturity, low-intensity [0, 0.25, 0.5, and 1 μmol·m-2 ·s -1 (PPFD)] semiconductor laser treatments were performed daily from 6:00 to 18:00 for 5months. The lasers were positioned 3 m above the ground with a diffuser to ensure uniform distribution over a 30 m² area. During the mature stage, the gas exchange parameters of strawberry leaves (net photosynthetic rate, intercellular CO2 concentration, stomatal conductance, and transpiration rate), aboveground nutrient accumulation (abundant and moderate nutrient elements such as nitrogen, phosphorus, potassium, magnesium, and calcium), growth morphology indicators (plant height, biomass, leaf area, and specific leaf weight), fruit yield and its constituent factors (fruit quantity and single fruit weight), fruit sugar and acid content (soluble solids, total soluble sugar, titratable acid and sugar/acid ratio), and other indicators were measured to explore the effects of low-intensity long-term laser irradiation mode on strawberry photosynthesis, nutrient accumulation, growth and development, yield, and flavor quality. 【Results】Low intensity laser treatment with 0.25, 0.5, and 1 PPFD increased the yield of strawberries. The yield enhancement showed an increasing trend followed by stability with increasing laser intensity, with no significant difference between 0.5 and 1 PPFD treatments, indicating optimal effectiveness. Compared with the control, 0.5 and 1 PPFD laser treatments significantly increased the number of fruits and single fruit weight. Low intensity laser improved strawberry fruit yield by increasing single fruit weight and fruit quantity. Under laser irradiation conditions, the number of strawberry fruits increased by 12.3%-14.0%, the weight of individual fruits increased by 19.8%-23.3%, and the overall yield increased by 34.5%-40.6%. The 0.5 and 1 PPFD laser treatments increased the plant height, aboveground nutrient organ biomass, and leaf area of strawberry plants, promoting plant nutritional growth, while the 0.25 PPFD laser treatment did not significantly improve plant height, biomass, and leaf area. The comparison of leaf weight between 0.5 and 1 PPFD laser treatments indicated that laser treatment did not affect leaf thickness. The 0.25 PPFD laser treatment had no significant effect on the gas exchange parameters of the leaves. The 0.5 and 1 PPFD laser treatments significantly increased the net photosynthetic rate by 8.9% to 9.4%, without affecting stomatal conductance and transpiration rate, but reducing intercellular CO2 concentration. Laser enhanced photosynthetic capacity, and the increase in net photosynthetic rate was related to non-stomatal factors. The laser treatments at 0.25, 0.5, and 1 PPFD significantly affected the accumulation of aboveground nutrient elements in strawberry plants. With the increase of laser intensity, the accumulation of large elements such as nitrogen, phosphorus, and potassium showed a trend of first increasing and then stabilizing, while the accumulation of medium elements like magnesium and calcium showed an increasing and unchanged trend, respectively. Laser treatment was beneficial for the accumulation of elements such as nitrogen, phosphorus, potassium, and magnesium, but had no influence on the accumulation of calcium. According to correlation analysis, strawberry fruit yield was significantly and positively correlated with leaf area, net photosynthetic rate, as well as nitrogen, phosphorus, potassium and magnesium accumulation, with strawberry fruit yield showing the highest correlation with phosphorus accumulation. Under laser irradiation conditions, larger leaf area, higher net photosynthetic rate, and accumulation of nutrients (nitrogen, phosphorus, potassium, and magnesium) were beneficial for increasing fruit yield. In addition, compared to the control, laser treatment had no effect on soluble solids, total soluble sugar, titratable acid, and sugar/acid ratio.【Conclusion】Long term treatment with low-intensity laser (0.5 and 1 PPFD) could promote biomass accumulation by improving photosynthetic and nutrient absorption abilities while balancing fruit quality, effectively increasing fruit quantity, single fruit weight, and comprehensive yield. Unlike traditional fill lights, semiconductor lasers can induce and promote plant growth, development, and yield increase in a low-intensity mode, providing a low-cost and high-efficiency“light fertilizer”for facility agriculture.