Effects Of Elevated Atmospheric CO₂ Concentration,Nitrogen Reduction,and LED Supplemental Light On Strawberry Growth,Quality,and Yield

The continuous increase in global atmospheric CO₂ concentration not only promotes crop photosynthesis but also affects various physiological and morphological traits of crops,improves plant water use efficiency,and thus affects crop growth and final yield.Due to atmospheric environmental pollution caused by climate change,fossil fuel combustion,deforestation,etc.,reduced solar radiation has occurred in most areas of China.Light intensity has a significant impact on crop growth and development,directly or indirectly affecting the structure and activity of crop photosynthetic apparatus.At the same time,due to rainy weather in spring and autumn,crop photosynthesis is inhibited,leading to a serious reduction in crop productivity.Nitrogen is one of the essential mineral elements for crop growth,and the nitrogen concentration directly affects crop nitrogen metabolism,thereby affecting crop growth and development.However,excessive use of nitrogen fertilizer not only reduces fertilizer utilization efficiency but also harms the ecological environment.To address the environmental pollution caused by future increases in atmospheric CO₂ concentration,weakened lighting,and solve the problem of environmental pollution caused by excessive application of nitrogen fertilizer,this experiment used"Hongyan"strawberries as materials and set up 12 treatments,including ambient CO₂ concentration and reduced nitrogen（CN^-）,ambient CO₂ concentration and normal nitrogen（CN）,elevated CO₂ concentration and reduced nitrogen（C⁺N^-）,elevated CO₂ concentration and normal nitrogen（C⁺N）,natural light and reduced nitrogen（LN-）,natural light and normal nitrogen（LN）,LED supplemental light and reduced nitrogen（L⁺N^-）,LED supplemental light and normal nitrogen（L⁺N）,environmental CO₂ concentration and natural light（CL）,environmental CO₂ concentration and LED supplemental light（CL⁺）,elevated CO₂ concentration and environmental light（C⁺L）,and elevated CO₂ concentration and LED supplemental light（C⁺L⁺）.The study investigated the pairwise interactive effects of atmospheric CO₂ concentration,nitrogen,and light on strawberry production from plant morphology,photosynthetic characteristics,quality indicators,and yield indicators.The purpose was to provide theoretical basis and technical support for rational application of nitrogen fertilizer and utilization of elevated atmospheric CO₂ concentration in future greenhouse fruit and vegetable production under the conditions of elevated atmospheric CO₂ concentration and low light intensity.The main resluts of this experiment are as follows:（1）Under conditions of elevated atmospheric CO₂ concentration,strawberry yield,fruit quantity,and fruit weight all increased,possibly due to CO₂increasing the plant’s photosynthetic rate,thereby increasing dry matter accumulation.At the same time,under conditions of elevated atmospheric CO₂ concentration,the above-ground biomass of nitrogen-depleted plants is lower than that of normally fertilized plants,with no significant difference in yield.Elevated atmospheric CO₂ concentration and nitrogen reduction have no significant effect on morphological indexes of strawberry,but elevated atmospheric CO₂ concentration has a greater effect on fruit texture,increasing total soluble sugar content and decreasing organic acid content.Under conditions of elevated atmospheric CO₂ concentration,both normally fertilized and nitrogen-depleted plants cause a decrease in the soluble protein content of strawberry fruit,total antioxidant capacity,and antioxidant content,and elevated atmospheric CO₂ concentration significantly reduces the concentration of N,P,and K in various organs.（2）LED supplemental light can improve strawberry growth and yield.In normally fertilized and nitrogen-reduced treatments,LED supplemental light can increase total above-ground biomass by 14.52%and 15.78%,respectively.Looking at the total strawberry yield harvested during the entire growing season,LED supplemental light and nitrogen reduction have no significant interactive effect on strawberry yield.LED supplemental light significantly increased the total fruit yield throughout the growing season,but different nitrogen levels had no significant effect on the total fruit yield throughout the growing season.Nitrogen supply has a certain impact on strawberry growth and mineral element absorption.The total above-ground biomass of normally fertilized plants is 7.02%higher than that of nitrogen-depleted plants.Light intensity also affected the absorption and metabolism of mineral elements in strawberries.Different light intensities and nitrogen supply levels had no significant interactive effect on the phosphorus concentration in strawberry stems,leaves,and fruit,but have a significant effect on the potassium concentration in strawberry stems,leaves,and fruit.In normally fertilized and nitrogen-reduced treatments,LED supplemental light treatments reduce the potassium concentration in plant stems by 4.03%and 3.67%,in leaves by 2.32%and 2.69%,and in fruit by 5.62%and 3.51%,respectively.（3）LED supplemental light treatments also had a certain effect on the soluble sugar content of strawberry,and light intensity and nitrogen supply levels also affect the quality of strawberry fruit.Different light intensities and nitrogen supply levels had no significant interactive effect on the soluble sugar and titratable acid content of strawberry fruit.In normally fertilized and nitrogen-reduced treatments,LED supplemental light treatments increased the soluble sugar content of strawberries,but had a lowering effect on the titratable acid content.Due to the warming effect,the fruit quality of strawberry at different growth stages showed seasonal differences.（4）Elevated atmospheric CO₂ concentration can enhance the photosynthesis of C₃plants such as strawberry,but long-term exposure to high CO₂ concentration can lead to a strong down-regulation of photosynthesis in strawberries.Elevated atmospheric CO₂ concentration and LED supplemental light significantly promoted the growth and aboveground biomass of strawberries,with a 51.3%increased in the combined treatment of elevated atmospheric CO₂ concentration and LED supplemental light compared to the control treatment.（5）Elevated atmospheric CO₂ concentration significantly increased the soluble sugar content of strawberry fruits,but significantly reduces the soluble protein content,titratable acidity,total flavonoid content,total phenolic content,and total antioxidant capacity.LED supplemental light significantly increases the soluble sugar content,soluble protein content,anthocyanin content,total flavonoid content,total phenolic content,and total antioxidant capacity of strawberry fruits.In the future,under conditions of elevated atmospheric CO₂ concentration,LED supplemental light can partially mitigate the down-regulation effect of crop photosynthesis and compensate for the negative effect of decreased antioxidant compound content caused by the increase in atmospheric CO₂ concentration by supplementing light with LED lamps.In summary,reducing nitrogen application under elevated atmospheric CO₂ concentration conditions will not significantly affect the growth,quality,and yield of strawberry.Elevated atmospheric CO₂ concentration and LED supplemental light can enhance the photosynthesis of C₃plants such as strawberry,promote crop growth,and had a positive impact on yield and yield components.In the future,LED supplemental light can partially or completely counteract the negative impact of elevated atmospheric CO₂ concentration on the content of antioxidant compounds.