Effects Of Elevated Co₂and Temperature On Plant Growth, Fruit Yield And Quality Of Strawberry（Fragaria×Ananassa Duch.） At Two Levels Of Nitrogen Application

Photosynthesis, root growth, nitrogen allocation, yield and quality of strawberry {Fragaria×ananassa Duch.) grown in growth chambers were investigated in a factorial design of carbon dioxide (CO2), nitrogen and temperature.Photosynthesis, chlorophyll fluorescence, root architecture and nitrogen content were measured in strawberry during fruit development. Number, size, dry weight, total achenes and total aborted achenes of fruit per plant were determined. Quality indices such as fruit nitrogen content, non-structural carbohydrate (glucose, fructose and sucrose), total antioxidant capacity and antioxidant compounds were measured.Photosynthesis and stomatal conductance acclimated to elevated CO2independently. Photosynthetic acclimation at elevated CO2was resulted from reduced investment of nitrogen into carboxylation, electron transport, and Pi-regeneration capacity. Under elevated CO2, reduced nitrogen concentrations in different organs were not only caused by dilution effect of photosynthate, but also the effect of nitrogen redistribution from vegetative into generative organs by increasing nitrogen-use efficiencies of leaf and root during fruit development. Root at low nitrogen sensitively increased in response to elevated CO2. This response might be caused by forming of root cortical aerenchyma (RCA) which could increase nitrogen use efficiency by reallocating nitrogen in root. Strawberry yield was negatively impacted by elevated temperature and the adverse effects were more severe at elevated CO2. Warmer foliage temperature at elevated CO2inhibiting flower induction through devernalization and changing gibberellins’biosynthesis was assumed to cause yield reduction. Meanwhile, nitrogen application reduced fruit number by reducing the increasing export of sucrose towards the shoot apical meristem at floral transition. The increased dry matter-content of fruit was probably due to increased non-structural carbohydrates sourced from the increased net photosynthetic rate of strawberries at elevated CO2. The fruit nitrogen content, antioxidant compounds and total antioxidant capacity decreased at elevated CO2. These decreases mainly resulted from dilution due to accumulation of non-structural carbohydrates, and were also modified by the effect of elevated CO2on the reduction of plant antioxidant status, because these decreases were proportional to the increase of dry matter-content at elevated CO2.Redistribution of nitrogen during generative growth at elevated CO2might further exacerbate photosynthetic down-regulation, accelerate leaf senescence, influence seedling establishment and affect seed quality, but increase seed quantity. It may be a fairly common phenomenon in generative plants that seed competition increases at the cost of mother plant’s growth capacity at elevated CO2. Meanwhile, our study confirmed that the warmer temperature at elevated CO2might decrease fruit yield, especially the species grown under low temperature condition or had a strict requirement for winter chilling.