Induced Leaf Intercellular CO₂, Photosynthesis, Potassium and Nitrate Retention and Strawberry Early Fruit Formation Under Macronutrient Limitation

Relationships between induced high leaf intercellular CO₂ concentrations, leaf K⁺ and NO₃⁻ ion movement and early fruit formation under macronutrient limitation are not well understood. We examined the effects and interactions of reduced K/N input treatments on leaf intercellular CO₂, photosynthesis rate, carboxylation and water use efficiency, berry formation as well as leaf/fruit K⁺, NO₃⁻ and photosynthate retention of strawberry (Fragaria × ananassa Duch.) to enhance low-input agriculture. The field study was conducted in Nova Scotia, eastern Canada during 2009-2010. The experimental treatments consisted of five K₂O rates (0, 6, 12, 18, and 24 kg ha(-1)) and five N rates (0, 5, 10, 15, and 20 kg ha(-1)), representing respectively, 0, 25, 50, 75, and 100 % of regular macronutrient recommendations based on the soil testing. The treatments were arranged in a split-plot design with three blocks in the field. The cultivar was 'Mira', a June-bearing crop. The results showed that strawberry plants treated with 25 %-reduced inputs could induce significantly higher leaf intercellular CO₂ concentrations to improve plant photosynthesis, carboxylation and water use efficiency and translocation of leaf/fruit K⁺ and dissolved solids, which could advance berry formation by 6 days and produce significantly higher marketable yields (P < 0.05). Higher leaf intercellular CO₂ inhibited leaf/fruit NO₃⁻ ion retention, but this inhibition did not occur in leaf/fruit K⁺ retention. Linear interactions of the K/N treatments were significant on fruit marketable yields, intercellular CO₂, net photosynthesis, leaf transpiration rates, and leaf temperatures (P < 0.05). It was concluded that higher leaf CO₂ could enhance plant photosynthesis, promote plant carboxylation and water use efficiency, and advance berry formation, but it could inhibit leaf NO₃⁻ retention. This inhibition did not find in leaf K⁺ ion and dissolved solid retention. Overlay co-limitation of leaf intercellular CO₂ and translocation of leaf/fruit K(+)/NO₃ (-) and total dissolved solids could constrain more fruit formation attributes under full macronutrient supply than reduced inputs. It was suggested that low input would be an optimal and sustainable option for improving small fruit crop physiological development and dealing with macronutrient deficiency challenge.