Correlations of Strawberry Leaf CO2, Cell Transpiration, and Potassium and Nitrate Ion Translocations on Fresh Fruit Yield and Quality, Poster Board #291

Strawberry (Fragaria × ananasa Duch.) fruit contains high levels of organic acids and soluble mineral compounds that may be related to plant assimilation of potassium (K) and nitrogen (N) nutrition and translocation of K⁺ and NO₃^- ions from leaves and fruits. A 2-year field study (2010–11) of optimizing strawberry plant K/N nutrition has been conducting on a Hebert sandy loam in Cobequid Bay, Nova Scotia. The objectives were to quantify the changes of strawberry leaf intercellular CO₂ concentrations, cell transpiration, stomatal conductance and K⁺/NO₃^- ion translocations under various N/K treatments and the correlations of these plant physiological and nutritional variables with marketable yield and fruit quality attributes. The strawberry crop was cv. ‘Mira’, a June-bearing type fruit. The field experimental treatments in the first fruiting year (2010) consisted of five rates of K₂O inputs (0, 6, 12, 18, and 24 kg/ha) and five levels of N fertilizer inputs (0, 5, 10, 15, and 20 kg/ha), determined based on the soil testing and mean values of recommendations for strawberry fruit production in several states in North American. The treatments were arranged in a split-plot design with 3 blocks in the field. The results showed that leaf cell CO₂ concentrations varied between 252 ± 23 mg/L and cell transpiration rates changed within 8.7±1.4 nmol/m² per sec., measured at flowering. Mean leaf sap K⁺ and NO₃^- concentrations were 2150 mg/kg and 575 mg/kg, respectively. The leaf K⁺/NO₃^- ratio was 3.8 at flowering, leading to a translocation of 73%—leaf K⁺/NO₃^- concentrations from leaves to the fruits, with a K⁺/NO₃^- ratio 3.0 at fruit maturity. The strawberry total marketable fruit yield varied between 2208 ± 390 g/m². The effects of K/N treatments and their interactions were significant on strawberry leaf CO₂ concentrations, leaf temperature, transpiration rate and fruit marketable yields. Leaf CO₂ concentrations, cell transpiration rates, leaf K⁺ and NO₃^- ions were correlated with strawberry marketable fruit yield (0.42 < r < 0.68, P < 0.01). The combination K₁₈-N₁₅ treatment stimulated significantly strawberry plant physiological development, fruit bearing and fruit maturity, resulting in 6-day advanced fruit harvest period compared to the other treatments. It is suggested that optimizing K⁺ and NO₃^- temporary storage in leaf sources could promote leaf photosynthesis and translocation of leaf K⁺ and NO₃^- ions for improving strawberry productivity and quality.