Effect of root zone aeration on the growth and bioactivity of cucumber plants cultured in perlite substrate

This study was aimed at investigating the growth and nutrient uptake of cucumber plants affected by forced aeration of supplying oxygen and stimulating gas exchange rate in root zone in a substrate. Five aeration levels during the growth (0, 0.5, 1.0, 1.5 and 2.0 L/min) were applied. Maximum leaf area and leaf fresh and dry weights were obtained at an aeration level of 0.5 L/min. Excessive aeration in root zone inhibited leaf area expansion, relative leaf growth rate and crop growth rate. An optimum leaf area index of 3.0 to 3.5 was estimated in range of 0 and 0.5 L/min. The highest fruit yield was measured of 1.13 kg/plant at 0.5 L/min, whereas at 2.0 L/min it was 0.62 kg/plant. Potassium concentration in petiole sap was lower at 63 days after transplanting than that at 32 days after transplanting. Ethylene concentrations increased with higher aeration values, however, CO₂ concentration reduced with increased aeration. All bioactive compounds (polyphenols, flavonoids, flavanols, tannins and ascorbic acid) and the levels of antioxidant activities by ferric-reducing/antioxidant power and cupric reducing antioxidant capacity in ethanol extracts of cucumbers differed significantly in the investigated samples and were the highest at aeration level of 0.5 L/min in comparison with other samples (P <0.05). In conclusion, antioxidant status (bioactive compounds and antioxidant activities) improved with the appropriate aeration, which is effective for higher fruit yield and bioactivity. Excessive aeration inhibited root respiration, nutrients, bioactivity, and water uptake, and it resulted in the reduction of plant growth and fruit yield.