Interactions of Leaf Photosynthesis, Nitrate Reductase Activity, Phosphatase Induction, and Leaf Elongation of Two Kale Genotypes, Poster Board #147

Plant phosphorus (P) and nitrogen (N) deficiency can be related to low leaf photosynthesis, poor phosphatase induction and reduced nitrate reductase activity, insufficient plant water holding and reduced leaf elongation and fresh appearance of rapid top-growth leafy crops. An environmentally controlled study was conducted in two growth chambers to examine the interactions of leaf photosynthesis rate, leaf water holding and leaf elongation with leaf phosphatase induction and nitrate reductase activity (NRA) of two different genotypes of kale (Brassica oleracea var. acephala) and NP input rates. The treatments consisted of two kale cultivars (‘Blue Ridge’ and ‘Redbor’), two levels of N (N₁ = 1 mM and N₂ = 10 mM in the form of NH₄NO₃) and three levels of P (P₁ = 0.05 mM, P₂ = 0.5 mM, and P₃ = 5 mM in the form of KH₂PO₄). Seeds of the two cultivars were planted in 2-L plastic pots and the pots were placed in two growth chambers in a completely randomized design. The controlled environmental conditions were day/night temperature 16 °C, relative humidity 75%, and light density at photosynthetically active radiation (PAR) 300 μM·m^-2·s^-1 of photons using high pressure sodium lamps. The NP treatments were applied using modified Hoagland nutrition solution with six replicates. The results showed that the effects and interactions of kale genotypes and NP treatments were significantly on kale leaf photosynthesis and induction of acidic phosphatase activity (APA) and NRA (P < 0.05). The N₂P₃ treatments increased kale leaf photosynthesis rate (46.6 μmol·m^-2∙s^-1), plant NP assimilation, NO₃^- concentrations (4500 μg·g^-1) and induction of high leaf APA (8-10·μM·p-NP·h^-1) and NRA (25 µM/h of NO₂), which in return boosted kale root mass, total dissolved solids and. Kale leaf water holding, intercellular CO₂ concentrations, leaf transpiration, leaf stomatal conductance and fresh weights were positively correlated with leaf APA and NRA concentrations. The plants treated with the N₂P₃ treatment had significantly higher whole plant marketable fresh yields. The acquisition of nutrients of low mobility such as P was related to plant water holding, photosynthesis rate, phosphatase activity and nitrate reductase activity. It was suggested that plant P deficiency could be contributed to a reduced induction of both phosphatase activity and nitrate reductase activity, leading to a decrease in root mass, plant photosynthesis, foliar expansion, and leaf water holding in rapid top-growth vegetables.