Photosynthesis of newly matured leaves during the ontogeny of barley grown at different nutrient levels

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Abstract
Various growth characteristics were measured throughout ontogeny for barley plants (Hordeum vulgare L. cv. Brant) grown in silica sand and irrigated daily with one-eighth (0.125 N), one-fourth (0.25 N), and one-half (0.5 N) dilutions of a modified Hoagland nutrient solution, at day–night temperatures of 25–20 °C, an irradiance of 53 nE cm−2 s−1 (400–700 nm), and a day length of 15.5 h.The net CO2 exchange rate (NCE) of newly matured leaf laminae did not differ between measurements made at the same irradiance before and after noon. By contrast, NCE was greater at all stages except stem elongation for plants supplied with 0.5 N nutrient solution than for those receiving 0.25 N and 0.125 N solutions. The nutrient effect was apparent even for the first leaf produced. A distinct ontogenetic pattern of change in leaf NCE was apparent under all nutrient treatments: NCE increased from leaf 1 to leaf 3, remained constant between leaf 3 and leaf 5, declined between leaf 6 and leaf 9, and then increased markedly from leaf 10 onwards. The changes in leaf NCE appeared to be associated with major events in ontogeny.Rate of leaf appearance was constant through ontogeny and was not affected by nutrient supply. Final leaf number was greater for the 0.5 N nutrient solution. Leaf length, width, area, and specific weight increased throughout the early stages of ontogeny, and decreased later. The decrease in leaf length and area was less for plants supplied with more nutrients.

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