Stability of leaf anatomy and light response curves of field grown maize as a function of age and nitrogen status

Little information exists linking leaf anatomical characteristics, gas exchange rates and the effects of irrigation and nitrogen applications in field grown maize. The objectives of this study were: (i) to characterize the light response curves of leaves 13 and 17; (ii) to, characterize leaf anatomical features (leaf thickness; bundle sheath diameter; separation between bundle sheaths; number of mesophyll cells between bundle sheaths; number of mesophyll cells separating the bundle sheaths from the epidermis; bundle sheath area ratio) over the season as a function of leaf position (leaves 13 and 17, counting from stem base), and (iii) to relate these anatomical features to the net assimilation rate at a PPFD of 2000 mumol m(-2)s(-1) (A(max)) and to the convexity parameter of a light response curve of field grown maize in response to extremes in irrigation and nitrogen. Experiments were conducted in 1995 and 1996 with the maize hybrid Pioneer 3394. A randomized complete block with split-plot treatment design with two replications was used. Irrigation/no irrigation was the main plot and nitrogen (120 kg nitrogen ha(-1) or no nitrogen) was the split plot treatment. Leaves from tagged plants were measured and then fixed for anatomical measurements. Environmental conditions during each year were markedly different providing a wide range of responses. Leaf thickness as well as other anatomical features were influenced by water stress and nitrogen in a coordinated fashion such that environmental conditions had little or no effect on the ratio of mesophyll and bundle sheath tissue. Amax increased with leaf thickness but the correlation was. weak. The convexity parameter and Amax decreased with leaf age, with no correlation to the anatomical features described here.