Comparative effects of light during growth on the photosynthetic properties of NADP‐ME type C4 grasses from open and shaded habitats. I. Gas exchange, leaf anatomy and ultrastructure*
Abstract Maximum photosynthetic rate (Pmax in Zea mays L. was reduced to a much greater extent by neutral shading during growth than in the shade-adapted C4 grass Paspalum conjugatum Berg., although under a high light regime the Pmax of Z. mays was two-fold higher than that of P. conjugatum. In both species the shade-induced reductions of Pmax were not of stomatal origin since the intercellular CO2 concentration (Ci) was not decreased by growth under low light levels. The Ci of P. conjugatum (∼200 μPa Pa−1) measured at air levels of CO2 and high photon flux densities was 30% greater than that of Z. mays and, concomitantly, leaf water use efficiency was less. As with Pmax, specific leaf weight, leaf thickness and chlorenchyma volume were reduced to a greater extent by shading in Z. mays than in P. conjugatum. In contrast to Z. mays, bundle sheath chloroplasts of P. conjugatum contained well-defined stacks of grana. Mesophyll chloroplasts of P. conjugatum developed under a high light regime also contained large amounts of starch. This was not the case with Z. mays.