Ap. Gay et H. Thomas, LEAF DEVELOPMENT IN LOLIUM-TEMULENTUM L - PHOTOSYNTHESIS IN RELATION TO GROWTH AND SENESCENCE, New phytologist, 130(2), 1995, pp. 159-168
Length, area, weight and concentrations of pigment were measured from
just after emergence until senescence of the fourth leaf of Lolium tem
ulentum L. seedlings grown in nutrient solution in a controlled enviro
nment. At the same time the progress of photosynthesis, respiration an
d carbon contents of the leaf were recorded. A new approach to calcula
ting plastochron indices for grasses was developed, based on logistic
curves fitted to leaf lengths. Dry weight and photosynthetic rates per
unit area were greatest in young leaves. Subsequently photosynthetic
capacity at light saturation declined, as did photosynthetic rates at
the light incident on the leaf, although the decrease was less pronoun
ced in the latter case. Dry weight per leaf remained fairly constant o
nce full expansion was reached, with perhaps a slight rise in the olde
st leaves. The photosynthesis and carbon content data were combined to
calculate the carbon balance of leaf 4, with respect both to the atmo
sphere and to the rest of the plant. Net gas exchange became positive
about 7 d before full leaf expansion. Leaf weight continued to increas
e so that the carbon balance with the rest of the plant did not become
positive until just after final leaf size had been attained. These re
sults are discussed in relation to the likely contribution of the vari
ous components of the balance to plant productivity.