01894naa a2200217 a 450000100080000000500110000800800410001910000180006024500620007826000090014052013140014965000190146365000180148265000110150065300190151165300130153065300220154365300210156570000180158677300720160417876242013-08-15       1971    bl ---       0--  u    #d1 aLUDLOW, M. M.  aPhotosynthesis of tropical pasture plants. III. Leaf age.  c1971  aGrass and legume plants were grown under near-optimum conditions in controlled-environment cabinets. Changes in net ohotosynthetic rate, dark respiration rate, and carbon dioxide transfer resistances during leaf ontogeny, and variability between leaves on grass tillers and legumes runners were studied under controlled conditions in an open gas analysis system. As leaves aged dark respiration rate, light compensation point, and light saturation point declined progressively, whereas the initial slope of the light response curve and net photosynthetic rate measured at 10,000 f.c. increased to a maximum before decli- ning. Immediately after unfolding, grass leaves photosynthesized at a rate more closely ap- proximating the maximum than legume leaves which had a relatively low rate initially. For both grasses and legumes, the lower photosynthetic rate of young leaves was accompanied by high mesophyll resistances, but the decline from the maximum rate as leaves aged was associated with increases in both stomatal and mesophyll resistances. Stomatal resistance exerted a major control over the net photosynthetic rate of grasses, whereas mesophyll resistance predominated for legumes. The influence of chlorophyll concentration on the relationship between net photosynthesis and leaf age is discussed.  aphotosynthesis  aFotossíntese  aLegume  aIdade da folha  aLeaf age  aPastagem tropical  aTropical pasture1 aWILSON, G. L.  tAustralian Journal of Biological Sciencesgv.24, p.1077-1087, 1971.