DYNAMICS OF CHANGE OF LEAF ATTRIBUTES OF BRUSSELS-SPROUTS IN RESPONSETO SWITCHES BETWEEN HIGH AND LOW SUPPLY OF NITROGEN

In previous research nitrogen supply was shown to affect several compo nents of foliar growth and development of Brussels sprouts (Brassica o leracea L. var. gemmifera DC.). This paper extends the analysis of dat a on Brussels sprouts and focuses on the dynamics of change in compone nts of leaf growth and nitrogen concentrations upon change in nitrogen supply. Four treatments were compared: a control without nitrogen lim itation, a continuously nitrogen-deficient control, and two treatments with a switch from limiting supply to non-limiting supply or vice ver sa. Plant nitrogen concentrations changed first and fast upon change i n soil nitrogen regime. Upon increase in supply rate, nitrogen concent ration also increased in leaves that had completed their expansion. Ch anges in leaf growth started about 15 days after the switch in nitroge n regime. Leaves that were expanding at the switch responded by an inc rease in area when nitrogen supply became larger without a change in m ass, i.e. specific leaf area increased. Areas of leaves as well as spe cific leaf area of expanding leaves decreased when the nitrogen supply became smaller. Control of leaf size during initiation and expansion is discussed.