EFFECT OF TEMPORARY N STARVATION IN MAIZE ON LEAF SENESCENCE

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Abstract
A prerequisite for an informed strategy regarding nitrogen application in maize (Zea mays L.) is a knowledge of the physiology of plant responses to nitrogen. This study consisted of two experiments on maize plants grown in pails. One experiment was conducted in controlled-environment growth rooms, the other was conducted in the field. N-deficient and control maize plants were evaluated for photosynthetic rate (P), chlorophyll content (CC), nitrogen content, and green leaf area; comparisons between these four parameters were made. During N starvation, rate of senescence (i.e. decrease in green leaf area) of the old leaves was higher in N-deprived plants than in control plants. P and CC of all leaves in the N-deficient treatment decreased during nitrogen withdrawal. After the deprivation period, when the plants were resupplied with N, senescence was delayed relative to control plants. The increase of CC in treatment plants was slower than the recovery of photosynthetic rate; in fact, CC was a poor indicator of photosynthetic activity. The delay in leaf senescence corresponded with regreening in leaves of N-deprived plants following N addition. This delay could be partly explained by an overcompensation in plant N requirement involving both a rapid increase in P, and a slower increase in CC. The effects of resupplying plants with nitrogen following a N-deprivation period lead us to believe that the observed leaf yellowing is actually a premature senescence which is reversible, and that a low N content is not the single causal factor of senescence.Key words: Chlorophyll content, leaf area, photosynthetic rate, Zea mays L.