Seasonal Factors of Correlation Between Climatic Factors, Photosynthetic and Agronomic Traits in Maize

The dry matter accumulation and photosynthetic traits of upper leaves were studied twice weekly in 1983, under field conditions, for two early maturing maize cultivars. Analysis of correlation between climatic data and those traits were based on four week periods. Seasonal patterns of correlation coefficients were drawn by shifting the beginning of these four week periods from one sampling data to the next until four weeks before the end of the sampling period. Most traits were significantly correlated with climatic factors at one time or another; only those correlations which were of longer duration will be mentioned here. Net assimilation rate was positively correlated with maximum temperature during intensive leaf growth. The relative growth rate was closely correlated with photosynthetic photon irradiance (PPI) during the second half of June and with phosphofructokinase activity during the second part of July. The chlorophyll content showed a close and positive relationship with minimum temperature until the end of June and with PPI during most of August. The content of carotenoids was, for the most part, negatively correlated with climatic factors, the closest relationship existing with the PPI at the previous sampling date until the beginning of July. The activity of photosynthetic enzymes such as RuBP carboxylase, NADP malate dehydrogenase and PEP carboxylase was generally less closely correlated with climatic factors over longer periods. Patterns of correlation were remarkably similar for the two cultivars.