Crescimento de mudas de café (Coffea arabica L.cv. 'Bourbon') sob quatro níveis de luz, em Viçosa, Minas Gerais

Resumo

Growth of Coffea arabica L. seedlings under 25%, 50%, 75% and 100% light levels, in Vigosa, Minas Gerais, Brazil, was measured 64, 85, 121 and 142 days after transplantation from the seedbed. 

The best growth,as measured by dry matter accumulation, was obtained under 55% light. There was a gradual change in shoot-to-root ratios with age. In the oldest plants the ratios decreased linearly with increasing light levels, but in the younger plants the ratio was curvilinear with greatest values in full sunlight,and with minimum values around the 55% level. No differences could be detected in net assimilation rates and relative growth rates between treatments, although leaf area ratios decreased with both age and light intensity up to the 75% level. Leaf weight ratios followed a trend similar to that for leaf area ratios but with a steeper rise in open light. Light levels at which minimum values occurred increased from 55 to 75% as plant age increased.

Leaf area per plant decreased with decreasing light inten- sities, the older plants showing a tendency to have larger leaf areas at the 50% level. The average area of individual leaves decreased with increasing light levels, but increased with plant age. Specific leaf area decreased with both light and age of plants. In the oldest plants the number of leaves per plant was greatest under the 55% light level. With the Sxception of the youngest plants full light intensity resulted in fewer leaves.

Coffee seedlings in Vigosa behaved as shade plants. The great restriction imposed by light on leaf expansion may have affected the carbohydrate status of the plants thus affecting root extension and impairing water and mineral uptake, especially nitrogen.