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The Effects of Increased Illumination and Shading on the Low‐Light‐Induced Decline in Photosynthesis in Cotton Leaves
Author(s) -
NAGARAJAH S.
Publication year - 1976
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1976.tb02253.x
Subject(s) - photosynthesis , thinning , shading , canopy , biology , compensation point , shoot , photosynthetic capacity , botany , horticulture , light intensity , agronomy , ecology , art , physics , transpiration , optics , visual arts
An experiment was carried out to study whether low‐light‐induced damage to the photosynthetic system in leaves of cotton ( Gossypium hirsutum cv. Deltapine) which are below the compensation point in the canopy can be arrested and reversed by increased illumination. In addition it was intended to find out whether the photosynthetic system in leaves of shade plants show a greater resistance to low‐light‐induced damage than leaves of plants from more exposed habitats. The plants were grown at high density, and increased illumination to the shade leaves in the canopy was achieved by thinning the stand. Thinning was carried out at two stages and its effects on the decline in the photosynthetic capacity of the 4th leaf were followed. An early thinning was carried out shortly after the 4th leaf dropped below the compensation point and a late thinning 2 weeks later. Comparison was also made between the low‐light‐induced damage to the photosynthetic capacity of the 4th leaf in plants grown under two light regimes during the progressive increase in self‐shading of the 4th leaf within the canopy. It was observed that both types of thinning arrested the low‐light‐induced damage to the photosynthetic system in shade leaves. The decline in photosynthetic capacity of the 4th leaf was stopped after both early and late thinning. The dry weight of the shoot system in the early and late thinned plants was not significantly different. It was double that of the control plants. The plants thinned early did not have higher shoot weight than the late thinned plants since there was a rapid shedding of flowers and fruits after early thinning. The 4th leaf in the early thinned plants showed a 30% increase in chlorophyll content and dry weight per unit leaf area. It is suggested that shedding of flowers and fruits, and increases in chlorophyll and dry weight per unit leaf area in the early thinned plants were caused by a change in the hormonal balance of the plants. The photosynthetic system in leaves of shade plants showed a greater resistance to damage by low light intensity than the photosynthetic system in leaves of plants grown at higher light intensities.