Effect of Light Intensity on Growth of Natural Populations of Dactylis glomerata L.

Abstract

The growth of two natural populations of cocksfoot from contrasting climatic regions, Norway and Portugal, was studied in two photoperiods at three temperatures with three levels of light energy (48, 144, and 240 W m−2 in the wavelength interval 400–700 nm). There was a consistent increase in relative growth-rate (RGR) in response to increased light energy up to 144 W m−2, but above this energy level there was either no change, or, in some treatments, a decline. Net assimilation rate (NAR) increased, whilst leaf area ratio decreased from the lowest to the highest energy level in most treatments. The decrease of LAR with increased light energy could be attributed to a decrease of both leaf weight ratio (LWR) and specific leaf area (SLA), a greater proportion of dry matter being distributed to plant parts other than leaf. This effect occurred although there was a positive relationship between light energy and relative leaf growth-rate (RLGR). Population differences in these growth attributes were most marked in the treatments with low-temperature and short-day conditions. The efficiency of energy conversion of visible radiation declined from 3–4 per cent at the lowest energy level to 1–2 per cent at the highest energy level.