EFFECT OF STAND DENSITY OF ANNUAL RYE GRASS ON LEAF-AREA AND PLANT PRODUCTIVITY

The effects of Lolium multiflorum Lam. population density on leaf area , net assimilation rate, and gross photosynthesis to respiration ratio were studied in field experiments. The accumulated dry matter of stan ds with densities of 300 - 1200 plants per m2 by the end of the vegeta tion season was 850 g/m2 on average. Leaf area indices of closed canop ies (CC) during the period of ear formation and flowering were two to three times higher than those of open canopies (OC). Plant adaptation to a high population density resulted in an increase in the leaf area ratio (LAR) from 0.05 to 0.11 m2/g and a decrease in the unit leaf wei ght from 0.25 to 0.18 g/m2. The changes in source-sink relations durin g plant ontogeny also affected unit leaf weight. The net assimilation rate of OC was higher than that of CC by a factor 1.5 - 2.5, but its m aximum values in both canopies were similar [19 - 22 g/(m2 day)]. Resp iration of the canopies correlated positively with their gross photosy nthesis in the course of biomass increase up to 350 - 400 g/m2. This l evel of biomass production corresponded to the beginning of intracenot ic relations, which were detectable by the decrease in crop growth rat e. It was observed two weeks earlier in CC than in OC. Rapid saturatio n of gross photosynthesis occurred during the development of intraceno tic relations, and the respiratory losses of biomass increased, especi ally in the CC plants. It resulted in a 15 - 25% decrease in the effec tiveness of the crop growth in CC stand in comparison with OC. It was concluded that the changes in relative respiration losses could result , at least partially, in diminishing the difference between the biomas s production in the stands of various density.