Tk. Golovko et Ov. Lavrinenko, EFFECT OF STAND DENSITY OF ANNUAL RYE GRASS ON LEAF-AREA AND PLANT PRODUCTIVITY, Russian journal of plant physiology, 41(3), 1994, pp. 286-291
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.