CO2 EXCHANGE AND GROWTH OF RHAPONTICUM CARTHAMOIDES UNDER THE CONDITIONS OF THE MIDDLE TAIGA SUBZONE OF NORTHEASTERN EUROPE .2. PHOTOSYNTHESIS RESPIRATION RATIO AS AN INDEX OF THE PRODUCTIVITY AND ADAPTIVE RESPONSES OF PLANTS/
Tk. Golovko et Ev. Garmash, CO2 EXCHANGE AND GROWTH OF RHAPONTICUM CARTHAMOIDES UNDER THE CONDITIONS OF THE MIDDLE TAIGA SUBZONE OF NORTHEASTERN EUROPE .2. PHOTOSYNTHESIS RESPIRATION RATIO AS AN INDEX OF THE PRODUCTIVITY AND ADAPTIVE RESPONSES OF PLANTS/, Russian journal of plant physiology, 44(6), 1997, pp. 746-753
The ratio of respiration (R) to gross photosynthesis (P-g) in Rhaponti
cum carthamoides plants of various ages was studied by measuring CO2 e
xchange. The effects of irradiance, day length, and nitrogen supply on
the components of the dry matter balance and R/P-g ratio were examine
d in two-year-old plants. P value was calculated by adding respiratory
losses to the amount of substrate assimilated per day. When growth ra
tes of one-to four-year-old plants were at their highest, respiratory
losses comprised about 45% of P-g. Plant adaptive responses to environ
mental factors were aimed at the maintenance of a constant R/P-g ratio
, In moderately shaded plants, this was attained by retaining the prod
uctivity of net photosynthesis and decreasing respiration rates, where
as, in severely shaded plants or at a shortened day length, this was a
ttained by decreasing plant weight. For plant productivity, the optimu
m nitrogen content in plant biomass was 25-30 mg/g. At higher nitrogen
contents, the R/P-g ratio increased, and the net assimilation rate an
d relative growth rate decreased. It is concluded that Rhaponticum car
thamoides plants can adapt to light conditions to maintain maximum eff
iciency of growth; however, they are not adapted to high levels of nit
rogen supply. It is shown that daily photosynthetic production can be
calculated from the net photosynthetic rate at the adaptive radiation
intensity.