IMMEDIATE RESPONSES OF PHOTOSYNTHESIS AND DARK RESPIRATION OF LATE SUMMER STANDS OF EQUISETUM-FLUVIATILE L TO INCREASING CONCENTRATIONS OF ATMOSPHERIC CO2
A. Ojala et al., IMMEDIATE RESPONSES OF PHOTOSYNTHESIS AND DARK RESPIRATION OF LATE SUMMER STANDS OF EQUISETUM-FLUVIATILE L TO INCREASING CONCENTRATIONS OF ATMOSPHERIC CO2, Journal of Applied Botany, 69(5-6), 1995, pp. 169-176
Short-term responses of net photosynthesis, apparent dark respiration
and gross photosynthesis of Equisetum fluviatile to increasing concent
rations of atmospheric CO2 were studied by using transplanted stands o
f natural origin. Three transplantations with biomasses of 274, 407, a
nd 401 g dry weight m(-2) were established six weeks before the measur
ements in late August. Net photosynthesis and apparent dark respiratio
n was measured from the change of CO2 concentration inside polycarbona
te chambers with diameter of 0.455 m and volume of 0.207 m(3). Altoget
her 50 experiments for determination of CO2 influx rates and 24 for ef
flux rates were run without any pre-treatment to higher CO2 and each o
f them lasted 20-30 min. The response of net photosynthesis of E. fluv
iatile to CO2 enrichment was less clear than the response to temperatu
re or irradiance. Nevertheless, the stands showed an increase of ca. 2
5 % in net photosynthesis when the CO2 concentration in air was increa
sed from ambient to 500-600 ppm. When the CO2 concentration was > 600
ppm the increase was ca. 60 %. A multilinear regression model combinin
g solar radiation, temperature and CO2 concentration could only explai
n 46.4 % of the variation in the observed rates of net photosynthesis.
The apparent dark respiration was positively correlated with temperat
ure but inversely related to CO2 concentration. When the CO2 concentra
tion was doubled from ambient the stands of E. fluviatile reduced thei
r apparent dark respiration by ca. 50 %. Under higher CO2 concentratio
n E. fluviatile appeared more effective than in the ambient concentrat
ion, as the production lost through respiration decreased. When the co
ncentration of atmospheric CO2 was < 500 ppm, 57.5 % of gross producti
on was respired whereas above 500 ppm of CO2 the corresponding proport
ion was only 34.2 %. As the enrichment with CO2 resulted in decreased
respiration rates and it was known from long-term growth and photosynt
hesis experiments that neither shoot growth in length in E. fluviatile
is stimulated by higher CO2 concentrations nor do the stands show dow
n-regulation of photosynthesis after several weeks of CO2 enrichment,
it was concluded that the extra carbon fixed was allocated to storage
through growth of below-ground biomass.