ConclusionThe momentary induction equilibrium of the leaf was affected by the temperature in C. morifolium. It was shown that both the rate of induction (τ) and its momentary steady-state value (ISeq) was affected by PAR at which the leaf was previously exposed to. The initial stomatal conductance (gSini) played a major role in determining the induction state of the leaf.

The effect of temperature on photosynthetic induction under fluctuating light in Chrysanthemum morifoliumOzturk I.1, Ottosen C.O.2, Ritz C.3 1Department of Agroecology, Aarhus University, Blichers Alle 20, DK-8830, Tjele, Denmark, 2 Department of Food, Aarhus University, Kirstinebjergvej 10, DK-5792, Aarslev, Denmark. 2Department of Basic Sciences and Environment/Statistics, Faculty of Life Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1958 Frederiksberg, Denmark,

Figure 2: Time required to reach until 90% of equilibrium induction state as a function of initial stomatal conductance. When the differences in temperature were disregarded, a significant inverse exponential relationship was observed.

ResultsUsing the non-linear regression methods, we estimated the values of the gradient constant for induction that depends on time (τ), induction state 60s after exposure to PAR (IS60), and time required the reach 90% of ISeq at a particular PAR (t90). The effect of temperature and PAR on the parameters was presented in Table 1. A significant correlation between IS60 and gSini, as well as a significant inverse relation between t90 and gSini indicated that gSini controlled how quickly the photosynthetic induction gain proceeded.

The light history of the leaf and the temperature significantly affected the maximum rate, and the velocity of induction

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Figure 2: Induction state after 60 seconds exposure to light (IS60) as a function of initial stomatal conductance (gSini). The slopes of the regression lines were not significantly different from each other. The linear fits at 30, 20 and 25 °C were significant (P<0.01).

Table 1: ANOVA results for induction parameters. The effect of temperature, PAR and their interaction on the parameters was shown. F-statistic and P values are reported.

maximum assimilation rate was used to calculate the induction states. Identical measurements were carried out at 20, 25, 30 and 35 °C.

  Factors

 Parameters

 

Temperature PAR Temperature x PAR

τ FP

2.6899ns

12.9224<0.01

3.8651<0.01

t90 FP

2.7933ns

20.9142<0.01

2.6198<0.05

IS60 FP

3.8454ns

8.4795<0.01

3.2413<0.01

ISeq(PAR,T)  FP

3.85333<0.01

32.5028<0.01

0.6627ns

Figure 2: The momentary induction equilibrium across temperature at 50 , 100 and 200 μmol m-2 s-1

PAR. The fitted lines are based on

MethodsA leaf of dark adapted sample was sealed in a leaf chamber. After CO2 respiration was reached a steady-state in darkness, the leaf was exposed to 50, 100, 200 μmol m-2 s-1 PAR for each 1.5, 5, 12, and 50 min periods. The periods were terminated by a 30s light-fleck at a saturating intensity. The ratio between the post-fleck assimilation rate and