Example of Application: Standard Configuration

Measuring simultaneously PAM fluorescence, PAR, leaf temperature
and relative humidity

The MINI-PAM-II combined with the newly developed digital leaf clip 2035-B measures simultaneously PAM fluorescence, photosynthetically active radiation (PAR), leaf temperature and air humidity.

The present experiment demonstrates how these parameters vary during a partly cloudy spring day. The photosynthetic sample was an attached leaf of Ilex aquifolia growing the garden of the Walz Company.

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Figure 1

Figure 1 shows that, during the first half of the day, PAR increased occasionally to values around 500 μmol m-2 s-1 and the quantum yield of photosystem II, Y(II), varied in an opposite manner to PAR.

 

Figure 2

As expected, air temperature increased with PAR and relative humidity decreased with increasing temperature.

Figure 3

Using Y(II) and PAR (see Fig. 1), and standard parameters (84% of incident light absorbed by the leaf and equal partitioning of absorbed light quanta between photosystems I and II), electron transport rates (ETR) were calculated by the software of the MINI-PAM-II. These ETR data are plotted against the respective PAR values. Clearly, all ETR versus PAR data during the course of a day can be described by a single curve. Fitting the model of Jassby and Platt (1976, Limnol Oceanogr 21: 540-547) to the data resulted in the blue curved line of Fig. 3.

The three cardinal points of this best fit curve are indicated in Fig. 3: α, initial slope. ETRmax, maximum electron transport rate. IK, minimum saturating PAR. These cardinal points are useful to characterize the light acclimation status of a sample. Often, in high light acclimated leaves, the ETRmax and IK parameters are elevated.