Az Eszterházy Károly Tanárképző Főiskola Tudományos Közleményei. 2004. Sectio Biologiae. (Acta Academiae Paedagogicae Agriensis : Nova series ; Tom. 25)

Makrai, L., Dulai, S., Polyánka, H., Ertli, T. and Lehoczki, E.: Monitoring of the Functional State of Beds of Common Reed (Phragmites australis) in Shallow Lake Balaton (Hungary) by Means of Chlorophyll Fluorescence Studies

144 Makra, L. et al. values resulting from the slow fluorescence induction measurements. The mean Rfd value of 1.55±0.28 calculated from over 13 000 slow fluorescence induction measurements in 1996-1998 indicate a moderate functional state of the reed-beds in Lake Balaton. Outstanding mean values of Rfd (higher than 2) were measured in some northern reed-beds, such as those at Zánka, Keszthely Bay, Balatonkenese, Balatonfüred and the area of Kis-Balaton. In 1996, the Rfd parameters of the reeds at Keszthely Bay and Zánka were measured in several series to be around 3, which indicates the very good physiological state of the reeds. The lowest Rfd values (~1) were measured on the northern side, in the reed-beds around Szigliget Bay and Révfülöp. Correlation between Rfd values and the rate of CO2 assimilation of Phragmites leaves During our research programme, measurements were also made to justify the correlation between the Rfd values and the C0

2 assimilation rates in the reeds. The light responses of the photosynthetic activities for intact reed leaves were measured to determine the light intensity saturation point and the maximum assimilation rate (A). Samples from various locations gave A values between 0.3 and 21.3 pmol C0

2 m

2 s"

1, i.e. a wide interval. The fluorescence induction measurements revealed that, in parallel with the increase in the Rfd values, the C0

2 assimilation rates also increased (Fig. 3). It is obvious that the maximum assimilation rate correlated with the increase in the Rfd values. To establish the correlation between the maximum C0

2 fixation rate and Rfd, the corresponding rates of C0

2 assimilation were plotted against Rfd (Fig. 4). Below an Rfd value of 1, there was no net activity in photosynthesis. Above this level, however, there was a strong linear correlation between the two variables, characterized by R

2=0.85, at P0.05. These results unambiguously prove that Rfd, the ratio of the chlorophyll fluorescence decrease, furnishes very similar information on the photosynthetic activity of the reeds to that provided by C0

2 fixation. Figure 4 can also be regarded as a calibration curve, from which, in the knowledge of Rfd, the activity of C0

2 assimilation can be determined. Discussion In three consecutive years (1996-1998), measurements were made throughout the entire shore area of Lake Balaton and Kis-Balaton, with the aim of monitoring the functional state of the reed population. The results of the fluorescence induction measurements in 1997 and 1998 revealed a gradual deterioration of the functional state of the reed-beds as compared with the 1996 situation. The mean Rfd value of 1.55±0.28 calculated from over 13 000 slow chlorophyll fluorescence induction measurements in this period, indicates a moderate functional state of the reed-beds in Lake