Field Crop Production Original scientific paper
Changes of some chlorophyll-fluorescence parameters under biofertilization Szilvia Veres, László Lévai, Marianna Marozsán, Éva Gajdos, Nóra Bákonyi, Brigitta Tóth Debrecen University, Institute of Plant Science, Division of Agricultural Botany and Crop Physiology, Böszörményi street 138., Debrecen, Hungary, H-4032 e-mail:
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Abstract This research has aimed to investigate how biofertilization influences plant production, what effects the application of biofertilizers exercise on the parameters of chlorophyllfluorescence. The different nitrogen deficiency level cause reduction in the potential photochemical activity (Fv/Fm) compared to the normal nitrogen amount. The applied biofertilizer could compensate the effect of nitrogen deprivation. The Fv/Fm was higher if the reduced nitrogen supply was supplemented with biofertilizer as compared to the values of different nitrogen deficiency levels without biofertilizer treatments. The absence and normal amount of nutrients reduce positive effect of biofertilization. Key words: biofertilizer, chlorophyll-fluorescence, plant nutrition Introduction Environmental protection is getting more important for the agrarian, because of the purpose of sustainable agriculture. Although the quantitative growth of dry matters, the sufficient extent of plant production are essential factors with respect to the efficiency of agricultural production. It is an important issue whether the replacement of organic fertilizers and chemical fertilizers with biofertilizers causes a beneficial increase in dry weight (Lévai et al., 2006). From the point of view the dry matter production, which is very important in agronomy, the photosynthetic efficiency and the dry matter production has a questionless role. Changes in the potential photochemical activity and the amount of dry matter are indicative for the adverse circumstances (Veres et al., 2000). The applied biofertilizer contains plant growth promoting bacteria (PGPB). These non-infecting PGPB rhizosphere bacteria might affect mineral nutrition of plants through their influence on: 1. growth, morphology and physiology of roots; 2, the physiology and development of plants; 3. the availability of nutrients; and nutrient uptake processes. A lot of microorganisms, for example species of Bacillus and Pseudomonas have a direct effect on the plant growth (Kloepper et al, 1986). The method of chlorophyll fluorescence is widely use to detect physiological status of plants under different abiotic situations for example, in presence of nutrient deficiency, cold-, high temperature-, drought-, light- and UVB-stress (Lichtenthaler and Rinderle, 1988; Tóth et al., 2002). It has recently been shown that a parameter derived from chlorophyll fluorescence, the ratio of variable/maximum fluorescence, Fv/Fm, is a quantitative measure of the photochemical efficiency of photosystem II (Maxwell and Johnson, 2000). The accumulation of excessive excitation energy can cause photoinhibition or photooxidation in the photosynthetic apparatus, and the reduced values of Fv/Fm indicate that a proportion of PSII reaction centres are damaged. According to Björkmann and Demmig-Adams (1987) the estimated value of
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44th Croatian & 4th International Symposium on Agriculture
Ratarstvo
Fv/Fm under optimal growing condition in higher plants is 0.832 ±0.004, but it depends on some different parameters of plant species. Material and methods The seeds of corn (Zea mays, L cv. Norma sc.) were germinated for three days, and after that were grown on nutrient solution under controlled laboratory conditions. To investigate the effect of biofertilizer, different nutrient supplies were applied. First of all, complete nutrient solution (totals) containing 2.0 mM Ca(NO3)2, 0.7 mM K2SO4, 0.5 mM MgSO4, 0.1 mM KH2PO4, 0.1 mM KCl, 1 µM H3BO3, 1 µM MnSO4, 1 µM ZnSO4, 0.25 µM CuSO4, 0.01 µM (NH4)6Mo7O24, 10-4 M FeEDTA. In the second applied nutrient solution (1/2ns) was the 50% diluted variant of complete nutrient solution. Thirdly, only distilled water (dw) was used. The other treatments differed only in nitrogen contents: 0.1 and 0.5 percentage nitrogen compare to the control. Parallel of these treatments plant growth promoting bacteria containing biofertilizer (Phylazonit MC®) was added to the solutions (1ml l-1). Phylazonit MC® is a viscous solution containing Azotobacter chroococcum and Bacillus megatherium, microorganisms which help uptake of nitrogen and other elements and their mobilization in the rhizosphere. The parameters of in vivo chlorophyll fluorescence were detected with a PAM-2001 (Walz, Germany) modulated light fluorometer as described by Schreiber et al. (1986). Samples were dark-adapted for 30 minutes. After dark adaptation, the initial fluorescence (Fo) was excited by weak light. The maximal fluorescence (Fm) was induced by white saturating flash. Ratio of Fv/Fm was used for characteristics potential photochemical efficiency of PSII. Results and discussion The chlorophyll fluorescence induction method is widely used for the examination of the physiological conditions of plants under various stress circumstances. This method excellently characterizes photosynthetic efficiency. The fast and slow phases of chlorophyll fluorescence induction were examined with a PAM-2001 fluorometer (WALZ GmbH, Germany). The parameters established with use of the induction curve are properly applicable to the description of photosynthetic efficiency. Thus, from the fast phase of chlorophyll fluorescence induction the optimal photochemical efficiency of PSII can be determined, and it is quantified as Fv/Fm. The Fo characterises the basic fluorescence and Fm is the maximum value of chlorophyll fluorescence. The different levels of nitrogen deficiency cause reduction in the optimal photochemical activity as compared to the normal nitrogen amount. Neither photoinhibition nor photooxidation was experienced under applied light intensity in laboratory conditions. Table 1. Values of potential photochemical activity (Fv/Fm) of maize growing different nitrogen level and with bio-fertilizer supplementation n=10 ±s.e., p
