Gloser, V. (1998): The modifying effect of mineral nutrition on plant reactions in changing environment. PhD thesis, Masaryk University, Brno.

Summary:

The modification of the response of plants to elevated atmospheric CO2 concentration by different nitrogen forms was studied on Lolium perenne (L.) cv. Bastion. A growth analysis, chemical analysis and measurements of photosynthetic and respiratory rates were conducted. Stimulation of plant growth was found under elevated CO2 atmosphere in the first 14 days of cultivation. This was mainly due to an increase in NAR because SLA and LWR significantly decreased. The changes in SLA and LWR under elevated CO2 in the first time period of cultivation were only partly influenced by the total nonstructural carbohydrate (TNC) content. However, in the second period of cultivation no stimulation of growth by elevated CO2 was observed and the differences in structural characteristics were mediated only by higher TNC content in plants exposed to elevated CO2. The RGR of ammonium and nitrate grown plants was similar, but the nitrate grown plants compare to ammonium grown ones had higher SLA and lower LWR. The highest RGR showed the plants with mixed nitrate + ammonium nutrition irrespective the CO2 level. Both the nitrogen form and CO2 level had a significant effect on plant growth and morphology, but there was practically no interaction between these two factors.
    The total nitrogen content of leaves decreased under elevated CO2. This was caused by decrease in organic nitrogen fraction since nitrate content remained unchanged. In the first period of cultivation this effect was caused by both lower nitrogen concentration and lower relative allocation of organic nitrogen to leaves. In the end of cultivation, the decrease in leaf N concentration was caused only by higher TNC accumulation. The organic N concentration in ammonium grown plants was the highest of all N and CO2 treatments. Despite of high N concentration these plants did not grow faster under elevated CO2 which suggests that plant growth rate was under given experimental conditions regulated by some other factor(s) than carbon and nitrogen supply.
    The rate of photosynthesis (PS) of the youngest fully developed leaves was under elevated CO2 about 33% higher compare to control plants. The nitrate grown plants had higher PS rates compare to other two types of nutrition irrespective the CO2 level. The PS rate of older leaves of control plants was similar to young leaves but older leaves of plants exposed to elevated CO2 showed significant down regulation of PS rate. The response of PS to elevated CO2 was the lowest in both groups of leaves in plants grown in mixed nutrition, which might reflect the fast development and senescence of these plants. Respiration of roots exposed to elevated CO2 was reduced in plants supplied by ammonium and mixed nitrogen nutrition.


The modifying effect of form of nitrogen on nutrient uptake rates in strongly acidified environment was investigated in seedlings of two wild grasses - Calamagrostis villosa and Avenella flexuosa and two trees - Acer pseudoplatanus and Larix decidua. The effect of acid pre-treatment on uptake mechanisms and sensitivity to different nitrogen forms was also studied.
    There was found a strong negative effect of pH 3.5 on a net nutrient uptake rates in all investigated species. The presence of ammonium ions in nutrient solution also decreased the uptake rates of base cations and this negative influence was even more pronounced under low pH. Total net N uptake in strongly acid nutrient solution was the highest when both forms of N were present.
    The long-term exposition of experimental plants to acid environment induced acclimatory changes which enabled the plants to take up majority of nutrients at pH 3.5 with similar rates as in case of the control plants grown and measured in solution with pH 5.5. The negative effect of ammonium ions on uptake rates of basic cations was also diminished by acclimation to low pH.

 
The modifying effect of form of nitrogen on plants response to radiation environment was studied on Calamagrostis epigejos (L.) Roth. The relative growth rate (RGR), the respiration rate and the contribution of the different respiratory pathways in roots was measured in C. epigejos grown at two levels of irradiance and with nitrate or ammonium as N-source. The respiration rate as well as the RGR decreased significantly but the leaf area ratio (LAR) increased upon transfer to shade. The LAR increase was caused by both a higher specific leaf area (SLA) and a leaf weight ratio (LWR). The relative contribution of the alternative and the cytochrome pathways to total respiration rate was the same in both radiation regimes. The ammonium form of N-nutrition had a significant stimulative effect on alternative respiratory pathway activity in shaded plants. The alternative pathway capacity was significantly higher in ammonium-fed plants grown at both irradiance levels. A possible role of the alternative pathway in plants with low energy input and with ammonium ions as N-source is discussed.