Differential Absorption And Utilization Of Nitrogen And Magnesium By Plants Under Different Light Irradiation Levels

Nitrogen and magnesium are important elements for photosynthesis It is assumed that nitrogen limits photosynthesis in high level light regimes with regard to CO2 fixation and magnesium limits photosynthesis in low light regimes with regard to light harvesting. Nitrogen and magnesium contribute to photosynthesis in different ways in different light regimes. Thus plants may adapt to light regimes by adjusting absorption and utilization of nitrogen and magnesium pattern. To test this hypothesis, three herbaceous plants were selected: Conyza japonica, Iris japonica and Reineckia carnea. The absorption, allocation of nitrogen and magnesium as well as their contents changes in leaves under different light regimes were studied. The aim of this thesis is to evaluate the importance of nitrogen and magnesium absorption and utilization to adaptation of photosynthesis to light regimes. The results of the experiments showed that:(1) Nitrogen and magnesium were absorbed by Conyza japonica in a differential way under different light levels: nitrogen absorption increased and magnesium absorption decreased with the light levels. The result may suggest more nitrogen and less magnesium are needed by plants with increasing light level and is well accordant with the hypothesis addressed above.(2) The allocation of nitrogen and magnesium and biomass to leaves of Conyza japonica decreased with the light levels while that to roots increased with light levels, the allocation to stems was not changed by light level significantly. The allocation pattern of nitrogen and magneium is very similar to that of biomass...