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Effects of phosphorus availability on physiological aspects of hydroponically grown Chinese broccoli (Brassica alboglabra)
Author
Lalitha Jothinathan
Supervisor
He, Jie
Abstract
The effects of P availability on photosynthesis, productivity, root morphology, nitrogen (N) metabolism and mineral uptake and transport were investigated in this study. In the present study, all Chinese broccoli (Brassica alboglabra) plants were first grown at full strength of nutrient solution. Four weeks after transplanting, the plants were subjected to nutrient solutions with different P concentrations There were 5 different P treatments (0-P, P-deprivation of 0 ppm; 0.5P, P –deficiency of 16 ppm; F-P, P- sufficient level of 32 ppm; 1.25-P, P-in excess of 40 ppm and 1.5P, P in excess of 50 ppm). P deprivation had the greatest negative impact on shoot and root productivity and 1.5P had the greatest positive impact on shoot and root productivity. Root morphology factors, root length, root surface area, root average diameter and the number of root tips were most affected for 0-P plants. There was no significant difference in root morphology for plants subjected to excess P treatments. P-deprivation caused the greatest reduction in photosynthetic CO2 assimilation (A) and stomatal conductance (gs). 1.25P treatment caused the greatest increase in photosynthetic CO2 assimilation (A) and stomatal conductance (gs). Declines in A and gs in young leaves were greater than in old leaves. All plants experienced dynamic photoinhibition [midday depression of chlorophyll (Chl) fluorescence Fv /Fm ratio] on sunny days. However, plants under P stress were more susceptible to high light. Chronic photoinhibition (lower predawn Fv /Fm ratio and Chl content) was observed for plants under P stress. The time course studies indicate that the magnitudes of midday depression of photosynthetic parameters were greater for plants subjected to P stress than F-P plants and plants with elevated treatment levels of P. These results indicate that while P stress affected growth and photosynthesis of Chinese broccoli (Brassica alboglabra) negatively, elevating P levels in the nutrient solution did not significantly improve the growth and photosynthesis of plants from 1.25P to 1.5P. P availability also affected the uptake and transport of mineral nutrients such as P, nitrate (NO3-), Zn, Mg and Mo between the root and shoot. P availability did not seem to affect the uptake and transport of mineral nutrients such as K and Ca. The nitrate reductase activity (NRA) in leaves was more affected than in roots. Effects of P availability on (NO3-) of leaves and root were similar to those of nitrate reductase activity. Increasing P levels increased (NO3-) and NRA levels. The relationship among the carbon and N metabolism, mineral uptake and transport are discussed.
Date Issued
2008
Call Number
QK495.C9 Lal
Date Submitted
2008