Effects Of Cadmium On Nitrogen Metabolism In Two Genetype Of Chinese Cabbage And Nitrogen Transformation In Soil

Pot and rhizobox trial experiments were conducted to investigate the effect of cadmium on nitrogen metabolism of low nitrate accumulator (L45) and high accumulator (H64) Chinese cabbages [Brassica campestris L. ssp. Chinensis(L.)], and N transference in acid yellow-brown soil. The main results are as follows:1. Pot and rhizobox trial experiments were conducted to investigate the effect of cadmium on yield, dry matter and photosynthesis of low nitrate accumulator (L45) and high accumulator (H64) Chinese cabbages. The results showed that: the fresh weight and dry matter of L45significantly decreased with the Cd treatment. With the0.5and1.0mg Cd/kg soil treatments, net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2(Ci) and transpiration rate (Tr) of both Chinese cabbage cultivars increased, while at high Cd concentrations (5.0and7.0mg Cd/kg soil) these parameters decreased. It was concluded that cadmium decreased net photosynthetic rates to variable extents in the different Chinese cabbage genotypes. Furthermore, all indices of change for the low nitrate accumulator were greater than for the high nitrate accumulator.2. Pot and rhizobox trial experiments were conducted to investigate the effect of cadmium on nitrogen metabolism of low nitrate accumulator (L45) and high accumulator (H64) Chinese cabbages. The results showed that: the concentrations of nitrogen and soluble protein in the leaves of the low nitrate accumulator decreased with an increase in Cd concentration. Accumulations of ammonium and free amino acid in the leaves of both Chinese cabbage cultivars were observed under Cd stress, especially in the low nitrate accumulator. Cadmium induced a significant inhibition of the activities of nitrate reductase (NR) in both cultivars. The activities of nitrate reductase (NR) and glutamine synthetase (GS) in leaves of the low accumulator were more perturbed by Cd than in leaves of the high nitrate accumulator. It was concluded that cadmium disturbed nitrogen metablism to variable extents in the different Chinese cabbage genotypes. Furthermore, all indices of change for the low nitrate accumulator were greater than that of the high accumulator. 3. Pot and rhizobox trial experiments were conducted to investigate the effect of cadmium on N transference in acid yellow-brown soil weith low nitrate accumulator (L45) and high accumulator (H64) Chinese cabbages. The results showed that: under low cadmium concentration treatment conditions, the total N in soil was decreased. Under high cadmium concentration treatment conditions, the total N in rhizosphere soil was increased, especially in H64. Cd treatment increased NO3-and NH44+in soil, particularly in rhizosphere soil. The increased extent of NH4+was much larger than for NO3-.4. Pot and rhizobox trial experiments were conducted to investigate the effect of cadmium on Cd and essential nutrient element uptake and accumulation with low nitrate accumulator (L45) and high accumulator (H64) Chinese cabbages. The results showed that: the content and accumulation of Cd in both Chinese cabbage cultivars were significantly increased under Cd treatment. The content and accumulation of Cd in shoots of L45were much higher than of H64. Compared with the no-plant control, the decrease in total Cd and available Cd in rhizosphere soil was greater than that in non-rhizosphere soil. The content of available Cd in soil growing L45was lower than with H64. The content and accumulation of P and K in L45were decreased under Cd treatment. Under low Cd concentration treatment conditions, both the accumulation of Ca in shoots of H64and the content of Mg in shoots of L45were increased. Cadmium at low dose (0.1and1.0mg Cd/kg soil) increases uptake and accumulation of Fe, Mn and Zn in shoots of Chinese cabbage, while at high dose decreased uptake. The content and accumulation of Cu in shoots of both Chinese cabbage cultivars were increased under Cd treatment, especially in L45.