Differences In Uptake And Utilization Of Zinc And Mechanisms In Various Pakchoi (Brassica Campestris Ssp.chinensis (L.) Makino) Cultivars

The main materials used for the experiment were the pakchoi with various Zn efficiency and the calcareous purple soils derived from purple sandstone. Seeds of different pakchoi cultivars used were obtained from the middle and lower reaches of Changjiang river. The soil used was a Zn-deficient soil collected from the Xinzhou district of Wuhan municipality. The differences in uptake and utilization of Zn among various pakchoi cultivars were investigated by using the solution culture, soil pot experiments and chemical analysis methods. The Zn-efficient mechanisms (the term Zn-efficiency used in this study reflects the ability of a genotype to grow and yield better than other genotypes under Zn-deficient conditions) also were studied in terms of the roots morphology, root exudates, micro-ecotope environment of rhizosphere, etc. The major findings are summarized as follows:1. Methods and indices for screening Zn-efficient pakchoi cultivars were studied by using soil pot experiment and solution culture. It was observed that: 1) the differences in ability to absorb and utilize Zn from soils among various Pakchoi cultivars could be embodied fuller in the soil pot culture as compared with the solution experiment; 2) the shoot dry weight and the shoot Zn content as screening indices were better than the shoot Zn concentration and others. Based on these, we think pakchoi cultivars tested can be basically divided into two groups: Zn-efficiency and Zn-inefficiency. Cultivar Wuyueman, and cultivars Heiyoubaicai, etc. are their specific representatives, respectively.2. There were remarkable differences in the roots morphology among these various pakchoi cultivars. Results from the correlation analysis of the related data showed that there was a significantly positive correlation between the shoot Zn content and their root parameters under Zn-deficient conditions. Cultivar Wuyueman has the capability to tolerate zinc deficiency and to absorb, utilize and accumulate zinc from soils by reason of its larger active surface area of roots, the longer root length, and the higher root/shoot ratio.3. Both the composition and quantity of root exudates for various pakchoi cultivars demonstrated: 1) The total amount of low-molecular-weight organic acids (LMWOAs) and amino acids in root exudates of cultivar Wuyuman was higher than that of cultivar Heiyoubaicai at both low and high Zn level (significant at P 0.05 under Zn deficiency). 2) The content of oxalic and alanine in root exudates of cultivar Wuyuman was also significantly higher than that of cultivar Heiyoubaicai under Zn deficiency condition. 3) The total amount of root exudates for cultivar Wuyuman was higher and the content of oxalic and alanine in its root exudates also was raised obviously under Zn deficiency condition. Those might be the basis for the higher Zn accumulation and Zn efficiency of cultivars Wuyuman.4. The effect of pakchoi root exudates and low-molecular-weight compounds (organic acids and amino acids) on mobilization of Zn in calcareous purple soil was studied. Results showed the amount of extracted Zn from soil by root exudates of Zn-deficient cultivar Wuyueman was higher significantly than that by root exudates of Zn-deficient cultivar Heiyoubaicai. It was more noticeable that the amount of extracted Zn from soil by root exudates of Zn-deficient cultivar Wuyueman was 2.5-fold higher compared to that of Zn-sufficient cultivar Wuyueman, but only 1.1-fold higher for cultivar Heiyoubaicai. It means that the root exudates of Zn-deficient cultivarWuyumen has more powerful mobilization of Zn in calcareous purple soilthan the other cultivars. Results of the reaction between low-molecular-weight organic acids or amino acids and soil zinc showed that the amount of soil zinc extracted by oxalic acids was the highest among low-molecular-weight organic acids used, and the mobilization of alanine to soil Zn was most noticeable among amino acids. Thus, it could be concluded that both oxalic and alanine in pakchoi...