| Split plot experiment was taken to investigate the physiological mechanism of calcium on growth, yield and quality of welsh onion. hydro cultural trails with four Ca levels: 0, 4, 6, 8 mmol/L and field fertilized by Ca Cl2 trials with four Ca application levels: 0, 225, 450, 675 kg/ha(calculated as Ca O) were taken. ‘Zhaohe' and ‘Zhangqiu' were used as test materials, and then calculated growth, yield and quality, mineral elements absorption, nitrogen metabolism, chlorophyll fluorescence parameters and exchange characteristics of water as well as gas in leaf. The chief results are showed as follows:1. With the increase of solution Ca level, plant height, cauloid diameter of potted welsh onion as well as root and shoot fresh weight were advanced significantly, especially for 6 mmol/L Ca level of which biomass per plant was 211.13 g, but that was only 185.83 g as calcium level continued to increase to 8 mmol/L, and no significant differences with 4 mmol/L treatment whose biomass per plant was 183.29 g. ‘Zhangqiu' was shown significantly higher change in plant height, cauloid diameter and shoot fresh weight except for root fresh weight. All the quality-related indexes of two cultivars were higher at 6 mmol/L Ca level, but decreased at 8 mmol/L Ca level, so was the pot culture experiment. For instance, the yield of ‘Zhaohe' and ‘Zhangqiu' at 6 mmol/L Ca level significantly increased by 79.94%, 74.42%, respectively, compared to the control, and the quality value in cauloid was higher by 18.42%, 26.14%, respectively. For the field trial, the yield in treatment of ‘Zhaohe' and ‘Zhangqiu' with Ca O of 450 kg/ha were increased by 12.30%, 19.00%, respectively.2. With the increase in solution Ca level, dry weight of roots and cauloids as well as leaves were increased significantly especially for 6 mmol/L Ca level, but then decreased as Ca level continued to increase. Dry weight in different organs of the two welsh onion cultivars showed ‘slow-fast-slow' trend as growth stage prolonged, and ‘Zhangqiu' showed significantly higher dry weight compared to ‘Zhaohe'. Content of Ca in different organs increased as Ca level increased and growth stage prolonged, and was the highest at 8 mmol/L Ca level, while the control decreased sustainly. Although content of N, P, K in different organs changed during various stages, high Ca level still improved the content and was higher at vigorous growth stage and cauloid forming stage, but that was lower at harvest stage in which absorption of N, P, K, Ca had significant difference among various Ca levels, especially for absorption of Ca. Alternately, appropriate Ca level promoted absorption of N, P, K, Ca particular for 6 mmol/L treatment.3. Appropriate Ca application enhanced the activities of NR, GS, GOGAT and GDH dramatically in welsh onion leaves, particularly for 6 mmol/L Ca level, but the reactions to Ca were differently during various growth stages. Activities of NR, GS, and GOGAT in leaves of the two cultivars increased firstly but then decreased as growth stage prolonged, however, GDH showed strong activity at seeding oversummer stage. Solution Ca level also had significant effect on the content of ammonium nitrogen(NH4+-N), nitrate nitrogen(NO3--N), soluble protein and free amino acid in onion leaves which were increased initially then decreased and was the highest 6 mmol/L Ca level. All the different forms of nitrogen except for ammonium nitrogen were highest at vigorous growth stage.4. Appropriate Ca level increased chlorophyll and carotenoid content in leaves and net photosynthetic rate and stomatal conductance as well as water use efficiency of the two cultivars of welsh onion, and that was highest at 6 mmol/L Ca level in solution, and lower as Ca level continued to increase to 8 mmol/L. Photosynthetic rate and stomatal conductance except for water use efficiency were highest at vigorous growth stage. Fv/Fm, q P and ?PS? of the two cultivars were lowest at 13:00 during one day but that was highest for NPQ, Moreover, appropriate Ca level decreased the drop of Fv/Fm, q P and ?PS? of welsh onion leaves so that favorable to production and accumulation of assimilation.5. Appropriate Ca level in solution significantly increased activities of SOD, POD, CAT of welsh onion, but the reactions to Ca were differently during various growth stages, and generally higher at 6 mmol/L Ca level. MDA content in leaves were continued to increase as prolonged of growth, while higher Ca levels significantly reduced the increase amplitude of MDA content. Activities of protective enzymes in root were also enhanced as Ca levels increased, while the MDA, H2O2 content and O2- production rate reduced so as to decreasd the degree of membrane lipid peroxidation. |
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