| Cadmium (Cd) is one of the most mobile and toxic heavy metals in environment. Spinach has high ability to accumulate cadmium and is a very important green leafy vegetables in China. In the production, spinach is easily polluted by Cd, which is one of the most toxic heavy metalsto both plants and animals. Therefore, it's necessary to reduce Cd uptake and accumulation in spinach. In this study, these experiments will be carried out to study the physiological mechanism in effects of Cd contents in plants of spinach with a plot experiment. Meanwhile, the possibility to reduce Cd uptake and accumulation in spinach by application of Silicon (Si) or microorganisms will be also studied. The major results were summarized as follows:(1) Cd toxicity experiment results: In a plot experiment, five Cd levels, i.e. 0.17, 2.13, 6.20, 8.47 and 19.60 mg·kg-1 were designed based on the Qiangli Quanneng and Yinong398 which are the different tolerance spinach varieties of cadmium. With the levels of cadmium added in soil, the results showed that: the fresh weight and dry weight of shoot and root, soluble sugar content, Vitamin C content, POD and CAT activities in two varieties all showed upward significantly; Cd contents of shoot and root, available-Cd content, reducing sugar content, Relative electrolyte leakage proline content and MDA content all showed downward significantly; Cd accumulation of shoot and root, K content of shoot, proline content and SOD activity showed significant upward first and then downward significantly; N and K contents of shoot showed significant downward first and then upward significantly. Meanwhile, The chloroplast pigment of two spinach varieties had the different change to Cd with decrease significantly of Qiangli Quanneng and no significant of Yinong398; solutable protein content showed downward first and then upward, but no significantly.Cd accumulation of shoot in two spinach varieties was higher than that of root. The Cd accumulation of shoot in Qiangli Quanneng spinach was 5.53-13.13 times than that of root while 9.15-16.26 times in Yinong398. The Cd contents of shoot were less than standard in no Cd added treatment and then the opposite in Cd added treatments. Values of PAF and TF in two spinach varieties under different Cd levels were all less than 1, and so spinach was not hyperaccumulator.(2) Si alleviating Cd toxicity experiment results: In a plot experiment, five Cd levels, i.e. 0.17, 2.13, 6.20, 8.47, 19.60 mg·kg-1, and three Si levels, i.e. 0, 100, 200 mg·kg-1 were designed based on the Qiangli Quanneng. With the levels of Si added in soil, the increasing rates of dry weight of shoot and root, N and K contents of shoot, SOD, POD and CAT activities were 14.4%-75.0%, 0.0%-60.9%, 2.6%, 2.9%, 2.0%-15.1%, 1.2%-34.2% and 2.9%-27.8% respectively; the decreasing rates of Cd contens of shoot and root, available-Cd content, K content of shoot and MDA content were 0.7%-46.2%, 3.9%-47.9%, 0.6%-35% and 7.2%-32.1% respectively. The decreasing rates of Cd accumulation reflected that Cd content of shoot decreased relatively. We also concluded that the T2 treatment was better than the T1 in alleviating Cd toxicity.(3)Microorganisms alleviating Cd toxicity experiment results: Effect of three kinds of microorganisms on growth and cadmium uptake in spinach was investigated with a pot experiment in greenhouse based on the Yinong398. When plants were supplied with microorganisms, fresh and dry weight per plant were average increased 18.8% and 15.7% respectively and Cd conent in spinach was average decreased 14.5%. Besides, we also concluded that Cd content in plant was negative correlated with microbial concentration significantly.
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