Effects of nickel on growth and nutritional ingredients of water spinach（ Ipomoea aquatica Forsk.）

The paper investigated the effects of various concentrations of nickel on growth，urease activity and some nutritional ingredients of hydroponic water spinach by supplying urea nitrogen as the only nitrogen source. The results indicated that appropriate quantity of nickel could enhance the growth，urease activity and amino acids synthesis of water spinach，while excessive nickel was toxic to water spinach. The treatment of 20 μg/L nickel resulted in the highest fresh weight of water spinach，12.1% higher than that in control，while significant reduction of water spinach fresh weight was detected with nickel supply higher than 320 μg/L，and significant plant damage symptoms were observed with 1 280 μg/L nickel treatment. This results also showed that appropriate concentrations of nickel（ 20-80 μg/L） could significantly increase the urease activity up to 13.6%，while the urease content also raised up to 19.0%，but excessive nickel supply（ more than 640 μg/L） inhibited the urease activity. Physiological analysis demonstrated that adequate nickel concentration（ 60 μg/L） firstly enhanced the specific activity of urease， then participated in the urease synthesis to improve the urease yield，and ultimately improved the overall urease activity. This results also identified that the total amino acids content increased simultaneously as the concentrations of nickel raised within the range of 0-40 μg/L with a highest increase of 44.7%，this effect became significant and stable with nickel over 10 μg/L；the content of soluble carbohydrates in leaves significantly increased with treatments of over-concentrated nickel（ more than 640 μg/L）.