不同氮形态对镉胁迫下小白菜生长及镉含量的影响

【目的】研究施用速效氮肥（全铵、全硝、硝铵复合和尿素）对镉（Cd）污染土壤小白菜生长和Cd含量的影响，为合理选择氮肥，缓解Cd对植物生长的胁迫并减少Cd在作物体内的积累提供依据。【方法】以小白菜为试材，采用菜园土进行了盆栽试验。以CdCl2溶液模拟土壤Cd胁迫，设土壤Cd含量0、1、3和5 mg/kg 4个水平，每个胁迫水平分别供应小白菜铵态氮、硝态氮、硝铵（1:1）和尿素4种氮形态，总氮添加量均为N 400 mg/kg土。收获后分析各处理间小白菜的生长、光合、氧化胁迫及Cd含量的差异。【结果】 1）与无Cd对照相比，Cd 1 mg/kg处理水平下，全铵、全硝、硝铵和尿素处理的小白菜可食部分鲜重分别下降了31%、16%、21%和26%；Cd 3 mg/kg处理水平下分别下降了58%、28%、35%和39%；Cd 5 mg/kg处理水平下分别下降了83%、38%、52%和69%。全硝和硝铵处理间小白菜Cd耐受系数（TICd）差异不显著，但均高于全铵和尿素处理。2）与无Cd对照相比，Cd 1 mg/kg处理下，全铵、全硝、硝铵和尿素处理小白菜叶片的光合速率分别下降了14%、10%、12%和13%；Cd 3 mg/kg处理分别下降了33%、22%、25%和40%；Cd 5 mg/kg处理分别下降了53%、42%、41%和56%。与无Cd对照相比，1 mg/kg Cd浓度时全铵、全硝、硝铵和尿素处理小白菜叶片的丙二醛含量分别增加了11%、4%、9%和11%；超氧自由基产生速率分别增加了5%、1%、2%和4%，综合比较，以全硝处理下小白菜受Cd的光合抑制及氧化胁迫相对最小。3）3个Cd处理水平，均以施用全铵和尿素处理的小白菜体内Cd含量最高，硝铵处理次之，全硝处理最低。【结论】在供试菜园土上，小白菜施用铵态氮和尿素易引起Cd在小白菜体内的积累。施用硝态氮可缓解Cd诱导的光合抑制和氧化胁迫，减轻Cd对小白菜的生长胁迫，降低作物体内Cd的含量。

Effects of nitrogen forms on the growth and Cd concentration of pakchoi (Brassica chinensis L.) under Cd stress

Objectives] Effects of common nitrogen (N) supply forms (ammonium,nitrate,ammonium/nitrate and urea) on the growth of Chinese cabbage pakchoi (Brassica chinensis L.) grown in the cadmium (Cd)-contaminated soil were studied to develop proper nitrogen management strategies for Cd-contaminated soils.Methods] A pot experiment was conducted using soils from vegetable garden in Hangzhou.The tested soil was adjusted to four Cd contamination levels (0,1,3 and 5 mg/kg) with CdC12 solution in advance.Four N supply forms ammonium,nitrate,ammonium/nitrate (1 ∶ 1) and urea] were supplied for the pakchoi respectively,with the addition amount of N 400 mg/kg soil.After the harvest,the biomass,photosynthesis,Cd-induced oxidative stress and Cd concentration of the plants in different treatments were investigated.Results] 1) Compared with the Cd 0,the fresh weights of the edible parts ofpakchoi were reduced by 31％,16％,21％ and 26％ in Cd 1,by 58％,28％,35％ and 39％ in Cd 3,and by 83％,38％,52％ and 69％ in Cd 5 in the presence of ammonium,nitrate,ammonium/nitrate and urea,respectively.There were no significant differences in the tolerance index (TIcd) between the nitrate and ammonium/nitrate treatments,and the tolerance indices of the nitrate and ammonium/nitrate treatments were higher than those of the ammonium and urea treatments.2) Compared with Cd 0,the photosynthetic rates in the plants exposed to ammonium,nitrate,ammonium/nitrate,and urea were significantly decreased by 14％,10％,12％ and 13％ in Cd 1,by 33％,22％,25％ and 40％ in Cd 3,and by 53％,42％,41％ and 56％ in Cd 5;the levels of MDA and O2-production rates were increased by 11％,4％,9％ and 11％,and 5％,1％,2％ and 4％ in Cd 1,respectively.The Cd induced-photosynthesis inhibition and oxidative stress were relatively lower in the pakchoi with nitrate supply.3) The content of Cd in pakchoi were in the order of:nitrate ＜ ammonium/nitrate ＜ urea and ammonium treatments.Conclusions] In the Cd-contaminated soils,nitrate N was more effective than ammoniam N in alleviating the Cd induced photosynthesis inhibition and oxidative stress and ultimately decreased the Cd contents in plants.