铵硝比和磷素营养对菠菜生长、氮素吸收和相关酶活性的影响

通过水培试验研究了不同铵硝比的氮素营养和磷素营养对菠菜生长、氮素吸收及硝酸还原酶活性（NRA）和谷氨酰胺合成酶活性（GSA）的影响。结果表明：在供磷水平相同时，菠菜的生物量随着铵硝比的降低而降低，但铵硝比为25：75与0：100两个处理之间没有显著差异；在铵硝比相同时，随着营养液中磷含量的增加，菠菜的生物量随之增加。菠菜茎叶中硝酸盐的含量随着铵硝比和磷水平的降低而升高。不同铵硝比处理，菠菜含氮量没有明显差异，随着磷水平的提高，菠菜植株含氮量有升高的趋势，但各处理之间差异不显著；受到生物量显著差异的影响，菠菜植株中氮素累积量随着铵硝比的降低和磷素水平的增加而增加。在铵硝混合营养条件下，缺磷会显著抑制菠菜对铵态氮和硝态氮的吸收，且磷索缺乏对菠菜吸收硝态氮的抑制作用要大于对铵态氮吸收的抑制作用。铵硝比相同时，随着营养液中磷索供应量的增加，菠菜茎叶中NRA显著增加；但是营养液中铵硝比较高时，会显著抑制菠菜茎叶中NRA，而铵硝比较低时，则有利于提高菠菜的NRA。缺磷会严重抑制GSA；在磷素水平相同时，随着营养液中铵比例的增加，菠菜茎叶中GSA显著增加。为此，在一些硝酸盐含量较高的土壤上栽培蔬菜时，可以采取增施适量磷肥的方法，以降低叶菜的硝酸盐含量。

EFFECTS OF NH4+ -N/NO3- -N RATIO AND PHOSPHORUS LEVELS ON GROWTH, NITROGEN UPTAKE AND RELEVANT ENZYMES ACTIVITY OF SPINACH ( SPINACIA OLERACEA L. )

A solution culture experiment was conducted to study effects of NH₄⁺-N/NO₃^--N ratio and phosphorus level on growth,and nitrogen uptake of spinach and activities of nitrate reductase (NRA),glutamine synthetase (GSA) therein.Results show that spinach plants in nutrient solutions,the same in phosphorus supply level,decreased in biomass with decreasing NH₄⁺-N/NO₃^--N ratio,but differed slightly between solutions of 25 75 and 0 100 in NH₄⁺-N/NO₃^--N ratio.In treatments the same in NH₄⁺-N/NO₃^--N ratio,spinach plants increased in biomass with rising phosphorus level in the nutrient solutions.Nitrate levels in spinach shoots increased with decreasing NH₄⁺-N/NO₃^--N ratio and phosphorus level,but did not vary much between treatments different in NH₄⁺-N/NO₃^--N ratio.Spinach nitrogen content increased with phosphorus level,but did not show much difference between treatments different in NH₄⁺-N/NO₃^--N ratio.Nitrogen accumulation in spinach markedly increased with decreasing NH₄⁺-N/NO₃^--N ratio and increasing phosphorus level,which were concurrent with the increase in spinach biomass.In solutions of mixed NH₄⁺-N and NO₃^--N,phosphorus deficiency significantly inhibited spinach uptake of NH₄⁺-N and NO₃^--N.When the NH₄⁺-N/NO₃^--N ratio was 25 100,the NH₄⁺-N amount absorbed by spinach growing in the solution deficient in phosphorus ac counted for 27.2% of the total nitrogen uptake,however,it dropped to 16.9% in the solution adequate in phosphorus.When the NH₄⁺-N/NO₃^--N ratio was kept at 50 50,the value was 45.4% and 23.9%,respectively.Apparently,the uptake of NH₄⁺-N was less depressed by phosphorus deficiency than the uptake of NO₃^--N.With increasing phosphorus level,NRA of spinach markedly increased in treatments the same in NH₄⁺-N/NO₃^--N ratio,but with higher NH₄⁺-N/NO₃^--N ratios,NRA of spinach was depressed,and it increased when the ratio was lower.Moreover,phosphorus deficiency depressed GSA seriously.At the same phosphorus level,GSA of spinach shoot increased pronouncedly with increasing NH₄⁺ N in nutrient solutions.There fore,it is feasible to decrease nitrate level of some leafy vegetables that are grown on those soils high in nitrate by applying more phosphorus fertilizer.