莴笋对不同形态氮素的反应

探讨了不同形态氮素对莴笋生长发育的影响及其营养特性。结果表明，莴笋幼苗根系对NH4^+ -N的亲和力稍大于NO3^- -N的亲和力；分别供给NO3^- -N+NO3^- -N及NH4^+ -N，莴笋的生物学产量和吸N量均依次递减（分别为100：56.9：12.4，100：48.9：8.6），因此在水培条件下，NO3^- -N是最适合莴笋生长发育的氮源，NH4^+ -N与NO3^- -N各占50％时对莴笋的生长发育已有一定的抑制作用，仅以NH4^+ -N作氮源则莴笋很难生长；NH4^+ -N与NO3^- -N各占50％时，莴笋倾向于吸收较多的NH4^+ -N，而且在培养不同阶段NH4^+/NO3^-吸收比例均大于1，莴笋表现出喜铵性，但NH4^+ -N并非莴笋很适合的氮源；营养液中NO3^- -N不足，主要影响莴笋茎叶的生长，而NH4^+ -N所占比例达50％时，莴笋根系生长受到抑制，且有明显的受害症状；以NO3^- -N作氮源预培养两周，以含微量NO3^- -N的自来水为水源，再单独以NH4^+ -N为氮源，对莴笋生长有极大的促进作用，同时还大幅度降低了体内硝酸盐的含量。尿素作氮源莴笋未出现受害症状，但莴笋的生长发育状况明显劣于其它氮源。

Response of lettuce to different nitrogen forms

Solution culture experiment was adopted to investigate the influence of different nitrogen forms on lettuce growth and development and their nitrogenous nutritional characteristics. The results showed that the affinity of the roots of lettuce seedlings to ammonium nitrogen (NH4(+)-N) was slightly higher than that to nitrate nitrogen (NO3(-)-N). Among three treatments of NO3(-)-N, NH4(+)-N+ NO3(-)-N and NH4(+)-N, the relative proportion of biological yields of lettuce was 100:56.9:12.4, and that of nitrogen uptake amount was 100:48.9:8.6, respectively. Nitrate nitrogen was the most suitable N source to lettuce growth. When the respective proportion of NH4(+)-N and NO3(-)-N was 50%, the growth of lettuce was inhibited to some extent. When the nitrogen source supplied as solely NH4(+)-N, lettuce was hard to grow normally. When supplying the same amount of NH4(+)-N and NO3(-)-N, lettuce showed a tendency to absorb more NH4(+)-N than NO3-N. At different culture stages, the ratio of NH4(+)-N to NO3(-)-N absorbtion was less than 1. It seemed that lettuce did prefer NH4(+)-N to NO3-N in absorbtion. However, ammonium nitrogen as nitrogen source was not suitable to lettuce for its metabolism. When nitrate nitrogen was not sufficient, it mainly affected the growth of lettuce shoot; when the ammonium nitrogen in nutrient solution was 50%, the root growth of lettuce seedlings was greatly inhibited, and some pathological symptoms appeared. Taking running water as water source (in which, NO3(-)-N concentration was about 0.5 mol.L-1) and lettuce was cultured by supplying sole NO3(-)-N for two weeks and then supplying NH4(+)-N, the growth of lettuce was greatly stimulated, in the meantime, the NO3(-)-N contents and total accumulation amount greatly decreased. Supplying urea as N source, the growth rate of lettuce was apparently inferior to other nitrogen forms, but no pathological symptoms appeared.