[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.
Tian
Xiaohong
X
Department of Resources and Environmental Sciences, Northwest Sci-tech University of Agriculture and Forestry, Yangling, Shaanxi 712100, China. txhong@hotmail.com
Li
Shengxiu
S
Wang
Zhaohui
Z
Yin
Xiangtao
X
Chen
Shixiang
S
D000042:Absorption; D018545:Lactuca / Q000254:growth & development / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism
D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D009584:Nitrogen