[Effects of purified humic acid on the growth and nitrogen metabolism of cucumber seedlings under nitrogen stress.]

in cucumber seedlings was affected by PHA, showing increased nitrate content in cucumber seedlings under low nitrogen stress and decreased under high nitrogen stress. PHA significantly decreased ammonium content in roots and leaves under low and high nitrogen stress. Compared with normal level of nitrogen (CK), NR, GS, GOGAT, GDH activity in roots and leaves and NiR activity in roots significantly decreased under low and high nitrogen stress. PHA increased the activities of NR, NiR, GS, GOGAT, and GDH to different extents. PHA increased amino acid and soluble protein content in cucumber seedling roots and leaves. In summary, PHA addition alleviated the inhibitory effect of nitrogen stress on the growth of cucumber seedlings.