Effect of nitrate inhibitors on endogenous nitrate metabolism in Chinese cab-bage

Soil-pot experiment consisting of a control treatment (with nitrate-N∶ammonium-N = 2∶3 denoted as S1) and 3 trial treatments (with application of dicyandiamide, imidazole and pyridine nitration inhibitors on the base of S1 and respectively denoted as S2, S3 and S4) were conducted to study the effects of nitrate inhibitors on endogenous nitrate metabolism in Chinese cabbage. Results showed that the 3 nitrate inhibitors increased vegetable cabbage yield by 6.06%~28.55%, N absorption by 2.38%~38.42% compared with S1. S2, S3 and S4 treatments decreased plant nitrate concentration by 2.69%~19.66% and increased leaf NRA (nitrate reductase activity), MPS (metabolic pool size), SPS (storage pool size) and MPS/SPS by 24.28%~77.32%, 29.45%~272.17%, 2.78%~17.38% and 0.04%~0.59%, respectively. This subsequently enhanced the availability of endogenous nitrate in Chinese cabbage. Treatment S2 had the highest improvement in yield, N absorption and availability of endogenous nitrate in Chinese cabbage. Treatment S2 yield and absorption amounts of N were 56.72 g·pot^-1 and 0.156 g·pot^-1, respectively. However, plant nitrate content in S2 (1 749 mg·kg^-1) was relatively low. Leaf NRA and MPS in S2 were 1.90 μg(NO₂^--N)·30 min^-1·g^-1(FW) and 0.33 μg(NO₂^--N)·g^-1(FW), respectively.