Genotypic Responses of Rice to Ammonium and Nitrate under Contrasting Water Regimes: Agronomic, Biochemical, and Gene-Expression Analyses

In the study examining the responses of rice to ammonium and nitrate under various water regimes, researchers analyzed 48 recombinant inbred lines in both irrigated and rainfed environments over two growing seasons. Agronomic, physiological, biochemical, and molecular traits were assessed to determine the impact of genotype, nitrogen source, and environmental conditions.

Rainfed cultivation resulted in significantly lower grain and biological yields compared to irrigated conditions. Ammonium application resulted in a 26.2 g m-2 higher grain yield under irrigated conditions and 154.2 g m-2 under rainfed conditions, although the response varied among genotypes. Biological yield and SPAD values were generally higher with ammonium, while total chlorophyll exhibited season and environment-dependent responses.

Glutamine synthetase activity peaked under ammonium treatment, whereas glutamate synthase activity was higher under nitrate conditions. Grain yield was strongly correlated with biological yield, but correlations between grain yield and glutamine synthetase or glutamate oxidoreductase activity were insignificant. Gene expression of OsGln1.2, OsGln2, and OsGlt1 differed according to genotype, tissue, and nitrogen treatment.

The findings indicate that responses to nitrogen forms are influenced by genotype and environment, and that ammonium may offer a yield advantage in rainfed systems. By combining field performance with biochemical and molecular traits, researchers can identify rice varieties suited to water-limited conditions.