Thirty-years long-term rice-rice-rape rotation optimizes 1,2-benzenediol concentration

Differences in soil metabolites from the rice root rhizosphere and the effects of 1,2-benzenediol on nitrogen use efficiency and rice growth were examined under 30-years long-term rice-rice-fallow and rice-rice-rape rotations.

The metabolite composition of rice rhizospheres was analyzed using the gas chromatography mass spectrometry. A range of 0.2, 2.0 and 200 μmol L−1 concentrations of external 1,2-benzenediol were applied to examine their effects on rice growth, nitrate reductase and glutamine synthetase activities, and physiological nitrogen-use efficiency. The metabolite composition of rhizospheres differed significantly between rice-rice-fallow and rice-rice-rape rotations. Soil total nitrogen and 1,2-benzenediol concentrations during the early rice season were significantly lower under rice-rice-rape than under rice-rice-fallow rotations. Rice growth and nitrogen use efficiency significantly enhanced at 0.20 μmol 1,2-benzenediol L−1 , but inhibited at 2.0 μmol 1,2-benzenediol L −1 or higher. Changes in root morphology and uptake associated with 1,2-benzenediol possibly had contributed to a higher nitrogen use efficiency of the early season rice under rice-rice-rape rotations. The activity of nitrate reductase and glutamine synthetase in rice roots were significantly higher with external 0.2 μmol 1,2-benzenediol L−1 application than without 1,2-benzenediol treatment. Crop rotation significantly affected rice rhizosphere metabolites. An optimal soil 1,2-benzenediol concentration under 30-years long-term rice-rice-rape rotation may be associated with an enhanced nitrogen use efficiency and root nitrogen uptake and assimilation, resulting in an increased rice growth and yield.