Different genotypes of tartary buckwheat can regulate the transformation of nitrogen through the secretion of organic acids under low nitrogen stress

Abstract

Roots respond to nitrogen deficiency by altering their physiological and metabolic responses. Soil nitrogen invertase activity and the diversity of nitrifying microorganisms (AOA and AOB) significantly affect the nitrogen cycle in soil. As an important part of root exudates, organic acids can reflect the dynamic changes of plant roots in soil. However, it is not clear how the barren-tolerant genotype plant varieties show their stress resistance through organic acids regulating nitrogen transformation under low nitrogen environment. Here, we selected two Tartary buckwheat varieties: HeiFeng1 (HF, low nitrogen sensitive cultivar) and DiQing (DQ, low nitrogen tolerance cultivar) for a two-year experiment. The urea addition levels of 0, 80, and 160 mg kg−1 soil were respectively set as nitrogen sources, and ozone sterilization experiments were designed to completely remove microbial effects to distinguish the contribution of plant roots and microorganisms to nitrogen invertase and organic acids (400 ml 1 mol L−1 ozone water daily, 0 nitrogen fertilizer, O3). The results showed that malic acid and tartaric acid were the main organic acids secreted by tartary buckwheat. The total amount and richness of organic acids in Diqing were higher than those in Heifeng, and organic acids directly affected the diversity of ammonia-oxidizing microorganisms (AOA and AOB), changed the soil environment by affecting soil water content, and indirectly affected the activity of nitrogen invertase. At the same time, it was found that the increase of nitrogen application rate would increase the proportion of key bacteria such as Nirtrosomonas and Nitrosospira in AOB of tartary buckwheat soil. Finally, Diqing tartary buckwheat was proved to be more suitable for planting in the nitrogen-deficient Loess Plateau, but attention should be paid to the negative effects of AOB and organic acids.