Quantification of Glucose Metabolism and Nitrogen Utilization in Two Species under Bicarbonate and Variable Ammonium Soil Conditions.

In karst habitats under drought conditions, high bicarbonate (high pH), and an abundant nitrate soil environment, bicarbonate regulates the glycolysis (EMP) and pentose phosphate pathways (PPP), which distribute ATP and NADPH, affecting nitrate (NO) and ammonium (NH) utilization in plants. However, the relationship between EMP PPP and NO, and NH utilization and their responses to bicarbonate and variable ammonium still remains elusive. In this study, we used (, a non-karst-adaptable plant) and (, a karst-adaptable plant) as plant materials, employed a bidirectional nitrogen-isotope-tracing method, and performed the quantification of the contribution of EMP and PPP. We found that bicarbonate and ammonium inhibited glucose metabolism and nitrogen utilization in under simulated karst habitats. On the other hand, it resulted in a shift from EMP to PPP to promote ammonium utilization in under high ammonium stress in karst habitats. Compared with , bicarbonate promoted glucose metabolism and nitrogen utilization in at low ammonium levels, leading to an increase in photosynthesis, the PPP, carbon and nitrogen metabolizing enzyme activities, nitrate/ammonium utilization, and total inorganic nitrogen assimilation capacity. Moreover, bicarbonate significantly reduced the growth inhibition of by high ammonium, resulting in an improved PPP, RC, and ammonium utilization to maintain growth. Quantifying the relationships between EMP, PPP, NO, and NH utilization can aid the accurate analysis of carbon and nitrogen use efficiency changes in plant species. Therefore, it provides a new prospect to optimize the nitrate/ammonium utilization in plants and further reveals the differential responses of inorganic carbon and nitrogen (C-N) metabolism to bicarbonate and variable ammonium in karst habitats.