ABSTRACT
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 (NO3-) and ammonium (NH4+) utilization in plants. However, the relationship between EMP PPP and NO3-, and NH4+ utilization and their responses to bicarbonate and variable ammonium still remains elusive. In this study, we used Brassica napus (Bn, a non-karst-adaptable plant) and Orychophragmus violaceus (Ov, 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 Bn under simulated karst habitats. On the other hand, it resulted in a shift from EMP to PPP to promote ammonium utilization in Ov under high ammonium stress in karst habitats. Compared with Bn, bicarbonate promoted glucose metabolism and nitrogen utilization in Ov 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 Ov by high ammonium, resulting in an improved PPP, RCRUBP, and ammonium utilization to maintain growth. Quantifying the relationships between EMP, PPP, NO3-, and NH4+ 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.
ABSTRACT
Karst habitats are uniquely characterized by high bicarbonate, high nitrate, and low ammonium, which are in-conducive to their growth and biodiversity. The occurrence of inorganic carbon and nitrogen in karst soil profoundly affects the carbon/nitrogen metabolism and adaptability of plants. However, there has been no final conclusion to the joint interactions of carbon and nitrogen metabolism in plants under karst habitats. In this study, we selected a karst-adaptable plant Orychophragmus violaceus (Ov), and a non-karst-adaptable plant Brassica napus (Bn) as experimental plants, and compared their joint effects of carbon and nitrogen metabolism under simulated karst habitats. It was found that the two species had different joint effects of carbon and nitrogen metabolisms. Bicarbonate and nitrate joint promoted photosynthetic activity and glucose metabolism, facilitating the carbon/nitrogen metabolism and growth of Ov, but their impacts on the carbon and nitrogen metabolism were insignificant in Bn. Bicarbonate and ammonium joint inhibited the photosynthesis and nitrogen metabolism, but promoted water use efficiency in Ov, leading to its enhance of growth reduction, ammonium toxicity alleviation, and drought resistance, while they inhibited the water use efficiency of Bn. In general, bicarbonate and nitrate/ammonium more significantly joint affected the carbon and nitrogen metabolism in Ov than Bn, which is vital for Ov to adapt to karst habitats.
