AUTHOR=Zhu Yunna , Qi Baifu , Hao Yanwei , Liu Houcheng , Sun Guangwen , Chen Riyuan , Song Shiwei 

TITLE=Appropriate NH4+/NO3– Ratio Triggers Plant Growth and Nutrient Uptake of Flowering Chinese Cabbage by Optimizing the pH Value of Nutrient Solution

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 12 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.656144

DOI=10.3389/fpls.2021.656144

ISSN=1664-462X

ABSTRACT=Compared with sole N, the nutrition mixture of ammonium (NH4+) and nitrate (NO3-) is known to better improve crop yield and quality. However, the mechanism underlying this improvement remains unclear. In the present study, we analyzed the changes in nutrient solution composition, content of different N forms in plant tissues and exudates, and expression of plasma membrane H+-ATPase genes (HAs) under different NH4+/NO3- ratios (0/100, 10/90, 25/75, 50/50 as control, T1, T2, and T3) in flowering Chinese cabbage. We observed that compared with the control, T1 and T2 increased the economical yield of flowering Chinese cabbage 1.26- and 1.54-fold, respectively, whereas T3 significantly reduced plant yield. Compared with the control, T1–T3 significantly reduced the NO3- content and increased the NH4+, amino acid, and soluble protein contents of flowering Chinese cabbage to varying extents. T2 significantly increased the N use efficiency, whereas T3 significantly decreased it to only being 70.25% of that of the control. Owing to the difference in N absorption and utilization among seedlings, the pH value of the nutrient solution differed under different NH4+/NO3- ratios. At harvest, the pH value of T2 was 5.8; in the control and T1, it was about 8.0, and in T3 it was only 3.6. We speculated that appropriate NH4+/NO3- ratios may improve N absorption and assimilation and thus promote the growth of flowering Chinese cabbage, owing to the suitable pH value. On the contrary, addition of excessive NH4+ may induce rhizosphere acidification, causing plant growth inhibition. We further analyzed the transcription of plasma membrane H+-ATPase genes (HAs). HA1, HA6–8, HA10, and HA11 in the roots of flowering Chinese cabbage were significantly down-regulated by the addition of the mixture of NH4+ and NO3-, whereas HA2, HA3, and HA9 in the roots and HA6, HA9, and HA10 in the leaves were significantly up-regulated by the addition of this mixture. Our results provide valuable information about the effects of treatments with different NH4+/NO3- ratios on plant growth and N uptake and utilization.