Biochar induced improvement in root system architecture enhances nutrient assimilation by cotton plant seedlings

Lei Feng,Zengchao Geng,Wanli Xu,Guangmu Tang,Meiying Gu

doi:10.1186/s12870-021-03026-1

Lei Feng, Zengchao Geng + Show 3 more

Open Access

https://doi.org/10.1186/s12870-021-03026-1

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Abstract

BackgroundRaising nitrogen use efficiency of crops by improving root system architecture is highly essential not only to reduce costs of agricultural production but also to mitigate climate change. The physiological mechanisms of how biochar affects nitrogen assimilation by crop seedlings have not been well elucidated.ResultsHere, we report changes in root system architecture, activities of the key enzymes involved in nitrogen assimilation, and cytokinin (CTK) at the seedling stage of cotton with reduced urea usage and biochar application at different soil layers (0–10 cm and 10–20 cm). Active root absorption area, fresh weight, and nitrogen agronomic efficiency increased significantly when urea usage was reduced by 25% and biochar was applied in the surface soil layer. Glutamine oxoglutarate amino transferase (GOGAT) activity was closely related to the application depth of urea/biochar, and it increased when urea/biochar was applied in the 0–10 cm layer. Glutamic-pyruvic transaminase activity (GPT) increased significantly as well. Nitrate reductase (NR) activity was stimulated by CTK in the very fine roots but inhibited in the fine roots. In addition, AMT1;1, gdh3, and gdh2 were significantly up-regulated in the very fine roots when urea usage was reduced by 25% and biochar was applied.ConclusionNitrogen assimilation efficiency was significantly affected when urea usage was reduced by 25% and biochar was applied in the surface soil layer at the seedling stage of cotton. The co-expression of gdh3 and gdh2 in the fine roots increased nitrogen agronomic efficiency. The synergistic expression of the ammonium transporter gene and gdh3 suggests that biochar may be beneficial to amino acid metabolism.

Highlights

Raising nitrogen use efficiency of crops by improving root system architecture is highly essential to reduce costs of agricultural production and to mitigate climate change
Our results show that 25% urea reduction combined with biochar application led to nitrogen agronomic efficiency increase; in addition, ammonia-oxidizing bacteria (AOB) and mineral nitrogen increased in both the rhizospheres of the very fine and fine roots, with larger increases for the very fine roots
The increased Glutamic-pyruvic transaminase activity (GPT) and glutamate dehydrogenase (GDH) activities were the reason for the higher nitrogen assimilation at the seedling stage under reduced urea plus biochar application conditions

Summary

Introduction

Raising nitrogen use efficiency of crops by improving root system architecture is highly essential to reduce costs of agricultural production and to mitigate climate change. Studies suggest that biochar changes crop nitrogen utilization efficiency and increases rhizosphere microbial community diversity [13, 14] which is strongly associated with root order [15]. Biochar increases microbial biomass [16] and especially the abundance of ammonia-oxidizing bacteria (AOB) which are closely related to the nitrogen cycle [17] and cause great variation in the NO3−-N/ NH4+-N ratio in the rhizosphere of different root orders. Though there are many studies on the effects of AOB on the NO3−-N/NH4+-N ratio, little is known about the mutual effects between mineral nitrogen, rhizosphere AOB community, and root order when biochar is applied in gray desert soils

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