Effects of nitrogen levels on root characteristics of ramie genotypes possessing different nitrogen recovery efficiency

The root is the main organ of ramie for absorbing nitrogen. It is therefore, important to study the responses of ramie root under different nitrogen levels for variety improvement and agronomic-trait modification. This paper focused on root characteristics and response by root, and their relationship to nitrogen recovery efficiency (NRE). A potted experiment was conducted using two ramie varieties with different nitrogen utilization efficiency, and there were: 0, 6, 9, 12 and 15 mmol·L-1 nitrogen levels. The results showed that different parameters of ramie root had different responses under different nitrogen levels. The total absorption area (TAA), active absorption area (AAA) and root area∶volume ratio (A∶V), all were found to increase with the increasing nitrogen levels, but no significant effect was detected on root length (RL) in the experiment. Ramie root volume (RV) and activity (RA) were enhanced by increasing nitrogen levels. RV of H2000-03 with high NRE peaked at 12 mmol·L-1, which was 3.06 times of unfertilized N. RV of Ceheng Jiama with low nitrogen efficiency peaked at 9 mmol·L-1, which was 2.38 times of unfertilized N. RV and RA reduced after exceeding a certain amount of nitrogen, among which the RA of Ceheng Jiama was reduced by 67.5% at the rapid growth stage of the plant. Highest NRE was detected for 9 mmol·L-1 due to the significant changes in root parameters measured. H2000-03 showed significantly higher RL, RV, TAA and AAA than Ceheng Jiama. These parameters also could be maintained at a higher level in H2000-30 along its growth stages. Unfertilized N significant difference was detected in A∶V and RA between the two varieties, which was key for improvement of ramie root characteristics. The key periods which affected NRE and nitrogen accumulation of ramie shoots mostly were the later stages of plant growth and the key attributes were root quantity and root surface characteristics.