Fine root dynamics, longevity, and canopy characteristics of cotton under varying water and nitrogen levels

Purpose This study was conducted to understand the effects of water and nitrogen (N) on net root productivity, root longevity, root length, and canopy characteristics of cotton ( Gossypium hirsutum L.), and to quantify the associations between canopy characteristics and indicators of root dynamics. Methods A two-year field experiment was performed to evaluate the variation in canopy growth and root dynamics of cotton in response to three nitrogen levels (320 kg ha −1 , high N; 272 kg ha −1 , moderate N; 224 kg ha −1 , low N) and two water levels (400 mm, high-water group; 267 mm, low-water group) during the growing seasons of 2019 and 2020 in Xinjiang, China. Results Plants exposed to low-water environments increased root longevity more than all other high-water treatments. Under high-water conditions, a moderate N rate obtained a higher root longevity compared to high-N and low-N treatments. Net root productivity (NRP) was strongly associated with leaf area expansion rate and leaf number. A moderate N rate under high-water conditions exhibited a significant 30.0% increase in NRP, resulting in a relatively high leaf area and the highest leaf relative water content, and had an equivalent canopy photosynthetic rate compared with high-N plots. Plants receiving moderate N in the high-water group had greater total root length by increasing root longevity and productivity. Conclusions Estimates of NRP may need to be included along with leaf growth estimates in future efforts to scale from root to canopy level developmental performance in cotton. Graphical abstract