2.3 Measurements of total N and carbohydrates content

Leaf-age, plant height and tiller numbers were measured at true leaf-age four and six, respectively. Tiller occurrence percentage was calculated as total tiller number divided by main stem number, reflecting plant consistency at 4th true leaf emerging stage as each plant usually has only one tiller. Plants were harvested at true leaf-age six for biomass measurement (at 25-27 days post-seeding). The plants were separated into leaf, sheath, and new-born tillers (with less than 3 true leaves) for N content analysis using Kjeldhal method with an automatic Kjeltec 8400 Analyzer Unit (Foss Analytical AB, Höganäs, Sweden) following the manufacturer’s recommendations. For carbohydrates measurement, plants were further separated into new-born tillers, leaves (leaf positions 1-5), or sheaths (upper and lower parts). Carbohydrates were measured by anthrone reagent (Zhang et al, 2019).