Response of Macleaya cordata biomass and its distribution characteristics to nitrogen in the reclamation area of a coal mine

To study dynamic changes in biomass and total biomass allocation of Macleaya cordata at different growth stages and nitrogen application gradients, a two-year continuous nitrogen application experiment was conducted from 2020, and the growth adaptation characteristics of M. cordata in poor soil were revealed. Five nitrogen application levels were set up: CK (0 kg·hm⁻²), N₁ (75 kg·hm⁻²), N₂ (150 kg·hm⁻²), N₃ (225 kg·hm⁻²), and N₄ (300 kg·hm⁻²). The results were as follows: (1) The shoot biomass, root biomass, and total biomass of M. cordata were significantly higher than those of CK, N₁, and N₂ (P < 0.05). (2) The root/shoot ratios of M. cordata varied in different years. The root/shoot ratios of all treatments in the first year were the lowest in June (0.04, 0.12, 0.09, 0.15, and 0.16) and the lowest in August in the second year (0.20, 0.18, 0.08, 0.06, and 0.10) in June and August 2021, and the root/shoot ratios of CK were higher than those of other treatments. (3) In 2020, the stem/leaf ratio of N₃ was significantly higher than that of other treatments in October (P < 0.05). The stem/leaf ratio of other treatments had no significant difference between months. The stem/leaf ratio of 2021 treatments increased gradually with the recovery time and peaked in November (2.82, 1.19, 1.23, 1.89, and 2.05). In conclusion, 225 kg·hm⁻² to 300 kg·hm⁻² should be applied to M. cordata in coal mine reclamation areas to promote rapid colonization of M. cordata in poor soil. This study may provide a theoretical basis for the study of growth adaptability of M. cordata in nitrogen-deficient soil.