Objective In the context of increasing atmospheric nitrogen deposition in China, clarifying the effects of exogenous nitrogen input on the growth of Metasequoia glyptostroboides shelterbelts is helpful, which is beneficial for providing scientific guidance for nutrient management to support the healthy growth of shelterbelts.

Method The study focused on 12-year-old Metasequoia glyptostroboides shelterbelt on the muddy coast of Dontai City, Jiangsu Province, China, by applying four levels of continuous nitrogen addition treatments over eight years, including a control treatment (CK, 0kg·hm⁻²·a⁻¹), low nitrogen addition (LN, 56 kg·hm⁻²·a⁻¹), medium nitrogen addition (MN, 168 kg·hm⁻²·a⁻¹), and high nitrogen addition (HN, 280 kg·hm⁻²·a⁻¹), to investigate the effect of nitrogen addition on annual growth of the diameter at breast height (DBH) of Metasequoia glyptostroboides, and the its large trees and small trees (classified based on initial average DBH).

Result Nitrogen addition level, year, and their interaction, significantly affected the DBH annual growth of Metasequoia glyptostroboides. Nitrogen addition had a non-linear impact on the DBH annual growth of Metasequoia glyptostroboides, and the promotion effect of medium nitrogen addition was stronger than those of low and high nitrogen levels. The trends in DBH annual growth of Metasequoia glyptostroboides was consistent across years: the promotion effect of nitrogen addition gradually increased in the early stage (nitrogen addition in 1-3 years), then the promotion gradually weakened (nitrogen addition in 4-6 years), and then turned into an inhibitory effect (nitrogen addition in 7-8 years). Under the same nitrogen addition treatment level, DBH class and year significantly affected growth of Metasequoia glyptostroboides but there was no interaction. For small trees, nitrogen addition level, year, and their interaction significantly affected DBH growth. For large trees, only the year of nitrogen addition significantly affected DBH growth. The DBH annual growth of small trees was lower than that of large trees, while their response to growth (lnRR) was higher than that of large trees.

Conclusion The DBH growth of large trees is higher than small ones of Metasequoia glyptostroboides, but the promoting effect of nitrogen addition on the DBH growth of small trees is stronger than that on large trees, indicating that the growth of small trees is more easily influenced by exogenous nitrogen input. At the same time, with the increase of years, nitrogen addition first promotes and then inhibits the DBH growth of of Metasequoia glyptostroboides, suggesting that long-term nitrogen deposition will be unfavorable to the growth of Metasequoia glyptostroboides shelterbelts along the muddy coastal areas.