Abstract:

Objective: This study aims to investigate the effects of different fertilization treatments on the growth and wood quality parameters of Chinese fir (Cunninghamia lanceolata), thereby providing a theoretical basis for cultivating high-quality large-diameter timber and achieving sustainable forest management. Method: Based on a long-term fertilization experimental platform for Chinese fir plantations, four treatments were set up: control, nitrogen application alone (100 kg·hm^?2 a^?1), phosphorus application alone (50 kg·hm^?2 a^?1), and combined application of nitrogen and phosphorus (100 kg·hm^?2 a^?1 N + 50 kg·hm^?2 a^?1 P). The fertilization experiment was initiated in 2012, with fertilizers applied four times annually (in March, June, September, and December, at proportions of 30%, 30%, 20%, and 20%, respectively). Nitrogen and phosphorus fertilizers were applied in the forms of ammonium nitrate and sodium dihydrogen phosphate, respectively, mixed uniformly with river sand. Tree-ring analysis was employed to measure annual ring width and latewood rate for each year from 2011 to 2023. The responses of growth and wood property indicators to long-term fertilization were analyzed based on the inter-annual coefficient of variation (CV) of ring width and latewood rate, along with fertilization effect values. The piecewise linear regression and mixed-effects models were used to identify the impacts of fertilization duration and tree diameter class on these indicators. Result: 1) Compared to single-nutrient applications, the combined application of the N+P dampened the interannual fluctuations in ring width and latewood rate caused by extreme drought, buffering tree growth sensitivity and yielding wood uniformity comparable to the control. 2) Under the N+P treatment, the cumulative promoting effect on growth peaked after four consecutive years of fertilization, resulting in a 31.8% increase in cumulative ring width compared to the control. Concurrently, the decrease in cumulative latewood rate was more moderate than that under the P-alone treatment and remained similar to the control levels. 3) The N+P combination alleviated competition among trees of different diameter classes, promoted overall stand growth, and effectively suppressed the diameter class differentiation phenomenon induced by single-nutrient fertilization. Conclusion: It is recommended to implement a combined nitrogen and phosphorus application regimen on a four-year cycle in mid-aged C. lanceolata stands. This approach aims to enhance growth rates while ensuring uniformity in wood texture and maintaining hardness.

Key words: Cunninghamia lanceolata; nitrogen and phosphorus fertilization, tree-ring width, latewood rate, drought response, sustainable management