Table 2.

Equations used to estimate ecosystem N stocks, N fluxes, nitrogen use efficiency, and nitrogen strategy indices

No.	Formula	Variable Explanation
Formula 1		w: Biomass (kg);  D: Denote diameter at breast height (cm);  H: Tree height (m); For stem biomass estimation, a = 0.0334 and b = 0.9171; For branch biomass, a = 0.0028 and b = 0.9417; For leaf biomass, a = 0.0050 and b = 0.7309; For coarse root biomass, a = 0.0226 and b = 0.8520.
Formula 2		: Stock of total nitrogen (t·ha− 1) or alkali-hydrolyzable nitrogen (t·ha− 1) in a specific soil layer;  BD: Denotes soil bulk density (g·cm− 3) of the corresponding layer; : Concentration of total nitrogen (g·kg− 1) or alkali-hydrolyzable nitrogen (mg·kg−¹) in that soil layer;  Z: Thickness of the soil layer (cm);  10: A conversion coefficient used for unit standardization.
Formula 3		: Amount of nitrogen resorption from litter collected at the i-th sampling (t·ha− 1); : Nitrogen concentration in the litterfall needles collected at that sampling (g·kg− 1); : Nitrogen concentration in mature needles (g·kg− 1);  MLCF: Correction factor for mass loss during leaf senescence; in this study, the average correction coefficient of 0.745 for conifer functional groups proposed by Vergutz et al. was adopted;Litterfall needle biomass collected at the i-th sampling (t·ha−¹).
Formula 4		ANRA:Calculated as the sum of the nitrogen resorption() from needles across all sampling events within one year (t·ha− 1).
Formula 5		NUE: Nitrogen use efficiency;: Annual increment in tree biomass (t·ha− 1); : Annual increment in tree N stock (t·ha− 1).
Formula 6		NCC: Nitrogen cycling coefficient; : Annual nitrogen return (t·ha− 1); : Annual nitrogen uptake (t·ha− 1).
Formula 7		NUpE: Nitrogen uptake efficiency; : Total soil nitrogen stock in the 0–30 cm soil layer (t·ha− 1).
Formula 8		SSNE: Nitrogen enrichment in topsoil; : Nitrogen stock in the 0–1 cm topsoil (t·ha− 1); : Nitrogen stock in the 0–10 cm soil layer (t·ha− 1).
Formula 9		SANP: Proportion available nitrogen in soil; : Available soil nitrogen stock in the 0–30 cm profile (t·ha− 1).
Formula 10		FFNA: Accumulation of nitrogen in forest floor litter; : Nitrogen stock of areal accumulated litter (t·ha− 1).
Formula 11		LTR: Turnover rate of forest floor litter;  ALB: Annual litterfall biomass (t·ha− 1);  FLB: Forest floor litter biomass (t·ha− 1).
Formula 12		INC: Internal nitrogen cycling; : Nitrogen concentration in mature green needles during the growing season (g·kg− 1); : Nitrogen concentration in freshly fallen needle litter (g·kg− 1).