The species-specific responses of nutrient resorption and carbohydrate accumulation in leaves and roots to nitrogen addition in a subtropical mixed plantation

Ephemeral tissues such as leaves and fine roots are sensitive to nutrient alteration. Whether nutrient addition can influence the linkage between nutrient resorption and carbohydrate accumulation in leaves and roots is not clear. We measured nitrogen (N) and phosphorus (P) concentrations and nonstructural carbohydrates (NSC) of the <one- and >one-year-old leaves and absorptive and transportive roots in two species of a mixed plantation during the dormant and growing seasons within an N-addition experiment. Nitrogen addition decreased N and P resorption efficiencies (NRE and PRE, respectively) in leaves of Chinese fir and increased PRE in absorptive roots of Chinese fir but did not alter either efficiency in any tissues of Chinese sweetgum. Nitrogen addition increased starch accumulation efficiency (STAE) in >one-year-old leaves of Chinese fir but decreased soluble sugar accumulation efficiency (SSAE) in absorptive roots of Chinese sweetgum. Both NRE and PRE were negatively correlated with SSAE, STAE, and NSC accumulation efficiency (NSCAE) in >one-year-old leaves of Chinese fir, but this pattern was not found in leaves of Chinese sweetgum. Our study indicates that N addition can influence the linkage between nutrient resorption and NSC in leaves and roots, and this response to nutrient availability is species-dependent.