Contrasting effects of N addition on the N and P status of understory vegetation in plantations of sapling and mature Larix principis-rupprechtii

Aims The productivity of forest plantations in temperate areas is often lim-ited by nitrogen(N),but may shift towards phosphorus(P)limitation with increasing atmospheric N deposition.Nutrient resorption is a nutrient conservation strategy in plants.Although data on nutrient resorption are available for overstory trees,there are few data for understory vegetation.Methods We examined leaf N and P concentrations and N and P resorption efficiencies(NRE and PRE,respectively)in eight understory species in 11-and 45-year-old Larix principis-rupprechtii stands subjected to N supplementation over a 3-year period.Important findings Leaf N concentrations and N:P ratios increased and P concentrations decreased,with N input in species within the 45-year-old stand,but not in the 11-year-old stand.NRE and PRE were not altered by N input in any of the species in either stand,but N resorption pro-ficiency decreased and P resorption proficiency increased,in the species in the 45-year-old stand.Thus,the growth of understory species may be more P-limited in the 45-versus 11-year-old stand,and nutrient resorption proficiency was more sensitive to N add-ition than nutrient resorption efficiency.These results will improve the understanding of nutrient use strategies and their responses to N addition in understory vegetation.The contrasting effects of N addition on nutrient status between stand ages cannot be ignored when modeling ecosystem nutrient cycling under global N depos-ition conditions.