Leaf nitrogen resorption pattern along habitats of semi-arid sandy land with different nitrogen status

To assess nitrogen (N) resorption patterns in semi-arid sandy land, N concentrations in green leaves (N_g) and senesced leaves (N_s) of 35 species of shrubs and herbages were measured along habitats of decreasing soil total N (0.54 to 0.041 g g^-1 d.w. of top soil level) in Horqin Sandy Land (Inner Mongolia, China). These habitats are following: inter-dune grassland (IDG), fixed sand dune (FD), semi-fixed sand dune (SFD), semi-mobile sand dune (SMD), and mobile sand dune (MD) were considered. Results showed that Ng and Ns (i.e. nitrogen resorption proficiency, NRP) increased and leaf nitrogen use efficiency (NUE) decreased significantly with increasing soil N status across the above habitas, but nitrogen resorption efficiency (NRE) was not affected. The levels of N_g, N_s and NUE experience two stages across habitats: first, there were low N_g and N_s and high NUE in MD and SMD; second, there were high N_g and N_s and low NUE in IDG, FD and SFD. Plants from IDG, FD and SFD had incomplete N resorption during foliar senescence, but plants from MD and SMD had complete N resorption. Leaf NRE was determined by life forms which had no significant effect on Ng but on Ns and NUE. For all plants in the five habitats, NRE and NUE decreased with the sequence of grass, herb, shrub, while Ns showed a contrary tendency. Plants from strong N limitation habitats did not show higher NRE, but showed higher NRP and leaf NUE, so NRP was a more sensitive indicator of changes in N status than NRE. In conclusion, Leaf N resorption patterns were mainly determined by soil N status across habitats, and there were some consistent patterns among life forms.