Nitrogen resorption from senescing leaves in 28 plant species in a semi-arid region of northern China

Nitrogen resorption efficiency (NRE) and proficiency of 28 plant species belonging to five different life-forms were studied in a semi-arid region of northern China. NRE in these species ranged from 29.8% to 76.1% and averaged about 48.0%, depending upon the species and the life-form. The pattern of NRE in different life-forms followed the order of herbs>shrubs>trees>graminoids>N fixers. Nitrogen resorption proficiency (NRP) ranged from 8.0 to 20.6 mg g−1, the average value of which was lowest in graminoids and highest in N fixing species. Leaf-level nitrogen use efficiency (NUE) ranged from 48.5 g g−1 to 125.8 g g−1, with the average NUE being lowest in the N fixing species and highest in the graminoids. Our findings show that most of the 28 species examined in this study can be categorized as low N-proficiency plants. The lower nitrogen concentration in living tissues and the greater nitrogen resorption during senescence could have contributed jointly to the leaf-level NUE of the species. It was noted that NRP was negatively correlated to NRE, while a positive correlation between the leaf-level NUE and NRE was found for all the species. We had also found a significant positive relation between NRE and the N concentration in green leaves for all the species pulled together, suggesting that green leaf N content might have partially controlled the leaf N resorption.