Responses and mechanisms of leaf nitrogen and phosphorus resorption efficiency to nutrient addition in an alpine meadow

  Objective  Leaf nutrient resorption is the ability of plants to recycle nutrients from senescent leaves and transport them to other tissues and organs, which is one of the main strategies for plant nutrient utilization. Previous studies show that nitrogen (N) or phosphorus (P) addition generally reduces or does not affect leaf nutrient resorption efficiency. However, there are still few studies on the effects of N and P addition and their interaction on leaf nutrient resorption efficiency and the underlying mechanisms.

  Method  To answer this question, we performed an experiment of N and P addition in an alpine meadow, measuring leaf nutrient resorption efficiency in four dominant species (Elymus nutans, Deschampsia cespitosa, Artemisia roxburghiana, Potentilla anserina).

  Result  We found that (i) N addition had positive effects or no impact on leaf N resorption efficiency (NRE) in graminoids and forbs, while it did not affect P resorption efficiency (PRE) among four plant species. (ii) P addition had no effect on leaf NRE among four species or PRE in forbs, but it significantly increased leaf PRE in graminoids. (iii) N + P addition together reduced leaf NRE in E. nutans, A. roxburghiana and P. anserina, but increased NRE in D. cespitosa. Moreover, the combination of N + P addition did not affect leaf PRE among four species.

  Conclusion  Overall, our study indicates that alpine plants adopt three nutrient resorption strategies for more nutrient supply: full resorption (increased green leaf nutrient but no change in senescent leaf), partial resorption (more increase in green leaf nutrient than senescent leaf) and no resorption (similar increase in green and senescent leaf nutrient). These findings reveal the diversity and complementarity of plant strategies of nutrient internal cycle in alpine grasslands.