Nitrogen and phosphorus concentrations, N:P ratio and resorption efficiency of leaves in different forest types.

Nitrogen and phosphorus concentrations,N∶P ratio,nutrient resorption efficiency and their relationship in mature and senescent leaves in pure and mixed protection forest of Casuarina equisetifolia,Acacia crassicarpa,Eucalyptus ABL 12 W5 and Pinus elliottii were discussed in this paper.The results showed that nutrient concentration and resorption efficiency of leaves were higher in pure forest and N fixing species than in mixed forest and non-N-fixing species,respectively.This indicated that soil nutrient availability increased in mixed forest and N-fixing species,so the trees could absorb more nutrients from soil and depended less on nutrient resorption from senescent leaves.The N∶P ratios of mature leaves were all above 14,nitrogen was less limiting than phosphorus,and accordingly phosphorus resorption efficiency(RE_P)was higher than nitrogen resorption efficiency(RE_N).N∶P ratio was increased with leaf senescence.There was significant positive relationship between N∶P ratio in mature and in senescent leaves.Inter-and intraspecific correlations among nutrient concentrations,nutrient resorption and N∶P ratio of mature and senescent leaves in various forest types were different in N-fixing and non-N-fixing species.Due to the difference of nutrient use strategy for various life-forms,there was a significant correlation in N-fixing species,but no correlation in non-N-fixing species,and vice versa.Nutrient conservation species,such as P.elliottii,with low leaf nutrient and high nutrient resorption efficiency should be prior selected for afforestation.