Increasing N and P Resorption Efficiency and Proficiency in Northern Deciduous Hardwoods With Decreasing Foliar N and P Concentrations

The objective of this study was to assess the relationships between pre-senescence leaf N and P concentrations, and resorp- tion efficiency and proficiency of eight deciduous hardwood tree species. Trees were sampled on two sites of contrasting fertility/pro- ductivity in southern Quebec. Measured resorption efficiencies ranged from 56 to 71% for N, and from 30 to 78% for P. Linear and exponential models between leaf N and litter N, and between leaf P and litter P were significant. Intercepts of linear models were signifi- cantly different from zero. Resorption efficiency and proficiency increased with a decrease in leaf N and P, and the rate of change of re- sorption efficiency increased with leaf nutrient concentration. Concentrations corresponding to ultimate potential resorption were calculated to be 3.2 mg N g –1 and 0.09 mg P g –1 . Maximum resorption efficiencies were estimated at 70% for N and 80% for P. The concept of ultimate potential resorption in hardwoods is discussed