The productivity of natural ecosystems is affected by human activities, such as pollution and fertilization, through their effects on nutrient cycling. We examined the effects of fertilization with nitrogen and/or phosphorus on resorption, the process by which trees reabsorb foliar nutrients prior to leaf abscission in the fall. Previous studies attempting to link soil nutrient availability of single elements with that element’s resorption in the tree have been inconclusive; other studies point to multiple element limitation driving resorption. We collected green leaves and litter of five species from northern hardwood stands in the White Mountains of New Hampshire that have been treated with a 2x2 NP factorial annually since 2011. We compared proficiency and efficiency of resorption of eleven elements (C, N, Al, Ca, Na, K, Mg, Mn, P, Sr, and S).
Results/Conclusions
Green leaf N concentrations were lowest in the P plot (x=22.47 mg g-1) and highest in the N plot (x = 27.86 mg g-1). Nitrogen resorption was 15% more efficient in the NP plot compared to the control plot. Phosphorus efficiency was almost 20 percentage points higher in the N plot (x = 73.99%) than in the P plot (x = 54.09%). Nitrogen proficiency was better in the P plots (x = 9.02 mg g-1) compared to the N plots (x = 12.66 mg g-1), and phosphorus resorption was over two times more proficient in the N plots than in the P plots. These results indicate a process driven by multiple elements. Sulfur concentrations were correlated with many elements, possibly due to the important and varied roles sulfur plays in tree physiological processes. A better understanding of interconnected nutrient cycles and the feedback mechanisms they affect can assist recognition of the influences of anthropogenic nutrient additions on ecosystem functions.