Patterns of physical, chemical, and metabolic characteristics of sugar maple leaves with depth in the crown and in response to nitrogen and phosphorus addition.

This article focuses on how leaf physical, chemical, and metabolic characteristics of mature sugar maple (Acer saccharum Marsh.) trees vary with depth in the crown and respond to experimental nitrogen (N) and phosphorus (P) additions. Conducted in three forest stands in central New Hampshire, USA, as part of the Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE) study, the research found that 32 of 44 measured leaf traits significantly varied with crown depth, notably leaf area, photosynthetic pigments, and polyamines. Nitrogen addition increased foliar N, chlorophyll, carotenoids, and several amino acids, while phosphorus addition elevated foliar P and boron and altered their vertical distribution. The study highlights that ignoring vertical gradients in leaf traits may lead to inaccurate assessments of whole-canopy function, emphasizing the importance of sampling leaves throughout the crown to understand nutrient effects and canopy physiology in shade-tolerant species like sugar maple.