Interspecific vs intraspecific patterns in leaf nitrogen of foresttrees across nitrogen availability gradients

摘要

Leaf nitrogen content (d) coordinates with total canopy N and leaf area index (LAI) to maximizewhole-crown carbon (C) gain, but the constraints and contributions of within-speciesplasticity to this phenomenon are poorly understood. Here, we introduce a game theoretic, physiologically based community model of heightstructuredcompetition between late-successional tree species. Species are constrained by anincreasing, but saturating, relationship between photosynthesis and leaf N per unit leaf area.Higher saturating rates carry higher fixed costs. For a given whole-crown N content, a C gain-maximizing compromise exists between dand LAI. With greater whole-crown N, both d and LAI increase within species. However, ashift in community composition caused by reduced understory light at high soil N availability(which competitively favors species with low leaf costs and consequent low optimal d) counteractsthe within-species response, such that community-level d changes little with soil Navailability. These model predictions provide a new explanation for the changes in leaf N permass observed in data from three dominant broadleaf species in temperate deciduous forestsof New England. Attempts to understand large-scale patterns in vegetation often omit competitive interactionsand intraspecific plasticity, but here both are essential to an understanding of ecosystem-level patterns.