Abstract: The nitrogen (N) vs. phosphorus (P) scaling exponent, indicating the allocation strategies of the two nutrients, plays an important role in predicting plant and ecosystem functioning. Besides the constant scaling relationship of N vs. P, plasticity of scaling exponents has been demonstrated, with proposed potential causes including plant functional groups (PFGs) or environmental factors. However, relatively little is known about whether the N vs. P scaling exponent of different PFGs response similarly to different environmental conditions. We measured N and P concentrations in leaves and twigs of 964 shrub individuals in a secondary subtropical forest in Eastern China and explored how the N vs. P scaling exponent vary with different light or soil nutrient conditions for deciduous and evergreen shrubs. The leaf N vs. P scaling exponent of evergreen but not deciduous shrubs was affected by light condition, with higher scaling exponent of understory shrubs than that of typical shrubs. The twig scaling exponent of understory shrubs was lower than that of typical shrubs for both PFGs. With increasing soil N availability, responses of scaling exponents in both organs for both PFGs consistent with compliant type first and resistant type later. The scaling exponents of deciduous and evergreen shrubs in both organs showed opposite trends at a relatively high soil P availability level. Our results reveal that environmental factors may alter the N vs. P scaling exponent differently across PFGs. These findings have important implications for improving predictions of stoichiometric models and broadening our understanding of plant responses to varying environments.

Key words: leaves, leaf habit, light condition, scaling exponent, soil nutrient availability, twigs