Nutrient Allocation Strategies of Woody Plants: An Approach From the Scaling of Nitrogen and Phosphorus Between Twigs and Leaves

Abstract:

Allocation of limited nutrients, such as nitrogen (N) and phosphorus (P), among plant organs reflects the influences of evolutionary and ecological processes on functional traits of plants, and thus is related to functional groups and environmental conditions. In this study, we tested this hypothesis by exploring the stoichiometric scaling of N and P concentrations between twigs and leaves of 335 woody species from 12 forest sites across eastern China. There were significant scaling relationships between twig N (or P) and leaf N (or P) using reduced major axis (RMA) regression analysis; yet their scaling exponents varied among functional groups and changed with environmental factors. Evergreen broad-leaved plants had a higher exponent (α_P) of twig P to leaf P than that of deciduous broad-leaved plants (1.26 vs. 0.96, p < 0.05), but they had a similar exponent (α_N) of twig N to leaf N (1.20 vs. 1.19). For both N and P, legume species exhibited a higher exponent than non-legume species (1.44 vs. 0.99 for α_N; 1.86 vs. 0.88 for α_P). Moreover, with increasing latitude, both α_N and α_P significantly decreased from > 1 at low latitude (23.2°N) to < 1 at high latitude (50.9°N), and this trend was consistent among the different forest types (i.e., tropical, temperate and boreal forests) across the study area. These results suggested that, as plant nutrient concentration increased, plants at low latitudes showed a faster increase in twig nutrient concentration, whereas plants at high latitudes presented a faster increase in leaf nutrient concentration. Such shifts in nutrient allocation strategy from low to high latitudes may be controlled by temperature. Overall, our findings provide a new approach to explore plant nutrient allocation strategies by analysing the stoichiometric scaling of nutrients among organs, which could broaden our understanding of the interactions between plants and their environments.