Global leaf nitrogen and phosphorus stoichiometry and their scaling exponent

Abstract

Leaf nitrogen (N) and phosphorus (P) concentrations constrain photosynthetic and metabolic processes, growth and the productivity of plants. Their stoichiometry and scaling relationships regulate the allocation of N and P from subcellular to organism, and even ecosystem levels, and are crucial to the modelling of plant growth and nutrient cycles in terrestrial ecosystems. Prior work has revealed a general biogeographic pattern of leaf N and P stoichiometric relationships and shown that leaf N scales roughly as two-thirds the power of P. However, determining whether and how leaf N and P stoichiometries, especially their scaling exponents, change with functional groups and environmental conditions requires further verification. In this study, we compiled a global data set and documented the global leaf N and P concentrations and the N:P ratios by functional group, climate zone and continent. The global overall mean leaf N and P concentrations were 18.9 mg g −1 and 1.2 mg g −1 , respectively, with significantly higher concentrations in herbaceous than woody plants (21.72 mg g −1 vs. 18.22 mg g −1 for N; and 1.64 mg g −1 vs. 1.10 mg g −1 for P). Both leaf N and P showed higher concentrations at high latitudes than low latitudes. Among six continents, Europe had the highest N and P concentrations (20.79 and 1.54 mg g −1 ) and Oceania had the smallest values (10.01 and 0.46 mg g −1 ). These numerical values may be used as a basis for the comparison of other individual studies. Further, we found that the scaling exponent varied significantly across different functional groups, latitudinal zones, ecoregions and sites. The exponents of herbaceous and woody plants were 0.659 and 0.705, respectively, with significant latitudinal patterns decreasing from tropical to temperate to boreal zones. At sites with a sample size ≥10, the values fluctuated from 0.366 to 1.928, with an average of 0.841. Several factors including the intrinsic attributes of different life forms, P-related growth rates and relative nutrient availability of soils likely account for the inconstant exponents of leaf N vs. P scaling relationships.

Variations and determinants of carbon content in plants: a global synthesis

“…4), which was consistent with the results of Fyllas et al (2009) and other studies about plant nutrient stoichiometry at global scales (Han et al, 2011;Zhao et al, 2016;Tian et al, 2017). Further, the interactive effects of climatic factors with life forms were higher than the independent explanations of climate (0.7-15.7 %, Fig.…”

Nutrient addition affects scaling relationship of leaf nitrogen to phosphorus in Arabidopsis thaliana

“…This study also provides important implications for the parameterization in modelling stoichiometric growth and nutrient cycles in terrestrial ecosystems (Niklas et al, ; Peñuelas et al, ; Tang et al, ; Wright et al, ), and for understanding plant adaptation and evolution under varying nutrient environments (Kerkhoff et al, ). Moreover, our results consolidate one recent finding that there is no universal N‐P scaling exponent (Tian et al, ). The general 0.667‐power law of leaf N versus P scaling (Reich et al, ) may be counterintuitive when considering the role of nutrient changes.…”

“…Based on a global dataset of leaf N and P concentrations with more than 9,300 pairwise entries, Reich et al () noted that variation in the scaling exponent from specific case studies likely arose from insufficient sample sizes, and concluded that the scaling exponent was a uniform constant of 0.667 across major life‐forms and biomes. In contrast, one recent study cautioned against the ubiquity of the general 0.667‐power law and revealed inconstant scaling exponents across multiple scales based on analyses of one more comprehensive global dataset of leaf N and P concentrations (Tian et al, ). Further, the effects of nutrient addition on the coupling of N and P in terrestrial ecosystems have been studied extensively (e.g., Bracken et al, ; Ostertag & DiManno, ; Deng, Hui, Dennis, & Reddy, ).…”

Ecological stoichiometry of the epiphyte community in a subtropical forest canopy

“…Element concentrations and mass ratios of epiphytes differed significantly among functional groups and organs (Figure ). Differences among functional groups are also widespread in other terrestrial plants (Güsewell, ; Han et al, ; Sardans et al, ; Tian et al, ). In this study, these differences might be caused by the large differences in morphological, anatomical, and physiological traits among lichens, bryophytes, ferns, and spermatophytes that led to differences in nutrient uptake, nutrient metabolism, and nutrient retention (Aerts & Chapin, ; Benzing, ).…”

“…The ecological stoichiometry in plants can be influenced not only by environmental factors but also by species, organs, and functional types. In large‐scale studies, the elemental composition and stoichiometry of terrestrial plants are influenced by forest type, climate, and soil (Chen, Han, Tang, Tang, & Fang, ; Han, Fang, Reich, Woodward, & Wang, ; Sardans et al, ; Tian et al, ). In a European forest, the identity of tree species can explain 56.7% of the variance of the overall foliar elemental composition and stoichiometry (Sardans et al, ).…”