Variation and evolution of C:N ratio among different organs enable plants to adapt to N‐limited environments

• Published in: Global change biology 2020-04, Vol.26 (4), p.2534-2543
• Main Authors: Zhang, Jiahui, He, Nianpeng, Liu, Congcong, Xu, Li, Chen, Zhi, Li, Ying, Wang, Ruomeng, Yu, Guirui, Sun, Wei, Xiao, Chunwang, Chen, Han Y. H., Reich, Peter B.
• Format: Article
• Language: English
• Subjects: adaptation; Biological evolution; Body organs; carbon; Convergence; Divergence; ecological stoichiometry; Ecosystem models; Environment models; Environmental changes; Evolution; forest; Growth; latitude; Leaves; Nitrogen; Organs; Phylogeny; Plant organs; Ratios; Recycling centers; Spatial variations; Survival; Temperate forests; Tropical climate; Tropical forests; variation; Yard waste
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.14973

Carbon (C) and nitrogen (N) are the primary elements involved in the growth and development of plants. The C:N ratio is an indicator of nitrogen use efficiency (NUE) and an input parameter for some ecological and ecosystem models. However, knowledge remains limited about the convergent or divergent variation in the C:N ratios among different plant organs (e.g., leaf, branch, trunk, and root) and how evolution and environment affect the coefficient shifts. Using systematic measurements of the leaf–branch–trunk–root of 2,139 species from tropical to cold‐temperate forests, we comprehensively evaluated variation in C:N ratio in different organs in different taxa and forest types. The ratios showed convergence in the direction of change but divergence in the rate of change. Plants evolved toward lower C:N ratios in the leaf and branch, with N playing a more important role than C. The C:N ratio of plant organs (except for the leaf) was constrained by phylogeny, but not strongly. Both the change of C:N during evolution and its spatial variation (lower C:N ratio at midlatitudes) help develop the adaptive growth hypothesis. That is, plants with a higher C:N ratio promote NUE under strong N‐limited conditions to ensure survival priority, whereas plants with a lower C:N ratio under less N‐limited environments benefit growth priority. In nature, larger proportion of species with a high C:N ratio enabled communities to inhabit more N‐limited conditions. Our results provide new insights on the evolution and drivers of C:N ratio among different plant organs, as well as provide a quantitative basis to optimize land surface process models. This study demonstrated how the C:N ratio can provide new insights on the adaptation strategies of plants in different environments. High C:N ratios enabled communities to promote nitrogen use efficiency (NUE) in strong N‐limited conditions to ensure survival priority, whereas low C:N ratios in less N‐limited environments facilitate growth at the expense of reducing NUE. In addition, this study provided high‐quality C:N parameters of different plant organs among different forest types that could be used to optimize land surface process models.