Jiahui Zhang, Ning Zhao, Congcong Liu, Hao Yang, ML Li, Guirui Yu, Kevin Wilcox, Qiang Yu, Nianpeng He


Mineral nutrient elements have received wide attention in forest ecosystems because more than 16 elements support the growth and development of plants. Carbon (C, the main element of both structure and energy, i.e. sugars), nitrogen (N, key element of protein), and phosphorus (P, key element of nucleic acids) are especially crucial. Some have suggested that changes in plant physiological functioning can be indicated by changes in element ratios. Through the scaling up of C:N:P ratios, the relations of different levels of biology, from the gene to the globe, also can be revealed.

In natural forest ecosystems, plant communities arise from the interaction of adaptation of species to specific environments and competition between species. Therefore, investigations at the community (rather than the species) level  might better reflect the characteristics of a forest ecosystem and provide a better foundation for improving ecological models. However, such studies have still not been reported at large scales.

We used data from 803 plant species on the C, N, and P content of different plant organs, litter, and soil in 9 natural forest ecosystems from cold-temperate to tropical zones in China. We  explored C:N:P ratios for different plant organs (leaves, branches, trunks, and roots) and for different components of the forest ecosystem (plant community, soil, litter, and ecosystem).

We found that the ratios of C:P and N:P decreased with increasing latitude, and the spatial patterns were primarily regulated by climate (i.e. mean annual temperature and mean annual precipitation). We also found that more active organs have a higher capacity to maintain relatively stable element contents and ratios, for example, homeostasis (the ability of plants to maintain stable element contents and ratios) of N, P, and N:P was highest in leaves, followed by branches, roots, and trunks. The leaf N:P ratio at the community level indicated increasing P limitation in forests of lower latitude  in the Northern Hemisphere. Our results demonstrate the adaptive allocation of C:N:P and indicate how forest ecosystems regulate element content and ratios at the large scale.

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