Reviews and syntheses: Ecological Stoichiometry of Carbon, Nitrogen, and Phosphorus in Shrubs and Shrublands

Abstract. Ecological stoichiometry examines the balance and ratios of multiple elements in ecological processes. In shrubs, characterized by their adaptability to extreme environments such as alpine and arid, stoichiometric traits likely differ from those in trees and grasses, reflecting unique ecological adaptations of shrubs. However, this hypothesis remains underexplored. Here we review the state of the art of stoichiometry in shrubs and then identify research hotspots of shrub stoichiometry. Then, we summarize the effects of climate, soil properties, phylogeny, ontogenetic differences, and human activities on stoichiometry of shrub leaves. In addition, we compared the stoichiometry of shrublands with that of forests and grasslands. The development process of shrubland stoichiometry research can be roughly divided into three main periods: the initial development stage (before 2010), the fast development stage (2011–2018), and the high-quality development stage (from 2019 to the present), with the two turning points occurring in 2011 and 2019 possibly related to the launch of major projects associated with shrublands in China. Current studies predominantly focus on shrub leaves, with limited attention to stems, roots, and seeds. Mean values of C, N, P, C:N, and N:P in shrub leaves globally were 454.66 mg g⁻¹, 18.93 mg g⁻¹, 1.20 mg g⁻¹, 23.4, and 15.8, respectively. Shrub leaf N and P content were higher than those of trees and lower than herbs, while C content and C:N ratio showed opposite trends. N and P content correlated positively with soil nutrients and precipitation and negatively with temperature. Functional types also influenced stoichiometry, with deciduous and leguminous shrub species showing higher N and P content than evergreen and non-leguminous shrubs. Overall, shrubs showed C and N content intermediate between trees and grasses, while P content was similar across life forms. Higher N:P ratios in shrublands and grasslands suggest stronger P limitation than in forests. Future studies should integrate above- and below-ground stoichiometry, consider phylogenetic influences, and investigate evolutionary processes to better understand shrubland adaptation and formation mechanisms under global change.