Stoichiometric patterns of assimilative branches of four dominant shrubs and the drivers in a Central Asian desert

Shrubs with assimilative branches (ABs) are unique, drought-resistant, and constructive species in temperate deserts in Central Asia. Understanding the nutrient traits and drivers of ABs are crucial to predict the response and adaptation of desert shrubs to environmental changes. Four dominant shrub species with ABs (i.e., Ephedra przewalskii, Calligonum mongolicum, Haloxylon ammodendron, and Haloxylon persicum) widely distributed in the Junggar Desert in northwestern China were selected as the research objects, and then the intra-and interspecific differences in C, N, and P stoichiometric traits, variation patterns and the drivers were comparatively explored. The ABs had lower C, N, P, and N:P, but higher C:N and C:P than leaves of most terrestrial plants worldwide. The variability of C and N:P in ABs was relatively low, whereas N, P, C:N, and C:P showed great variation. According to the theory of stoichiometric ratio, E. przewalskii and C. mongolicum were most likely limited by N, whereas H. ammodendron and H. persicum were co-limited by N and P. A common N-P scaling exponent (1.171) among the four shrubs was determined, revealing that all the four shrubs faced strong environmental stress. The intra-and interspecific stoichiometric traits exhibited different longitudinal and latitudinal patterns, and their relationships with climatic and soil factors also differed. Soil properties presented the greatest influence on E. przewalskii, whereas C. mongolicum were mainly affected by the interaction of soil properties and climate. The influencing factors on different stoichiometric traits of two saxaul species were diverse and inconsistent, and climatic, soil, and geographic factors played different roles. Consequently, during the long-term adaptation to the desert environment, the shrubs with ABs have formed unique, differentiated but partly convergent stoichiometric patterns. The results are greatly significant for deep understanding of the survival strategy of desert shrubs. In the future, researches on the anatomical structure, physiological traits, trait association of assimilative branches, and the responses to changing environment should be strengthened to comprehensively reveal the adaptation stra-tegies of these desert shrubs.