Leaf C:N:P stoichiometrical and morphological traits of <Emphasis Type="Italic">Haloxylon ammodendron</Emphasis> over plantation age sequences in an oasis-desert ecotone in North China

Haloxylon ammodendron, a typical C₄ desert shrub, is widely used in vegetation reestablishment programs to stabilize shifting sand dunes and to control shifting sands encroaching into oases in the oasis-desert ecotones in northwestern China. In this study, we investigated the morphological traits and analyzed leaf carbon (C), nitrogen (N), and phosphorus (P) stoichiometrical characteristics in an age sequence of 2-, 5-, 9-, 13-, 16-, 31-, and 39-year old H. ammodendron plantations, to assess their growth development and degeneration processes. Results showed that the height, stem diameter, and canopy increased rapidly in the early establishment stage (2–9 years), and thereafter, showed a slower increase from 13 to 39 years. The leaf C and N concentrations and N:P ratio showed a rapid increase from ages 2–5, but C:N exhibited a significant decline. After 5 years, plantation leaf C, N, C:N, and N:P were stable, and leaf P and C:P showed no significant difference among all plantation ages. Leaf C and N concentrations were mainly affected by soil properties. Limiting nutrient factors in soil changed from nitrogen before 2 years to phosphorus after 5 years. The findings suggested that leaf stoichiometrical characteristics combined with morphological traits can be used to reflect the degeneration trend of H. ammodendron. Further research is needed to reveal the processes and mechanisms of H. ammodendron growth development and degeneration, and its adaption to the soil environment.