Abstract: Abstract Aims Populus euphratica and Tamarix ramosissima are widely distributed in arid desert regions, playing a significant role in shaping the local ecological environment. There exist intrinsic connections among similar functional traits across different species, as well as among various functional traits within the same species, which collectively respond to environmental changes. Furthermore, biomass allocation serves as a crucial indicator of the mechanisms through which plants adapt to their surroundings. Methods In the coexisting community of P. euphratica and T. ramosissima seedlings at the Oasis located in the Tail of the Keriya River situated in the hinterland of the Taklamakan Desert, a total of eleven P. euphratica seedlings and ten T. ramosissima seedlings were selected for this study (P. euphratica basal diameter range: 2.61-6.18 mm; T. ramosissima basal diameter range: 2.03-8.86 mm). The investigation focused on leaf functional traits, root functional traits, and biomass allocation characteristics of both P. euphratica and T. ramosissima seedlings within their natural habitats, employing a whole-root excavation method. Based on the distribution patterns of root systems for both P. euphratica and T. ramosissima within the soil profile, we calculated ecological niche overlap values for these two species using the Pianka index. Important findings The analysis revealed both similarities and differences in the functional traits and biomass allocation between P. euphratica and T. ramosissima seedlings: ①The specific leaf area, foliar carbon, nitrogen, phosphorus content of P. euphratica were significantly higher than those observed in T. ramosissima leaves; conversely, the carbon-to-phosphorus ratio was notably greater in T. ramosissima leaves compared to those of P. euphratica. Furthermore, soluble sugar levels in P. euphratica leaves exceeded those found in T.ramosissima; however, the starch-to-soluble sugar ratio was significantly elevated in T. ramosissima relative to that seen in P. euphratica seedlings. No significant differences were noted regarding starch or non-structural carbohydrate (NSC) contents between the two species. ② The specific root area and root phosphorus content of the root systems of P. euphratica seedlings were significantly higher than those observed in T. ramosissima roots; conversely, the root tissue density of T. ramosissima was markedly greater than that of P. euphratica. However, no significant differences were found concerning the carbon-nitrogen ratio, carbon-phosphorus ratio, or nitrogen-phosphorus ratio within their respective root systems between these two species. Additionally, soluble sugars and non-structural carbohydrates (NSC) concentrations within the root system of P. euphratica seedlings were significantly elevated compared to those present in T. ramosissima seedlings; however, no notable difference was detected regarding starch content or the starch/soluble sugar ratio between these two species. ③ As both P. euphratica and T. ramosissima seedlings progressed through growth stages, a general trend towards decreased biomass allocation to their respective root systems was observed; notably, this decline is more pronounced for P. euphratica than for T. ramosissima seedlings. The ecological niche overlap value between P. euphratica and T. ramosissima is 0.97, indicating a very high potential for competition between the two species in their utilization of soil moisture and nutrients during the seedling stage.

Key words: Seedlings, Leaf functional traits, Root functional traits, Biomass allocation, Taklamakan Desert