4.1. The differences in variation patterns of different root traits enhance the adaptability of the root system
Interspecific variation in plant traits is the basis for coexistence of different species in similar habitats (Diaz et al., 2004). Analogy to leaf trait variation, interspecific variation in root system architecture trait can partly explain the impact of habitat filtering and interspecific competition on plant root strategies at a local scale (Bu et al., 2017; Hajek et al., 2013; Hogan et al., 2020). In the present study, the degree of CV inter of the six root system architecture traits is distinct (Table 1). Among them, the RTD is the highest, and the TI is the lowest (Table 1). The results manifested that the RTD of annual ephemerals showed a divergent adaptation, while the branching pattern (TI) showed a convergent adaptation due to the combined effects of environmental filtering and similarity constraints (Grime, 2006). The divergence adaptation of RTD is conducive to these plants to reduce biological competition by adopting different root resource defense strategies when dealing with highly heterogeneous desert environments (Tjoelker et al., 2005; Lan and Zhang, 2008; Xu et al., 2021). Meanwhile, the convergence of root branching patterns caused by environmental filtering towards more simple herringbone branching patterns can effectively reduce the carbon investment cost of underground root construction, allowing annual ephemerals to allocate more resources to the growth of the aboveground parts (Qiu et al., 2007; Spanos et al., 2008; Tsakaldimi et al., 2009).
Intraspecific variation refers to the differences in genetic material and phenotypic characteristics between different botany individuals from the same species (Albert et al., 2010b). The variation of genetic material between different individuals of the same species and the phenotypic plasticity in response to environmental changes may cause intraspecific variation of plant functional traits (Jung et al., 2014). In the present study, the variation range ofCV intra in root architecture traits related to acquisition of resources (e.g., SRL, SRA) and resistance to environmental (e.g., RTD) interference is relatively large, showing a certain degree of divergence (Fig. 3). This may be because the annual ephemeral species collected in this study are all distributed in heterogeneous desert habitats with low species richness and relatively scarce resources, which causes some species to exhibit high plasticity in root resource acquisition or defense traits (Siefert et al., 2015). This may be crucial for them to adapt to desert environment, because when resource availability changes rapidly in time and space, high phenotypic plasticity represents that plants have certain adaptive advantages (Hajek et al., 2013). Additionally, this divergence in the plasticity of resource acquisition traits and defense traits of different species may help plant individuals (even different individuals from the same species) occupy different ecological niche, thus promoting the coexistence of annual ephemeral plants in limited resource habitats (Bu et al., 2017).