4.3. The coordinated changes between root system architecture traits and RMF and LMF optimizes adaptive strategy
Plants can achieve a balance between resource acquisition and allocation through coordinated changes in biomass allocation and morphological characteristics (Chapin, 1991; Nicotra et al., 2010; Freschet et al., 2018). The LMF and RMF determines their future morphological changes and ultimately affects the way they obtain resources (Freschet et al., 2015b; Yin et al., 2019). The LMF is closely related to the water consumption capacity of plants, and the higher the LMF, the greater the water consumption and demand of its leaves (Yin et al., 2019). In the present study, LMF is significantly positively correlated with SRA and SRL (Fig. 5cd). This indicates that plants can mitigate water and water loss caused by high LMF by improving the absorption efficiency of root water and nutrient (Isaac et al., 2017; Wang et al., 2018). In addition, LMF and MRD also showed a significantly positive correlation (Fig. 5a). This may be another ecological strategy for plants to cope with the water consumption caused by high LMF, that is, by increasing the ability of root systems to explore the vertical space of the soil, greatly increasing the probability of encountering water rich areas (Martínez-Sánchez et al., 2003; Tsakaldimi et al., 2009). Moreover, the results of this study indicate a significant negative correlation between LMF and RTD (Fig. 5e). This may be because RTD is closely related to the resource conservation ability of the root system (Bergmann et al., 2020; Carmona et al., 2021), so plants must achieve a balance between resource conservation and consumption among organs through the trade-off between LMF and RTD.
There may have a significant positive correlation between morphological characteristics and biomass proportion of ephemerals (Cheng et al., 2006; Zhang et al., 2020). In the present study, the positive correlation between RMF and MRD is significant (Fig. 6a), which further indicates that the exploration of soil vertical space by roots depends on the biomass investment of plants in the roots. Furthermore, the negative correlation between RMF and RD is significant (Fig. 6b). Roots with high root diameters have been proven to be resource conserving roots with slow metabolism and effective resistance to mechanical damage, herbivores, and drought stress (Withington et al., 2006; Kong et al., 2014; Weemstra et al., 2016). According to the functional equilibrium hypothesis, the increase in root biomass is due to resource constraints on root growth (Poorter et al., 2012; Freschet et al., 2018). Therefore, when the scarcity of underground resources leads to an increase in root biomass investment, what the root system most needs is to increase the ability to explore resources or the efficiency of acquiring resources, rather than conservating resource. The trade-off between RMF and RD enables the root system to achieve the optimal balance between resource investment and return. In addition, the phylogenetic relationship significantly affects the relationship between root architecture traits and the proportion of root and leaf biomass. This indicates that the coordinated changes between root architecture traits and the proportion of organ biomass may partly depend on the phylogenetic relationships between species.