4.2. The phylogenetic relationship is an underlying factor
affecting root system architecture traits
Some functional traits of plants may be influenced by phylogenetic
relationships among species, and exhibit a conservatism of phylogeny
(Felsenstein, 1985). The closer the genetic relationship, the more
similar the traits are (Ackerly and Reich, 1999; Kraft et al., 2010).
Root system architecture, as an important functional trait that reflects
the resource strategy of underground parts of plants, may also be
significantly influenced by phylogenetic relationships among species
during their formation and development (Kong et al. 2014; Ma et
al. 2018; Zhou et al. 2018). This study examined theK values of phylogenetic signals for six root system architecture
traits and found that different root system architecture traits were
affected differently by the phylogenetic relationship (Table 2). Among
them, significant and weak phylogenetic signals were detected for MRD,
indicating that the root diameter of 47 annual ephemerals was affected
to the same extent by phylogenetic relationship and environmental
factors during their development (Table 2). In addition, in the present
study, no significant phylogenetic signals were detected for the other
root system architecture traits, which suggests that RD, SRL, SRA, RTD,
and TI were not significantly affected by phylogenetic relationship
among species (Kramer-Walter et al., 2016).
The results of this study indicate that RD does not exhibit a
significant phylogenetic structure, which is consistent with some
studies on woody plants (Kramer-Walter et al., 2016; Wang et al., 2019).
However, the present result is not similar to the research results of
Kong et al. (2014) and Ma et al. (2018) on the root system architecture
traits of woody plants, whose research found that phylogenetic
relationships have a significant impact on RD. The reasons for these
differences may be related to differences in spatial scale, life types
of plant, soil conditions, sampling time and methods, and sample size.
On the one hand, compared to herbaceous plants, the growth and
development of the root systems of woody plants may be subject to
stronger directional selection and exhibit strong phylogenetic signals
(ValverdeāBarrantes et al., 2017). On the other hand, convergent
evolution caused by habitat filtering may cause species with distant
genetic relationships to exhibit similar functional traits (Wake, 1991),
while divergent evolution caused by biological competition may cause
species with closer genetic relationships to exhibit completely opposite
functional traits (Blomberg et al., 2003).