4.3 Fine root vertical profile varied between species
The vertical distribution of fine roots differed significantly between
the four species (Fig. 1–3 and 5). Significantly different from the
three woody species, in A. vestita , the fine root biomass and
length density were highly concentrated in the surface soil, especially
under 50–75% of RFC (Fig. 3,
S1, and S2). This result suggests thatA. vestita tends to
rapidly acquire transient resources in shallow soils
(Jobbágy and Jackson, 2001;
Valverdes et al., 2007; Li et al., 2020), such as during occasional
rainfall events but might be poor at adapting to long-term resource
limitations. The other three woody species had more roots in deep soils
(Fig. 1); therefore, they were more resistant to environmental pressure
(Schenk and Jackson, 2005; Zhou
et al., 2020).
We also found interspecific differences in the degree of variation and
vertical profiles of fine roots across RFC gradient and age (Fig. 1–4
and S2–S5). The fine root depth of the three woody species showed an
increasing trend with an increase in RFC and age (Fig. 2 and 4). Woody
plants deepen root distribution to obtain resources in
resource-constrained, highly rocky soil, but this trend became weaker
with increasing age (Fig. 2). In contrast, A. vestita showed
shallow fine root profiles in soils with high RFC and in older plants
(Fig. 1 and 2). The results further confirmed that A. vestitadiffers significantly from woody species; it exhibits an opportunistic
resource acquisition strategy but has poor resistance to environmental
pressure (Jobbágy and Jackson, 2001; Valverdes et al., 2007; Schenk and
Jackson, 2005; Zhou et al., 2020). Thus, the fine root biomass ofA. vestita decreased with age, whereas that of woody species
increased with each passing year (Fig. 4).