The genetic contribution (G)
We found heritable variation in branches for both total NSCs and
proportion of NSCs in starch (Table 1, Branch
H2TNC = 0.19, Branch
H2PropStarch = 0.31). As previously
reported, this is similar heritability as total NSC storage in P.
trichocarpa stems and roots (Table S1; Blumstein et al., 2020). Here we
found that the proportion of starch to total stores is also heritable in
roots (Root H2PropStarch = 0.37), but
not stems (Stem H2PropStarch = 0.01).
Branch genetic variation does not exhibit high degrees of across
population variation in either total NSCs or proportion of stores in
starch (Qst TNC = 0.07, Qst Proportion =
0.04; Table 1). This stands in contrast to stems and roots, which
demonstrate extensive differentiation across populations in total stores
(Qst Roots = 0.30, Qst Stems = 0.31) and
stem partitioning between sugar and starch (Qst Stems =
0.66) (Table S1). However, the finding of high Qst value
for stems in the partitioning between sugar and starch is unlikely
biologically meaningful. H2 for stems is only 0.01 for
this trait, thus the high Qst value is calculated using
just 1% of the phenotypic variation measured.