3.2 Shade avoidance cues shortly after emergence irreversibly
affect leaf development
Sugar beet leaf angle was affected by the duration of weed presence
(Figures 3 A & B). In the presence of weeds, sugar beet had greater
leaf angles (hyponastic; Figure 4), especially when weeds were present
at sugar beet emergence (Figure 3A). Similarly, late-emerging weeds
impacted leaf angle (Figure 3B), although the relationship between
duration of weed presence and leaf angle was nonlinear; where weeds
emerging before 500 GDD resulted in leaf angles similar to the
season-long weedy treatment and weeds emerging after 500 GDD resulted in
leaf angles similar to the season-long weed-free treatment (Figures 3B).
Early-season exposure to weeds had a season-long impact on sugar beet
leaf number and leaf area, even if the weeds were removed at the two
true-leaf stage (~330 GDD). Weeds present from sugar
beet emergence to 330 GDD reduced leaf number by 10% (25.8 to 23.3
leaves per plant; Figure 3C) and reduced leaf area by 22% (3576 to 2786
cm2; Figure 3E). Season-long weed presence had no
additional effect on sugar beet leaf area compared to the early-season
weed presence but reduced the number of leaves by an additional 7%
compared to removal at the two true-leaf timing (23.3 to 21.6 leaves per
plant). There was a positive linear relationship between the duration of
weed-free period and sugar beet leaf number and leaf area in the
late-season weed addition series (Figure 3D, 3F). Compared to the
season-long weed-free treatment, weeds added at the sugar beet two
true-leaf stage (~330 GDD) and remaining until the end
of the growing season (~1240 GDD) reduced leaf number by
12% (25.5 to 22.4) and leaf area by 18% (3555 to 2929
cm2).