2.2 Data collection
Number of leaves was measured weekly after seedling emergence. Leaf
angle (from the soil horizon) of the oldest, healthiest leaf was
measured using a protractor between 648 to 760 GDD (41 to 49 days after
planting), depending on the year. The angle of the oldest leaves was
measured because it was not possible to measure the angle of younger
leaves without breaking the older leaves. Also, the angle of the younger
leaves depends on the angle or position of the older leaf. Thus, the
angle of the healthy older leaf provided a good estimate of the plant
leaf angle. Sugar beet plants from the field study were harvested on
September 16, 2015; August 10, 2016; August 14, 2018; and August 19,
2019. At harvest, leaves were separated from the roots, and roots were
washed to remove potting media. Leaves were counted, and total leaf area
per plant was measured by feeding leaves through an LI-3100C (LI-COR
Inc., Lincoln, Nebraska, USA), respectively. Leaves were then dried at
60 C for 48 hours and weighed to obtain shoot biomass per plant. Roots
were sliced (to speed drying) and dried for 72 hours at 60 C then
weighed to obtain root biomass per plant.
In the greenhouse study, plants were harvested on Feb 5, 2019, and the
leaves were separated from the crown according to the order of
appearance or developmental stage (i.e according to phyllotaxy). The
oldest leaf pair were assigned position numbers one and two, the second
oldest leaf pair assigned position numbers three and four, and so forth.
Thus, a lower leaf position corresponds to an older leaf and higher leaf
position corresponds to a younger leaf at the time of harvest. Length of
each leaf and petiole was measured using a ruler, and leaf width (at the
widest part of the lamina) and leaf area were measured using a leaf area
meter (LI-3100C, LI-COR Inc., Lincoln, Nebraska, USA).