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).