Supplemental Materials

Figure S1 Crown root number per first (S1A), second (S1B), and third (S1C) whorl of

maize 28 days after planting under high N and low N conditions in soil mesocosms. Data

shown are means with 4 replicates ± SE of the means. Means with the same letters are not

significantly different (p < 0.05)

Figure S2: Correlations between crown root number and rooting depth (measured as D95;

R2=0.68, p=0.04) at flowering under low N conditions in the field in USA.

Figure S3: Root length density at different soil depths for each genotypes and its crown root number (CN) under low nitrogen conditions in the field in USA with corresponding D95. D95 measures the depth above which 95% of root length is present.

Figure S4: Soil nitrate levels at different soil depths 9 weeks after planting in the field in

South Africa (SA2012).

Table S1 Mean and Standard Error (SE) of shoot traits at 28 days after planting under

high and low N conditions in six maize RILs in greenhouse mesocosms.

Genotype

Shoot dry weight (g) Tissue N content (g)

Mean_HN SE Mean_LN SE Mean_HN SE Mean_LN SE

IBM123 0.31 0.05 0.120.02 0.041 0.006 0.013 0.001

IBM133 0.22 0.01 0.080.01 0.048 0.005 0.015 0.002

OHW170 0.23 0.02 0.100.01 0.043 0.005 0.010 0.001

OHW3 0.21 0.02 0.140.02 0.034 0.003 0.012 0.001

OHW61 0.25 0.02 0.150.00 0.030 0.007 0.018 0.001

OHW74 0.26 0.03 0.150.01 0.048 0.008 0.017 0.001

Genotype

Photosynthesis rate(μmol CO2m-2s-1)

Whole plant carbon assimilation rate(μmol CO2 plant-1s-1)

Mean_HN SE Mean_LN SE Mean_HN SE Mean_LN SE

IBM123 13.51 0.36 12.750.69 0.31 0.05 0.12 0.02

IBM133 16.65 0.44 11.250.61 0.22 0.01 0.08 0.01

OHW170 16.90 0.53 10.291.43 0.23 0.02 0.10 0.01

OHW3 16.90 1.25 13.981.09 0.21 0.02 0.14 0.02

OHW61 16.28 0.46 14.581.31 0.25 0.02 0.15 0.00

OHW74 16.33 1.03 11.830.74 0.26 0.03 0.15 0.01

Table S2 Mean and Standard Error (SE) of shoot traits at flowering under high and low N conditions in six maize RILs in SA2011 and US2011 and in seven maize RILs in SA2012.

SA2011 Shoot dry weight (g) SA2012 Shoot dry weight (g)

Genotype Mean_HN SE Mean_LN SE Genotype Mean_HN SE Mean_LN SE

IBM123 69.47 3.76 51.83 0.78 IBM1 68.52 4.83 53.83 2.91

IBM133 77.33 4.26 60.29 2.88 IBM9 77.69 4.50 43.16 0.99

OHW170 75.34 4.57 54.07 1.26 IBM13 53.92 5.08 47.07 3.75

OHW3 70.41 4.28 63.70 1.16 IBM165 57.91 5.54 46.79 0.98

OHW61 68.65 4.45 63.32 1.21 IBM77 72.04 3.38 53.91 4.02

OHW74 65.11 2.20 49.62 1.23 IBM133 57.93 6.26 49.69 2.28

IBM187 53.86 0.51 42.28 3.29

US2011 Shoot dry weight (g) US2011 Yield (g/plant)

Genotype Mean_HN SE Mean_LN SE Genotype Mean_HN SE Mean_LN SE

IBM10 92.47 10.74 55.87 2.35 IBM10 72.66 8.10 45.98 5.59

IBM218 116.97 9.61 94.49 4.25 IBM218 50.96 4.64 28.13 7.17

IBM85 74.26 6.96 47.29 3.72 IBM85 52.32 2.14 30.62 6.09

NYH212 79.27 6.00 56.12 4.58 NYH212 40.92 5.31 33.45 3.43

NYH57 113.92 5.86 68.23 7.62 NYH57 77.93 5.42 39.19 5.45

NYH76 74.36 11.92 41.23 3.77 NYH76 87.11 9.55 55.04 5.79