Nitrogen Levels Influence Biomass, Elemental Accumulations, and Pigment Concentrations in Spinach

ABSTRACT

Spinach (Spinacia oleracea L.) has one of the highest United States per capita consumption rates among leafy vegetable crops, and also ranks second for lutein and β-carotene carotenoid concentration. The objectives of this study were to determine the effects of nitrogen (N) concentration on elemental and pigment accumulation in spinach. Two spinach cultivars (‘Melody’ and ‘Springer F1’) were greenhouse grown in nutrient solution culture under N treatments of 13, 26, 52, and 105 mg L^{− 1}. Leaf tissue biomass increased from 45.6 to 273.2 g plant^{− 1} and from 127.0 to 438.6 g plant^{− 1} as N increased from 13 to 105 mg L^{− 1} for ‘Springer F1’ and ‘Melody’, respectively. Leaf tissue N, phosphorus (P), calcium (Ca), magnesium (Mg), copper (Cu), and zinc (Zn) responded to N treatments. Lutein accumulations, expressed on a fresh weight basis, responded quadratically to increasing N treatments for ‘Springer F1’. Maximum lutein values were 110 and 76 μ g g^{− 1} on a fresh weight basis, and maximum β-carotene values were 85 and 57 μ g g^{− 1} on a fresh weight basis for ‘Springer F1’ and ‘Melody’, respectively. Interestingly, N levels had a significant effect on carotenoid accumulation in both ‘Springer F1’ and ‘Melody’ when the pigments were expressed on a dry weight basis. Leaf tissue lutein increased from 0.59 to 1.06 mg g^{− 1} and from 0.59 to 0.90 mg g^{− 1} on a dry weight basis with increasing N treatments for ‘Springer F1’ and ‘Melody’, respectively. Reporting lutein and β-carotene on both a fresh and dry weight basis may be the most accurate way to express the carotenoid values of spinach.

Keywords:

• β-carotene
• carotenoids
• chlorophyll a and b
• HPLC
• lutein
• macronutrient
• micronutrient
• Spinacia oleracea L.

ACKNOWLEDGMENTS

This material is based upon work supported by the Cooperative State Research, Education, and Extension Service, U.S. Department of Agriculture, under Agreement No. 2001-52102-11254. The authors wish to thank Joanne Curran-Celentano and Laura Dukach for their technical support of this research.

Notes

^zMean composition of sampled leaf tissue of 4 replications and 6 plants each.

^yFW = shoot tissue fresh weight; DW = shoot tissue dry weight.

^xSignificance for linear (L) and quadratic (Q) orthogonal contrasts for N rates.

^zMean composition of sampled leaf tissue of 4 replications and 6 plants each.

^ySignificance for linear (L) and quadratic (Q) orthogonal contrasts for N rates.

^zMean composition of sampled leaf tissue of 4 replications and 6 plants each.

^ySignificance for linear (L) and quadratic (Q) orthogonal contrasts for N rates.

^zMean composition of sampled leaf tissue of 4 replications and 6 plants each.

^yChl a = chlorophyll a; Chl b = chlorophyll b.

^xSignificance for linear (L) and quadratic (Q) orthogonal contrasts for N rates.

^zMean composition of sampled leaf tissue of 4 replications and 6 plants each.

^ySignificance for linear (L) and quadratic (Q) orthogonal contrasts for N rates.