MINERAL DEFICIENCY STRESS: Reflectance Properties, Leaf Photosynthesis and Growth of Nitrogen Deficient Big Bluestem (Andropogon gerardii)

Abstract

A pot-culture experiment was conducted under outdoor conditions to determine effects of nitrogen (N) deficiency on big bluestem (Andropogon gerardii Vitman, cv Bonelli) growth, photosynthesis and leaf reflectance (R) properties. Big bluestem was seeded on 14 May 2004 and grown in 120 twelve-litre pots filled with fine sand and irrigated with Hoagland’s nutrient solution (with 81 mg L−1 as N). Treatments initiated at 60 days after sowing (DAS) included: (1) the control (100N) continued receiving the Hoagland’s nutrient solution; (2) reduced N to 20 % of the control (20N); and (3) withheld N from the solution (0N). Chlorophyll (Chl) and N, and reflectance of the uppermost fully expanded leaves were determined at 10-d intervals from 60 to 115 DAS during the N treatments. Plant growth and developmental parameters were measured at the end of the experiment, 115 DAS. Nitrogen deficiency caused a reduction in leaf Chl content, rate of photosynthesis (A), and dry weight (DW) of biomass components. Deficit N increased leaf reflectance at 555 (R555) and 715 (R715) nm and caused a shift in red-edge (685–745 nm) to shorter wavelengths. Leaf N and Chl concentrations were linearly correlated with not only the reflectance ratios of R545/R1605 (r2 = 0.82) and R555/R405 (r2 = 0.81), respectively, but also the first derivatives of the reflectance (dR/dλ) in red-edge centred 690 or 700 nm (r2 = 0.74–0.83). Leaf and panicle DW had the greatest, while root DW had the smallest decrease under N deficiency. It was concluded that the specific reflectance ratios or dR/dλ may be used for rapid and non-destructive estimation of leaf Chl and plant N status of big bluestem to detect changes in N for appropriate nitrogen management strategies during the growing season.