Water-conducting roots responsible for nitrogen uptake in maize ( Zea mays )

Nitrate (NO ₃ ^- ) uptake is primarily driven by mass flow and varies among maize root types. The importance of embryonic and crown roots in acquiring NO ₃ ^- was determined here in wet and dry soils. Maize was grown in a split-root pot that segregated the embryonic and crown roots. The soil was moistened to water potentials of either -5kPa or -30kPa. A partial N mass balance was made by destructively sampling shoots, roots, and soils after 0, 24, and 48 h following ¹⁵ N-KNO ₃ injection at the V3 and V6 stages. Gross nitrification was assessed using a ¹⁵ N isotope dilution technique. At the V3 stage, crown roots had 202% more N uptake than embryonic roots in wet soil (-5 kPa). However, in dry soil (-30 kPa), N uptake was similar for embryonic and crown roots, possibly due to an 80% reduction of hydraulic conductance in crown roots. By the V6 stage, crown roots dominated N uptake, with embryonic roots supplying < 20% of N uptake. Soil gross nitrification rate was similar for root types. The present studies indicated that maize NO ₃ ^- uptake depends primarily on the crown roots, due to their capacity to extract water and NO ₃ ^- from soil, even under dry conditions.