Abstract
Suboptimal nitrogen (N) availability is a primary constraint for crop production in developing countries, while in developed countries, intensive N fertilization is a primary economic, energy, and environmental cost for crop production. We tested the hypothesis that under low-N conditions, maize (Zea mays) lines with few but long (FL) lateral roots would have greater axial root elongation, deeper rooting, and greater N acquisition than lines with many but short (MS) lateral roots. Maize recombinant inbred lines contrasting in lateral root number and length were grown with adequate and suboptimal N in greenhouse mesocosms and in the field in the USA and South Africa (SA). In low-N mesocosms, the FL phenotype had substantially reduced root respiration and greater rooting depth than the MS phenotype. In low-N fields in the USA and SA, the FL phenotype had greater rooting depth, shoot N content, leaf photosynthesis, and shoot biomass than the MS phenotype. The FL phenotype yielded 31.5% more than the MS phenotype under low N in the USA. Our results are consistent with the hypothesis that sparse but long lateral roots improve N capture from low-N soils. These results with maize probably pertain to other species. The FL lateral root phenotype merits consideration as a selection target for greater crop N efficiency.
Highlights
Suboptimal nitrogen (N) availability is a primary limitation to plant growth in terrestrial ecosystems (Tilman et al, 2002)
Lateral root-branching density of crown, primary, and seminal roots was not influenced by N treatment in either RS or South Africa (SA)
Our results support the hypothesis that the phenotype of few but long (FL) lateral roots is superior to many but short (MS) lateral roots under N limitation, as evidenced by decreased root respiration, greater rooting depth (ARL and Depth above which 95% (D95)), increased N uptake, greater photosynthesis (Pn), leaf greenness (SPAD), plant biomass, and reproductive output (Figs 3, 5, 7, 9–13)
Summary
Suboptimal nitrogen (N) availability is a primary limitation to plant growth in terrestrial ecosystems (Tilman et al, 2002). Low-N availability is a principal, pervasive constraint to crop production and food security and economic development, as most smallholder farmers have limited access to fertilizer (Azeez et al, 2006; Worku et al, 2007). Intensive N fertilization sustains high yields, but N use is generally inefficient, with only 30–40% of total N applied being harvested in grain (Raun and Johnson, 1999). It is estimated that a 1% increase in N utilization efficiency could save ~$1.1 billion annually (Kant et al., 2011). Improved N efficiency would afford multiple global benefits
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