Fractal Analysis for Morphological Description of Corn Roots under Nitrogen Stress

A means of quantification of plant root branching, specifically under stress, is of importance for evaluating the contribution of plant roots to water and nutrient uptake and subsequently plant growth. An experiment was conducted to describe the morphology of corn (Zea mays L.) root systems using fractal analysis and also to determine if a roots fractal dimension (D) is altered by N stress. Corn genotypes (B73 ✕ LHI05 and N74 ✕ Mo17) were planted in peg boxes, 1.2 m long, 1.2 m deep, and 0.05 m wide filled with 20:80 soil to sand mixture and were grown with N rates of 0, 10, 20 and 30 mg kg⁻¹. Thirtynine days after planting, the mixture was gently washed from the roots and the roots were divided into nine sections (squares of side 304.8 mm) and slide photographs were taken from each section. The slides were projected on grids made up of 12², 24², and 48² squares of sides (r) 25.4, 12.7, and 6.35 mm, respectively. Regression of log of number of squares intersected by roots vs. long of r levels was used to determine the slope (— D). Fractal dimension was significantly smaller for zero N compared to applied N with no detectable difference among applied N levels. Fractal dimension was highest for the section directly below the crown (D = 1.73) indicating high root branching and was lowest for the sections in deeper soil (D = 1.19, average of 3 sections in the 0.6 to 0.9-m depth) indicating less branching. The intercept of the regression line (log K), which indicates root abundance, was lowest for zero N. Amount of roots in the section directly below the crown was 45% of total roots. Nitrogen stress changed the morphology of corn root system and caused less root branching. Fractal analysis was a useful method for describing the morphology of corn root systems, both quantitatively and qualitatively. Contribution of the Nebraska Exp. Stn., Lincoln, NE as paper no. 9629