Root morphology and its relationship with nitrate uptake in Kentucky bluegrass

Intraspecific variation in nitrate absorption by turfgrasses has been studied but differences in turfgrass root morphology which may contribute to this variation have not been ascertained. Such information may benefit breeding programs aimed at improving the ability of turfgrasses to absorb nitrate from low fertility soils. The present study quantifies belowground morphological traits of Kentucky bluegrass (Poa pratensis L.) and establishes their relationships with nitrate uptake rate (NUR). Tiller-generated plants were grown in silica sand, mowed weekly, and watered daily with nutrient solution containing 1 mM nitrate for 5 mo. Following transfer to solution culture, nitrate depletion of the nutrient solution was monitored for eight consecutive days, after which the belowground portion of each plant was separated into adventitious roots, fibrous roots, and rhizomes. Estimates of total Length, total area, average diameter, and length distribution among root thickness classes, were made by scanning and image analysis systems. NUR expressed as micromoles nitrate absorbed per plant per hour was significantly (P less than or equal to 0.05) and positively correlated with the total biomass, length and area of the belowground organs. Fibrous roots contributed to > 80% of the total belowground length. Approximately 80% of the total fibrous root length had diameters < 0.2 mim. The fibrous root length, surface, and volume of every diameter class were significantly and positively correlated with NUR. Larger numbers of thick roots (diameter greater than or equal to 0.5 mm) appeared to have no effects on NUR, while increased rhizome number appeared to have a negative effect on NUR.