Root morphology and its relationship with nitrate uptake in Kentucky bluegrass

Intraspecific variation in nitrate absorption by turfgrasses has been studi ed but differences in turfgrass root morphology which may contribute to thi s variation have not been ascertained. Such information may benefit breedin g programs aimed at improving the ability of turfgrasses to absorb nitrate from low fertility soils. The present study quantifies belowground morpholo gical 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 soluti on containing 1 mM nitrate for 5 mo. Following transfer to solution culture , nitrate depletion of the nutrient solution was monitored for eight consec utive days, after which the belowground portion of each plant was separated into adventitious roots, fibrous roots, and rhizomes. Estimates of total L ength, total area, average diameter, and length distribution among root thi ckness classes, were made by scanning and image analysis systems. NUR expre ssed as micromoles nitrate absorbed per plant per hour was significantly (P less than or equal to 0.05) and positively correlated with the total bioma ss, length and area of the belowground organs. Fibrous roots contributed to > 80% of the total belowground length. Approximately 80% of the total fibr ous root length had diameters < 0.2 mim. The fibrous root length, surface, and volume of every diameter class were significantly and positively correl ated with NUR. Larger numbers of thick roots (diameter greater than or equa l to 0.5 mm) appeared to have no effects on NUR, while increased rhizome nu mber appeared to have a negative effect on NUR.