INTEGRATED ROOT-SYSTEM AGE IN RELATION TO PLANT NUTRIENT-UPTAKE ACTIVITY

The age of a root segment is inversely related to its nutrient uptake activity (uptake rate per unit root length). It is uncertain how this information should be incorporated into nutrient uptake models, due to our inability to characterize the age of a whole root system. A metho d of calculating an integrated root system age (IRSA) was defined, and two solution experiments were conducted to relate the N uptake activi ty of spring wheat (Triticum aestivum L.) to root age. Literature data also were analyzed to characterize the relationship between IRSA and nutrient uptake activity of whole plant root systems, Integrated root system age was defined as the summation of the mean ages of root segme nts produced during each growth period weighted by the ratio of the ro ot length generated during each growth period to total root length. Th e NH4 and NO3 uptake activity of spring wheat decreased with plant age as IRSA increased, while plants with similar IRSA at 14 and 21 d had similar N uptake activity. These relationships between IRSA and the up take activity of N, P, K, Ca, and Mg of corn (Zea mays L,) were also r evealed from an analysis of published data. In young root systems, nut rient uptake activity declined rapidly as IRSA increased, while older root systems (IRSA >10 to 15 d) maintained a relatively low and gradua lly declining nutrient uptake activity with increasing IRSA, The IRSA is a useful parameter for characterizing nutrient uptake activity of a n entire root system, providing a potential tool for modeling nutrient uptake.