Growth and branching of the taproot of young oak trees--a dynamic study

The growth and branching of the taproot of young oak trees werestudied on seedlings grown in root observation boxes over aperiod of 30–45 d. The development of shoots and rootswere recorded daily on a set of eight plants, and additionalobservations on the initiation of primordia were made on anotherset of 18 plants. Taproot growth was typically indeterminateand linear, with growth rates in the range of 1.5–2.5cm d^–1. In some cases, however, growth slowed down orstopped, and resumed a few days later. The growth of shootsand roots were not synchronized. Taproots branched in two ways:acropetal branches emerged from 4–8-d-old taproot tissues,and late branches emerged from older tissues (up to 30 d inour experiment). The latter appeared especially when taprootgrowth slowed down or stopped. New primordia were initiatedon tissues older than 1.4 d, and lateral roots emerged aftera minimal development duration of 2.3 d. These time-relatedparameters described the emergence of branching very effectivety,since they were quite stable over a wide range of taproot growthrates. However, emergence duration decreased slightly in fastgrowing taproots. Branching density tended to increase withthe taproot growth rate. Physiological significance and consequences for modelling rootsystem development are discussed. Key words: Quercus robur, root system, growth, branching, primordium initiation