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

Abstract

The growth and branching of the taproot of young oak trees were studied on seedlings grown in root observation boxes over a period of 30–45 d. The development of shoots and roots were recorded daily on a set of eight plants, and additional observations on the initiation of primordia were made on another set of 18 plants. Taproot growth was typically indeterminate and linear, with growth rates in the range of 1.5–2.5 cm d−1. In some cases, however, growth slowed down or stopped, and resumed a few days later. The growth of shoots and 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 in our experiment). The latter appeared especially when taproot growth slowed down or stopped. New primordia were initiated on tissues older than 1.4 d, and lateral roots emerged after a minimal development duration of 2.3 d. These time-related parameters described the emergence of branching very effectivety, since they were quite stable over a wide range of taproot growth rates. However, emergence duration decreased slightly in fast growing taproots. Branching density tended to increase with the taproot growth rate. Physiological significance and consequences for modelling root system development are discussed.