Timelapse scanning reveals spatial variation in tomato (Solanum lycopersicum L.) root elongation rates during partial waterlogging

Root systems show considerable plasticity in their morphology and physiology in response to variability within their environment. Root elongation below a water-table was expected to slow due to hypoxia, whilst roots above the waterlogged zone were expected to compensate by increasing elongation rates. Tomato plants (Solanum lycopersicum L.) were grown in peat in root chambers (300 x 215 x 6 mm) with a transparent front. Root chambers were maintained in flatbed scanners tilted at 30A degrees to vertical and scanned every 3 h before, during and after waterlogging the lower layer for 24 h or 5 days. Root elongation rates were calculated from the displacement of randomly selected root tips between successive scans. Oxygen content was determined in the waterlogged layer and plant and root parameters were determined at cessation of the experiment. Root elongation rates decreased rapidly when waterlogged. Growth rates of the waterlogged roots decreased, while growth rates of roots above the waterlogged zone increased. In 24 h waterlogged roots new lateral root growth occurred in the lower layer of the root chamber when water was drained while after 5 day waterlogging new root growth had to be initiated from roots above the waterlogged zone. Plants increased growth rates in roots above the waterlogged zone probably as compensation for the suboptimal conditions in the waterlogged zone which eventually led to roots dying.