The Influence of Growing Temperature on the Growth and Morphology of Cereal Seedling Root Systems

Abstract

The root systems of cereal seedlings (wheat, rye, barley, oats), grown in a series of liquid and solid media at 5, 15 and 25 °C, were measured at intervals between sowing and emergence (shoot length 4.0 cm). In all cases, the length of seminal axes increased linearly with time, and the rate of root extension was increased significantly by each 10 °C increment in growing temperature. In general, extension rates were lower in the solid media than in water culture; however, there was a strong interaction between medium and growing temperature, indicating that higher temperatures can compensate partly for the detrimental effects of mechanical impedance. Examination of the influence of growing temperature upon root axis diameter was hampered by the observation that, for all four species, apical root diameter was inversely related to root length. It was concluded that comparison of the diameters of roots grown at different temperatures was valid only if the roots were of the same length (but different ages). Following this principle, it was found that, although cereal roots grown at 5 °C tended to be slightly thicker than those at 15 °C or 25 °C, this effect was small and rarely exceeded 10%. Published reports of very large differences in root diameter at different growing temperatures were examined and found to be generally unreliable. Lateral roots did not represent a significant fraction of the root system in any of the treatments studied. Root: shoot relationships at different growing temperatures were examined by plotting root system length against shoot length for each sample. It was found that, for the same shoot length, the root systems at 5 °C were much shorter than at 25 °C, the response at 15 °C being rather more variable. This finding, which indicates that plants grown at low temperatures have a lower capacity for water and solute uptake than those grown at laboratory temperatures, has important implications for the design of laboratory experiments. The influence of root zone temperature upon root growth and physiology can be determined unequivocably only if the roots have been exposed to the experimental temperature throughout their growth.