Diurnal dynamics of fine root growth in grapevines

Fine roots can grow more rapidly at certain points during the day depending on species and environmental conditions. The grapevine is a large perennial that has an extensive below-ground structural system; however its diurnal root growth pattern has received little attention. The aim of this study was to characterize the diurnal fine root growth dynamics of four grapevine genotypes and to assess the impact of soil temperature on this growth. One-year-old vines of Shiraz (Vitis vinifera), and the rootstocks Ramsey (V. champinii), 140 Ruggeri (V. berlandieri x V. rupestris) and Schwarzmann (V. rupestris x V. riparia) were grown in tapered rectangular pots with transparent acrylic windows to assess diurnal root growth dynamics using sequential image acquisition with a high resolution scanner. All four genotypes displayed a pronounced diurnal root growth pattern that positively followed daily soil temperature fluctuations. Maximum growth rates did not differ between the genotypes and were highest in the afternoon, declined through the night and reached a minimum the next morning. While diurnal root growth rates were influenced by soil temperature, this was not the only factor as evidenced by an extensive range of growth rates between the individual roots of a plant even when exposed to optimal temperatures. It is argued here that other environmental and endogenous factors will likely have an influence on the maximum rate of growth.