Root architecture characteristics of differing size-controlling rootstocks and the influence on the growth of 'Red Fuji' apple trees.

• Root number is a key factor influencing root system characteristics. • Root projected and surface areas define the correlation of above and belowground traits. • Larger root distribution positively correlated with photosynthesis capacity. High-density cultivation using dwarfing rootstocks is widely practiced worldwide. The root is an essential organ for apple rootstocks, especially for dwarfing rootstocks. However, few studies about the root traits of apple rootstocks have been published. In this study, the root growth characteristics of the 'Red Fuji' apple cultivar scions grafted onto Shao series no. 40 (RF/SH.40) and Baleng Crab (RF/BC) rootstocks, which have apparent size-controlling differences, were investigated. Subsequently, the tree morphological and leaf photosynthetic parameters were measured, and the correlation between the roots and branches was studied. Thus, the root system of RF/BC was more widely distributed than that of RF/SH.40, with higher volume, projected area, surface area, root number, and length of the root system. Multiple comparisons revealed that the number of roots might be the critical factor contributing to differences in the two root systems. Furthermore, RF/BC had higher leaf photosynthetic rates, water use efficiency, and branch numbers and length than RF/SH.40. RF/BC had a wider branch distribution in a vertical orientation; however, a wider branch distribution in a horizontal orientation and a higher rate of branches shorter than 15 cm was observed for RF/SH.40. The above-ground tree architecture and below-ground root traits tend to be positively correlated. The parameters that primarily affected the correlation between above- and below-ground were branch volume, branch number, total projected, and total surface area of the root system. [ABSTRACT FROM AUTHOR]