Seasonal changes and spatial distribution of citrus fine roots in different rootstocks

Understanding fine roots' spatial distribution and dynamics in citrus can enable proper site and time of fertilizing to improve the nutrient uptake efficiency below the root zone, reduce agricultural non-point source pollution and improve the performances. However, the seasonal changes and spatial distribution of citrus fine roots remain unclear. Here we investigated the dynamical changes and spatial distribution of fine roots in four rootstocks by 30° angle tube instillation and monthly capturing within a year with minirhizotrons. The results indicated that in the whole investigation, root diameter of Trifoliate (Poncirus trifoliata) was smallest, while root diameter and root number of Carrizo (Citrus sinensis × P. trifoliata) was biggest. In winter under water scarcity condition, root diameter, root length and root surface area of Trifoliate changed rapidly, then moderately in other seasons. However, the change pattern of Trifoliate differed obviously from that of the other three rootstocks. Fine roots of Trifoliate distributed nearest to the trunk and deepest belowground, while that of Rusk (C. sinensis × P. trifoliata) and Xiangcheng (C. junos) distributed the longest distance and the shallowest depth, respectively. Root length of Trifoliate and Rusk distributed mainly in depth of -45∼-30 cm, that of Xiangcheng distributed mostly in depth of -30∼-15 cm. However, root length of Carrizo distributed mostly in different depths in varied seasons. This research not only uncovered the differences in root traits and their changes of different rootstocks, which indicates the differences root phenology and probably contribute the differences in performances, but also revealed their root space distribution, which is very essential for citrus precise cultivation.