In Citrus L. sp., specific root length of whole root systems has been correlated positively with root hydraulic conductivity, but there is little mechanistic understanding of the causes for this association. The hydraulic conductivity of individual roots in relation to root anatomical characteristics in seedlings of three citrus rootstocks [sour orange (SO) (Citrus aurantium L.), trifoliate orange (TO) (Poncirus trifoliate (L.) Raf.), and Swingle citrumelo (SC) (C. paradisi Macf. × P. trifoliata)] that vary widely in specific root length (SRL) was measured. Among fibrous roots, first-order and secondorder laterals were examined. Relative differences among rootstocks in the overall hydraulic conductivity (LP) and radial conductivity (LR) for individual 1-month-old and 6-month-old second- and first-order roots generally were consistent with hydraulic conductivity determined previously for entire root systems. There were no significant differences in axial conductance per unit pressure (Kh) in either first- or second-order roots among the rootstocks. This was consistent with the similarity in number and diameter of xylem vessels. One-month-old second-order roots had no suberized exodermis but varied in cortical radius. Six-month-old second-order roots of TO, however, had more nonsuberized cells (passage cells) in the exodermis than roots of SC and SO, although the cortical radius of SC and SO roots were not different. Compared to 6-month-old second-order roots, 1-month-old second-order roots had much higher LP and LR but lower Kh. Differences in overall root hydraulic conductivity among the citrus rootstocks were mainly related to structural differences in the radial pathway for water movement, suggesting that radial hydraulic conductivity was the primary determining factor of water uptake in citrus rootstocks.
length (centimeters). Samples were then dried for 48 h at 70 °C, and root weight was used to calculate specific root length [SRL (centimeter per gram)]. Data analysis. Average total root biomass was calculated by depth (0–10 cm, 10–20 cm, and 20–30 cm
weighed. Specific root length (SRL; in centimeters per gram) measures root length per dry weight and was calculated by dividing TRL by dry root weight. And the root:shoot ratio was calculated by the dividing dry weight of the harvested root system with the
Industries, Canada). Specific root length was determined after calculating the dry weight of the scanned sample using the fresh weight to ash-free dry weight ratio of the whole sample. The calculated dry weight of the scanned sample was then divided by the
75 °C for 48 h and carefully weighed to the nearest 0.1 mg. Specific root length (SRL, m·g −1 ) was calculated as the ratio of root length and root dry weight of the corresponding root system. Root vitality measurement using the triphenyltetrazolium
.0; Regent Instruments, Quebec, Canada) (Cavelier et al., 1992). After that, leaf, stem, and root were firstly dried at 105 °C for 30 min, then further dried at 75 °C for 48 h to obtain constant dry weight (DW). Specific root length and SRA were calculated as
cm −3 soil) by considering the diameter of the tubes and the length of each horizon. Subsequently, RDW was obtained after drying at 60 °C for 72 h. Specific root length (m·g −1 ), which represents the amount of absorptive root tissue produced per
from the growth chamber and placed in a cooler at 5 °C until harvest. Bermudagrass plants were harvested, and seedling number, tiller number, shoot dry weight (SDW), root length density (RLD), root mass density (RMD), specific root length (SRL), and
were dried at 70 °C for 60 h and weighed. Root volume, surface area, root specific volume (root volume per unit dry mass) and SRL (length per unit dry mass of the samples) were calculated. The relative amount of aerenchyma in the root cortex was
) were acquired directly by the software. Root-to-shoot ratio (RSR), specific root length (SRL), and root tissue density (RTD) were computed. Trait abbreviation and explanations are described in Table 1 . Table 1. Summary of measured shoot and root