Rootstock selection profoundly influences citrus tree performance by modulating growth, biomass allocation, xylem anatomy, and hydraulic function. This study evaluated the contrasting effects of two widely used Poncirus trifoliata rootstocks, Trifoliate Orange (TO) and Flying Dragon (FD), on vegetative, anatomical, hydraulic, and physiological traits of lemon ( Citrus limon cv. Femminello Siracusano 2KR) and clementine ( Citrus clementina cv. Comune SRA 63) over two growing seasons. TO markedly increased plant height, leaf area, absorbing root length, and total biomass, confirming its strong vigor-inducing effect, whereas FD consistently reduced vegetative growth in both scions. Xylem anatomical analyses revealed that TO promoted larger vessel diameters and greater conductive xylem areas in both rootstock and scion, resulting in substantially higher theoretical hydraulic flow. Conversely, FD increased the proportion of narrow vessels and hydraulic resistance, particularly in root and stem segments. Physiological measurements highlighted species-specific responses: clementine exhibited higher photosynthetic activity than lemon, while FD enhanced stomatal conductance, transpiration, and net photosynthesis in both scions despite its dwarfing effect. Principal Component Analysis further distinguished three functional axes associated with structural vigor, physiological performance, and specific root–shoot traits, clearly separating the four graft combinations. Overall, TO and FD express two divergent hydraulic–functional strategies: TO enhances growth and hydraulic efficiency, whereas FD promotes reduced vigor coupled with higher hydraulic safety. These findings provide mechanistic insight into rootstock-driven modulation of citrus performance and offer practical guidance for selecting rootstocks under variable environmental and production scenarios.
Dattola et al. (Fri,) studied this question.
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