Contrasting responses of two Camellia oleifera rootstocks differing in phosphorus efficiency to low-phosphorus stress

Camellia oleifera Abel, the dominant woody oil crop of southern China, often suffers from limited productivity due to the prevalence of phosphorus (P) stress in acidic soils. While grafting is an effective strategy to mitigate nutrient scarcity, the mechanistic basis of rootstock-mediated P tolerance in this species remains poorly understood. This study investigated the morphological, physiological, and molecular responses of two contrasting C. oleifera rootstocks, the P-tolerant Ganwu 1 (GW1) and the P-sensitive Ganwu 2 (GW2) under P-deficient conditions.

Our findings identified rootstock types as the primary determinant of P tolerance. GW1 exhibited superior resilience by re-engineering its root architecture, achieving a 4.12-fold higher root biomass and significantly greater 66.5% increase in fine root volume than GW2 under low P stress. In contrast, GW2 showed a compensatory but inefficient root expansion that failed to enhance soil exploration. Specifically, GW1 demonstrated a 3.7-fold higher root P accumulation and a 52.4% increase in root P-utilization efficiency under stress, reflecting a significantly higher capacity for P acquisition and internal allocation. This was coupled with enhanced nutrient rebalancing, particularly through robust potassium (K) accumulation in shoots, whereas GW2 suffered from a significant decline in soluble protein content and higher lipid peroxidation (MDA). Additionally, GW1 sustained high root acid phosphatase (ACP) activity during late-stage stress to further mobilize P. At the molecular level, GW1 was characterized by the accelerated induction of the CoARF22, CoPHR1, and CoPHT1;1 and earlier activation (70 days) of CoALMT-mediated organic acid genes. These proactive responses enabled GW1 to effectively mobilize soil P and maintain structural integrity, establishing it as a highly efficient rootstock for P-limited acid soils.

This integrated "morphology-physiology-signaling" framework grants GW1 a superior low-P adaptive advantage. These results identify GW1 as a promising, P-efficient rootstock for sustainable C. oleifera production in P-deficient environments.