Enhanced Phosphorus Acquisition Contributes Substantially to Arbuscular Mycorrhizal Fungus-Mediated Drought Tolerance in Trifoliate Orange
TL;DR
It is demonstrated that enhanced phosphorus acquisition is an important component of AMF-mediated drought tolerance in trifoliate orange, whereas coordinated regulation of phytohormone homeostasis and antioxidant defense provides additional protection against drought stress.
Abstract
Arbuscular mycorrhizal fungi (AMF) have been widely recognized for their ability to enhance plant drought tolerance. However, the contribution of improved phosphorus (P) nutrition to AMF-mediated drought tolerance in citrus and its relationship with other physiological processes remain unclear. Here, we investigated the physiological mechanisms underlying AMF-mediated drought tolerance in trifoliate orange (Poncirus trifoliata) by combining AMF inoculation with exogenous phosphorus supplementation under drought stress. AMF inoculation markedly alleviated drought-induced growth inhibition, increased plant biomass, enhanced root and rhizosphere phosphatase activities, promoted phosphorus accumulation, and strongly induced the expression of the mycorrhiza-specific phosphate transporter genes PtaPT4 and PtaPT5. Exogenous phosphorus supplementation largely mimicked the beneficial effects of AMF on plant growth and drought tolerance, indicating that enhanced phosphorus acquisition contributes substantially to AMF-mediated drought tolerance in trifoliate orange. However, the combined application of AMF and exogenous phosphorus conferred greater drought tolerance than phosphorus supplementation alone, suggesting that, in addition to improved phosphorus nutrition, AMF further enhances drought adaptation through the regulation of multiple physiological processes. Furthermore, AMF promoted the accumulation of growth-related phytohormones, enhanced antioxidant capacity, and reduced reactive oxygen species (ROS) accumulation, thereby further improving plant drought tolerance. These findings demonstrate that enhanced phosphorus acquisition is an important component of AMF-mediated drought tolerance in trifoliate orange, whereas coordinated regulation of phytohormone homeostasis and antioxidant defense provides additional protection against drought stress.