<i>Trichoderma asperellum</i> benefits nitrogen acquisition and K+/Na+ homeostasis in wolfberry under salt stress via activation of root plasma membrane H+-ATPase

Trichoderma is reported to enhance plant salt adaptability, but the mechanisms still need in-depth investigation. This study sought to dissect how Trichoderma asperellum manipulates root ions exchange in salt-stressed wolfberry (Lycium chinense) to satisfy nitrogen acquisition and preserve K+/Na+ homeostasis. Trichoderma agent (TA) was supplemented around the roots of potted plants, and salt stress was conducted by watering with NaCl solution. Salt adaptability of wolfberry was enhanced by T. asperellum, as TA supplement protected photosynthesis, alleviated biomass reduction and increased tissue N accumulation and K+/Na+ under salt stress. Consistently, T. asperellum enhanced root Na+ extrusion and K+ retention in salt-stressed wolfberry, which was related to Na+/H+ antiporter and K+ outward-rectifying channels, as pretreatments with their inhibitors depressed root Na+ efflux but caused K+ efflux. Considering inhibited plasma membrane (PM) H+-ATPase synchronously dampened root Na+ extrusion and K+ retention under salt stress, T. asperellum was inferred to enhance root Na+ extrusion and K+ retention in salt-stressed wolfberry by inducing PM H+-ATPase. Elevated root plasma membrane H+-ATPase activity by T. asperellum was actually observed in salt-stressed wolfberry and had nothing with constitutive transcript expression. The activated H+-ATPase by T. asperellum also provided more driving force for H+/NO3- symporter and increased root NO3- absorption. Trichoderma asperellum prevented salt-induced great root NH4+ efflux and retained mild NH4+ influx likely because NH4+ efflux was not required for restricting Na+ entry. Overall, T. asperellum activated root plasma membrane H+-ATPase to optimizing root ions exchange and then improved nitrogen acquisition and K+/Na+ homeostasis in wolfberry under salt stress. According to the structural equation model analysis, PM H+-ATPase had a positive effect on photosynthesis, root sugar content, root respiration and itself sequentially, highlighting that the activated root PM H+-ATPase by TA supplement enhanced wolfberry salt adaptability by driving a favorable cooperation between roots and aerial part.