The theory that describes immediate impact of heating power on pressure-gradient-driven turbulence and turbulent transport (without waiting for the evolution of global parameters and the mean distribution function) is reported. A new mechanism, which is an external source directly coupling with plasma fluctuations in the phase space so as to affect turbulence and transport, is investigated. Application is made to the cases of trapped particle instability and long-range fluctuations, which are driven by background microscopic fluctuations. This theory can predict an abrupt change in transport at the on/off of heating, which has been indicated by experimental observations. The derivative of heating power density by plasma pressure is a key parameter, in addition to conventional spatial gradients. The condition under which this new effect can be observed is also evaluated.