In recent years, terahertz communication has attracted extensive attentions due to its large bandwidth for supporting terabit-per-second capacity. Along with the rapid evolution of terahertz optoelectronic devices, remarkable achievements have been witnessed in developing photonic terahertz communication systems with large capacities. In fact, photonics-assisted terahertz communication systems have exhibited some advantages, for instance, bridging a seamless connection between the existing optical fiber network and wireless network, offering flexible carrier switching over a wide radio frequency range, as well as supporting easy implementation of high-order complex modulation formats and multicarrier multiplexing terahertz channels. However, due to high atmospheric propagation loss, limited terahertz component bandwidth and low terahertz emission power, achieving simultaneous transmission of single-lane data rates beyond 200 Gbps is still challenging based on a single pair of terahertz transceivers. In this work, by employing subcarrier (SC) multiplexing, high-order 64-ary quadrature amplitude modulation (64-QAM) format, well-defined digital signal processing (DSP) and wideband terahertz transceivers, a multicarrier terahertz photonic-wireless communication link operating in the 300 GHz band is proposed and experimentally demonstrated. At the transmitter side, a baseband pseudo-random binary sequence (PRBS-15) signal with a baud rate of 12 Gbaud is generated from an arbitrary waveform generator (AWG), and then modulated onto an optical carrier centered at 193.414 THz. The modulated optical signal is combined with three optical carriers centered at 193.7035 THz, 193.7165 THz, and 193.7295 THz, for multi-carrier THz generation at a uni-traveling carrier photodiode (UTC-PD) featuring large bandwidth (100 GHz), which consists of three SCs centered at 286.5 GHz, 299.5 GHz and 312.5 GHz, respectively. At the receiver side, we employ a Schottky diode mixer with high sensitivity to down-convert the three terahertz SCs into the intermediate frequency (IF) domain, with three IF signals cantered at 6.5 GHz, 19.5 GHz, and 32.5 GHz, respectively, which are then processed using home-made advanced DSP routine, including a linear adaptive equalizer, compensation algorithms of frequency offset and phase noise. In the experiment, a total line data rate of 216 Gbps (72 Gbps/SC ×3 SC) over a wireless distance of 30 m is successfully transmitted, and the performance of all three SCs can reach below the hard decision forward-error-correction (HD-FEC) with 6.25 % overhead, reaching an aggregated net transmission capacity of up to 202.5 Gbps. This achievement of single-lane simultaneous transmission of beyond 200 Gbps using a single pair of 300 GHz transceivers is considered a significant step towards next-generation wireless communications.