Response of phytoplankton to nitrogen addition in the Taiwan strait upwelling region: Nitrate reductase and glutamine synthetase activities

► NRA and GSA of phytoplankton in the Taiwan Strait during an upwelling period were studied. ► NRA and GSA reflect the status of ambient nitrogen levels and Chl-a concentration in situ. ► A time-lag existed between nitrate addition and NRA and GSA. No time-lag was found between ammonium addition and GSA.