Comparing the three species studied, P. australis exhibited the highest exudated POD activity and specific activity in winter (p ⩽ 0.03), spring (p < 0.0001) and summer (p = 0.002) ( Table 1 and Fig. 2). For P. australis, secretions increased from winter to summer: POD activity was 1 U/g root DW in winter and reached 4 U/g root DW in summer (p = 0.004) while that of T. latifolia was always at the detection limit.