Influence of PPFD and VPD (A) on sap flow in two seedlings according to measurements obtained with Dayau-gauges (B) and two with EMS-type gauges (C) from DOY 171 to 173. In both B and C data for a seedling with a high transpiration rate and a seedling with a low transpiration rate are shown (seedlings 6 and 3 in B, seedlings 4 and 1 in C, respectively). The arrow in panel A indicates the period in which transpiration measurements were acquired by the gravimetrical method (used in the analyses presented in Fig. 4). The relative humidity of the air was set to 80% during night why VPD did not approach zero (A).