Abstract: We investigated the effects of resin-tapping on the radial differences of sap flow density and whole-tree transpiration in Pinus massoniana. We used the Granier's thermal diffusion probe method to measure sap flow density at different sapwood depths on non-resin-tapped P. massoniana and both the non-resin-tapped surface and resin-tapped surface of resin-tapped P. massoniana, that had undergone continuous resin tapping from 2004 to 2015. The results showed that the radial distribution patterns of sap flow density in the non-resin-tapped P. massoniana and on the non-resin-tapped surface of resin-tapped P. massoniana were unimodal, while that on the resin-tapped surface of resin-tapped P. massoniana was irregular. Resin-tapping altered the radial distribution pattern of sap flow density on the resin-tapped surface of resin-tapped P. massoniana. In addition, the sap flow density on the resin-tapped surface of P. massoniana was significantly lower than that on the non-resin-tapped surface, indicating that resin tapping reduced water transport capacity of the tapped surfaces. Except for the outer layer (0-2 cm), the density of sap flow on the non-resin-tapped surface was higher than that on the corresponding sapwood depth of the non-resin-tapped P. massoniana in other layers (2-10 cm), which would compensate the decreased water transport capacity of the resin-tapped surface. Furthermore, the whole-tree average daily sap flow density in resin-tapped P. massoniana (710.4 kg·m^-2·d^-1) was 82.9% of that in the non-resin-tapped P. massoniana (856.63 kg·m^-2·d^-1), indicating that the increase in sap flow density on the non-resin-tapped surface could not fully compensate for the decline in water transport capacity of the resin-tapped surface, resulting in a decrease in the overall water transport capacity of the resin-tapped P. massoniana. Moreover, the appearing time of whole-tree daily maximum sap flow density in resin-tapped P. massoniana occurred approximately 1 hour earlier than that of non-resin-tapped P. massoniana, indicating that the decrease in whole-tree water transport capacity caused by resin-tapping had led to moisture deficiency in resin-tapped P. massoniana. There was significant correlation between whole-tree sap flow density and sap flow density in various depths on the non-resin-tapped surface of resin-tapped P. massoniana and non-resin-tapped P. massoniana. By developing an estimation method for the average tree sap flow density based on the easily measurable surface sap flow density, we could obtain a more accurate assessment of overall tree transpiration.

Key words: Pinus massoniana, resin-tapped, sap flow, radial variation, compensation effect