Sap Flow Partitioning between Different Branches of Apricot Trees

The objective is to measure and compare the hydraulic conductance of the main branches of a mature apricot tree. We use measurements of branch sap flow, and observations of leaf water potential, to examine the effect of microclimate on total plant hydraulic conductance and its partitioning across different plant organs. The results indicate that sap flow was dependent on orientation, but hydraulic conductance per unit area was independent and equal in the four branches. Thus, there was "branch autonomy" for transpiration, but not for hydraulic conductance. These results, in a sense, are a validation of the pipe model theory that states that tree stems and branches can be considered as unit pipes each supporting a unit amount of photosynthetic organs.