In trees, xylem conduits transport water from roots to leaves. Conduit walls represent resistance to water transport, which accumulates with transport pathway length. To counteract, conduit dimensions increase with distance from the treetop (dtreetop). Water travels between conduits via pits. Little is known about the scaling of pits along the water transport pathway. Larger conduits and pits conduct more water but are more vulnerable to hydraulic failure. Furthermore, conduit formation is sensitive to environmental conditions, which may affect conduit numbers and dimensions.
This thesis aimed to a) bring evidence on within-tree variation and coordination of conduit and pit dimensions, particularly their scaling along the water transport pathway, b) explore interspecific differences, and c) better understand effects of environmental conditions on the timing of conduit formation phases and on conduit and pit dimensions.
We analyzed conduits and pits from inner to outer tree rings at breast height and from treetops to coarse roots in outer rings in Scots pine, Norway spruce, and silver birch on sites with different growing conditions. We also analyzed the timing of conduit formation phases in pine and spruce along a latitudinal gradient. We used light and scanning electron microscopy to study conduits and pits.
Conduit and pit dimensions scaled with dtreetop indicating that their coordination along the water transport pathway is crucial for the survival of both conifers and angiosperms. Scaling but not coordination deviated in roots. In conifers, pit functional properties differed between sites and species, indicating that the relative size of torus and pit aperture may be particularly important for hydraulic safety. Lower latitudes and warmer years enabled longer conduit formation phases and a greater number of conduits. Thus, global warming may enhance wood production in boreal forests until another factor than temperature becomes limiting.