Comparison of whole-tree water transport and storage coordination in four tree species of contrasting hydraulic strategies

Our knowledge about coordination of water transport at the whole-tree scale has been limited in its consideration of water storage and release from different tissues (i.e., sapwood and heartwood) along the xylem pathway. Here, we measured water transport and storage at spatially and temporally intensive scales in four tree species of contrasting hydraulic strategies (loblolly pine (Pinus taeda), southern red oak (Quercus falcata), Douglas-fir (Pseudotsuga menziesii), and trembling aspen (Populus tremuloides)) over the growing season in North Carolina (mesic) and Idaho (semi-arid), USA. We quantified the coordination of sap flow and volumetric water content at different heights along the main tree trunk and xylem tissue depths. Further, we investigated seasonal patterns of daily water storage and use in the different systems. Coordinated lags in sap flow between upper and lower heights along the trunk were present in all study species except oak. Whole-tree coordination of water transport and storage was more evident in the mesic system than in the semi-arid system. The angiosperm species displayed greater water storage use than the gymnosperm species in both systems, with water storage use patterns related to rain events in the mesic system and related to soil-moisture dry down in the semi-arid system. Our findings emphasize the importance of understanding water transport and storage at species- and ecosystem-specific levels inferred from spatially and temporally intensive tree measurements.