Coordination of whole-tree water transport and storage is more synchronized in mesic than semi-arid species

We are limited in our knowledge about coordination of water transport at the whole-tree level, which is influenced by water storage and release 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, southern red oak, Douglas-fir, and trembling aspen) over summer seasons in two environmental systems (mesic/semi-arid). We quantified the coordination of sap flow and volumetric water content at different trunk heights and xylem tissue depths. Further, we compared seasonal patterns of daily water storage and use in the different systems. Coordinated lags in sap flow between upper and lower trunk heights were present in all study species except oak. There was less whole-tree coordination of water transport and storage in the semi-arid compared to the mesic 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.