ABSTRACT:

Studies have shown that water can reside inside trees for up to several months, but how the duration of long-term stored water relates to species-specific water management strategies is not known. We studied water residence time, tracervelocity, and internal mixing in two tree species with differing water management strategies by injecting deuterated water into Douglas fir (Pseudotsuga menziesii) and trembling aspen (Populus tremuloides) trees and then monitored tracer concentration in leaves collected daily for several weeks post-injection. In a second study, we injected tracer into trees and collected leaves at sub-daily timescales to explore sub-daily patterns of tracer arrival in canopy leaves. For the first experiment, we hypothesized that the tracer would remain in both species for days to weeks and that the tracer would have a longer residence time in the more isohydric Douglas fir trees. For the sub-daily study, we explored if the tracer would arrive at a sharp peak, or be more spread out over time. The tracer resided in the trees for 7-11 days for both species. Interestingly, the tracer reached the canopy leaves of aspen sooner yet remained in trees for longer compared to Douglas fir, which exhibited sharp pulses of tracer breakthrough in canopies. Surprisingly, the tracer arrival in aspens occurred in two distinct pulses, separated by 1-2 days. Combined, the results from both experiments suggest that water inside trees may not flow through trees in simple “in-up-and-out” ways and that there may be some complex mixing of water reservoirs and water-flow pathways in some tree species.

ABSTRACT:

Since the 1950’s balsam woolly adelgid (Adelges piceae) has been infesting true fir species (Abies sp.) within the Northwestern United States. Balsam woolly adelgid infestations within subalpine fir (Abies lasiocarpa) stands have led to the deterioration of tree stands throughout the northern Intermountain Northwest. Currently, there are only a few studies quantifying the physiological impacts of balsam woolly adelgid infestation on subalpine fir trees. Thus it is unclear how subalpine fir morphology and physiology are altered when infested by balsam woolly adelgid, especially at drier and/or warmer edges of subalpine fir’s range. Here, we quantified the impacts of balsam woolly adelgid infestation on whole-tree water relations in subalpine fir, at cellular to whole-tree scales. We hypothesized that tree morphology would be significantly altered in infested trees, and scale with the intensity of infestation. Additionally, we hypothesized that water stress in infested trees would be evident at cellular to whole-tree scales. Finally, we predicted that hydraulic efficiency would decrease as infestation-level increased. We found that morphological traits such as gouting and crown area were not different between trees of varying infestation levels, nor were branch-tip water potentials. However, cell water relations parameters such as osmotic water potential and turgor loss point were more negative compared to values from non-infested trees in the literature. Finally, sapwood- and leaf area-specific hydraulic conductivity in branches in all infested trees were orders of magnitude lower than conductivities reported for healthy trees. Collectively, our findings demonstrate that balsam woolly adelgid has a strong impact on subalpine fir morphology and whole-tree water relations, and provide insights into the mechanisms causing mortality in infested trees.