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Abstract Detail


Augustine, Steven [1], McCulloh, Kate [2].

Going for broke: carbon and water relations of germinant conifer seedlings exposed to drought.

Germinant (1st-year) seedlings represent a critical life stage in conifers, with mortality often greater than 90% in typical environmental conditions. Few studies have investigated the effect of drought on 1st-year seedling physiology, but these studies have yet to look at the ontogenetic differences of these responses from the cotyledonous stage to the formation of fascicles. We used two pine species found at the lower treeline in a greenhouse study to research these responses. Germinated seedlings were exposed to a gradual dry-down for 12 weeks until mortality was reached, and compared to control (well-watered) seedlings. Diurnal gas exchange, growth, and non-structural carbohydrate concentrations were measured to quantify the carbon balance of the seedlings. Leaf vulnerability and pressure-volume curves were conducted at the cotyledonous stage and when primary needles were dominant to determine developmental changes in drought-vulnerability and cell-water relations, and the plasticity of these parameters to drought. We hypothesized that 1st-year conifer seedlings would (1) maintain a positive carbon balance despite decreasing soil moisture to ensure for sufficient growth and storage to survive to the next growing season; and (2) have mortality associated with hydraulic dysfunction, as maintaining a positive carbon balance would force seedlings to operate under increasing xylem tensions. Species-specific responses to drought were highlighted by the initial trends in gas exchange and mortality rates. Pinus ponderosa decreased transpiration and photosynthesis a week into the drought treatment, while Pinus contorta maintained gas exchange for several weeks. Both species lost the majority of their leaf conductance daily, but failed to reach their turgor loss point (TLP) until mortality. TLP and the osmotic water potential decreased throughout development, with drought further decreasing the values. Seedlings maintained narrower hydraulic safety margins while cotyledonous, relying on hydraulic capacitance to buffer against changes in xylem pressure. P. ponderosa had a greater initial relative root and shoot growth rate, most likely due to high seed reserves. This spurt of growth lead to increased gas exchange in the cotyledonous stage, which allowed P. ponderosa to maintain a positive carbon balance 11 weeks into the drought. Comparatively, P. contorta was only able to maintain a positive carbon balance for 9 weeks even through gas exchange persisted during the drought, leaving it vulnerable to both depleted carbon reserves and hydraulic dysfunction. Mortality in P. contorta was persistent throughout the drought, while P. ponderosa had no mortality until 12 weeks of drought, experiencing 100% mortality over a few days.

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1 - University of Wisconsin - Madison, Botany, 430 Lincoln Drive, Madison, WI, 53706, US
2 - Department Of Botany, 430 Lincoln Dr, Madison, WI, 53706, United States

none specified

Presentation Type: Poster
Session: P, Ecophysiology Posters
Location: Arizona Ballroom/Starr Pass
Date: Monday, July 29th, 2019
Time: 5:30 PM This poster will be presented at 6:15 pm. The Poster Session runs from 5:30 pm to 7:00 pm. Posters with odd poster numbers are presented at 5:30 pm, and posters with even poster numbers are presented at 6:15 pm.
Number: PPE010
Abstract ID:750
Candidate for Awards:Physiological Section Best poster presentation,Physiological Section Physiological Section Li-COR Prize

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