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Abstract Detail


Kerr, Kelly [1], Woodruff, David [2], Meinzer, Frederick [2], McCulloh, Katherine [3], Marias, Danielle [4].

Understanding physiological mechanisms underlying seedling establishment: a look at drought resistance traits in populations from contrasting climates from two conifer species.

Vegetation patterns and species distributions are strongly linked to soil moisture regimes. Populations within a species from contrasting climatic regimes could exhibit different establishment mechanisms. Germinant tree seedlings exhibit high rates of mortality, yet seedling survival is crucial for forest regeneration and may be more important in determining species distributions than adult tree performance. Therefore, a more thorough understanding of mechanisms underlying seedling establishment is critical for predicting future species distribution patterns. We investigated the extent to which species populations from different climate zones exhibit differential expression of drought resistance traits and strategies that facilitate their establishment. Seeds from two populations of ponderosa pine (Pinus ponderosa; PIPO) and Douglas-fir (Psuedostuga menziesii; PSME) from different climate zones in Oregon (dry site and wet site populations) were sown in a common garden and grown under two water availability treatments (control and drought) in 2013 and 2014. Morphological and physiological variables associated with growth, survival, and mortality were measured during the growing seasons and as seedlings experienced increasing water stress under the drought treatment. At the end of 2013, PIPO control seedlings had grown more than droughted seedlings, and PIPO wet site seedlings grew more than PIPO dry site seedlings under both treatments. Leaf-specific conductivity (kl) was more than twice as high in PIPO wet site population seedlings than in PIPO dry site population seedlings under both treatments and was consistently, but not significantly lower under drought. Intrinsic WUE based on δ13C values was higher in the PIPO dry site population seedlings, but there was no significant treatment effect on δ13C values. A strong negative relationship was found between values of δ13C and kl across PIPO populations and treatments, consistent with greater stomatal constraints on gas exchange with declining seedling hydraulic capacity. At the end of 2014, mortality was 56% higher in droughted PSME seedlings than control seedlings. During September of 2014, total sugar content was higher in whole PSME control seedlings, but no other significant differences were observed across treatments in either leaf, stem, or root non-structural carbohydrate (NSC) content for non-dying PSME seedlings. Total NSC content in dead/dying PSME seedling stems and roots was 205% and 32% of the non-dying PSME seedling stems and roots, respectively. This reduction in root NSC in dead/dying PSME seedlings, along with an increase in stem NSC, suggests that constraints on phloem transport contributed to PSME germinant seedling mortality.

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1 - University of Georgia, Plant Biology
2 - USDA Forest Service, Pacific Northwest Research Station
3 - The University of Wisconsin, Botany
4 - Oregon State University, Forest Ecosystems and Society

Seedling survival
Non-structural carbohydrates.

Presentation Type: Poster
Session: P, Ecophysiology Poster Session
Location: Exhibit Hall/Savannah International Trade and Convention Center
Date: Monday, August 1st, 2016
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: PEP004
Abstract ID:279
Candidate for Awards:None

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