Abstract Detail

Ecophysiology

Woodruff, David [1], Meinzer, Rick [1], Katherine, McCulloh [2], Kelly, Kerr [3], Danielle, Marias [4], Alicia, Magedman [4], John, Crandall [4].

How do seedlings survive? Hydraulics, carbon acquisition and drought tolerance in the earliest phases of growth in two conifer species.

The woody plant life stage with the greatest mortality is the germinant seedling. As the impact of climate change on vegetation increases, a more thorough understanding of young seedling biology and mortality becomes critical. However, very little work has focused on the ecophysiology of germinant seedlings. Douglas-fir (PSME) and Ponderosa pine (PIPO) first-year seedlings were grown in a common garden and experimentally droughted during the summer of 2014. In order to elucidate the mechanisms associated with seedling growth, survival and mortality under drought conditions, a range of physiological parameters were measured throughout the growing season as seedlings were gradually exposed to increasing water stress. To examine associations between seedling mortality and carbon starvation, non-structural carbohydrate (NSC) content was analyzed for different organs of seedlings that were fully vigorous, as well as for organs of seedlings at varying stages of mortality as assessed by needle browning and chlorosis. By the end of September, negligible mortality had occurred in both the control and droughted PIPO; whereas in PSME, mortality was 56% higher and total biomass 39% lower in the drought treatment than the control. No significant differences across treatments were found in either species in mean morning or afternoon photosynthesis throughout September. PSME stem specific hydraulic conductivity (K_s) was 35% higher in control than in droughted seedlings, but leaf specific hydraulic conductivity (K_L) was not significantly different between treatments, suggesting that droughted PSME seedlings adjusted their leaf area in order to maintain a relatively constant K_L. There were no significant differences across treatments in leaf, stem or root NSC content for non-dying seedlings of either species during September, with the exception of greater starch content in droughted PIPO stems, and greater total sugar content in control PSME stems. However, all components of stem and root NSC differed significantly between dead/dying vs. non-dying PSME seedlings, with total NSC content in dead/dying seedling stems and roots being 184% and 30% of that of the non-dying seedling stems and roots, respectively. The dramatic reduction in root NSC, in conjunction with a comparable increase in stem NSC of dead/dying seedlings suggests that constraints on phloem transport played a substantial role in PSME germinant seedling mortality. There were no significant trends in NSC content of dead/dying PSME organs with percent needle browning or chlorosis, suggesting that metabolism during or following mortality was not a confounding factor for NSC content in these samples.

1 - PNW Research, USDA Forest Service, 3500 SW Jefferson Way, Corvallis, OR, 97331, USA
2 - University of Wisconsin Madison, Department of Botany, 430 Lincoln Drive, Madison, WI, 53706, USA
3 - Oregon State University, Forest Ecosystems and Society Department, 321 Richardson Hall, Corvallis, OR, 97331, USA
4 - Oregon State University, Forest Ecosystems and Society Department, 321 Richardson Hall, Corvallis, OR, 97330, USA

Keywords:
Tree mortality
seedling survival.

Presentation Type: Oral Paper:Papers for Topics
Session: 25
Location: Salon 16/The Shaw Conference Centre
Date: Tuesday, July 28th, 2015
Time: 9:15 AM
Number: 25006
Abstract ID:641
Candidate for Awards:None