COS 33-5
Comparison of the ecophysiology of three local tree species at an early stage
Over the past decade, much has been learned about climate change and its potential impacts on vegetation. Many natural tree population distributions are predicted to change over the next century. However, most predictions about how these distributions will change are based primarily on parameters that have been measured on mature trees. The woody plant life stage with the greatest mortality, by far, is the germinant seedling stage and young seedling performance may be the most important for determination of species distributions. However, very little work has focused on the ecophysiology of seedlings (less than one year old).
To have a better understanding of the ecophysiology of seedlings, we decided to work on three local species (Pinus taeda, Liriodendron tulipifera and Liquidambar styraciflua). Young seedlings (8 weeks old) were transplanted in experimental field in Duke forest in April 2013 and we measured seedling hydraulic properties, seedling water status and leaf level gas exchange during a field season starting in June and finishing in October 2013.
Results/Conclusions
We studied the resistance to cavitation and seedlings of all species were less resistant to cavitation than mature trees (e.g., Liquidambar P50: -2.3MPa versus -2.8MPa, for seedlings and adults, respectively;P50: pressure at which 50% of hydraulic conductivity was lost)The Summer 2013 was abnormally wet so minimum water potentials never fell below -1.4 MPa, and therefore seedlings likely experienced little cavitation. We noted that for all species the daily maximum stomatal conductance (gS) was similar throughout the summer, but the the maximum assimilation rate of CO2 (Amax) varied. Amax increased during the early summer for all species and attained a maximum during the middle of September. After reaching this maximum, Amax decreased rapidly for two species, 51% and 79% of decreases for Liquidambar and Liriodendron respectively. However, Amax remained stable until the end of the season for Pinus.
The current study showed that species have different hydraulic and gas exchange parameters at the seedling stage, and showed that seedlings are less resistant to embolism than mature trees. Further studies on the ecophysiology of trees at early life stages will be critical to have a better understanding of the effects of climate change on tree species distributions.