Abstract Detail

Ecophysiology

Jordan, Rachel [1], Sink, Zane [2], Neufeld, Howard [3].

Comparative ecophysiology of two southern Appalachian conifers: the importance of winter.

Southern Appalachian spruce-fir forests are glacial relicts, found in just seven disjunct sky islands on the region’s highest peaks. Fraser fir (Abies fraseri), a rare endemic, dominates at elevations above 1650 m. Red spruce (Picea rubens) occurs at lower, warmer elevations (1380 – 1650 m) and is more widely distributed than A. fraseri, suggesting a potential adaptation to midwinter thaws. Previous research in northern latitude spruce-fir forests has suggested that co-occurring species may have different responses to midwinter thaws. However, very little winter research has occurred in the southern Appalachian spruce-fir forest, which has longer photoperiods, more frequent midwinter thaws, and less severe temperatures than those of the northern boreal forest in winter. Despite the potentially significant impact of winter, its importance to the ecophysiology of these trees is poorly understood, as are the potential impacts of milder winters resulting from future climate warming. It was hypothesized that red spruce would be more physiologically active than Fraser fir and have lower concentrations of photoprotective carotenoids during midwinter thaws. We compared the midday physiological behavior of both species during winter on Grandfather Mountain, NC, including current, first-year, and second-year needle pigment concentrations, photosynthesis/respiration, fluorescence, and twig water potentials.
Pigment concentrations (per gdw) were significantly higher in A. fraseri than in P. rubens, and concentrations declined with age in both species; no effect was found for canopy face (N or S). Photosynthetic rate was significantly higher in the one-year-old needles of P. rubens on the warmest day, but all other rates of photosynthesis did not differ by needle age. Chlorophyll fluorescence (Fv/Fm) did not differ between the two species but increased significantly with air temperature, and reduction in PSII activity increased with decreasing temperatures. Water potentials in A. fraseri were significantly more negative on two cold days, which may indicate a lower temperature threshold for stomatal opening. The results of this study suggest that while net photosynthesis for both species is at or near zero on cold days, the strategies by which they maintain compensation may be different and could have an influence on their relative ability to take advantage of midwinter thaws. Further exploration of differences in hydraulic conductivity, conduit diameter, and pigment cycling is necessary to conclude the underlying causes of the differential wintertime activity.

1 - University of Wisconsin-Madison, 430 Lincoln Dr, Madison, Wisconsin, 53703, United States
2 - Appalachian State University, Dept. of Biology, 572 Rivers St, ASU Box 32027, Boone, NC, 28607, USA
3 - Appalachian State University, Dept. of Biology, 572 Rivers St., Boone, NC, 28608, United States

Keywords:
climate change
Winter
ecophysiology
Freeze-thaw cycles
Midwinter thaw
Conifers
Spruce-fir forest
Warming.

Presentation Type: Oral Paper
Session: ECOPH1, Ecophysiology I
Location: San Pedro 2/Starr Pass
Date: Tuesday, July 30th, 2019
Time: 11:15 AM
Number: ECOPH1010
Abstract ID:322
Candidate for Awards:Physiological Section Physiological Section Li-COR Prize,Physiological Section Best Paper Presentation