@booklet {ARC29271,
	title = {Vertical gradients in photosynthetic physiology diverge at the latitudinal range extremes of white spruce},
	year = {2022},
	abstract = {<p>Light availability drives vertical canopy gradients in photosynthetic functioning and carbon (C) balance, yet patterns of variability in these gradients remain unclear. We measured light availability, photosynthetic CO2 and light response curves, foliar C, nitrogen (N) and pigment concentrations, and the photochemical reflectance index (PRI) on upper and lower canopy needles of white spruce trees (Picea glauca) at the species{\textquoteright} northern and southern range extremes. We combined our photosynthetic data with previously published respiratory data to compare and contrast canopy C balance between latitudinal extremes. We found steep canopy gradients in irradiance, photosynthesis, and leaf traits at the southern range limit, but a lack of variation across canopy positions at the northern range limit. Thus, unlike many tree species from tropical to mid-latitude forests, high latitude trees may not require vertical gradients of metabolic activity to optimize photosynthetic C gain. Consequently, accounting for self-shading is less critical for predicting gross primary productivity at northern relative to southern latitudes. Northern trees also had a significantly smaller net positive leaf C balance than southern trees suggesting that, regardless of canopy position, low photosynthetic rates coupled with high respiratory costs may ultimately constrain the northern range limit of this widely distributed boreal species. SUMMARY STATEMENT Canopy gradients in photosynthetic capacity of white spruce diminish at high compared to low latitudes. Low carbon balance in high latitude trees may determine the extent of northern treeline.</p>},
	keywords = {LTER-ARC},
	doi = {10.1101/2022.05.06.490824},
	url = {https://www.biorxiv.org/content/10.1101/2022.05.06.490824v2},
	author = {Schmiege, Stephanie C. and Kevin L. Griffin and Natalie T. Boelman and Vierling, Lee A. and Bruner, Sarah G. and Min, Elizabeth and Maguire, Andrew J. and Jensen, Johanna and Eitel, Jan U. H.}
}
@article {griffin_high_2021,
	title = {High Leaf Respiration Rates May Limit the Success of White Spruce Saplings Growing in the Kampfzone at the Arctic Treeline},
	journal = {Frontiers in Plant Science},
	volume = {12},
	year = {2021},
	note = {0 citations (Crossref) [2022-02-03]},
	pages = {746464},
	abstract = {Arctic Treeline is the transition from the boreal forest to the treeless tundra and may be determined by growing season temperatures. The physiological mechanisms involved in determining the relationship between the physical and biological environment and the location of treeline are not fully understood. In Northern Alaska, we studied the relationship between temperature and leaf respiration in 36 white spruce ( Picea glauca ) trees, sampling both the upper and lower canopy, to test two research hypotheses. The first hypothesis is that upper canopy leaves, which are more directly coupled to the atmosphere, will experience more challenging environmental conditions and thus have higher respiration rates to facilitate metabolic function. The second hypothesis is that saplings [stems that are 5{\textendash}10cm DBH (diameter at breast height)] will have higher respiration rates than trees (stems >=10cm DBH) since saplings represent the transition from seedlings growing in the more favorable aerodynamic boundary layer, to trees which are fully coupled to the atmosphere but of sufficient size to persist. Respiration did not change with canopy position, however respiration at 25{\textdegree}C was 42\% higher in saplings compared to trees (3.43{\textpm}0.19 vs. 2.41{\textpm}0.14μmolm -2 s -1 ). Furthermore, there were significant differences in the temperature response of respiration, and seedlings reached their maximum respiration rates at 59{\textdegree}C, more than two degrees higher than trees. Our results demonstrate that the respiratory characteristics of white spruce saplings at treeline impose a significant carbon cost that may contribute to their lack of perseverance beyond treeline. In the absence of thermal acclimation, the rate of leaf respiration could increase by 57\% by the end of the century, posing further challenges to the ecology of this massive ecotone.},
	keywords = {LTER-ARC, update-2021-02},
	issn = {1664-462X},
	doi = {10.3389/fpls.2021.746464},
	url = {https://www.frontiersin.org/articles/10.3389/fpls.2021.746464/full},
	author = {Griffin, Kevin L. and Schmiege, Stephanie C. and Bruner, Sarah G. and Boelman, Natalie T. and Vierling, Lee A. and Eitel, Jan U. H.}
}
