Griffin Kevin L, Schmiege Stephanie C, Bruner Sarah G, Boelman Natalie T, Vierling Lee A, Eitel Jan U H
Department of Earth and Environmental Sciences, Columbia University, Palisades, NY, United States.
Department of Ecology, Evolution and Environmental Biology, Columbia University, New York, NY, United States.
Front Plant Sci. 2021 Nov 1;12:746464. doi: 10.3389/fpls.2021.746464. eCollection 2021.
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 () 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 5-10cm 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°C was 42% higher in saplings compared to trees (3.43±0.19 vs. 2.41±0.14μmolm s). Furthermore, there were significant differences in the temperature response of respiration, and seedlings reached their maximum respiration rates at 59°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.
北极树线是从北方森林到无树苔原的过渡地带，可能由生长季节温度决定。决定物理和生物环境与树线位置之间关系的生理机制尚未完全了解。在阿拉斯加北部，我们研究了36棵白云杉（）树的温度与叶片呼吸之间的关系，对树冠上部和下部进行采样，以检验两个研究假设。第一个假设是，与大气直接接触更多的树冠上部叶片将经历更具挑战性的环境条件，因此具有更高的呼吸速率以促进代谢功能。第二个假设是，幼树[胸径（胸高直径）为5 - 10厘米的树干]的呼吸速率将高于树木（胸径≥10厘米的树干），因为幼树代表了从生长在更有利的空气动力学边界层中的幼苗向完全与大气耦合但大小足以存活的树木的过渡。呼吸作用并未随树冠位置而变化，然而，在25°C时，幼树的呼吸作用比树木高42%（3.43±0.19对2.41±0.14微摩尔·米·秒）。此外，呼吸作用的温度响应存在显著差异，幼苗在59°C时达到最大呼吸速率，比树木高出两度多。我们的结果表明，树线处白云杉幼树的呼吸特征带来了巨大的碳成本，这可能导致它们无法在树线以外持续生长。在没有热适应的情况下，到本世纪末，叶片呼吸速率可能会增加57%，这对这个巨大生态交错带的生态构成了进一步挑战。
