| Summary: | In recent decades the Arctic has been warming at a rate of almost twice the global average and this has led to changes in the composition, density, and distribution of arctic vegetation. These changes will have strong influences on the region’s net carbon (C) exchange between land and atmosphere and hold significant implications for future atmospheric [CO2]. However, the precise nature of arctic vegetation change under future warming is not well constrained, highlighting the need for a better understanding of how arctic plants will respond to climate change. In this study, we investigated four key plant mechanisms in Betula pubescens ssp. tortusa: 1) Gross photosynthesis (GOP), 2) Respiration, 3) Rubisco carboxylation (Vc) and oxygenation (Vo), and 4) Mesophyll conductance (gm). Experiments were conducted under varying light intensity and [O2]. For the analysis we utilized a novel method for measuring leaf photosynthesis and respiration that relies on 18O-labelled water, which to the best of our knowledge has never been applied to terrestrial plants, and the measurements collected have not been conducted in this arctic species before. GOP was measured at 10.84 ± 2.11 μmol m-2 s-1 and Vc /Vo was approximately 0.5 for all examined lightintensities. For all [O2] we found that respiration in the light (RLight) was lower than dark respiration (RDark), indicating that respiration is inhibited in the light. The response of gm was shown to increase with increasing light intensity and decrease with decreasing [O2]. Measurements collected agreed with both previous studies and theoretical approximations, which demonstrates that this O2 method is a reliable method of measurement for a wide range of leaf processes. This study is a great development in our understanding of arctic plants, and the unique responses identified in Betula pubescens ssp. tortusa underscore the importance of expanding these measurements to characterize other arctic species.
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