Investigating the Role of Carbon Stress in the Mortality of Tamarack Seedlings Under a Warming Environment

Bridget K. Murphy, The University of Western Ontario

Abstract

Climate warming is increasing the frequency of climate-induced tree mortality events. While drought combined with heat is considered the primary cause of this tree mortality, little is known about whether high temperatures alone can induce mortality, or whether rising CO₂ will increase survival. I grew tamarack in two experiments combining warming (0-8 ˚C above ambient) and CO₂ (400-750 ppm) to investigate whether high growth temperatures led to carbon limitations and mortality. Using glasshouses, +8 ˚C warming with ambient CO₂ (8TAC) led to 40% mortality despite thermal acclimation of respiration. Dying 8TAC seedlings had lower needle carbon concentrations and lower ratios of photosynthesis to respiration, indicating carbon limitation. Using growth chambers, no seedlings died, and carbon flux results contradicted those of the glasshouses. Overall, environmental conditions in the glasshouses were more representative of the field than growth chamber conditions, and my work highlights that warming can directly induce mortality.