Within-species populations exhibit similar physiology under current climate but may diverge under warmer and drier conditions

Recent repeated episodes of drought and high temperatures have resulted in substantial dieback of silver fir in the Spanish Pyrenees. However, mortality has been much greater in populations from the westernmost Pyrenees than in eastern populations. It is hypothesized that drought-resistant eastern populations are less vulnerable to climate change-related stress than western populations. Given that seedling establishment is a bottleneck in species’ distributions in response to climate change, Matías et al. (2016) tested this hypothesis by exposing seedlings from western and eastern populations to experimental drought (current and reduced levels of water availability) and warming (current and elevated temperature). Growth and physiological responses were measured in response to treatments.

Consistent with the different population responses to climate change observed in the field, genetic analyses separated the eastern and western populations into different lineages. Interactions between treatment and population were observed for carbon isotope discrimination (δ¹³C), soluble sugars, and nitrogen content in the leaves. The results suggested that western populations were more sensitive to drought and elevated temperature, consistent with the lower dieback of eastern populations in the field. The nitrogen content results suggested that nutrient deficiency might play a role in the dieback of silver fir seedlings. Interestingly, the seedling populations in this study did not differ in physiological responses to current water and temperature regimes, but did display divergent physiological responses to simulated future drought and warming. This suggests that that population-specific variation in physiological responses may only be detectable under greater environmental stress.