Tue, Aug 16, 2022: 5:00 PM-6:30 PM
ESA Exhibit Hall
Background/Question/MethodsThe boreal forest is a region highly susceptible to climate change, and the impacts of climate change on tree reproduction may have strong consequences for future forests. While warming temperatures and elevated carbon dioxide (eCO2) independently alter tree reproduction, how these factors will interactively affect tree reproduction, specifically regarding seed viability, remains unknown. Our objective is to test the impacts of the combined effects of elevated temperature and eCO2 on cone and seed characteristics of black spruce, a widespread boreal forest species. Our research was conducted at the Spruce and Peatland Response Under Changing Environments (SPRUCE) experiment in northern Minnesota, USA, which combines five warming treatments (+0, +2.25, +4.5, +6.75, and +9°C) with ambient and eCO2 (~400 and ~900 ppm. respectively) in 10 open-top chambers (12m wide, 8m high). We collected cones from reproducing trees under all ten treatments in late summer 2021, and quantified cone characteristics (e.g., cone length, seed number, cone and seed mass). Generalized linear mixed effects models were performed on cone characteristics with temperature, CO2, and their interaction as main effects and with individual trees as a random effect; we used AIC modes for selecting the best model(s) of cone characteristics.
Results/ConclusionsWe found nonlinear relationships and a temperature-CO2 treatment interaction in cone characteristics. The best model based on AIC model selection for both cone length and seed number included temperature, CO2, and the interaction. Cone length and seed number increased with warming until a maximum at +4.5°C, with cone length and seed number being the smallest at +6.75°C, and then these characteristics increased again at +9°C. In the +9°C/eCO2 treatment, while fewer cones were produced on trees than in other treatments, cones were larger and contained more seeds. There are also treatment effects on mean seed mass, with potential differences in germination success. The best model for mean seed mass per cones based on AIC model selection also included temperature, CO2, and their interaction. Principal Components Analysis on cone morphology shows that PC1 was defined primarily by whole cone characteristics (dry cone mass, cone length cone with, total dry seed mass) accounting for 67% of the variation, while PC2 was related to seed number, cone scale number, and scale length, accounting for 12% of the variation. Our findings show black spruce reproduction is sensitive to climate change through temperature-CO2 interactions, and this can influence future forest regeneration and composition.
Results/ConclusionsWe found nonlinear relationships and a temperature-CO2 treatment interaction in cone characteristics. The best model based on AIC model selection for both cone length and seed number included temperature, CO2, and the interaction. Cone length and seed number increased with warming until a maximum at +4.5°C, with cone length and seed number being the smallest at +6.75°C, and then these characteristics increased again at +9°C. In the +9°C/eCO2 treatment, while fewer cones were produced on trees than in other treatments, cones were larger and contained more seeds. There are also treatment effects on mean seed mass, with potential differences in germination success. The best model for mean seed mass per cones based on AIC model selection also included temperature, CO2, and their interaction. Principal Components Analysis on cone morphology shows that PC1 was defined primarily by whole cone characteristics (dry cone mass, cone length cone with, total dry seed mass) accounting for 67% of the variation, while PC2 was related to seed number, cone scale number, and scale length, accounting for 12% of the variation. Our findings show black spruce reproduction is sensitive to climate change through temperature-CO2 interactions, and this can influence future forest regeneration and composition.