Interactive effects of elevated CO2 and temperature, nutrition, and ectomycorrhizas on morphological traits and summer shoot formation in jack pine

Abstract

Understanding the responses of trees, ectomycorrhizal fungi (ECM) and their association to climate change can be challenging due to their interactions with multiple environmental factors. The combined impacts of elevated CO2 and elevated temperature on tree growth are mostly positive, but the impacts to ECM are less well understood. The objective of this study was to investigate how the elevations of CO2 and temperature and soil nutrient supply interactively affect the formation and growth-enhancing efficiency of ECM, as well as the formation of summer shoots and morphology of jack pine seedlings. One-year old jack pine seedlings were exposed to ambient CO2 and temperature treatment (ACT: 410µmol/mol CO2 and current average temperature) and elevated CO2 and temperature (ECT: 750µmol/mol CO2 and current +6°C temperature) as a single treatment, two nutrient levels (low nutrient LN vs. very low nutrient VLN) and with or without Hebeloma longicaudum (Pers.)P.Kumm (yes ECM or no ECM) inoculation. The ECT treatment increased total seedling biomass, root biomass and root collar diameter (RCD), and most summer shoot formation and growth attributes. The VLN treatment reduced all growth attributes except for height increment, and height increment + lammas shoot length. An interactive effect of the CT and N treatment was observed for the RCD, suggesting that lower nutrient sites may limit the positive affects of elevated CO2 and temperature on tree growth, and the interactive effect on specific leaf area (SLA) suggests that the lower nutrients limited the needles’ ability to accumulate carbon at ECT. Another interactive effect observed on SLA suggests that ECM inoculation allowed for better nutrient uptake and caused seedlings to demonstrate a higher SLA at VLN under ECT. Both ECT and LN increased the probability of summer shoot formation. The results suggest that jack pine is less likely to produce summer shoots on nutrient poorer sites, and in current CO2 and temperature growing conditions. Furthermore, we observed significant two-way and three-way interactions that suggest the ECT treatment increased the effectiveness of ECM inoculation in forming mycorrhizae clusters, and reduced the degree of nutrient suppression to mycorrhizal root cluster formation. The results of this study highlight the importance of incorporating multiple factors when evaluating tree responses to climate change, particularly in controlled-environment studies.