Dynamics of leaf and root phenology in European temperate deciduous tree species under climate change

• Applicant: Dr. Lena Muffler-Weigel
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 527050950

Tree species phenology is changing with global warming, which may have implications for plant fitness and the species composition of communities. It is usually predicted that the aboveground phenology of European deciduous tree species will start earlier due to rising temperatures. In contrast, warmer winters might lead to chilling requirements not being met, which would delay the start of the growing season. Autumn phenology is also controversially discussed, as leaf senescence could either happen earlier due to increased photosynthesis with warming, or later due to a warmer fall. In contrast to leaf phenology, studies on the response of belowground phenology to warming are underrepresented, even though changes in root phenology would likely affect nutrient, water, and carbon fluxes and thus the entire ecosystem. Belowground phenology is determined by both exogenous factors such as temperature and endogenous drivers such as carbon assimilation and allocation, but the respective importance of these factors to belowground phenology and differences among species are still unclear. Depending on the phenological strategy, which differs between early- and late-successional species, the growing season could simply begin and end earlier, or it could extend into the fall, with or without an increase in productivity. It is not adequately understood whether above- and belowground phenology is synchronized or whether soil warming independently extends the belowground growing season, which in turn could affect carbohydrate allocation and NSC reserves. To answer these questions, the overall aim of the proposed project is to examine the effects of increasing temperatures on above- and belowground phenology in the three deciduous tree species, European beech (Fagus sylvatica), silver birch (Betula pendula), and sessile oak (Quercus petraea). The phenological responses will be related to tree productivity and forest carbon cycling. Two experiments will be conducted at the Göttingen Experimental Botanical Garden. In the first experiment, potted young trees will be warmed to investigate the effects of increasing temperatures on above and belowground phenology, biomass production, seasonal dynamics of C/N ratio and non-structural carbohydrates, and on photosynthetic rate and root respiration. In the second experiment, we will isolate the effects of soil warming on above- and belowground phenology by warming only the soil in the Göttingen Rhizolab, where root dynamics of young trees can be observed directly without root-space restriction using rhizotrons. The proposed project will improve our mechanistic understanding of the effects of tree phenology on tree carbon relations. This understanding is critical for better understanding the effects of climate change on tree physiology and for predicting biogeochemical cycles in forest ecosystems in a warmer climate.

• DFG Programme: Research Grants