CANCELLED - How tree species interactions modify the leaf-level photosynthetic properties of two deciduous tree species in a warmer and drier climate.

Background/Question/Methods

In temperate climates, chronic temperature rise and prolonged moisture reduction are critical environmental drivers for forest dynamics because of their impacts on the acquisition of atmospheric carbon dioxide through leaf-level photosynthesis and overall tree carbon cycling. However, although nearly all studies caution that higher temperatures and reduced soil moisture are increasingly co-occurring, little is known about their prolonged and combined impacts on plant photosynthetic capacity. Furthermore, favoring interspecific forests is often describe as a climate-smart management measure to reduce negative effects of extreme events. However, the potential mitigating role of species interactions on photosynthetic responses to warming and soil moisture reduction remains unclear. We analyzed how European beech (Fagus sylvatica L.) and Downy oak (Quercus pubescens Willd.) photosynthetic properties (i.e., light‐saturated assimilation, maximum rate of carboxylation by Rubisco, maximal photosynthetic electron transport rate, maximal photochemical efficiency, and chlorophyll concentration) were impacted by warming and soil moisture reduction alone or simultaneously, and how species interaction (inter- vs. intraspecific) modulate these responses.

Results/Conclusions

Warming enhanced leaf-level photosynthetic properties of oak, but not beech, while soil moisture reduction decreased photosynthetic capacity for both species. Warming combined with soil moisture limitation exacerbated the reduction in photosynthetic properties for both species. The impact of warming and soil moisture reduction acting alone was similar in interspecific vs. intraspecific conditions for both species. For beech, species interactions had no impact on the photosynthetic responses to warming and soil moisture reduction. However, oak showed less adverse warming and soil moisture reduction impacts when interacting with beech. We demonstrated that beech and oak photosynthetic properties will be strongly reduced by warming and soil moisture reduction acting simultaneously. Our work also revealed that species interactions is a major determinant of climate impacts with a mitigating role for some species.