Plant Secondary Compounds in Forest Ecosystems Under Global Change: From Defense to Carbon Sequestration

Most plant species produce secondary compounds (or metabolites) to cope with biotic and abiotic stresses. These molecules play no role in primary processes and are referred to as Plant Secondary Compounds (PSCs). They are important tools for a plant´s interaction with the environment, and thus indispensable for a plant´s survival. Extractable PSCs constitute up to 30% of the dry weight of terrestrial plants in forest ecosystems. However, their concentration is species- and organ-specific, and influenced by biotic and abiotic factors. The approx. 50,000 PSCs isolated so far are categorized in three major groups: terpenes, phenolic compounds (including tannins), and alkaloids; minor groups include for example cyanogenic glycosides. The chemical diversity and abundance of PSCs indicate multiple potential functions; however, the fate of PSCs in ecosystem processes is far from being fully understood.

The functional diversity of PSCs includes different levels, for example, protection against UV radiation and excess of light as antioxidants at the plant level, or defense against pathogens and herbivores, allelopathy, competition and signalling between plants at the ecosystem level. Another important role of PSCs in ecosystems is the regulation of carbon and nutrient cycling, such as their influence on carbon sequestration via the regulation of litter and soil organic matter decomposition. 

The role of PSCs may differ at spatial and temporal scale due to their chemical structure, but also at the biome level, i.e. when comparing boreal, temperate and tropical forest ecosystems. Moreover, climate change and biological invasions may lead to changes in PSC chemistry, thus likely also modifying their functions in forest ecosystems. For example, the invasion of a new species into the system with a different set of PSCs could change the regulatory effect on litter and soil organic matter decomposition. In addition, PSC chemistry could be modified by enhanced temperature and/or drought. Thus, there is an urgent need to understand the processes and underlying mechanisms steering the interactions of plants with their environment to predict and develop strategies for the management of forest ecosystems in the future. In conclusion, PSCs present crucial compounds in forest ecosystems that orchestrate plant interactions with their surrounding biotic and abiotic environment from a single plant to the biome level.

This research topic aims to collect state-of-art studies on the role of PSCs in forest ecosystems and their response to climate change. We aim to link the chemistry of PSC with their function at different levels. We welcome the following article types: Original Research, Review, Opinion, and Methods. Potential topics include PSC and their chemistry, their role in forests as for example plant defence strategy or in carbon and nutrient cycling, at different scales (i.e. temporal, spatial) and levels (i.e. boreal, temperate, tropical forests) and in response to climate change and/or biological invasions.