Abstract
The atmospheric carbon dioxide (CO2) concentration and air temperatures are rising at unprecedented rates. Increases in CO2 and tropospheric ozone (O3) concentrations drive global warming, and projections indicate that these levels will continue to rise, increasing the frequency of extreme climatic events. Forest ecosystems provide numerous ecological and economic services to humankind and have potential to mitigate global climate change by serving as CO2 and O3 sinks. Environmental changes threaten these valuable ecosystems and trees must adapt rapidly in order to survive. Specialized metabolites are essential for the adaptative phenotypic plasticity of plants, as they moderate interactions with the environment and combat biotic and abiotic stresses. Despite substantial research efforts to understand the phenotypic responses of trees to elevated atmospheric CO2 and O3, few studies have investigated how plant specialized metabolism is regulated under these conditions. Furthermore, many of these studies are relatively short-term based, using seedlings and artificial environmental growth conditions. These experimental constraints pose difficulties for the extrapolation of how long-lived mature trees will respond to climate change.
Eucalyptus is a diverse genus of long-lived trees comprising approximately 800 different species. The majority of species are native to the Australian continent, where they dominate a wide range of different forest ecosystems including temperate, alpine and arid zones. Furthermore, Eucalyptus species are among the most widely cultivated hardwood forest trees in the world, producing valuable biomaterials. The natural biogeographical diversity and adaptability of Eucalyptus to different environments, combined with their successful exploitation into industry, are partly due to their ability to produce a plethora of volatile and non-volatile specialized metabolites, including terpenes and phenolics. While significant advances have been made towards identifying different chemical constituents within this genus, the effects of elevated CO2 and O3 are less understood. Consequently, this iconic Australian genus provides an excellent model system by which to understand how long-lived trees regulate their plant specialized metabolism in response to climate change.
This thesis aims to investigate how elevated CO2 and O3 affects the concentration of Eucalyptus specialized metabolites, specifically by examining the response of different volatile and non-volatile components. To achieve this, an improved analytical method using UHPLC-DAD-ESI-Q-TOF-MS/MS was developed to detect and quantify formylated phloroglucinol compounds (FPCs); a group of non-volatile specialized metabolites particularly abundant in Eucalyptus. The results from nine different Eucalyptus species show that FPCs are more abundant and diverse than previously reported, with high FPC levels detected in flower buds and flowers. Localization by mass spectrometry imaging suggest that in addition to their known role as marsupial folivore deterrents, FPCs may be involved in other functions such as
defense of the reproductive tissue. To investigate the role and regulation of FPCs under abiotic and biotic stress, E. globulus seedlings were subjected to increased O3 concentration and wounding stress. Analysis of FPC concentrations showed that various subclasses were differently affected by each treatment, whereby macrocarpals mainly increased in response to O3, whereas sideroxylonals increased in response to wounding. Taken together, the results from this thesis suggest FPCs play multiple physiological roles in planta, potentially serving as antioxidants to combat biotic and abiotic stress, which is especially relevant in the future climate change scenario.
To understand further how climate change affects mature natural Eucalyptus forests, volatile specialized metabolites were measured in E. tereticornis trees growing under elevated atmospheric CO2 concentration (eCO2) during summer and fall. Specifically, this experiment was performed in a state-of-the-art climate change facility in Australia that provides canopy access to a natural Eucalyptus forest growing under free-air CO2 enrichment. Eucalyptus species are among the highest emitters of plant volatile organic compounds (VOCs), and here we show that during fall, eCO2 increased total VOC emission rates. This increase was driven by significant higher monoterpene emissions. Other important benzenoid and sesquiterpene metabolites showed unique emission patterns in response to the treatment. Together, these findings have implications to atmospheric chemistry and may affect important biological interactions, such as pollinator attraction and plant-plant communication.
Collectively, the data presented in this thesis provides unique insight into the chemical complexity, role and regulation of Eucalyptus specialized metabolism in response to elevated CO2 and O3 conditions. The results indicate that specific compounds may play multiple roles in planta and their response depends on other environmental conditions affecting the plant physiology, such as the interaction of other stress factors and the seasonal variation. The findings of this work provide valuable information to improve atmospheric chemistry models and shed light on the effect of climate change in the carbon budget of Eucalyptus forest
Eucalyptus is a diverse genus of long-lived trees comprising approximately 800 different species. The majority of species are native to the Australian continent, where they dominate a wide range of different forest ecosystems including temperate, alpine and arid zones. Furthermore, Eucalyptus species are among the most widely cultivated hardwood forest trees in the world, producing valuable biomaterials. The natural biogeographical diversity and adaptability of Eucalyptus to different environments, combined with their successful exploitation into industry, are partly due to their ability to produce a plethora of volatile and non-volatile specialized metabolites, including terpenes and phenolics. While significant advances have been made towards identifying different chemical constituents within this genus, the effects of elevated CO2 and O3 are less understood. Consequently, this iconic Australian genus provides an excellent model system by which to understand how long-lived trees regulate their plant specialized metabolism in response to climate change.
This thesis aims to investigate how elevated CO2 and O3 affects the concentration of Eucalyptus specialized metabolites, specifically by examining the response of different volatile and non-volatile components. To achieve this, an improved analytical method using UHPLC-DAD-ESI-Q-TOF-MS/MS was developed to detect and quantify formylated phloroglucinol compounds (FPCs); a group of non-volatile specialized metabolites particularly abundant in Eucalyptus. The results from nine different Eucalyptus species show that FPCs are more abundant and diverse than previously reported, with high FPC levels detected in flower buds and flowers. Localization by mass spectrometry imaging suggest that in addition to their known role as marsupial folivore deterrents, FPCs may be involved in other functions such as
defense of the reproductive tissue. To investigate the role and regulation of FPCs under abiotic and biotic stress, E. globulus seedlings were subjected to increased O3 concentration and wounding stress. Analysis of FPC concentrations showed that various subclasses were differently affected by each treatment, whereby macrocarpals mainly increased in response to O3, whereas sideroxylonals increased in response to wounding. Taken together, the results from this thesis suggest FPCs play multiple physiological roles in planta, potentially serving as antioxidants to combat biotic and abiotic stress, which is especially relevant in the future climate change scenario.
To understand further how climate change affects mature natural Eucalyptus forests, volatile specialized metabolites were measured in E. tereticornis trees growing under elevated atmospheric CO2 concentration (eCO2) during summer and fall. Specifically, this experiment was performed in a state-of-the-art climate change facility in Australia that provides canopy access to a natural Eucalyptus forest growing under free-air CO2 enrichment. Eucalyptus species are among the highest emitters of plant volatile organic compounds (VOCs), and here we show that during fall, eCO2 increased total VOC emission rates. This increase was driven by significant higher monoterpene emissions. Other important benzenoid and sesquiterpene metabolites showed unique emission patterns in response to the treatment. Together, these findings have implications to atmospheric chemistry and may affect important biological interactions, such as pollinator attraction and plant-plant communication.
Collectively, the data presented in this thesis provides unique insight into the chemical complexity, role and regulation of Eucalyptus specialized metabolism in response to elevated CO2 and O3 conditions. The results indicate that specific compounds may play multiple roles in planta and their response depends on other environmental conditions affecting the plant physiology, such as the interaction of other stress factors and the seasonal variation. The findings of this work provide valuable information to improve atmospheric chemistry models and shed light on the effect of climate change in the carbon budget of Eucalyptus forest
| Original language | English |
|---|
| Publisher | Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen |
|---|---|
| Publication status | Published - 2019 |