Monoterpene emissions in response to long-term night-time warming, elevated CO2 and extended summer drought in a temperate heath ecosystem

Measuring BVOC emissions released by tomato plants grown in a soilless integrated rooftop greenhouse

Urban design is currently promoting the inclusion of plants in buildings. However, plants emit biogenic volatile organic compounds (BVOCs), which alone or in combination with other airborne molecules such as CO2, may result in a general increase in tropospheric pollution. Many studies have documented the effects of biotic and abiotic factors on plant BVOC responses, but few have assessed the contribution of typical CO2 levels found in indoor work and meeting spaces. To answer this question, we monitored CO2 and constitutive (MT-limonene) and induced (LOX-cis-3-hexenal) BVOC emissions of a fully developed tomato crop grown hydroponically inside an integrated rooftop greenhouse (i-RTG) in a Mediterranean climate. Two distinctive CO2 assays were performed at the level of the i-RTG by supplying or not CO2. The impact of CO2 on plant physiological emittance was then assessed, and the resulting BVOC rates were compared with reference to EU-LCI values. MT-limonene was ubiquitous among the assays and the most abundant, while LOX-cis-3-hexenal was detected only under controlled CO2 management. The highest levels detected were below the indicated LCIs and were approximately tenfold lower than the corresponding LCI for MT-limonene (50.88 vs. 5000 μg m-3) and eightfold (6.63 μg m-3) higher than the constitutive emission level for LOX-cis-3-hexenal. Over extended sampling (10 min) findings revealed a general emission decrease and significantly different CO2 concentration between the assays. Despite similar decreasing rates of predicted net photosynthesis (Pn) and stomatal conductance (gs) their correlation with decreasing CO2 under uncontrolled condition indirectly suggested a negative CO2 impact on plant emission activity. Conversely, increasing CO2 under the controlled assay showed a positive correlation with induced emissions but not with constitutive ones. Because of significantly higher levels of relative humidity registered under the uncontrolled condition, this factor was considered to affect more than CO2 the emission response and even its collection. This hypothesis was supported by literature findings and attributed to a common issue related with the sampling in static enclosure. Hence, we suggested a careful monitoring of the sampling conditions or further improvements to avoid bias and underestimation of actual emissions. Based on the main outcomes, we observed no evidence of a hazardous effect of registered CO2 rates on the BVOC emissions of tomato plant. Furthermore, because of the low BVOC levels measured in the i-RTG, we assumed as safe the recirculation of this air along building's indoor environments.

Anthropogenic changes to the nighttime environment

How the relative impacts of anthropogenic pressures on the natural environment vary between different taxonomic groups, habitats, and geographic regions is increasingly well established. By contrast, the times of day at which those pressures are most forcefully exerted or have greatest influence are not well understood. The impact on the nighttime environment bears particular scrutiny, given that for practical reasons (e.g., researchers themselves belong to a diurnal species), most studies on the impacts of anthropogenic pressures are conducted during the daytime on organisms that are predominantly day active or in ways that do not differentiate between daytime and nighttime. In the present article, we synthesize the current state of knowledge of impacts of anthropogenic pressures on the nighttime environment, highlighting key findings and examples. The evidence available suggests that the nighttime environment is under intense stress across increasing areas of the world, especially from nighttime pollution, climate change, and overexploitation of resources.

Seasonal Volatile Emission Patterns of the Endemic New Zealand Shrub Dracophyllum subulatum on the North Island Central Plateau

Volatile organic compounds (VOCs) produced by plants are essential indicators of their physiological response to environmental conditions. But evidence of natural variation in VOC emissions and their contributing factors is still limited, especially for non-cultivated species. Here we explored the natural volatile emissions of Dracophyllum subulatum Hook.f., an endemic shrub to the North Island Central Plateau of New Zealand, and determined some environmental factors driving the plant's emissions. Volatile emissions of D. subulatum were measured on four separate occasions from December 2017 to September 2018 using the "push-pull" headspace sampling technique and analyzed using gas chromatography-mass spectrometry (GC-MS). D. subulatum was classified based on the volatiles measured on each sampling occasion using linear discriminant analysis (LDA). On each sampling occasion, we also recorded and compared ambient air temperature, herbivory damage, total soil nitrogen (N), available phosphorus (P), potassium (K), and soil moisture content. The relationship between environmental variables that differed significantly between sampling occasions and volatile emissions were estimated using generalized linear models (GLMs). Based on VOCs measured on each sampling occasion, we were able to distinguish different chemical profiles. Overall, we found that total emission and the relative proportions of all major chemical classes released by D. subulatum were significantly higher during summer. The GLMs reveal that differences in environmental factors between the four sampling occasions are highly associated with changing emissions. Higher temperatures in summer had a consistently strong positive relationship with emissions, while the impacts of soil moisture content, P and K were variable and depended on the chemical class. These results are discussed, particularly how high temperature (warming) may shape volatile emissions and plants' ecology.

Review on plant terpenoid emissions worldwide and in China

Biogenic volatile organic compounds (BVOCs), particularly terpenoids, can significantly drive the formation of ozone (O₃) and secondary organic aerosols (SOA) in the atmosphere, as well as directly or indirectly affect global climate change. Understanding their emission mechanisms and the current progress in emission measurements and estimations are essential for the accurate determination of emission characteristics, as well as for evaluating their roles in atmospheric chemistry and climate change. This review summarizes the mechanisms of terpenoid synthesis and release, biotic and abiotic factors affecting their emissions, development of emission observation techniques, and emission estimations from hundreds of published papers. We provide a review of the main observations and estimations in China, which contributes a significant proportion to the total global BVOC emissions. The review suggests the need for further research on the comprehensive effects of environmental factors on terpenoid emissions, especially soil moisture and nitrogen content, which should be quantified in emission models to improve the accuracy of estimation. In China, it is necessary to conduct more accurate measurements for local plants in different regions using the dynamic enclosure technique to establish an accurate local emission rate database for dominant tree species. This will help improve the accuracy of both national and global emission inventories. This review provides a comprehensive understanding of terpenoid emissions as well as prospects for detailed research to accurately describe terpenoid emission characteristics worldwide and in China.

Long-term effects of elevated CO2, nighttime warming and drought on plant secondary metabolites in a temperate heath ecosystem

BACKGROUND AND AIMS

Plant secondary metabolites play critical roles in plant stress tolerance and adaptation, and are known to be influenced by the environment and climate changes, yet the impacts and interactions of multiple climate change components are poorly understood, particularly under natural conditions.

METHODS

Accumulation of phenolics and emissions of volatile organic compounds (VOCs) were assessed on heather, Calluna vulgaris, an abundant evergreen dwarf shrub in European heathlands, after 6 years of exposure to elevated CO2, summer drought and nighttime warming.

KEY RESULTS

Drought alone had the strongest effects on phenolic concentrations and compositions, with moderate effects of elevated CO2 and temperature. Elevated CO2 exerted the greatest impact on VOC emissions, mainly by increasing monoterpene emissions. The response magnitudes varied among plant tissue types and chemical constituents, and across time. With respect to interactive effects of the studied climate change components, the interaction between drought and elevated CO2 was most apparent. Drought mainly reduced phenolic accumulation and VOC emissions, while elevated CO2 mitigated such effects.

CONCLUSIONS

In natural ecosystems, co-occurring climate factors can exert complex impacts on plant secondary metabolite profiles, which may in turn alter ecosystem processes.

Natural Variation in Volatile Emissions of the Invasive Weed Calluna vulgaris in New Zealand

Invasive plants pose a threat to natural ecosystems, changing the community composition and ecological dynamics. One aspect that has received little attention is the production and emission of volatile organic compounds (VOCs) by invasive plants. Investigating VOCs is important because they are involved in vital ecological interactions such as pollination, herbivory and plant competition. Heather, Calluna vulgaris, is a major invasive weed in New Zealand, especially on the Central Plateau, where it has spread rapidly since its introduction in 1912, outcompeting native species. However, the chemical behaviour of heather in its invaded ranges is poorly understood. We aimed to explore the natural variation in volatile emissions of heather and the biotic and abiotic factors influencing them on the Central Plateau of New Zealand. To this end, foliar volatiles produced by heather at four different sites were collected and analysed using gas chromatography coupled to mass spectrometry. Soil properties, herbivory and other environmental data were also collected at each site to investigate their effects on VOC emissions using generalised linear models (GLMs). Our results reveal significant differences in VOC emissions between sites and suggest that soil nutrients are the main factor accounting for these differences. Herbivory and temperature had only a minor effect, while soil water content had no impact. Further studies are needed to investigate how these variations in the invasive plant’s foliar volatiles influence native species.

Climate Change Effects on Secondary Compounds of Forest Trees in the Northern Hemisphere

Plant secondary compounds (PSCs), also called secondary metabolites, have high chemical and structural diversity and appear as non-volatile or volatile compounds. These compounds may have evolved to have specific physiological and ecological functions in the adaptation of plants to their growth environment. PSCs are produced by several metabolic pathways and many PSCs are specific for a few plant genera or families. In forest ecosystems, full-grown trees constitute the majority of plant biomass and are thus capable of producing significant amounts of PSCs. We summarize older literature and review recent progress in understanding the effects of abiotic and biotic factors on PSC production of forest trees and PSC behavior in forest ecosystems. The roles of different PSCs under stress and their important role in protecting plants against abiotic and biotic factors are also discussed. There was strong evidence that major climate change factors, CO2 and warming, have contradictory effects on the main PSC groups. CO2 increases phenolic compounds in foliage, but limits terpenoids in foliage and emissions. Warming decreases phenolic compounds in foliage but increases terpenoids in foliage and emissions. Other abiotic stresses have more variable effects. PSCs may help trees to adapt to a changing climate and to pressure from current and invasive pests and pathogens. Indirect adaptation comes via the effects of PSCs on soil chemistry and nutrient cycling, the formation of cloud condensation nuclei from tree volatiles and by CO2 sequestration into PSCs in the wood of living and dead forest trees.