Effects of Vegetation and Microhabitats on Peatland VOC Emissions and Seasonal Dynamics across one Summer

Peatlands store the largest carbon stocks per unit area and are key regulators of climate. Carbon cycling and emissions to the atmosphere from peatlands are of critical importance and responsive climate change, with changing precipitations patterns and temperatures causing a shift in plant community composition. Yet the underlying drivers for volatile organic compound (VOC) exchange remain poorly understood. This study aims to assess the influence of different functional plant groups and environmental drivers on peatland VOC emissions.

A field study was conducted utilizing an established long-term plant removal experimental setup with 40 plots evenly distributed across four plant removal treatments (control, removal of ericoid plants, removal of graminoid plants and removal of both groups) and two microsite types (hummocks and hollows). VOC emissions were measured twice each month in the summer of 2025 using flow chambers connected to sorbent tubes analyzed by GC-MS. We measured environmental variables; PAR-light, soil and air water content/humidity and temperature concurrently with vegetation VOC measurements. We also collected species cover data on plot level.

A PCA analysis across all VOC emissions uncovered the sampling months to explain multivariate distribution with clustering of all months and especially June standing out. The emission profiles were dominated by isoprene in July (80.7%) and August (87.8%) while in June oxygenated VOCs dominated the total emission (66.8 %). Linear mixed models showed a significant effect of month, treatment, microsite and the interactive effects of month and treatment and month and microsite on isoprene emissions. The highest mean isoprene emission appeared in July; the emissions were higher from hollow microsites than hummocks and the treatments with removal of graminoid plants had lower isoprene emissions compared to both other treatments. Only difference in month had a significant effect on the oxygenated VOC emissions, with OVOC emissions in June being more than tenfold than in the other months. Difference in month also significantly affected all other VOC groups. PLS models showed emissions of all groups except sesquiterpenes to significantly increase with air temperature, while soil temperature, water table depth and soil moisture significantly influenced emissions of isoprene, sesquiterpenoids, and OVOCs. The presence of ericoid plant species correlated negatively with sesquiterpene emissions while graminoid species increased isoprene emissions.

The study supports the understanding that VOC emission abundance and composition are influenced by environmental drivers and plant species composition, while the seasonal variation, even within summer months can be of significant size. Especially OVOC emissions seem responsive to a change in soil moisture, dominating the total emissions in the driest month.