From Shoots and Roots: Ten Years of Warming and Elevated CO₂ Modify Plant Carbon Allocation and Lipid Chemistry in a Boreal Peatland

Ombrotrophic peatlands store a large fraction of global soil carbon, yet their long‑term response to climate warming and elevated atmospheric CO₂ remains uncertain, particularly regarding plant carbon allocation and biochemical inputs to peat. Experimental warming and CO₂ elevation can alter plant community composition, tissue chemistry and carbon partitioning, with potential feedbacks on peat accumulation and decomposition.

Previous work after 3 years of whole‑ecosystem warming and CO₂ elevation showed rapid shifts in carbon allocation and lipid composition in dominant bog plants. Ten years after the onset of these treatments, longer‑term acclimation, community changes and root responses may reinforce, dampen or qualitatively change these initial patterns. This study aims to assess how decadal warming and elevated CO₂ affect carbon partitioning and lipid composition in an ombrotrophic bog plant community, with an additional focus on roots as pathways of belowground carbon input.

The study is conducted on an ombotrophic peatland experiment (SPRUCE, Minnesota, USA), where whole ecosystems  have been exposed for ten years to a gradient of warming (+0, +2.25, +4.5, +6.75 and +9 ◦C), under ambient or elevated atmospheric CO₂ (+500ppm) concentrations in open-top chambers. Within each enclosure, representative samples of the dominant plant functional types (Sphagnum-dominated communities of mosses from hollows and hummocks, ericaceous shrubs Rhododendron groenlandicum and Chamaedaphne calyculata and trees Picea mariana and Larix laricina) were collected. For vascular plants, both aboveground tissues (leaves and branches) and belowground compartments (fine and coarse roots  retrieved from sieved peat) were collected. Bulk tissue analyses include carbon and nitrogen concentrations and stable carbon (δ¹³C) isotope composition to quantify treatment effects on carbon assimilation and partitioning among tissues. Lipids are extracted and separated into major classes such as n‑alkanes, n‑fatty acids, and n‑alcohols, which serve as biomarkers of plant functional types, membrane properties and potential stress responses.

Here, we show that long‑term warming enhanced allocation to shrubs and alter the elemental and lipid composition of both aboveground and belowground responses with species-specific differences, while elevated CO₂ did not show to alter lipid concentration or composition of plant tissues. In plant tissues, warming promoted shifts in lipid profiles towards more saturated and degradation‑resistant moieties and modified the relative abundance of lipid classes due to stress response and structural adaptation.

By combining new measurements with earlier data on the same plant community and soil profile, this work provides a decadal‑scale view of how warming and elevated CO₂ reshape plant carbon partitioning and molecular composition in an ombrotrophic bog. This will help constrain the trajectories of boreal peatland carbon cycling under global change.