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Abstract Peat mosses ( Sphagnum spp.) are keystone species in boreal peatlands, where they dominate net primary productivity and facilitate the accumulation of carbon in thick peat deposits. Sphagnum mosses harbor a diverse assemblage of microbial partners, including N 2 ‐fixing (diazotrophic) and CH 4 ‐oxidizing (methanotrophic) taxa that support ecosystem function by regulating transformations of carbon and nitrogen. Here, we investigate the response of the Sphagnum phytobiome (plant + constituent microbiome + environment) to a gradient of experimental warming (+0°C to +9°C) and elevated CO 2 (+500 ppm) in an ombrotrophic peatland in northern Minnesota (USA). By tracking changes in carbon (CH 4 , CO 2 ) and nitrogen (NH 4 ‐N) cycling from the belowground environment up to Sphagnum and its associated microbiome, we identified a series of cascading impacts to the Sphagnum phytobiome triggered by warming and elevated CO 2 . Under ambient CO 2 , warming increased plant‐available NH 4 ‐N in surface peat, excess N accumulated in Sphagnum tissue, and N 2 fixation activity decreased. Elevated CO 2 offset the effects of warming, disrupting the accumulation of N in peat and Sphagnum tissue. Methane concentrations in porewater increased with warming irrespective of CO 2 treatment, resulting in a ~10× rise in methanotrophic activity within Sphagnum from the +9°C enclosures. Warming's divergent impacts on diazotrophy and methanotrophy caused these processes to become decoupled at warmer temperatures, as evidenced by declining rates of methane‐induced N 2 fixation and significant losses of keystone microbial taxa. In addition to changes in the Sphagnum microbiome, we observed ~94% mortality of Sphagnum between the +0°C and +9°C treatments, possibly due to the interactive effects of warming on N‐availability and competition from vascular plant species. Collectively, these results highlight the vulnerability of the Sphagnum phytobiome to rising temperatures and atmospheric CO 2 concentrations, with significant implications for carbon and nitrogen cycling in boreal peatlands.
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This content will become publicly available on March 1, 2027
Global Synthesis Reveals Context‐Dependent Plant Diversity Responses to CO2 , Climate Change, and Nitrogen
ABSTRACT Global understanding of how plant diversity responds to multiple, co‐occurring global change drivers (e.g., elevated CO2, climate change, and nitrogen addition) remains fragmented, largely due to the highly context‐dependent nature of responses and disparate experimental evidence. To address this, we conducted a global meta‐analysis synthesising 6832 control‐treatment comparisons from 465 studies. We found that for individual drivers, elevated CO2had no effect on species richness, whereas increased precipitation enhanced it. In contrast, warming, decreased precipitation, and nitrogen addition generally reduced richness, with nitrogen addition consistently decreasing Shannon diversity and Pielou evenness. When drivers combined, warming‐driven losses were offset by elevated CO2and increased precipitation and those of nitrogen addition were counteracted by both increased and decreased precipitation. Interaction analyses further revealed that additive effects between drivers predominated, though significant antagonisms emerged for specific pairs. Importantly, these responses were strongly context‐dependent, being mediated by a combination of site‐specific conditions (i.e., local climate, soil, and background diversity) and experimental methodologies (i.e., treatment duration, intensity, and plot and sampling area). Our synthesis underscores that predicting future biodiversity trajectories necessitates that models evolve beyond main effects to explicitly represent both multi‐driver interactions and the critical, often‐dominant, moderating role of local contexts and experimental conditions.
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- Award ID(s):
- 2425352
- PAR ID:
- 10686809
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Ecology Letters
- Volume:
- 29
- Issue:
- 3
- ISSN:
- 1461-023X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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