Shading contributes to Sphagnum decline in response to warming

Richard J. Norby, Taylor Baxter, Tatjana Živković, David J. Weston

Research output: Contribution to journalArticlepeer-review

Abstract

Experimental warming of an ombrotrophic bog in northern Minnesota has caused a rapid decline in the productivity and areal cover of Sphagnum mosses, affecting whole-ecosystem carbon balance and biogeochemistry. Direct effects of elevated temperature and the attendant drying are most likely the primary cause of the effects on Sphagnum, but there may also be responses to the increased shading from shrubs, which increased with increasing temperature. To evaluate the independent effects of reduction in light availability and deposition of shrub litter on Sphagnum productivity, small plots with shrubs removed were laid out adjacent to the warming experiment on hummocks and hollows in three blocks and with five levels of shading. Four plots were covered with neutral density shade cloth to simulate shading from shrubs of 30%–90% reduction in light; one plot was left open. Growth of Sphagnum angustifolium/fallax and S. divinum declined linearly with increasing shade in hollows, but there was no response to shade on hummocks, where higher irradiance in the open plots may have been inhibitory. Shading caused etiolation of Sphagnum—they were thin and spindly under the deepest shade. A dense mat of shrub litter, corresponding to the amount of shrub litter produced in response to warming, did not inhibit Sphagnum growth or cause increases in potentially toxic base cations. CO2 exchange and chlorophyll-a fluorescence of S. angustifolium/fallax from the 30% and 90% shade cloth plots were measured in the laboratory. Light response curves indicate that maximal light saturated photosynthesis was 42% greater for S. angustifolium/fallax grown under 30% shade cloth relative to plants grown under 90% shade cloth. The response of Sphagnum growth in response to increasing shade is consistent with the hypothesis that increased shade resulting from shrub expansion in response to experimental warming contributed to reduced Sphagnum growth.

Original languageEnglish
Article numbere10542
JournalEcology and Evolution
Volume13
Issue number9
DOIs
StatePublished - Sep 2023

Funding

This research was supported by U.S. Department of Energy, Office of Science, Biological and Environmental Research Program at the Oak Ridge National Laboratory. Oak Ridge National Laboratory is operated by UT‐Battelle, LLC, under contract DE‐AC05‐00OR22725 with the U.S. Department of Energy. Taylor Baxter's participation was supported by funding from the New Phytologist Foundation.

FundersFunder number
U.S. Department of Energy
Oak Ridge National LaboratoryDE‐AC05‐00OR22725
New Phytologist Foundation

    Keywords

    • Sphagnum angustifolium
    • Sphagnum divinum
    • Sphagnum fallax
    • bog
    • climate change
    • peatland
    • shrubs
    • warming

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