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TL;DR
A field shading experiment in an ombrotrophic bog found that increasing shade linearly reduced Sphagnum growth in hollows but not on hummocks, consistent with shrub expansion contributing to moss decline under experimental warming.
Ecology and Evolution · 4 authors, 4 centres
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A field shading experiment in an ombrotrophic bog found that increasing shade linearly reduced Sphagnum growth in hollows but not on hummocks, consistent with shrub expansion contributing to moss decline under experimental warming.
In a northern Minnesota ombrotrophic bog, a field shading experiment tested whether light reduction from shrub expansion contributes to Sphagnum decline observed under experimental warming. Plots were established on hummocks and hollows in three blocks with shrubs removed and five shade levels (30%–90%) using neutral density cloth. Sphagnum angustifolium/fallax and S. divinum growth declined linearly with increasing shade in hollows, with about a 60% growth loss under deep shade, but hummocks showed no growth response, possibly because high irradiance in open hummock plots was inhibitory. Shading caused etiolation, with thin, spindly plants under deepest shade. Added shrub litter matching the litter amount in warmed plots had no apparent effect on Sphagnum growth or base cation concentrations. Laboratory measurements of S. angustifolium/fallax from 30% and 90% shade plots showed maximal light-saturated photosynthesis was 42% greater in plants from 30% shade.