Trophic cascades in the bryosphere: the impact of global change factors on top-down control of cyanobacterial N-2-fixation

• Trophic cascades in which predators regulate densities of organisms at lower trophic levels are important drivers of population dynamics, but effects of trophic cascades on ecosystem-level fluxes and processes, and the conditions under which top-down control is important, remain unresolved. We manipulated the structure of a food web in boreal feather mosses and found that moss-inhabiting microfauna exerted top-down control of N-2-fixation by moss-associated cyanobacteria. However, the presence of higher trophic levels alleviated this top-down control, likely through feeding on bacterivorous microfauna. These effects of food-web structure on cyanobacterial N-2-fixation were dependent on global change factors and strongly suppressed under N fertilisation. Our findings illustrate how food web interactions and trophic cascades can regulate N cycling in boreal ecosystems, where carbon uptake is generally strongly N-limited, and shifting trophic control of N cycling under global change is therefore likely to impact ecosystem functioning.

Ämnesord

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Skogsvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Forest Science (hsv//eng)

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Jordbruksvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Agricultural Science (hsv//eng)

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