Trophic cascades in the bryosphere: the impact of global change factors on top-down control of cyanobacterial N2 -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 N2 -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 N2 -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.
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83, Umeå, Sweden.
Paul
P
Kardol
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83, Umeå, Sweden.
Clydecia M
CM
Spitzer
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83, Umeå, Sweden.
Michael J
MJ
Gundale
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83, Umeå, Sweden.
Marie-Charlotte
MC
Nilsson
Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83, Umeå, Sweden.
David A
DA
Wardle
D000818:Animals; D044002:Bryophyta / Q000382:microbiology* / Q000502:physiology; D000458:Cyanobacteria / Q000502:physiology*; D020387:Food Chain; D009586:Nitrogen Fixation / Q000502:physiology*
Boreal forest; Pleurozium schreberi; bottom-up control; feather moss; food webs; nitrogen cycling; nitrogen deposition; precipitation; top-down control; trophic interactions