Above-ground arthropod fauna of four Swedish cropping systems and its role in carbon and nitrogen cycling.
Above-ground arthropod populations in field plots of barley receiving no nitrogen (barley 0), barley receiving 120 kg nitrogen per hectare per year (barley 120), meadow fescue (Festuca pratensis) leys and lucerne leys were D-vac sampled monthly between June and September in 1982 and 1983. One hundred and ninety-six arthropod species or higher taxonomic groups were recorded. Mean population densities ranged from 1098/m2 in barley 0 to 3683/m2 in lucerne; corresponding biomass values were 69 mg/m2 to 321 mg/m2 dry mass. Lowest mean population densities and biomass generally occurred in barley 0 and highest in the leys, particularly in lucerne. Herbivores contributed from 29% of the total arthropod biomass in lucerne to 52% in barley 120. The range for detritivores and microbivores was 20% in barley 120 to 51% in lucerne, while predators and parasites accounted for between 20% of arthropod biomass in lucerne and 37% in barley 0. Mean arthropod respiration ranged from 285 mg carbon/m2 in barley 0 to 1127 mg carbon/m2 in lucerne for the period 1 June to 30 September. Herbivores were estimated to consume 502 mg carbon/m2 in barley 0 and 2948 mg carbon/m2 in barley 120 on average when consumption was calculated from respiration; the corresponding figures for nitrogen consumption were 25 and 147 mg. Herbivore consumption represented 0.3% (barley 0) to 0.7% (barley 120) of the carbon, and 0.3% (grass ley) to 0.9% (barley 120) of the nitrogen fixed in above-ground net primary production. Estimates of herbivore consumption based on assumed mean daily ingestion rates were somewhat higher, ranging from 0.3% (grass ley) to 1.3% (barley 120) of the carbon and 0.3% to 1.6% of the nitrogen fixed in above-ground net primary production.