Urban belowground food-web responses to plant community manipulation - Impacts on nutrient dynamics

Transformation of soils by urbanization is known to pose drastic effects on the physical, chemical and ecological characteristics of urban soils, which are likely to hamper the important ecosystem services produced by belowground biota. The use of plants in improving/restoring soils is a well established practice in various disturbed ecosystems, but the knowledge of the ability of primary producers to modify urban soils is virtually lacking. To explore the effects of aboveground plant manipulation on belowground biota and soil processes we established a field experiment using four plant species (Lotus corniculatus, Holcus lanatus, Picea abies and Calluna vulgaris) of three functional traits according to their litter quality. The 2.5-year long study applying pan lysimeters to collect water leachates from the rhizospheres was conducted at two urban sites with differing soil characteristics. Plant species producing labile litter (legume Lotus and grass Holcus) produced a higher bacterial energy channel biomass in comparison to plants (Calluna and Picea) producing recalcitrant litter. The bacterial-dominating energy channel under Lotus plots leached higher amount of inorganic nitrogen than the plots with Calluna and Picea, which had relatively higher proportion of fungal biomass in the soil. However, when the leaching loss was compared to the potentially leachable soil inorganic nitrogen, the most species-diverse mixed communities, albeit increasing the bacterial biomass, showed a highest capacity for conserving nitrogen in the soil. Our study demonstrates the great potential of plant species/functional types to modify the urban belowground communities and consequently, the nutrient dynamics of disturbed urban soils. (C) 2010 Elsevier B.V. All rights reserved.