Although little is known about the relationship between aboveground and belowground biota and ecosystem services in urban soils, the scarce data suggests that plant coverage has a key role in influencing the urban C and N cycles. Plant litter quality and quantity have been addressed as one the major factors determining the rate of nutrient and organic carbon cycling in urban soils. However, the land-use history of urban soils, frequency of disturbances and abiotic-biotic conditions may largely contribute to the effects of aboveground biota on decomposition process. Here we studied the decomposition process of different litter types (labile and recalcitrant litter) in two structurally and chemically divergent urban soils (landfill sandy soil and richer park soil). At both of these urban sites, a reciprocal litter placement experiment was performed to distinguish the effects between plant coverage (plant treatment) and litter type on litter decomposition processes. As hypothesized, labile litter decomposed faster than recalcitrant litter at both urban soil types. Urban soil type however, had a clear impact on degradation rate of the litter: all litter types decomposed at higher rates in park soil with higher organic matter and soil moisture content. Unexpectedly, the plant treatment did not affect the degradation rate of the litter although it did have a significant influence on the abundance of litter-inhabiting Collembola in landfill soil. Our study suggests potentially higher carbon retention in urban soils under recalcitrant litter producing plants in comparison to plant-soil systems with labile-litter producing plants.
a b s t r a c tTransformation 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.
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