Dynamics of the soil nematode food web and nutrient pools under tall fescue lawns established on soil matrices resulting from common urban development activities

Abstract

Human activity in urbanizing areas often disturbs the soil profile, but little is known of its effects on subsequent soil food web dynamics and biogeochemical cycling. We assessed dynamics of the soil nematode food web and nutrient pools in tall fescue lawns created on either disturbed topsoil or subsoil, with or without compost amendment, and managed under three nitrogen fertilizer rates for one year. Overall, total nematodes and number of nematode genera were higher in topsoil than subsoil plots throughout the study. Compost amendment temporarily reduced number of nematode genera and this effect lasted for six months. Total number of nematodes also initially declined in the compost-amended plots, but increased within two months and remained high thereafter. The nematode food web enrichment index was initially lower in subsoil compared with topsoil plots and steadily increased overtime, but structure remained low in subsoil throughout the study period. The food web structure declined even in topsoil under turfgrass over time. Compost amendment only increased food web enrichment temporarily, but had little effect on structure. Nitrogen fertilizer had no effect on either enrichment or structure of the food web. Temporal faunal profile analysis indicated that the soil food webs under turfgrass in all treatments converged over time, representing a highly enriched but poorly structured food web, and a strong bottom-up control on the soil food web. Soil macronutrients Ca, P, K, total N, total C, microbial biomass, and soil organic matter contents were higher in topsoil than subsoil, and were increased by compost amendment in both substrates. Soil P was only 18 μg/g in subsoil and it further declined by about 20% during the year. During the first two months after seeding, topsoil plots had lower turfgrass cover than subsoil plots (63 ± 5% and 95 ± 0%, respectively), but had higher weed cover (29 ± 5% and 2 ± 0%, respectively). After one year, turfgrass quality (greenness) was higher in topsoil than subsoil plots, in plots with compost amendment than those without, and in high N than low and no N plots. We conclude that anthropogenic activities, resulting in the loss of topsoil, can have a profound effect on the structure of the soil food web, which may severely limit its capacity to support optimal nutrient cycling, plant growth, and other essential functions.