Introducing GLUSEEN: A New Open Access and Experimental Network in Urban Soil Ecology

Peer reviewe

Metagenomics Reveals Bacterial and Archaeal Adaptation to Urban Land-Use : N Catabolism, Methanogenesis, and Nutrient Acquisition

Urbanization results in the systemic conversion of land-use, driving habitat and biodiversity loss. The "urban convergence hypothesis" posits that urbanization represents a merging of habitat characteristics, in turn driving physiological and functional responses within the biotic community. To test this hypothesis, we sampled five cities (Baltimore, MD, United States; Helsinki and Lahti, Finland; Budapest, Hungary; Potchefstroom, South Africa) across four different biomes. Within each city, we sampled four land-use categories that represented a gradient of increasing disturbance and management (from least intervention to highest disturbance: reference, remnant, turf/lawn, and ruderal). Previously, we used amplicon sequencing that targeted bacteria/archaea (16S rRNA) and fungi (ITS) and reported convergence in the archaeal community. Here, we applied shotgun metagenomic sequencing and QPCR of functional genes to the same soil DNA extracts to test convergence in microbial function. Our results suggest that urban land-use drives changes in gene abundance related to both the soil N and C metabolism. Our updated analysis found taxonomic convergence in both the archaeal and bacterial community (16S amplicon data). Convergence of the archaea was driven by increased abundance of ammonia oxidizing archaea and genes for ammonia oxidation (QPCR and shotgun metagenomics). The proliferation of ammonia-oxidizers under turf and ruderal land-use likely also contributes to the previously documented convergence of soil mineral N pools. We also found a higher relative abundance of methanogens (amplicon sequencing), a higher relative abundance of gene sequences putatively identified as Ni-Fe hydrogenase and nickel uptake (shotgun metagenomics) under urban land-use; and a convergence of gene sequences putatively identified as contributing to the nickel transport function under urban turf sites. High levels of disturbance lead to a higher relative abundance of gene sequences putatively identified as multiple antibiotic resistance protein marA and multidrug efflux pump mexD, but did not lead to an overall convergence in antibiotic resistance gene sequences.Peer reviewe

Earthworm assemblages in urban habitats across biogeographical regions

In urban landscapes, humans are the most significant factor determining belowground diversity, including earthworms. Within the framework of the Global Urban Soil Ecology and Education Network (GLUSEEN), a multi-city comparison was carried out to assess the effects of soil disturbance on earthworms. In each of five cities (Baltimore, USA; Budapest, Hungary; Helsinki and Lahti, Finland; Potchefstroom, South Africa), covering four climatic and biogeographical regions, four habitat types (ruderal, turf/lawn, remnant and reference) were sampled. The survey resulted in 19 species belonging to 9 genera and 4 families. The highest total species richness was recorded in Baltimore (16), while Budapest and the Finnish cities had relatively low (5–6) species numbers. Remnant forests and lawns supported the highest earthworm biomass. Soil properties (i.e. pH and organic matter content) explained neither earthworm community composition nor abundance. Evaluating all cities together, earthworm communities were significantly structured by habitat type. Communities in the two adjacent cities, Helsinki and Lahti were very similar, but Budapest clearly separated from the Finnish cities. Earthworm community structure in Baltimore overlapped with that of the other cities. Despite differences in climate, soils and biogeography among the cities, earthworm communities were highly similar within the urban habitat types. This indicates that human-mediated dispersal is an important factor shaping the urban fauna, both at local and regional scales.Peer reviewe

Előzetes eredmények városi talajok lebontó hatásfokának vizsgálatáról (GLUSEEN-Projekt, Budapest)

A „Global Urban Soil Ecology and Education” hálózat előkészítő kutatása második éve folyik – a világ 4 régiójának 5 helyszínén –, Magyarország részvételével. A kutatás célja az ún. „konvergencia hipotézis” tesztelése különböző minőségű/zavartságú városi talajok szerves anyag lebontási hatásfokán keresztül. A konvergencia hipotézis szerint a természetes ökoszisztémák az urbanizáció hatására hasonló irányú változást mutatnak globális szinten. A cél mind tudományos igényű kutatások, mind az érdeklődő lakosság bevonására alkalmas egyszerű, könnyen kivitelezhető, költséghatékony módszerek kidolgozása, tesztelése. A kutatás során 4 élőhelytípust (5–5 ismétlésben) jelöltünk ki: 1) erősen zavart (ruderális), 2) városi gyep, 3) az urbanizáció eredményeként fragmentálódott erdőfoltok és 4) referenciaként szolgáló természetközeli erdők területei. A szervesanyag bomlásának mértékét 2013-ban leásott teafilterekkel vizsgáltuk, amelyeket 4, 6, 10, 12 hónap után gyűjtöttünk vissza. Eredményeink szerint a 6. hónaptól szignifikáns különbség mutatkozott az élőhelytípusok között a lebontási sebességben (F = 11,238; p < 0,0001), ami a városi gyepeken és ruderális élőhelyeken volt a legnagyobb. Ez összhangban van a többi 4 városban kapott eredménnyel, ami alátámasztja a konvergencia hipotézist: a különböző éghajlatú, alapkőzetű talajok kémhatása és humusztartalma az erősen zavart és városi gyep élőhelyek esetén azonos irányú változást mutatnak világszerte

Down by the riverside: urban riparian ecology

Riparian areas are hotspots of interactions between plants, soil, water, microbes, and people. While urban land use change has been shown to have dramatic effects on watershed hydrology, there has been surpris- ingly little analysis of its effects on riparian areas. Here we examine the ecology of urban riparian zones, focusing on work done in the Baltimore Ecosystem Study, a component of the US National Science Foundation's Long Term Ecological Research network. Research in the Baltimore study has addressed how changes in hydrology associated with urbanization create riparian "hydrologic drought" by lowering water tables, which in turn alters soil, vegetation, and microbial processes. We analyze the nature of past and cur- rent human interactions with riparian ecosystems, and review other urban ecosystem studies to show how our observations mirror those in other cities

SHORT AND LONG-TERM CHANGES IN URBAN FOREST SOILS

Human activities influence soil ecosystems, impacting soil properties, such as pH and bulk density, and functions, such as soil respiration. Local indirect human impacts include atmospheric deposition of elements such as nitrogen, calcium, and sulfur, and the introduction of species like jumping worms. Direct impacts include land cover conversion and soil compaction. A global human impact is climate change, which is another indirect factor affecting soil carbon cycling. This dissertation examines how soil properties and functions change over time due to these direct and indirect effects. The objectives of this study were 1) to characterize changes in soil properties over two decades along an urban-rural gradient in Baltimore, 2) to investigate the relationship between soil properties and the change in earthworm community composition, and 3) to assess soil respiration in response to extreme precipitation events between turf grass and forest cover types over a growing season. This work is necessary, because more accurate projections of changes in soil chemical, physical, and biological properties will enable better urban forest patch management, and understanding how soil respiration relates to land cover and extreme precipitation events improves climate change models. To achieve these objectives, in Chapter 1, surface soil properties were examined along an urban-rural gradient. Archived soils, collected in Baltimore City and County, were analyzed alongside recently sampled soils. In Chapter 2, earthworms were extracted and identified to determine their effect on soil properties and changes in community composition. Lastly, in Chapter 3, two land cover types, forest and turf grass in a suburban neighborhood, were outfitted with soil CO2, temperature, and moisture sensors at various depths to evaluate the effects of precipitation events on CO2 fluxes from August 2011 to October 2011. Over two decades soil calcium increased by 35%, pH increased from 4.1 to 4.5, carbon to nitrogen ratios decreased from 17.8 to 16.7, leaf litter decreased by 44%, and bulk density decreased 10% from 1.05 to 0.94 g cm-3. Despite significant correlations between soil properties and earthworm abundance within a given year, changes in soil chemistry were found to be independent of earthworm community shifts. Canonical correspondence analysis revealed that the soil variables pH and Ca explain 69% of the variation of the earthworm species composition for 2020. Earthworm assemblages appeared to be different in urban forests than rural ones, with a higher abundance of jumping worms present in rural forests. In terms of soil respiration, there were differences between turf grass and forest soils, with grass soils showing twice as high CO2 efflux rates (3.04 µmol m-2s-1) than forest (1.55 µmol m-2s-1). Temporal analyses revealed that while turf grass soil was less resistant to precipitation events than forest, both soil types exhibited resilience, returning to baseline CO2 concentrations post-event. In conclusion, the study demonstrates that human activities influence soil properties and functions even in the absence of significant soil physical alterations. Urban forest soils exhibited significant changes with potential impacts on local ecosystems, such as nutrient availability to seedlings and saplings due to altered soil pH values. Furthermore, the increased abundance of jumping worms in rural forests warrant close monitoring given that this invasive group can fundamentally alter the forest floor. Lastly, modeling of soil respiration in the context of extreme events, which are anticipated to increase with climate change, should incorporate land cover resistance measures of CO2 effluxes to reflect conditions more accurately

A global comparison of surface soil characteristics across five cities: a test of the urban ecosystem convergence hypothesis

As part of the Global Urban Soil Ecology and Education Network and to test the urban ecosystem convergence hypothesis, we report on soil pH, organic carbon (OC), total nitrogen (TN), phosphorus (P), and potassium (K) measured in four soil habitat types (turfgrass, ruderal, remnant, and reference) in five metropolitan areas (Baltimore, Budapest, Helsinki, Lahti, Potchefstroom) across four biomes. We expected the urban soil characteristics to “converge” in comparison to the reference soils. Moreover, we expected cities in biomes with more limiting climatic conditions, or where local factors strongly affect soil characteristics, would exhibit the greatest variance across soil types within and among cities. In addition, soil characteristics related to biogenic factors (OC, TN) would vary the most because of differences in climate and human efforts to overcome limiting environmental conditions. The comparison of soils among and within the five cities suggests that anthropogenic, and to a lesser degree native, factors interact in the development of soils in urban landscapes. In particular, characteristics affected by anthropogenic processes and closely associated with biogenic processes (OC, TN) converged, while characteristics closely associated with parent material (K, P) did not converge, but rather diverged, across all soil habitat types. These results partially supported the urban ecosystem convergence hypothesis in that a convergence occurred for soil characteristics affected by climatic conditions. However, the divergence of K and P was unexpected and warrants adjusting the hypothesis to account for variations in anthropogenic effects (e.g., management) that may occur within soil habitat types impacted by human

Urbanization minimizes the effects of plant traits on soil provisioned ecosystem services across climatic regions

An increasingly urbanized world is one of the most prominent examples of global environmental change. Across the globe, urban parks are designed and managed in a similar way, resulting in visually pleasing expansions of lawn interspersed with individually planted trees of varying appearances and functional traits. These large urban greenspaces have the capacity to provide various ecosystem services, including those associated with soil physicochemical properties. Our aim was to explore whether soil properties in urban parks diverge underneath vegetation producing labile or recalcitrant litter, and whether the impact is affected by climatic zone (from a boreal to temperate to tropical city). We also compared these properties to those in (semi)natural forests outside the cities to assess the influence of urbanization on plant-trait effects. We showed that vegetation type affected percentage soil organic matter (OM), total carbon (C) and total nitrogen (N), but inconsistently across climatic zones. Plant-trait effects were particularly weak in old parks in the boreal and temperate zones, whereas in young parks in these zones, soils underneath the two tree types accumulated significantly more OM, C and N compared to lawns. Within climatic zones, anthropogenic drivers dominated natural ones, with consistently lower values of organic-matter-related soil properties under trees producing labile or recalcitrant litter in parks compared to forests. The dominating effect of urbanization is also reflected in its ability to homogenize soil properties in parks across the three cities, especially in lawn soils and soils under trees irrespective of functional trait. Our study demonstrates that soil functions that relate to carbon and nitrogen dynamics-even in old urban greenspaces where plant-soil interactions have a long history-clearly diverged from those in natural ecosystems, implying a long-lasting influence of anthropogenic drivers on soil ecosystem services.Peer reviewe