Miklós Dombos

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

Abstract 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 humans.

Urbanization erodes ectomycorrhizal fungal diversity and may cause microbial communities to converge

Urbanization alters the physicochemical environment, introduces non-native species and causes ecosystem characteristics to converge. It has been speculated that these alterations contribute to loss of regional and global biodiversity, but so far most urban studies have assessed macro-organisms and reported mixed evidence for biodiversity loss. We studied five cities on three continents to assess the global convergence of urban soil microbial communities. We determined the extent to which communities of bacteria, archaea and fungi are geographically distributed, and to what extent urbanization acts as a filter on species diversity. We discovered that microbial communities in general converge, but the response differed among microbial domains; soil archaeal communities showed the strongest convergence, followed by fungi, while soil bacterial communities did not converge. Our data suggest that urban soil archaeal and bacterial communities are not vulnerable to biodiversity loss, whereas urbanization may be contributing to the global diversity loss of ectomycorrhizal fungi. Ectomycorrhizae decreased in both abundance and species richness under turf and ruderal land-uses. These data add to an emerging pattern of widespread suppression of ectomycorrhizal fungi by human land-uses that involve physical disruption of the soil, management of the plant community, or nutrient enrichment.

Demography of some non-native isopods (Crustacea, Isopoda, Oniscidea) in a Mid-Atlantic forest, USA.

Abstract Introduced species dominate the terrestrial isopod fauna in most inland habitats of North America, including urban landscapes. These non-native species are often very abundant and thus potentially play a significant role in detritus processing. We monitored isopod assemblages in an urban forest for a year to examine the relationship between surface activity and abiotic environmental factors, and to analyze reproductive characteristics that might contribute to their successful establishment. Using pitfall trap samples we recorded five species, two of which, Trachelipus rathkii and Cylisticus convexus, were highly abundant. We determined size, sex and reproductive state of each individual. Surface activity of both species reflected variability in abiotic stress factors for isopods, such as soil moisture and soil temperature. Early spring the main trigger was soil temperature while later in the season increasing temperature and decreasing soil moisture jointly affected population dynamics. Activity significantly correlated with soil moisture. The temporal pattern of sex ratios supported the secondary sex ratio hypothesis. Males dominated the samples on the onset of the mating season in search of females. The pattern was reversed as females searched for suitable microsites for their offspring. Size independent fecundity decreased as conditions became more stressful late in the season.

New Method for Automatic Body Length Measurement of the Collembolan, Folsomia candida Willem 1902 (Insecta: Collembola)

The collembolan, Folsomia candida, is widely used in soil ecotoxicology. In recent years, growth rate of collembolans has become as frequently used endpoint as reproduction rate in ecotoxicological studies. However, measuring collembolan body sizes to estimate growth rate is a complicated and time-consuming task. Here we present a new image analysis method, which facilitates and accelerates the body length measurement of the collembolan Folsomia candida. The new software package, called CollScope, consists of three elements: 1) an imaging device; 2) photographing software; 3) an ImageJ macro for image processing, measurement and data analysis. We give a complete description of the operation of the software, the image analyzing process and describe its accuracy and reliability. The software with a detailed usage manual is attached as Supplementary Material. We report a case study to demonstrate that the automated measurement of collembolan body sizes is highly correlated with the traditional manual measurements (estimated measuring accuracy 0.05 mm). Furthermore, we performed a dose-response ecotoxicity test using cadmium-sulfate by using CollScope as well as classical methods for size measurement. Size data measured by CollScope or manually did not differ significantly. Furthermore the new software package decreased time consumption of the measurements to 42% when tested on 35 animals. Consequently, methodological investigations performed in this study should be regarded as a recommendation for any other routine dose-response study where body growth is an endpoint.

EDAPHOLOG monitoring system: automatic, real-time detection of soil microarthropods

Summary Soil microarthropods as organic matter decomposers play an important role in soil functioning thus providing ecosystem services. However, ecosystem scale investigations on their abundance and dynamics are scarce because their high spatio-temporal heterogeneity requires huge sample size. Processing and identifying large number of individuals is extremely labour intensive. We prototyped a device called EDAPHOLOG monitoring system that consists of (1) a probe that catches and detects microarthropods and estimates their body size; (2) a data logger transmitting data to a central database, and (3) a Java application for retrieving data. We tested the device in three ways. First, we tested the precision and accuracy of detection and body size estimation of the device in the laboratory using microarthropods of five morphotypes: euedaphic Collembola, haired Collembola, scaled Collembola, Acari and Oribatida. Second, we compared the number of individuals collected by EDAPHOLOG traps, pitfall traps and soil extraction method in an alfalfa field. Third, we deployed a total of 100 EDAPHOLOG probes in nine different habitats for over three months to demonstrate the applicability of the monitoring system. In the laboratory, EDAPHOLOG detected 95.6% of individuals; even the smallest morphotype (Oribatida, body size (mean±SE): 0.58±0.04 mm) were detected in 87.5% of cases. For body length estimation we established a quadratic relationship between the estimated and measured body lengths, however, the R2 of the quadratic model was only 0.32. By comparing the three different sampling methods (EDAPHOLOG, pitfall traps and soil extraction), we concluded that EDAPHOLOG traps better select for soil microarthropods compared to classical pitfall traps, since the latter ones caught also many other arthropod species. Furthermore, the EDAPHOLOG traps caught more epigeic microarthropods and almost the same number of soil-dwelling euedaphic microarthropods as the numbers collected by soil extraction. During the three month-long field test the total numbers of detected and captured individuals agreed very well, although the device tended to overestimate the number probably due to counting also some soil particles falling into the probe. This trend was the same regardless of the total number caught. Surface-dwelling epigeic and litter-dwelling hemiedaphic microarthropods dominated the samples although soil-dwelling euedaphic microarthropods were also caught. EDAPHOLOG is a novel device that consumes little power, rugged enough to operate in the field for extended periods of time, and can be remotely controlled. It detects surface- and soil-dwelling microarthropods real-time, and with high accuracy, however, it is less accurate to estimate body size. The system is especially suitable in field research focusing on temporal activity of microarthropods. Because it is non-invasive, studies requiring long term monitoring, such as soil remediation or ecosystem restoration projects, will also find EDAPHOLOG useful. This article is protected by copyright. All rights reserved.

An Opto-Electronic Sensor for Detecting Soil Microarthropods and Estimating Their Size in Field Conditions

Methods to estimate density of soil-dwelling arthropods efficiently, accurately and continuously are critical for investigating soil biological activity and evaluating soil management practices. Soil-dwelling arthropods are currently monitored manually. This method is invasive, and time- and labor-consuming. Here we describe an infrared opto-electronic sensor for detection of soil microarthropods in the size range of 0.4–10 mm. The sensor is built in a novel microarthropod trap designed for field conditions. It allows automated, on-line, in situ detection and body length estimation of soil microarthropods. In the opto-electronic sensor the light source is an infrared LED. Two plano-convex optical lenses are placed along the virtual optical axis. One lens on the receiver side is placed between the observation space at 0.5–1 times its focal length from the sensor, and another emitter side lens is placed between the observation space and the light source in the same way. This paper describes the setup and operating mechanism of the sensor and the control unit, and through basic tests it demonstrates its potential in automated detection of soil microarthropods. The sensor may be used for monitoring activities, especially for remote observation activities in soil and insect ecology or pest control.

Sampling Design Optimization on Arable Lands for Integrated Soil Monitoring for Sustainable Production

Proper experimental design that ensures effective sampling of each recorded environmental variable is essential during planning integrated soil-monitoring programs with the aim of assessing the ecological state of soils. In our study, three different regular sampling designs (standard, 50,000 m2; reduced area, 635 m2; and reduced area and sampling size, 2500 m2) were tested, and the required sampling sizes for 10%, 20%, and 40% minimum detectable change were calculated. Sampling designs were tested from the aspect of the most effective sampling, a sampling with the greatest precision and the least bias. The parameters determined in this study were the following: total microbial activity, concentration of 14 potentially toxic microelements, and basic soil physical and chemical characteristics. The results are presented by the example of total microbial activity and microelement concentration studies. Twenty to 120 soil samples were taken from each selected arable land under intensive and organic cultivation as well as from a pasture and protected grassland, considered as a control. It was concluded that both for microbial activity and microelement concentration measurements of 10% minimum detectable change requires enormous sampling effort at each site and sampling design. The required sampling size is especially high at the organic sites and the grassland, because the high standard deviation, and especially high mean total microbial activity. With a sampling using either the standard or reduced area design, 20% difference in total microbial activity can be detected using a reasonable (<25) sampling size. However, reduced area design minimizes spatial heterogeneity, thus requires smaller sampling effort, and can be an ideal compromise. In the case of microelement concentration, standard sampling design was more sufficient to detect a 20% change. Designs that proved to be most efficient in this study have been combined into a joint sampling design that will be applied in the first cycle of the new Hungarian Soil Degradation Monitoring System.