Soil arthropod abundance under conventional and no tillage in a Mediterranean climate

We have studied the impact on arthropod populations of conventional tillage and no-tillage systems in maize. Two different corn–weed control programs were assayed: NT, direct drilling of seed genetically modified to tolerate herbicide plus a combination of two pre-emergence and post-emergence herbicides; CT, conventional drilling with an isogenic corn variety plus a pre-emergence herbicide. Management system affected the soil arthropod community, based on major groups. Lower number of arthropods occurred in CT than in NT. Spider and hymenopteran parasitoids, especially those belonging to the families Lycosidae and Diapriidae were the groups that were most clearly affected. The natural field environment seems to favour the presence of Diapriidae. Spiders, in addition to being abundant, behaved in a similar way during both years of each treatment and might therefore be considered as reliable indicator families of the effects of different soil managements on the arthropod population in corn crops. Management system implies alterations on abundance of arthropods populations and natural enemies present in the crop.     

Effects of vegetation removal on soil properties and decomposer organisms

The removal of understory vegetation has been a common forest management practice, especially in plantations, but the effects of understory removal on soil physico-chemical properties and decomposer organisms is poorly known. In the present study, the effects of understory vegetation removal and removal of all-plants (i.e. removal of understory vegetation and trees) on soil properties and soil biota were measured in a plantation of mixed native tree species in southern China. During the wet season, understory vegetation removal did not cause significant changes on soil microbial community and major soil faunal groups except for a marked reduction in the density of herbivorous nematodes. However, all-plants removal significantly decreased the fungal biomass, the fungal:bacterial ratio, the density of herbivorous nematodes, the structure of the nematode community, and the density of mites, collembola and total microarthropods. In the dry season, understory vegetation removal resulted in a marked reduction in the density of total and herbivorous nematodes. The effects of plant removal on soil biota were similar to that in dry season. For both seasons, understory removal had no significant effects on soil physico-chemical properties (soil water content, pH, total nitrogen and soil organic carbon) but removal of all-plants significantly decreased soil pH. In general, the effects of understory vegetation removal on soil biota and other soil properties were much less severe than those of all-plants removal. The soil biota did not show significant response to understory removal, suggesting that this part of the vegetation may not be a major governing factor on such biota.     

Determinants of litter accumulation and the abundance of litter-associated microarthropods in bird's nest ferns (Asplenium nidus complex) in the forest of Yambaru on Okinawa Island, southern Japan

We studied the distributional pattern of bird's nest ferns (Asplenium nidus complex) and the factors that determined litter accumulation and the abundance of litter-associated microarthropods in the ferns in the forest of Yambaru on the northern part of Okinawa Island, southern Japan. We located 53 bird's nest ferns (41 ferns on 27 live trees of 13 species, and 12 on 5 dead trees) in a ca. 4-ha plot, collected litter samples from 37 ferns on 25 live trees, and then extracted a total of 11 205 microarthropods (Acari and Collembola) from all the litter samples. The ferns preferred concave slopes and tended to be distributed on the tree species that had the typical characteristics of high population density and/or large basal area in the forest. The ferns were usually established on large trees [≥10 m high or ≥20 cm diameter at breast height (DBH)], although the number and size of the ferns were not related to the size of the host trees. The amount of litter accumulated in the ferns was correlated neither with the size (height and DBH) of the host tree nor with the height and position of the ferns. The amount of accumulated litter had a significant positive correlation only with fern size; this might have caused the positive correlations between fern size and the abundance of litter-associated microarthropods and the number of species of oribatid mites in the ferns.     

Physico-chemical indicators and microarthropod communities as influenced by no-till, conventional tillage and nitrogen fertilisation after four years of continuous maize

A multidisciplinary study was carried out over four years in Northern Italy on a silt loam under continuous maize. The experimental design was a split-plot with four replicates; the main factor was the soil management system, conventional tillage (CT) or no-tillage (NT), while the secondary factor was N fertilisation. At the end of the trial, soil samples were taken from all plots at four depths (from 0 to 20 cm). In these samples the following were determined: pH, soil organic carbon (SOC), total N, available P, exchangeable K, cation exchange capacity (CEC), electrical conductivity (EC) and water aggregate stability (WAS). Soil compaction was measured during the last three years, after maize harvesting. To study the microarthropod community, soil samples (0–10 cm depth) were taken six times over the four years. Our results show that NT significantly increased SOC (+15.8%), total N (+9.6%), C/N (+5.3%), exchangeable K (+37.1%) and WAS (+64.8%). The stratification ratio for exchangeable K reached 2.15 for NT plots. N fertilisation, on the other hand, had no significant effect on most of the physico-chemical indicators, except for pH, CEC and EC. Soil compaction was significantly higher for NT compared with CT up to a depth of 25–30 cm. During the last year, interesting reductions in soil penetration resistance for NT were measured, up to 300–430 kPa in the 2.5–12.5 cm layer. As for the microarthropods, Acari were more sensitive to tillage compared with Collembola, and the Wardle V index proved to be a good indicator of the response to tillage. N fertilisation with 300 kg N ha⁻¹ had a negative effect on the total microarthropod abundance. The Shannon diversity index gave fluctuating and significantly different results: over the years results were split alternately between the two tillage systems. The QBS-ar index, calculated for all the four years of the study, ranged between 48 and 72, values typical of intensively cultivated soils. The results obtained suggested that it was not influenced by the tillage system. Therefore, this index seems to be unsuitable for detecting the influence of tillage management and N fertilisation on the microarthropod community.     

Biomass distribution of a microarthropod community in spruce forest soil

It has been previously demonstrated that fractal habitat features, combined with the allometric relationship between body size and metabolic rate, can sufficiently predict the biomass distribution in arthropod communities. This study shows that the relationship between biomass B and abundance N in a community of soil microarthropods is flatter than might be predicted by a combination of hypotheses concerning the (1) fractal dimension of pore surface, (2) metabolic rate, and (3) accessibility of soil pores. The relationship between B and N is N B ^-0.80 for the size classes to the right of the mode of the biomass distribution. Since the relationship between B and metabolic rate M is M B ^0.81, the energy use per size class is independent of size (B ^-0.80×B ^0.81 B ⁰) for a broad range of size classes with the exception of very small microarthropods.     

Spatial relationships between roots and soil organisms under different tillage systems

This study was designed to clarify the relationship between the distributions of soil organisms and roots under conventional tillage (CT) and reduced tillage (RT) systems. We hypothesized that the distributional relationship would be changed by the stratified organic matter under RT. To test the hypothesis, we compared the vertical and horizontal distributions of soil organisms within and between rows at depths of 0–10 and 10–20 cm in a wheat field. With the exception of nematodes, the spatial distributions of microorganisms and microarthropods were correlated with root biomass. The ratio of microbial activity or the number of organisms in the soil within rows to the same parameter between rows at a depth of 0 and 10 cm, differed among different soil organisms (ranging from 0.9 to 8.2). The ratios for microorganisms and microarthropods were greater under CT than under RT. This suggests that the root effect is small or is offset by high organic matter content in the surface layer under RT, and that the magnitude of the effect was greater under CT.     

Can microbial inoculants boost soil food webs and vegetation development on newly constructed extensive green roofs?

Green roofs are a key to providing nature-based solutions in cities. However, most green roofs installed in the Northern hemisphere are shallow, stonecrop planted systems (“extensive” green roofs), which have been shown to support limited biodiversity and could be more effective at providing ecosystem services. One issue with this type of extensive green roof is that rootzones are almost sterile on construction, relying on natural colonisation to provide a soil food web. This is a slow process, meaning plant growth can also be slow. Our aim was to determine if a soil food web could be introduced when the green roof is built. We applied microbial inoculants (mycorrhizal fungi and bacteria (Bacillus spp.)) to a new green roof and monitored plant growth and the soil food web (bacteria, mycorrhizal fungi and microarthropods). Different inoculants altered the composition of microarthropod communities, potentially impacting later succession. In particular, bacterial inoculants increased microarthropod populations. This is one of the first studies to demonstrate that the addition of microbial inoculants impacts not only plant growth, but also faunal components of the soil food web, which could have implications for long-term resilience. Bacteria were effective at aiding mycorrhizal colonisation of plants roots, but this colonisation had no impact on the growth of our selected stonecrops, Sedum album, Petrosedum reflexum and Phedimus spurius. We suggest that if a beneficial mycorrhiza could be found to promote the growth of these specific species on green roofs, bacteria could be effective “helper” species to aid colonisation. This study enables green roof researchers and the industry to justify further exploration of the impact of microbial inoculants on green roofs.