Soil nematode communities in grasslands

This thesis summarizes the results of five studies investigating the effect of plant species on soil nematode communities in grasslands. Nematodes (roundworms) are ubiquitous members of the soil fauna and have been much used as indicators of soil conditions. Plants have the ability to affect soil organisms through structural modification of the soil habitat and through the quantity and quality of organic matter that is returned to soil, in the form of plant litter and root exudates. The influence of grassland plant species on the soil nematode fauna was investigated in an experimental grassland, a glasshouse experiment and in a semi-natural grassland. Monocultures of 12 grassland plant species belonging to three plant functional groups, viz. grasses, legumes and non-leguminous forbs, were investigated in the field experiment and a subset of these in the other two systems. Plant species effects were common, for example, plant feeding and bacterial feeding nematodes responded positively to legumes and grasses, while forbs enhanced fungal feeding nematodes. Plant species identity appeared to be much more important than plant functional group for the nematode fauna. The effects of plants were quite consistent between field and glasshouse experiments. The influence of plant species diversity and functional diversity on the nematode fauna was investigated in the experimental grassland. Plant species composition proved to be more important for soil nematode communities than any of the plant diversity measures, but the hypothesis that species or functional diversity of plants affect nematode diversity or composition could not be rejected. My results also suggest that plant species identity may be an important determinant of spatial structure in natural grasslands. There was a succession of the nematode fauna during the eight years after establishment of the experimental grassland, especially indicated by the increase in maturity index of the nematode fauna. The results highlight the need for long-term experiments to reveal successional trends in soil nematode communities after cessation of agriculture. The increase of plant feeders with time, the slow colonization rate and the enhanced abundance of fungal feeders in soil under forbs have implications for nature restoration of former agricultural land

Helminths associated with terrestrial slugs in Swedish agricultural fields

Slugs are important agricultural pests causing yearly yield losses. However, parasitizing helminths potentially could affect the size of the slug population. Here, a survey of terrestrial slug-parasitic helminths (nematodes and trematodes) was conducted for the first time in Sweden. In total, 268 terrestrial slugs were collected from 27 agricultural field edges in three seasons over 2020 and 2021 and dissected for presence of helminth parasites. Slugs belonging to the genus Arion were molecularly identified by mitochondrial DNA cytochrome c oxidase subunit I (COI) while parasites were identified using ribosomal RNA (18S). Overall, 13% of the collected slugs had helminth parasites and the likelihood of a slug being parasitized was highest in autumn. Slugs identified as Arion vulgaris were more likely to be parasitized than native slug species. The prevalence of nematodes and trematodes were similar; the dominant species found were Alloionema appendiculatum and Brachylaima thompsoni, respectively. This is the first record of the presence of these two species in Sweden

Development of Loop-Mediated Isothermal Amplification Assay for Rapid Detection and Analysis of the Root-Knot Nematode Meloidogyne hapla in Soil

Soil analysis is crucial for estimating the risk of crop damage by the root-knot nematode Meloidogyne hapla. Here, we developed an analysis assay based on Loop-mediated Isothermal Amplification (LAMP). The LAMP primers were verified for specificity against 10 different nematode species. A manual soil DNA extraction, referred to as SKMM, was developed and compared with a FastDNA kit followed by DNA purification. DNA was extracted with both methods from artificially inoculated soils as well as from naturally infested soil collected from farm fields. The primers exclusively amplified DNA from M. hapla with both colorimetric and real-time LAMP. The detection limit was 193 gene copies and 0.0016 juveniles (12 pg mu L-1) per reaction. DNA concentrations and purity (A(260)/A(230)) were significantly higher using the SKMM procedure compared with the kit. From the field samples collected in 2019, DNA was amplified from 16% of samples extracted with SKMM and from 11% of samples using the kit. Occurrence of M. hapla DNA was confirmed in soil samples from two out of six field soils in 2020 using both real-time LAMP and qPCR. In conclusion, the developed real-time LAMP is a fast and specific assay for detection and quantification of M. hapla DNA in soil

Type of organic fertilizer rather than organic amendment per se increases abundance of soil biota

Addition of organic amendments is a commonly used practice to offset potential loss of soil organic matter from agricultural soils. The aim of the present study was to examine how long-term addition of organic matter affects the abundance of different soil biota across trophic levels and the role that the quality of the organic amendments plays. Here we used a 17-year-old fertilization experiment to investigate soil biota responses to four different organic fertilizers, compared with two mineral nitrogen fertilizers and no fertilization, where the organic fertilizers had similar carbon content but varied in their carbon to nitrogen ratios. We collected soil samples and measured a wide range of organisms belonging to different functional groups and trophic levels of the soil food web. Long-term addition of organic and mineral fertilizers had beneficial effects on the abundances of most soil organisms compared with unfertilized soil, but the responses differed between soil biota. The organic fertilizers generally enhanced bacteria and earthworms. Fungi and nematodes responded positively to certain mineral and organic fertilizers, indicating that multiple factors influenced by the fertilization may affect these heterogeneous groups. Springtails and mites were less affected by fertilization than the other groups, as they were present at relatively high abundances even in the unfertilized treatment. However, soil pH had a great influence on springtail abundance. In summary, the specific fertilizer was more important in determining the numerical and compositional responses of soil biota than whether it was mineral or organic. Overall, biennial organic amendments emerge as insufficient, by themselves, to promote soil organisms in the long run, and would need to be added annually or combined with other practices affecting soil quality, such as no or reduced tillage and other crop rotations, to have a beneficial effect

Additive effect of the root-lesion nematode Pratylenchus penetransand the fungus Rhizoctonia solanion potato yield and damage

The significance of nematodes for disease development caused by other soil-borne pathogens has been demonstrated in many crops throughout the world and specifically prevalent are interactions between plant-parasitic nematodes and species of plant pathogenic fungi. Here, the interaction between the fungusRhizoctonia solani(AG2) and the migratory endoparasitic root-lesion nematodePratylenchus penetranswas investigated on potato. The hypotheses were that the combination ofR. solaniandP. penetranswould result in more severe canker lesions, reduced quality of the tubers and lower tuber yield, and we also expected higher nematode levels to render more nematode damage. To test this, potato plants were grown in pots in two replicate experiments and the presence and/or abundance of the two pathogens were controlled. The first three hypotheses were rejected as (1) the tuber yield decreased when the fungus and nematode occurred together but not more than the sum of their separate effects, i.e. additive, (2) there was no effect of presence of nematodes on the incidence of stem canker, and (3) the quality of tubers was actually partly improved as the presence of the nematodes reduced the likelihood of elephant hide on the tubers in one of the experiments. As expected, there were more visible nematode damages with addition of more nematodes, but beyond that the different nematode levels rendered in most cases similar responses. To have knowledge about interactions between pathogens, as the one showed here, is essential for disease control through appropriate management methods

Core taxa underpin soil microbial community turnover during secondary succession

Understanding the processes that underpin the community assembly of bacteria is a key challenge in microbial ecology. We studied soil bacterial communities across a large-scale successional gradient of managed and abandoned grasslands paired with mature forest sites to disentangle drivers of community turnover and assembly. Diversity partitioning and phylogenetic null-modelling showed that bacterial communities in grasslands remain compositionally stable following abandonment and secondary succession but they differ markedly from fully afforested sites. Zeta diversity analyses revealed the persistence of core microbial taxa that both reflected and differed from whole-scale community turnover patterns. Differences in soil pH and C:N were the main drivers of community turnover between paired grassland and forest sites and the variability of pH within successional stages was a key factor related to the relative dominance of deterministic assembly processes. Our results indicate that grassland microbiomes could be compositionally resilient to abandonment and secondary succession and that the major changes in microbial communities between grasslands and forests occur fairly late in the succession when trees have established as the dominant vegetation. We also show that core taxa may show contrasting responses to management and abandonment in grasslands.Soil microbial communities are compositionally stable across grasslands under secondary succession but differ from paired forest reference sites. Core taxa underpin whole-community turnover patterns, with the underlying assembly processes driven by site-variation in soil pH.imag

Undersowing oats with clovers supports pollinators and suppresses arable weeds without reducing yields

Sustainable food production requires agriculture to conserve biodiversity and facilitate ecosystem services to maintain productivity levels while reducing inputs detrimental to ecosystem functioning. Increasing within-field vegetation diversity by legume intercropping seems promising to facilitate cropping system multi-functionality. Effects of intercropping with legumes on biodiversity-mediated ecosystem services such as pollination or natural pest control are, however, not sufficiently understood. Using 26 observation plots in a paired field design, we studied the effects of undersowing oats with a mixture of three annual clovers across different aspects of cropping system multi-functionality. We investigated 16 below- and above-ground ecosystem service indicators related to soil mineral nitrogen, arable weed control, pollination, disease and pest pressures, natural pest control and crop yield. We found lower arable weed cover, higher flower cover and pollinator densities as well as decreased root-feeding nematode densities in intercropped observation plots compared with the non-intercropped controls. However, intercropping decreased spider activity densities and oat yield nitrogen content. Root diseases, pest damages, natural pest control and crop yield were not affected by intercropping. The biomass of undersown clovers was positively related with the differences in flower cover and pollinator densities, and negatively related with the differences in arable weed cover between the intercropped and the control treatment. Synthesis and applications: We demonstrate that undersowing annual clovers suppresses arable weeds and simultaneously support pollinators without reducing crop yields or taking land out of arable production. Undersown plant mixtures should, however, be tailored to support a wider spectrum of pollinators and benefit natural pest control to support a higher level of overall cropping system multi-functionality

Can field botany be effectively taught as a distance course? Experiences and reflections from the COVID-19 pandemic

The COVID-19 pandemic that started in 2020 forced a rapid change in university teaching, with large numbers of courses switching to distance learning with very little time for preparation. Courses involving many practical elements and field excursions required particular care if students were to fulfil planned learning outcomes. Here, we present our experiences in teaching field botany in 2020 and 2021. Using a range of methods and tools to introduce students to the subject, promote self-learning and reflection and give rapid and regular feedback, we were able to produce a course that allowed students to achieve the intended learning outcomes and that obtained similarly positive student evaluations to previous years. The course and its outcomes were further improved in 2021. We describe how we structured field botany as a distance course in order that we could give the best possible learning experience for the students. Finally, we reflect on how digital tools can aid teaching such subjects in the future, in a world where public knowledge of natural history is declining