Vertical distribution of arbuscular mycorrhizal fungi in agricultural soil

The major aims of this thesis were to describe how arbuscular mycorrhizal (AM) fungal communities vary with depth in agricultural land, and to gain insights into AM fungal community assemblage processes in subsoil. In chapter 1 I introduce basic aspects of AM fungal biology, review existing literature on the topic of this thesis and introduce the molecular methodology used in my studies. Chapter 2 and its appendices provide highthroughput sequencing evidence for the differences in AM fungal community composition in top- and subsoil, such as for the existence of phylotypes exclusively found in subsoil. As compared to topsoil, studied subsoil communities are less species rich, less even and have higher community turnover. However, they are not just a subset of topsoil communities and harbor unique taxa. In chapter 3 a top- subsoil mixing event is studied to trace the fate of subsoil phylotypes in topsoil. Here we observe the inability of these subsoil phylotypes to persist in topsoil, and interpret this as evidence for subsoil specialization in certain AM fungal taxa. Chapter 4 discusses the potential roles of subsoil AM fungi in agriculture, with a focus on sustainability and climate smart approaches. The major potential roles identified concern the access to greater nutrient and water pools, the resistance of the system to unfavorable conditions in topsoil, and the avoidance of nutrient leaching and greenhouse gas emissions. We also point out future research needs in this field. Chapter 5 puts the results of this thesis in the broader context of the literature, summarizing the conclusions 97 of previous chapters. In this chapter I also introduce ideas on AM fungal growth strategies and implications of subsoil AM fungi for the understanding of AM fungal biogeography

Evidence for Subsoil Specialization in Arbuscular Mycorrhizal Fungi

Arbuscular mycorrhizal (AM) fungal communities are now known to vary with depth in arable land. Here we use two previously published high-throughput Illumina sequencing data sets, and compare a 52 year long chronosequence of recultivated agriculture fields after a topsoil and subsoil mixing event, with a set of undisturbed topsoil and subsoil samples from a similar field. We show that AM taxa identified as subsoil indicators are exclusively present in early stages of the chronosequence, whereas topsoil indicator taxa can be found across the chronosequence, and that similarities from the chronosequence fields to the subsoil communities decrease with time. Our results provide evidence on the ecological specialization of certain AM fungal taxa to deep soil layers

Subsoil Arbuscular Mycorrhizal Fungi for Sustainability and Climate-Smart Agriculture: A Solution Right Under Our Feet?

With growing populations and climate change, assuring food and nutrition security is an increasingly challenging task. Climate-smart and sustainable agriculture, that is, conceiving agriculture to be resistant and resilient to a changing climate while keeping it viable in the long term, is probably the best solution. The role of soil biota and particularly arbuscular mycorrhizal (AM) fungi in this new agriculture is believed to be of paramount importance. However, the large nutrient pools and the microbiota of subsoils are rarely considered in the equation. Here we explore the potential contributions of subsoil AM fungi to a reduced and more efficient fertilization, carbon sequestration, and reduction of greenhouse gas emissions in agriculture. We discuss the use of crop rotations and cover cropping with deep rooting mycorrhizal plants, and low-disturbance management, as means of fostering subsoil AM communities. Finally, we suggest future research goals that would allow us to maximize these benefits

a solution right under our feet?

With growing populations and climate change, assuring food and nutrition security is an increasingly challenging task. Climate smart and sustainable agriculture, that is, conceiving agriculture to be resistant and resilient to a changing climate while keeping it viable in the long term, is probably the best solution. The role of soil biota and particularly arbuscular mycorrhizal (AM) fungi in this new agriculture is believed to be of paramount importance. However, the large nutrient pools and the microbiota of subsoils are rarely considered in the equation. Here we explore the potential contributions of subsoil AM fungi to this agriculture and suggest future research goals that would allow us to maximize their benefits

Subsoil Arbuscular Mycorrhizal Fungi for Sustainability and Climate-Smart Agriculture: A Solution Right Under Our Feet?

With growing populations and climate change, assuring food and nutrition security is an increasingly challenging task. Climate-smart and sustainable agriculture, that is, conceiving agriculture to be resistant and resilient to a changing climate while keeping it viable in the long term, is probably the best solution. The role of soil biota and particularly arbuscular mycorrhizal (AM) fungi in this new agriculture is believed to be of paramount importance. However, the large nutrient pools and the microbiota of subsoils are rarely considered in the equation. Here we explore the potential contributions of subsoil AM fungi to a reduced and more efficient fertilization, carbon sequestration, and reduction of greenhouse gas emissions in agriculture. We discuss the use of crop rotations and cover cropping with deep rooting mycorrhizal plants, and low-disturbance management, as means of fostering subsoil AM communities. Finally, we suggest future research goals that would allow us to maximize these benefits

Towards an integrated mycorrhizal technology: harnessing mycorrhizae for sustainable intensification in agriculture

Sustainability in Agriculture In order to meet future needs of a growing human population and to achieve food security in the context of climate change, food production will likely need to increase—among other measures—while at the same time minimizing negative environmental impact (Foley et al., 2011). Sustainable intensification of agriculture (Garnett et al., 2013; Pretty and Bharucha, 2014; Andres and Bhullar, 2016; Gunton et al., 2016), sometimes also called ecological intensification, is likely to include key aspects of conservation agriculture (e.g., Hobbs et al., 2008; Giller et al., 2015). Pillars of conservation agriculture (FAO, 2015) are no-till practices (Pittelkow et al., 2015), continuous crop cover (by various means, for example cover crops) and diversification practices (multi-cropping and crop rotations; Ponisio et al., 2015)

The relative importance of ecological drivers of arbuscularmycorrhizal fungal distribution varies with taxon phylogeneticresolution

The phylogenetic depth at which arbuscular mycorrhizal (AM) fungi harbor a coherent eco-logical niche is unknown, which has consequences for operational taxonomic unit (OTU)delineation from sequence data and the study of their biogeography. We tested how changes in AM fungi community composition across habitats (beta diver-sity) vary with OTU phylogenetic resolution. We inferred exact sequence variants (ESVs) toresolve phylotypes at resolutions finer than provided by traditional sequence clustering andanalyzed beta diversity profiles up to order-level sequence clusters. At the ESV level, we detected the environmental predictors revealed with traditional OTUsor at higher genetic distances. However, the correlation between environmental predictorsand community turnover steeply increased at a genetic distance ofc. 0.03 substitutions persite. Furthermore, we observed a turnover of either closely or distantly related taxa (respec-tively at or above 0.03 substitutions per site) along different environmental gradients. This study suggests that different axes of AM fungal ecological niche are conserved at dif-ferent phylogenetic depths. Delineating AM fungal phylotypes using DNA sequences shouldscreen different phylogenetic resolutions to better elucidate the factors that shape communi-ties and predict the fate of AM symbioses in a changing environment

Soil Saprobic Fungi Differ in Their Response to Gradually and Abruptly Delivered Copper

The overwhelming majority of studies examining environmental change deliver treatments abruptly, although, in fact, many important changes are gradual. One example of a gradually increasing environmental stressor is heavy metal contamination. Essential heavy metals, such as copper, play an important role within cells of living organisms but are toxic at higher concentrations. In our study, we focus on the effects of copper pollution on filamentous soil fungi, key players in terrestrial ecosystem functioning. We hypothesize that fungi exposed to gradually increasing copper concentrations have higher chances for physiological acclimation and will maintain biomass production and accumulate less copper, compared to fungi abruptly exposed to the highest copper concentration. To test this hypothesis, we conducted an experiment with 17 fungal isolates exposed to gradual and abrupt copper addition. Contrary to our hypothesis, we find diverse idiosyncratic responses, such that for many fungi gradually increasing copper concentrations have more severe effects (stronger growth inhibition and higher copper accumulation) than an abrupt increase. While a number of environmental change studies have accumulated evidence based on the magnitude of changes, the results of our study imply that the rate of change can be an important factor to consider in future studies in ecology, environmental science, and environmental management

Search for new particles in events with energetic jets and large missing transverse momentum in proton-proton collisions at root s=13 TeV

A search is presented for new particles produced at the LHC in proton-proton collisions at root s = 13 TeV, using events with energetic jets and large missing transverse momentum. The analysis is based on a data sample corresponding to an integrated luminosity of 101 fb(-1), collected in 2017-2018 with the CMS detector. Machine learning techniques are used to define separate categories for events with narrow jets from initial-state radiation and events with large-radius jets consistent with a hadronic decay of a W or Z boson. A statistical combination is made with an earlier search based on a data sample of 36 fb(-1), collected in 2016. No significant excess of events is observed with respect to the standard model background expectation determined from control samples in data. The results are interpreted in terms of limits on the branching fraction of an invisible decay of the Higgs boson, as well as constraints on simplified models of dark matter, on first-generation scalar leptoquarks decaying to quarks and neutrinos, and on models with large extra dimensions. Several of the new limits, specifically for spin-1 dark matter mediators, pseudoscalar mediators, colored mediators, and leptoquarks, are the most restrictive to date.Peer reviewe