Cheating belowground interactions : diversity, ecology and distribution of mycoheterotrophy

Mycoheterotrophy is a particular mode of life in which plants obtain carbohydrates from their associated fungal partners, instead of by using photosynthesis. Due to the complexity of mycorrhizal interactions and challenges in assessing the outcomes of this symbiosis, cheating has remained a poorly researched topic in plant ecology. This thesis aimed to shed light on the diversity, ecology and distribution of mycoheterotrophic interactions. In my approach, I considered that different drivers may be important at different scales and studied four levels of ecological complexity. In chapter 2, the specificity of mycoheterotrophic interactions within the arbuscular mycorrhizal symbiosis was assessed at the organism level. In chapter 3, biotic interactions between plants and fungi were studied in the framework of mycoheterotrophic plant coexistence scenarios at the population level. In addition, edaphic abiotic factors potentially influencing the occurrence of mycoheterotrophic plants were assessed at the community level in chapter 4, through a comparison of soil chemistry and nutrients in plots where mycoheterotrophic plants were present with those lacking these plants. Finally, in chapter 5 I derived the global drivers for the distribution of mycoheterotrophy for both the arbuscular and the ectomycorrhizal symbiosis from species occurrence data of these plants. Conservation Biolog

Mycoheterotrophic plants living on arbuscular mycorrhizal fungi are generally enriched in ¹³C, ¹⁵N and ²H isotopes

1. Fully mycoheterotrophic plants are thought to obtain carbon exclusively from their root-associated fungal partners. The general enrichment of these plants in the heavy isotopes 13C and 15N suggests that fungi are the main nutrient source for these plants. Yet, the majority of studies have targeted mycoheterotrophic plants associated with ectomycorrhizal, orchid mycorrhizal and saprotrophic fungi, while mycoheterotrophic plants living on arbuscular mycorrhizal fungi remain understudied. 2. Here, we sampled 13 species of arbuscular mycorrhizal fully mycoheterotrophic plants from five families and co-occurring autotrophic reference plants growing in forests of tropical South America, tropical South East Asia and temperate Australasia. We measured stable isotope natural abundances (δ13C, δ15N, δ2H and δ18O), determined total nitrogen concentrations and used high-throughput DNA sequencing to characterize the arbuscular mycorrhizal fungal communities associated with the sampled mycoheterotrophic plants. 3. We observed a general enrichment in 13C and 15N isotopes across mycoheterotrophic plant families and geographic regions. We confirm cases where no 15N enrichment is present, but we show that in general arbuscular mycoheterotrophic plants are enriched in 15N. Moreover, we demonstrate for the first time that these plants are significantly enriched in 2H but not in 18O in relation to their autotrophic references. The fungal communities targeted by the mycoheterotrophs mainly consist of Glomeraceae and show strong association with the isotopic signatures and geographic origin of the plants. 4. Synthesis. Our findings enlarge the limited knowledge on the multi-element stable isotopic signatures of mycoheterotrophic plants living on arbuscular mycorrhizal fungi. We show that these plants are enriched in 13C and 2H as expected due to their mycoheterotrophic nutrition, and that in general they are also enriched in 15N, despite some exceptions. Variation in stable isotope signatures is likely influenced by plant taxonomy, geography and fungal community composition

Environmental drivers for cheaters of arbuscular mycorrhizal symbiosis in tropical rainforests

Hundreds of nonphotosynthetic mycoheterotrophic plant species cheat the arbuscular mycorrhizal symbiosis. Their patchy local occurrence suggests constraints by biotic and abiotic factors, among which the role of soil chemistry and nutrient status has not been investigated.Here, we examine the edaphic drivers predicting the local‐scale distribution of mycoheterotrophic plants in two lowland rainforests in South America. We compared soil chemistry and nutrient status in plots where mycoheterotrophic plants were present with those without these plants.Soil pH, soil nitrate, and the interaction between soil potassium and nitrate concentrations were the best predictors for the occurrence of mycoheterotrophic plants in these tropical rainforests. Mycoheterotrophic plant occurrences decreased with a rise in each of these predictors. This indicates that these plants are associated with low‐fertility patches. Such low‐fertility conditions coincide with conditions that potentially favour a weak mutualism between plants and arbuscular mycorrhizal fungi according to the trade balance model.Our study points out which soil properties favour the cheating of arbuscular mycorrhizal networks in tropical forests. The patchy occurrence of mycoheterotrophic plants suggests that local soil heterogeneity causes the stability of arbuscular mycorrhizal networks to vary at a very small scale.Environmental Biolog

Microbiota in dung and milk differ between organic and conventional dairy farms

Organic farming is increasingly promoted as a means to reduce the environmental impact of artificial fertilizers, pesticides, herbicides, and antibiotics in conventional dairy systems. These factors potentially affect the microbial communities of the production stages (soil, silage, dung, and milk) of the entire farm cycle. However, understanding whether the microbiota representative of different production stages reflects different agricultural practices - such as conventional versus organic farming - is unknown. Furthermore, the translocation of the microbial community across production stages is scarcely studied. We sequenced the microbial communities of soil, silage, dung, and milk samples from organic and conventional dairy farms in the Netherlands. We found that community structure of soil fungi and bacteria significantly differed among soil types, but not between organic versus conventional farming systems. The microbial communities of silage also did not differ among conventional and organic systems. Nevertheless, the dung microbiota of cows and the fungal communities in the milk were significantly structured by agricultural practice. We conclude that, while the production stages of dairy farms seem to be disconnected in terms of microbial transfer, certain practices specific for each agricultural system, such as the content of diet and the use of antibiotics, are potential drivers of shifts in the cow's microbiota, including the milk produced. This may reflect differences in farm animal health and quality of dairy products depending on farming practices.Environmental Biolog

Bacteriën en schimmels op melkveebedrijf in beeld

Environmental Biolog

Observation of four-top-quark production in the multilepton final state with the ATLAS detector

This paper presents the observation of four-top-quark (tt¯tt¯) production in proton-proton collisions at the LHC. The analysis is performed using an integrated luminosity of 140 fb−1 at a centre-of-mass energy of 13 TeV collected using the ATLAS detector. Events containing two leptons with the same electric charge or at least three leptons (electrons or muons) are selected. Event kinematics are used to separate signal from background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The observed (expected) significance of the measured tt¯tt¯ signal with respect to the standard model (SM) background-only hypothesis is 6.1 (4.3) standard deviations. The tt¯tt¯ production cross section is measured to be 22.5+6.6−5.5 fb, consistent with the SM prediction of 12.0±2.4 fb within 1.8 standard deviations. Data are also used to set limits on the three-top-quark production cross section, being an irreducible background not measured previously, and to constrain the top-Higgs Yukawa coupling and effective field theory operator coefficients that affect tt¯tt¯ production

Search for heavy Majorana or Dirac neutrinos and right-handed W gauge bosons in final states with charged leptons and jets in pp collisions at √s = 13 TeV with the ATLAS detector

A search for heavy right-handed Majorana or Dirac neutrinos NR and heavy right-handed gauge bosons WR is performed in events with energetic electrons or muons, with the same or opposite electric charge, and energetic jets. The search is carried out separately for topologies of clearly separated final-state products (“resolved” channel) and topologies with boosted final states with hadronic and/or leptonic products partially overlapping and reconstructed as a large-radius jet (“boosted” channel). The events are selected from pp collision data at the LHC with an integrated luminosity of 139 fb−1 collected by the ATLAS detector at √s = 13 TeV. No significant deviations from the Standard Model predictions are observed. The results are interpreted within the theoretical framework of a left-right symmetric model, and lower limits are set on masses in the heavy righthanded WR boson and NR plane. The excluded region extends to about m(WR) = 6.4 TeV for both Majorana and Dirac NR neutrinos at m(NR) < 1 TeV. NR with masses of less than 3.5 (3.6) TeV are excluded in the electron (muon) channel at m(WR) = 4.8 TeV for the Majorana neutrinos, and limits of m(NR) up to 3.6 TeV for m(WR) = 5.2 (5.0) TeV in the electron (muon) channel are set for the Dirac neutrinos. These constitute the most stringent exclusion limits to date for the model considered

Software performance of the ATLAS track reconstruction for LHC run 3

Charged particle reconstruction in the presence of many simultaneous proton–proton (pp) collisions in the LHC is a challenging task for the ATLAS experiment’s reconstruction software due to the combinatorial complexity. This paper describes the major changes made to adapt the software to reconstruct high-activity collisions with an average of 50 or more simultaneous pp interactions per bunch crossing (pileup) promptly using the available computing resources. The performance of the key components of the track reconstruction chain and its dependence on pile-up are evaluated, and the improvement achieved compared to the previous software version is quantified. For events with an average of 60 pp collisions per bunch crossing, the updated track reconstruction is twice as fast as the previous version, without significant reduction in reconstruction efficiency and while reducing the rate of combinatorial fake tracks by more than a factor two

Cheating belowground interactions : diversity, ecology and distribution of mycoheterotrophy

Mycoheterotrophy is a particular mode of life in which plants obtain carbohydrates from their associated fungal partners, instead of by using photosynthesis. Due to the complexity of mycorrhizal interactions and challenges in assessing the outcomes of this symbiosis, cheating has remained a poorly researched topic in plant ecology. This thesis aimed to shed light on the diversity, ecology and distribution of mycoheterotrophic interactions. In my approach, I considered that different drivers may be important at different scales and studied four levels of ecological complexity. In chapter 2, the specificity of mycoheterotrophic interactions within the arbuscular mycorrhizal symbiosis was assessed at the organism level. In chapter 3, biotic interactions between plants and fungi were studied in the framework of mycoheterotrophic plant coexistence scenarios at the population level. In addition, edaphic abiotic factors potentially influencing the occurrence of mycoheterotrophic plants were assessed at the community level in chapter 4, through a comparison of soil chemistry and nutrients in plots where mycoheterotrophic plants were present with those lacking these plants. Finally, in chapter 5 I derived the global drivers for the distribution of mycoheterotrophy for both the arbuscular and the ectomycorrhizal symbiosis from species occurrence data of these plants

Cheating belowground interactions : diversity, ecology and distribution of mycoheterotrophy

Mycoheterotrophy is a particular mode of life in which plants obtain carbohydrates from their associated fungal partners, instead of by using photosynthesis. Due to the complexity of mycorrhizal interactions and challenges in assessing the outcomes of this symbiosis, cheating has remained a poorly researched topic in plant ecology. This thesis aimed to shed light on the diversity, ecology and distribution of mycoheterotrophic interactions. In my approach, I considered that different drivers may be important at different scales and studied four levels of ecological complexity. In chapter 2, the specificity of mycoheterotrophic interactions within the arbuscular mycorrhizal symbiosis was assessed at the organism level. In chapter 3, biotic interactions between plants and fungi were studied in the framework of mycoheterotrophic plant coexistence scenarios at the population level. In addition, edaphic abiotic factors potentially influencing the occurrence of mycoheterotrophic plants were assessed at the community level in chapter 4, through a comparison of soil chemistry and nutrients in plots where mycoheterotrophic plants were present with those lacking these plants. Finally, in chapter 5 I derived the global drivers for the distribution of mycoheterotrophy for both the arbuscular and the ectomycorrhizal symbiosis from species occurrence data of these plants. </table