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The earth laughs in flowers...

Ralph Waldo Emerson

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Experimental evidence of the importance of multitrophic structure for species persistence 

Bartomeus et al.,  2021.

Significance

It has been unclear whether understanding how biodiversity is maintained requires us to study species interactions within and across trophic levels simultaneously. Achieving this task remains, however, challenging for practical and theoretical reasons. Here, integrating a simple but detailed experimental plant–pollinator community and a tractable mathematical framework, we show that biodiversity is strongly affected by species competitive interactions among plants and among pollinators, as well as the mutualistic effects between pollinators on plants. Furthermore, we show that experimentally preventing some species to interact can modify the rest of the interactions and affect idiosyncratically the probability of species persistence. These effects are only observable within the empirical evaluation and not with traditional simulation approaches.

 

Abstract

Ecological theory predicts that species interactions embedded in multitrophic networks shape the opportunities for species to persist. However, the lack of experimental support of this prediction has limited our understanding of how species interactions occurring within and across trophic levels simultaneously regulate the maintenance of biodiversity. Here, we integrate a mathematical approach and detailed experiments in plant–pollinator communities to demonstrate the need to jointly account for species interactions within and across trophic levels when estimating the ability of species to persist. Within the plant trophic level, we show that the persistence probability of plant species increases when introducing the effects of plant–pollinator interactions. Across trophic levels, we show that the persistence probabilities of both plants and pollinators exhibit idiosyncratic changes when experimentally manipulating the multitrophic structure. Importantly, these idiosyncratic effects are not recovered by traditional simulations. Our work provides tractable experimental and theoretical platforms upon which it is possible to investigate the multitrophic factors affecting species persistence in ecological communities.

Scheme of the two network topologies empirically evaluated. The community consisted of three plants (radish: R. raphinastrum, tomato: S. lycopersicon, field bean: V. fava) and three pollinators (bumblebees: B. terrestris, mason bees: O. bicornis, green bottle flies: L. sericata). This figure portrays the number of visits recorded as links (the thickness of the line is proportional to the link strength, i.e., number of pollinator visits) and the observed reproductive success (proportional to circle sizes). For our studied community, we constructed two network topologies of species interactions. (A) A fully nested interaction network. (B) The topology when the interaction between bumblebee and radish is experimentally prevented from the fully nested topology. Note that the thickness of links and size of nodes are different between the two topologies due to the manipulation and subsequent reorganization of the rest of the interaction strengths.

 

Effects of multitrophic structure within a trophic level. (A–C) A graphical representation of the community structure within the trophic level formed by plants in each of the empirical scenarios investigated: plants with no pollinators, plants with pollinators, and plants with pollinators with the bumblebee–radish interaction experimentally prevented. In the illustration, plants’ intrinsic growth rates are proportional to circle size and the strength of their interactions is proportional to thickness of arrows. Solid and dashed lines imply negative and positive interactions, respectively. (D–F) The simplex representation of the feasibility domain (the sum of intrinsic growth rates is normalized to one). The size of the feasibility domain (colored area) corresponds to the fraction of directions of intrinsic growth rates compatible with the persistence of the three species. Note that the feasibility domain is a function of the species interactions (shown in A). The solid dot corresponds to the direction of the vector of the observed intrinsic growth rates (also shown in A). Note that this simplex is the normalized projection in an n−1 dimensional space of the original parameter space of intrinsic growth rates. Each vertex then represents a basis vector of this parameter space, that is (1,0,0),(0,1,0){1,0,0} or (0,0,1){0,0,1}. Consequently, each vertex represents the position where one species in particular dominates the entire parameter space.

https://www.pnas.org/content/118/12/e2023872118

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  With organic food you skip over 700 chemical!!!

How much of global greenhouse gas emissions come from food? 

Hannah Ritchie, 2021.

There are a wide range of estimates for how much of the world’s total greenhouse gas emissions come from food. Some studies say this figure is one-quarter, some say it’s more than one-third.

Where do these differences come from? There are three reasons why some of these estimates vary so much:

1) some studies do not include emissions from cooking and food waste;

2) different studies disagree about the emissions from land use change and deforestation; 

3) some, but not all, studies include non-food agricultural products such as cotton, wool, leather and biofuels

The specific number that answers this question depends on these three factors, but the range of possible answers is not too large: around 25% to 30% of global emissions come from our food systems, and this rises to around one-third when we include all agricultural products.

 

https://ourworldindata.org/greenhouse-gas-emissions-food

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Plant evolution driven by interactions with symbiotic and pathogenic microbes     

Pierre-Marc Delaux, Sebastian Schornack, 2021

BACKGROUND

Microbial interactions have shaped plant diversity in terrestrial ecosystems. By forming mutually beneficial symbioses, microbes helped plants colonize land more than 450 million years ago. In parallel, omnipresent pathogens led to the emergence of innovative defense strategies. The evolution of plant-microbe interactions encompasses ancient conserved gene modules, recurrent concepts, and the fast-paced emergence of lineage-specific innovations. Microbes form communities on the surface or inside plant tissues and organs, and most intimately, microbes live within single plant cells. Intracellular colonization is established and controlled in part by plant genes that underpin general cell processes and defense mechanisms. To benefit from microbes, plants also evolved genetic modules for symbiosis support. These modules have been maintained despite the risk of getting hijacked by pathogens.

ADVANCES

The hundreds of land plant and algal genomes that are now available enable genome-wide comparisons of gene families associated with plant immunity and symbiosis. Reconstruction of gene phylogenies and large-scale comparative phylogenomic approaches have revealed an ancient subset of genes coevolving with the widespread arbuscular mycorrhiza symbiosis, the most ancient plant intracellular symbiosis, and with other types of more recently evolved intracellular symbioses in vascular and nonvascular plants. Intercellular symbiotic interactions formed with cyanobacteria or ectomycorrhizal fungi seem to repeatedly evolve through convergent, but not necessarily genetically conserved, mechanisms. Phylogenetic analyses revealed occurrence of candidate disease-resistance genes in green algae, as well as orthologs of flowering plant genes involved in symbiosis signaling and sensing microbial patterns. Yet, more research is needed to understand their functional conservation.

The extent to which conserved symbiosis genes also fulfill often opposing roles during pathogen-plant interactions is being explored through studies of pathogen infections in plants capable of supporting symbiotic relationships. The development of plant-microbe systems in genetically tractable species covering the diversity of land plant lineages—including angiosperms and bryophytes, such as the liverwort Marchantia polymorpha—makes it possible to test hypotheses that emerge from phylogenetic analyses, linking genetic and functional conservation across land plants. Studies in bryophytes illustrate the range of possibilities for pathogen management: ancient genes, such as membrane receptors that perceive fungus-derived chitin; pathways with bryophyte clade–specific components, such as phenylpropanoid-derived auronidin stress metabolites; and jasmonate-like hormonal signaling for immunity.

OUTLOOK

Only a few plant-microbe interactions have been studied in depth, and those in only a few land plant lineages. Future investigations of interactions occurring across the diversity of plants may unravel new types of symbiotic or pathogenic interactions. The occurrence of microbe-sensing genes in streptophyte algae, harboring the closest algal relative to land plants, suggest the existence of overlooked and potentially ancient symbiotic associations. Genetically tractable plant-microbe model systems in diverse streptophyte algae, hornworts, liverworts, ferns, and the so far unsampled diversity of seed plants will enable dissection of the spectrum of molecular mechanisms that regulate the breadth of interactions occurring in plants. The actual function of the symbiotic genes present in bryophyte genomes also remains to be determined. Furthermore, our understanding of plant-microbe interactions will be enriched by more often combining evolutionary concepts with mechanistic studies. More efforts are needed to decipher the molecular changes that have enabled the emergence of new interactions, signaling pathways, and enzymatic specificities to support symbiosis and to protect against pathogens. Microbes manipulate plant processes, and complementary microbial studies are key to gaining a complete picture of plant-microbe evolution. Knowing the rules of engagement between distantly related plants and their microbes then helps genetic transplantation approaches into crops and the orthogonal engineering of bioprocesses aimed at achieving quantitative resistance against pathogens, improving phosphate uptake, or establishing nitrogen-fixing associations for efficient use in sustainable agriculture.

Ancient friends and recent enemies shape plant evolution.Some pathogens such as oomycetes are able to infect a wide range of extant plant lineages, including bryophytes (left), and plant pathogen interactions often evolve at a fast pace. By contrast, some symbiotic interactions that look exactly as they do today can be found in the most ancient land plant fossils, here depicted as an illustration of the Rhynie chert fossil plant Aglaophyton major (right). Still, both types of plant-microbe interactions feature evolutionarily ancient as well as rapidly evolving aspects. Extending plant-microbe studies across diverse groups of plant lineages has enriched our understanding of these processes and their evolution.

 

https://bit.ly/3s0JEsi

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Facing the Anthropocene Series: A Conversation with Timothy Ingold

Plant carbohydrate depletion impairs water relations and spreads via ectomycorrhizal networks 

Sapes et al., 2021

• Under prolonged drought and reduced photosynthesis, plants consume stored nonstructural carbohydrates (NSCs). Stored NSC depletion may impair the regulation of plant water balance, but the underlying mechanisms are poorly understood, and whether such mechanisms are independent of plant water deficit is not known. If so, carbon costs of fungal symbionts could indirectly influence plant drought tolerance through stored NSC depletion.
• We connected well‐watered Pinus ponderosa seedling pairs via ectomycorrhizal (EM) networks where one seedling was shaded (D) and the other kept illuminated (LD) and compared responses to seedling pairs in full light (L). We measured plant NSCs, osmotic and water potential, and transfer of ¹³CO₂ through EM to explore mechanisms linking stored NSCs to plant water balance regulation and identify potential tradeoffs between plant water retention and EM fungi under carbon‐limiting conditions.
• NSCs decreased from L to LD to D seedlings. Even without drought, NSC depletion impaired osmoregulation and turgor maintenance, both of which are critical for drought tolerance. Importantly, EM networks propagated NSC depletion and its negative effects on water retention from carbon stressed to nonstressed hosts.
• We demonstrate that NSC storage depletion influences turgor maintenance independently of plant water deficit and reveal carbon allocation tradeoffs between supporting fungal symbionts and retaining water.
  

https://bit.ly/3s7Slky

Video: 

 

Impact of what we eat on land use

 

https://bit.ly/3rh6EDC

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Maintaining symbiotic homeostasis: how do plants engage with beneficial microorganisms while at the same time restricting pathogens?  

Thoms et al., 2021

That plants recruit beneficial microbes while simultaneously restricting pathogens is critical to their survival. Plants must exclude pathogens; however, the majority of land plants are able to form mutualistic symbioses with arbuscular mycorrhizal fungi. Plants also associate with the complex microbial communities that form the microbiome. The outcome of each symbiotic interaction—whether a specific microbe is pathogenic, commensal or mutualistic—relies on the specific interplay of host and microbial genetics and the environment. Here, we discuss how plants use metabolites as a gate to select which microbes can be symbiotic. Once present, we discuss how plants integrate multiple inputs to initiate programs of immunity or mutualistic symbiosis, and how this paradigm may be expanded to the microbiome. Finally, we discuss how environmental signals are integrated with immunity to fine tune a thermostat that determines whether a plant engages in mutualism, resistance to pathogens, and shapes associations with the microbiome. Collectively, we propose that the plant immune thermostat is set to select for and tolerate a largely non-harmful microbiome while receptor-mediated decision making allows plants to detect and dynamically respond to the presence of potential pathogens or mutualists. 

 

This review discusses three principles by which plants may select for or restrict potential mutualists or pathogens. (A) Plants use selective metabolites (purple) to recruit or select for beneficial microbes (blue) and select against pathogens (gray). (B) Dual receptor recognition allows for precisely distinguishing potential pathogens or mutualists prior to energy investment in an immune or symbiotic response. MAMPs are common between pathogens and mutualists and so are not sufficient for a plant to  determine wither a microbe is friend or foe; however, MAMPs can provide information about the identity of a microbe. Coupling perception of MAMPs with LCOs, effectors, or DAMPs has the potential to trigger a strong and specific immunity or symbiotic program. (C) Integration of intrinsic and extrinsic signals with immune homeostasis allows plants to fine-tune decision making in symbiosis and dynamically shape symbiotic interactions over a plant’s life. This may allow for fine-tuning of microbiome community structure as well as changing a threshold for  strong immunity and symbiosis responses. 

 

To decide whether to engage in immunity or symbiosis, a plant must identify the type of microbe it is interacting with, and whether that microbe is mutualistic or pathogenic. Robust activation of a specific pathway depends on the combined input of MAMPs and one or more lifestyle associated factor [e.g. DAMPs/effectors/lipochitooligosaccharides (LCOs)]. In this example, chitin informs the plant that the symbiont is a fungus, and LCOs or effectors inform the plant whether it is a mutualist (blue components/arrows) or pathogenic (red components/arrows). The central boxes represent basal immunity pathways and common symbiotic pathways, which include the respective signaling cascades, post-translational modifications, and gene induction required for initiation of an immune or mutualistic response. At the bottom are the microbe-specific responses for resistance against or mutualism with a specific type of microbe. Activated pathways are indicated by white boxes and inactive pathwaysare shown in grey. Dotted lines indicate weak signaling and activation, while solid lines reflect stronger interactions. Wide arrows represent either a synergistic or additive response.

https://bit.ly/3d9bvSO

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