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Carbon-concentrating mechanisms (CCMs) are a widespread phenomenon in photosynthetic organisms. In vascular plants, the evolution of CCMs ([C44-carbon compound] and crassulacean acid metabolism [CAM]) is associated with significant shifts, most often to hot, dry and bright, or aquatic environments. If and how CCMs drive distributions of other terrestrial photosynthetic organisms, remains little studied. Lichens are ecologically important obligate symbioses between fungi and photosynthetic organisms. The primary photosynthetic partner in these symbioses can include CCM-presenting cyanobacteria (as carboxysomes), CCM-presenting green algae (as pyrenoids) or green algae lacking any CCM. We use an extensive dataset of lichen communities from eastern North America, spanning a wide climatic range, to test the importance of CCMs as predictors of lichen ecology and distribution. We show that the presence or absence of CCMs leads to opposite responses to temperature and precipitation in green algal lichens, and different responses in cyanobacterial lichens. These responses contrast with our understanding of lichen physiology, whereby CCMs mitigate carbon limitation by water saturation at the cost of efficient use of vapor hydration. This study demonstrates that CCM status is a key functional trait in obligate lichen symbioses, equivalent in importance to its role in vascular plants, and central for studying present and future climate responses., (© 2023 The Authors. Ecology published by Wiley Periodicals LLC on behalf of The Ecological Society of America.)

Lichens are the symbiotic outcomes of open, interspecies relationships, central to which are a fungus and a phototroph, typically an alga and/or cyanobacterium. The evolutionary processes that led to the global success of lichens are poorly understood. In this review, we explore the goods and services exchange between fungus and phototroph and how this propelled the success of both symbiont and symbiosis. Lichen fungal symbionts count among the only filamentous fungi that expose most of their mycelium to an aerial environment. Phototrophs export carbohydrates to the fungus, which converts them to specific polyols. Experimental evidence suggests that polyols are not only growth and respiratory substrates but also play a role in anhydrobiosis, the capacity to survive desiccation. We propose that this dual functionality is pivotal to the evolution of fungal symbionts, enabling persistence in environments otherwise hostile to fungi while simultaneously imposing costs on growth. Phototrophs, in turn, benefit from fungal protection from herbivory and light stress, while appearing to exert leverage over fungal sex and morphogenesis. Combined with the recently recognized habit of symbionts to occur in multiple symbioses, this creates the conditions for a multiplayer marketplace of rewards and penalties that could drive symbiont selection and lichen diversification., (© 2022 The Authors. New Phytologist © 2022 New Phytologist Foundation.)

Despite their ecological significance, non‐vascular photoautotrophs (NVPs) are frequently excluded from ecological experimental studies, leading to a limited comprehension of how their communities are affected by the ecosystem dynamics and an underestimation of their role in ecosystem functioning. We studied the impact of vascular plant taxonomic and functional diversity on three groups of ground NVPs (lichens, bryophytes, and cyanobacteria) within one of the longest‐running plant biodiversity experiments (Biodiversity and Ecosystem Function at Cedar Creek Ecosystem Science Reserve). Utilizing the permanent plot framework of this experiment, we analyzed the effects of almost 30 years of treatment across various levels of vascular plant taxonomic and functional diversity on NVPs. For each diversity level we documented NVP cover and richness. Using generalized linear models we evaluated the effect of vascular plant taxonomic and functional diversity, as well as environmental factors affected by vascular diversity (such as vascular plant cover, light penetration, soil nutrient content, and microtopography) on NVP richness and cover. Using these models, we conducted structural equation modeling analyses (SEM) that allowed us to differentiate the direct and indirect impacts of vascular plant taxonomic and functional diversity on NVPs. Our results showed that both lichen and bryophyte richness and cover decreased with higher vascular plant taxonomic and functional diversity, while cyanobacteria cover increased as a function of the same parameters. We also showed that microtopography serves as better predictor for lichens and bryophytes, while nutrient‐related factors perform better as predictors for cyanobacteria. Additionally, our findings indicate that NVP cover ranged from 0.001% to 100% (mean 15%) in the surveyed plots, representing a major, still ignored, component of the experimental plots. This study shows that vascular plant diversity directly and indirectly affects NVP communities, but the consequences of these effects at community and ecosystem levels are still to be explored. [ABSTRACT FROM AUTHOR]

Biological nitrogen fixation is critical for the nitrogen cycle of tropical forests, yet we know little about the factors that control the microbial nitrogen fixers that colonize the microbiome of leaves and branches that make up a forest canopy. Forest canopies are especially prone to nutrient limitation because they are (1) disconnected from soil nutrient pools and (2) often subject to leaching. Earlier studies have suggested a role of phosphorus and molybdenum in controlling biological N‐fixation rates, but experimental confirmation has hitherto been unavailable. Here we present the results of a manipulation of canopy nutrient availability. Our findings demonstrate a primary role of phosphorus in constraining overall N fixation by canopy cyanobacteria, but also a secondary role of molybdenum in determining per‐cell fixation rates. A conservative evaluation suggests that canopy fixation can contribute to significant N fluxes at the ecosystem level, especially as bursts following atmospheric inputs of nutrient‐rich dust. [ABSTRACT FROM AUTHOR]