Aims Some biogeographical regions act primarily as donors of colonists to other regions, while others act predominantly as recipient areas. How some biotas become dominant while others do not is a largely historical question that has received surprisingly little attention from biogeographers. Here, we seek to answer this question for the cold‐water North Pacific biota, which did not exist forty million years ago but which is now the principal donor biota outside the tropics. Location We focus on the cool‐temperate coastal North Pacific Ocean over the last 36.5 million years. Taxon We consider all multicellular taxa for which adequate fossil, phylogenetic and biogeographical data exist. Methods After placing North Pacific geographical events in the broader context of ocean gateways opening and closing elsewhere in the world, we discuss the history and factors affecting the planktonic and benthic productivity in the North Pacific based on a review and critical evaluation of the literature. A synthesis of primary sources was used to evaluate the origins and fates of North Pacific lineages, with special emphasis on movements to, within and from the North Pacific during the Cenozoic era. Results During the Late Eocene to earliest Miocene, the cooling North Pacific received colonists from adjacent warm‐water regions and the cold Southern Hemisphere, where temperate conditions had existed since at least the Cretaceous. From the Miocene onward, the North Pacific biota began to spread to the Southern Hemisphere and through Bering Strait to the Arctic and North Atlantic Oceans. Within the North Pacific, lineages during the early cooling phases spread predominantly from west to east, but in the Early Middle Miocene this pattern reversed, with later expansions going in both directions. An increase in productivity, powered by the evolution of highly productive seaweeds and by consumers with high metabolic rates, accompanied the transformation of the North Pacific from a recipient to donor biota. Main conclusions The North Pacific replaced the Southern Hemisphere temperate biota as the principal donor biota during the Miocene through a combination of increasing productivity, low magnitudes of extinction and intense competition and predation in an ocean basin with a long coastline.
The factors that control the assembly and composition of endophyte communities across plant hosts remains poorly understood. This is especially true for endophyte communities inhabiting inner tree bark, one of the least studied components of the plant microbiome. Here, we test the hypothesis that bark of different tree species acts as an environmental filter structuring endophyte communities, as well as the alternative hypothesis, that bark acts as a passive reservoir that accumulates a diverse assemblage of spores and latent fungal life stages. We develop a means of extracting high‐quality DNA from surface sterilized tree bark to compile the first culture‐independent study of inner bark fungal communities. We sampled a total of 120 trees, spanning five dominant overstorey species across multiple sites in a mixed temperate hardwood forest. We find that each of the five tree species harbour unique assemblages of inner bark fungi and that angiosperm and gymnosperm hosts harbour significantly different fungal communities. Chemical components of tree bark (pH, total phenolic content) structure some of the differences detected among fungal communities residing in particular tree species. Inner bark fungal communities were highly diverse (mean of 117–171 operational taxonomic units per tree) and dominated by a range of Ascomycete fungi living asymptomatically as putative endophytes. Together, our evidence supports the hypothesis that tree bark acts as an environmental filter structuring inner bark fungal communities. The role of these potentially ubiquitous and plant‐specific fungal communities remains uncertain and merits further study.
Fine root litter is a primary source of soil organic matter (SOM), which is a globally important pool of C that is responsive to climate change. We previously established that ~20 years of experimental nitrogen (N) deposition has slowed fine root decay and increased the storage of soil carbon (C; +18%) across a widespread northern hardwood forest ecosystem. However, the microbial mechanisms that have directly slowed fine root decay are unknown. Here, we show that experimental N deposition has decreased the relative abundance of Agaricales fungi (−31%) and increased that of partially ligninolytic Actinobacteria (+24%) on decaying fine roots. Moreover, experimental N deposition has increased the relative abundance of lignin‐derived compounds residing in SOM (+53%), and this biochemical response is significantly related to shifts in both fungal and bacterial community composition. Specifically, the accumulation of lignin‐derived compounds in SOM is negatively related to the relative abundance of ligninolytic Mycena and Kuehneromyces fungi, and positively related to Microbacteriaceae. Our findings suggest that by altering the composition of microbial communities on decaying fine roots such that their capacity for lignin degradation is reduced, experimental N deposition has slowed fine root litter decay, and increased the contribution of lignin‐derived compounds from fine roots to SOM. The microbial responses we observed may explain widespread findings that anthropogenic N deposition increases soil C storage in terrestrial ecosystems. More broadly, our findings directly link composition to function in soil microbial communities, and implicate compositional shifts in mediating biogeochemical processes of global significance.
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