High latitude vegetation changes will determine future plant volatile impacts on atmospheric organic aerosols

Strong, ongoing high latitude-warming is causing changes to vegetation composition and plant productivity, modifying plant emissions of Biogenic Volatile Organic Compounds (BVOCs). In the sparsely populated high latitudes, climatic feedbacks resulting from BVOCs as precursors of atmospheric aerosols could be more important than elsewhere on the globe. Here, we quantitatively assess the linkages between vegetation changes, BVOC emissions and secondary organic aerosol (SOA) under different climate scenarios and show that warming-induced vegetation changes determine the spatial patterns of BVOC impacts on SOA. The northward advances of boreal needle-leaved trees and shrubs result in an increase of up to 45% in regional SOA optical depth, causing a cooling feedback. In contrast, areas dominated by temperate broad-leaved trees show a large decline in monoterpene emissions and SOA formation, causing a warming feedback. We highlight the necessity of considering vegetation shifts when assessing radiative feedbacks on climate following the BVOC-SOA pathway.

Plant organic matter inputs exert a strong control on soil organic matter decomposition in a thawing permafrost peatland

Peatlands are a climate critical carbon (C) reservoir that will likely become a C source under continued warming. A strong relationship between plant tissue chemistry and the soil organic matter (SOM) that fuels C gas emissions is inferred, but rarely examined at the molecular level. Here we compared Fourier transform infrared (FT-IR) spectroscopy measurements of solid phase functionalities in plants and SOM to ultra-high-resolution mass spectrometric analyses of plant and SOM water extracts across a palsa-bog-fen thaw and moisture gradient in an Arctic peatland. From these analyses we calculated the C oxidation state (NOSC), a measure which can be used to assess organic matter quality. Palsa plant extracts had the highest NOSC, indicating high quality, while extracts of Sphagnum, which dominated the bog, had the lowest NOSC. The percentage of plant compounds that are less bioavailable and accumulate in the peat, increases from palsa (25%) to fen (41%) to bog (47 %), reflecting the pattern of percent Sphagnum cover. The pattern of NOSC in the plant extracts was consistent with the high number of consumed compounds in the palsa and low number of consumed compounds in the bog. However, in the FT-IR analysis of the solid phase bog peat, carbohydrate content was high implying higher quality SOM. We explain this discrepancy as the result of low solubilization of bog SOM facilitated by the low pH in the bog which makes the solid phase carbohydrates less available to microbial decomposition. Plant-associated lignins and tannins declined in the unsaturated palsa peat indicating decomposition, but accumulated in the bog and fen peat where decomposition was presumably inhibited by the anaerobic conditions. A molecular-level comparison of the aboveground C sources and peat SOM demonstrates that climate-associated vegetation shifts in peatlands are important controls on the mechanisms underlying changing C gas emissions.

Vegetation structure determines cyanobacterial communities during soil development across global biomes

Soil cyanobacteria play essential ecological roles and are known to experience large changes in their diversity and abundance throughout early succession. However, much less is known about how and why soil cyanobacterial communities change as soil develops from centuries to millennia, and the effects of aboveground vegetation on these communities. We combined an extensive field survey including 16 global soil chronosequences across contrasting ecosystems (from deserts to tropical forests) with molecular analyses to investigate how the diversity and abundance of soil cyanobacteria under vegetation change during soil development from hundreds to thousands of years. We show that, in most chronosequences, the abundance, species richness and community composition of soil cyanobacteria were relatively stable as soil develops (from centuries to millennia). Regardless of soil age, forest chronosequences were consistently dominated by non-photosynthetic cyanobacteria (Vampirovibrionia), while grasslands and shrublands were dominated by photosynthetic cyanobacteria. Chronosequences undergoing drastic vegetation shifts during soil development (e.g. transitions from grasslands to forests) experienced significant changes in the composition of soil cyanobacteria communities. Our results advance our understanding of the ecology of cyanobacterial classes, specially the understudied non-photosynthetic ones and highlight the key role of vegetation as a major driver of their temporal dynamics as soil develops.

Functionally explicit partitioning of plant β-diversity reveal soil fungal assembly in the subarctic tundra

ABSTRACT Metabarcoding technologies for soil fungal DNA pools have enabled to capture the diversity of fungal community and the agreement of their β-diversity with plant β-diversity. However, processes underlying the synchrony of the aboveground–belowground biodiversity is still unclear. By using partitioning methods for plant β-diversity, this study explored the process driving synchrony in tundra ecosystems, in which drastic vegetation shifts are observed with climate warming. Our methods based on Baselga's partitioning enabled the division of plant β-diversity into two phenomena and three functional components. Correlation of fungal β-diversity with the components of plant β-diversity showed that the spatial replacement of fungi was promoted by plant species turnover, in particular, plant species turnover with functional exchange. In addition, spatial variety of graminoid or forbs species, rather than shrubs, enhanced fungal β-diversity. These results suggest the importance of small-scale factors such as plant–fungal interactions or local environments modified by plants for the fungal community assemblage. The process-based understanding of community dynamics of plants and fungi allows us to predict the ongoing shrub encroachment in the Arctic region, which could weaken the aboveground–belowground synchrony.

Microbial Substrate Utilization and Vegetation Shifts in Boreal Forest Floors of Western Canada

Boreal forest soils are highly susceptible to global warming, and in the next few decades, are expected to face large increases in temperature and transformative vegetation shifts. The entire boreal biome will migrate northward, and within the main boreal forest of Western Canada, deciduous trees will replace conifers. The main objective of our research was to assess how these vegetation shifts will affect functioning of soil microbial communities and ultimately the overall persistence of boreal soil carbon. In this study, aspen and spruce forest floors from the boreal mixedwood forest of Alberta were incubated in the laboratory for 67 days without (control) and with the addition of three distinct 13C labeled substrates (glucose, aspen leaves, and aspen roots). Our first objective was to compare aspen and spruce substrate utilization efficiency (SUE) in the case of a labile C source (13C-glucose). For our second objective, addition of aspen litter to spruce forest floor mimicked future vegetation shifts, and we tested how this would alter substrate use efficiency in the spruce forest floor compared to the aspen. Tracking of carbon utilization by microbial communities was accomplished using 13C-PLFA analysis, and 13C-CO2 measurements allowed quantification of the relative contribution of each added substrate to microbial respiration. Following glucose addition, the aspen community showed a greater 13C-PLFA enrichment than the spruce throughout the 67-day incubation. The spruce community respired a greater amount of 13C glucose, and it also had a much lower glucose utilization efficiency compared to the aspen. Following addition of aspen litter, in particular aspen leaves, the aspen community originally showed greater total 13C-PLFA enrichment, although gram positive phospholipid fatty acids (PLFAs) were significantly more enriched in the spruce community. While the spruce community respired a greater amount of the added 13C-leaves, both forest floor types showed comparable substrate utilization efficiencies by Day 67. These results indicate that a shift from spruce to aspen may lead to a greater loss of the aspen litter through microbial respiration, but that incorporation into microbial biomass and eventually into the more persistent soil carbon pool may not be affected.

Snakes on an African plain: the radiation of Crotaphopeltis and Philothamnus into open habitat (Serpentes: Colubridae)

Background The African continent is comprised of several different biomes, although savanna is the most prevalent. The current heterogeneous landscape was formed through long-term vegetation shifts as a result of the global cooling trend since the Oligocene epoch. The overwhelming trend was a shift from primarily forest, to primarily savanna. As such, faunal groups that emerged during the Paleogene/Neogene period and have species distributed in both forest and savanna habitat should show a genetic signature of the possible evolutionary impact of these biome developments. Crotaphopeltis and Philothamnus (Colubridae) are excellent taxa to investigate the evolutionary impact of these biome developments on widespread African colubrid snakes, and whether timing and patterns of radiation are synchronous with biome reorganisation. Methods A phylogenetic framework was used to investigate timing of lineage diversification. Phylogenetic analysis included both genera as well as other Colubridae to construct a temporal framework in order to estimate radiation times for Crotaphopeltis and Philothamnus. Lineage diversification was estimated in Bayesian Evolutionary Analysis Sampling Trees (BEAST), using two mitochondrial markers (cyt–b, ND4), one nuclear marker (c–mos), and incorporating one fossil and two biogeographical calibration points. Vegetation layers were used to classify and confirm species association with broad biome types (‘closed’ = forest, ‘open’ = savanna/other), and the ancestral habitat state for each genus was estimated. Results Philothamnus showed an ancestral state of closed habitat, but the ancestral habitat type for Crotaphopeltis was equivocal. Both genera showed similar timing of lineage diversification diverging from their sister genera during the Oligocene/Miocene transition (ca. 25 Mya), with subsequent species radiation in the Mid-Miocene. Philothamnus appeared to have undergone allopatric speciation during Mid-Miocene forest fragmentation. Habitat generalist and open habitat specialist species emerged as savanna became more prevalent, while at least two forest associated lineages within Crotaphopeltis moved into Afromontane forest habitat secondarily and independently. Discussion With similar diversification times, but contrasting ancestral habitat reconstructions, we show that these genera have responded very differently to the same broad biome shifts. Differences in biogeographical patterns for the two African colubrid genera is likely an effect of distinct life-history traits, such as the arboreous habits of Philothamnus compared to the terrestrial lifestyle of Crotaphopeltis.

Congruent evolutionary responses of European steppe biota to late Quaternary climate change: insights from convolutional neural network based demographic modeling

Quaternary climatic oscillations had a large impact on European biogeography. Alternation of cold and warm stages caused recurrent glaciations, massive vegetation shifts and large-scale range alterations in many species. The Eurasian steppe biome and its grasslands are a noteworthy example; they underwent climate-driven, large-scale contractions during warm stages and expansions during cold stages. Here, we evaluate the impact of these range alterations on the late Quaternary demography of phylogenetically unrelated plant and insect species, typical of the Eurasian steppes. We contrast three explicit demographic hypotheses by applying a novel approach combining Convolutional Neural Networks with Approximate Bayesian Computation. We identified congruent demographic responses of cold stage expansions and warm stage contractions across all species, but also species-specific effects. The demographic history of Eurasian steppe biota reflects major paleoecological turning points of the late Quaternary, and emphasizes the role of the climate as a driving force behind patterns of genetic variance.

Dendrometer measurements of arctic-alpine dwarf shrubs and micro-environmental drivers of plant growth - Dataset from long-term alpine ecosystem research in central Norway

Here, we present fine-scale measurements of stem diameter variation from three common arctic-alpine dwarf-shrub species monitored in two mountain regions of Central Norway. All three species (Betula nana, Empetrum nigrum ssp. hermaphroditum, and Phyllodoce caerulea) are abundant within the studied regions and highly important contributors to potential future arctic-alpine vegetation shifts. A profound understanding of their radial growth patterns therefore has the potential to yield crucial information regarding climate-growth relations within these ecosystems. We used high-resolution dendrometers (type DRO) to monitor 120 specimens, taking measurements near the shoot base of one major horizontal stem. Along with the shrub growth measurements, we measured on-site micro-environmental data at each studied site, including shoot zone and root zone temperatures as well as soil moisture. All data were recorded at an hourly scale and are presented as daily mean values. The monitoring period spanned five full years (2015 - 2019), with additional data from 2014 and 2020. Data were collected within one of the most continental climate regions of Europe, the Vågå/Innlandet region, and in the oceanic climate region Geiranger/Møre og Romsdal, spanning a steep climate gradient over just ~100 km horizontal distance. Both study regions are characterized by steep elevational gradients and highly heterogeneous micro-topography. The studied sites were chosen to represent these natural conditions using the transect principle. The collection of our original data is subject of our long-term alpine ecosystem monitoring program since 1991, from which numerous publications function as the basis for a recent project on the use of dendrometer data in alpine ecosystem studies.

Light availability and light demand of plants shape the arbuscular mycorrhizal fungal communities in their roots

<p>Woody plant encroachment is influencing many open, grassy ecosystems across the globe, such as savanna, tundra and temperate grassland ecosystems. Drivers of woody plant encroachment are local land use change and global climate change, with shifts in grazing and mowing regimes as important local drivers and elevated CO2 levels, higher temperature and altered precipitation amounts as global drivers. Encroachment of woody species into open, herbaceous ecosystems comes along with substantial shifts in soil conditions, a reduction light availability and ultimately vegetation shifts in the understorey towards species better adapted to the ambient conditions. While vegetation shifts in response to woody plant encroachment in grassy ecosystems have been frequently investigated, e.g. regarding altered plant composition and functional traits related to resource acquisition and dispersal, consequences for biotic interactions have been less studied.</p><p>The symbiosis of plant roots with mycorrhizal fungi is one of the most relevant biotic interaction for plants species, with over 90% of all plants forming mycorrhizal symbiosis and arbuscular mycorrhizal symbiosis as the most prominent mycorrhizal type among herbaceous species. Plants involved in the arbuscular mycorrhizal (AM) symbiosis trade photosynthetically derived carbon for fungal-provided soil nutrients. However, little is known about how plant light demand and ambient light conditions influence root-associating AM fungal communities, and thus their response to prominent climate change processes like shrub encroachment.</p><p>We conducted a manipulative field experiment to test whether plants’ shade tolerance influences their root AM fungal communities in open and shaded grassland sites. We found that light-dependent shifts in AM fungal community structure were similar for experimental bait plant roots and the surrounding soil. Yet, lower AM fungal beta and gamma diversity for shade-intolerant plants in shade likely reflected preferential carbon allocation to specific AM fungi due to the limited plant carbon available to support symbiotic fungi. We conclude that favourable environmental conditions, including optimal light availability, widen the plant biotic niche, i.e. selectivity for specific AM fungi is reduced, and compatibility with a larger number of AM fungal taxa is promoted. With respect to predicted stronger woody plant encroachment predicted under current climate change scenarios, these results indicate that we might be losing AM fungal diversity and the functions associated with these fungal taxa. This calls for continous investment into conservation efforts and management practices to counteract this trend and keep savanna, tundra and grassland ecosystems open. </p>