|Wednesday, July 07|
Sphagnum traits and growth in a changing world
* Fia Bengtsson, Lund University, Sweden
Different Sphagnum species’ growth responses to changes in the environment will affect the development of peatlands as sphagna maintain and engineer peatlands in the northern hemisphere. I will present results from a couple of different studies about Sphagnum production and traits, and discuss what is needed for continued Sphagnum and peat growth. In one study with >45 scientists and 100 peatlands across the Holarctic, we analysed the importance of previously proposed abiotic and biotic drivers for Sphagnum growth (climate, N deposition, water table depth, and vascular plant cover). Precipitation and temperature were among the most important factors, but the species’ (S. magellanicum s.l. and S. fuscum) responses differed. In another study - a lab experiment with manipulated water level, most hummock species had a relatively high water-loss resistance, and we argued that such species, e.g. S. magellanicum, are able to maintain a high water content at drawdown by storing large amounts of water when water availability is high. The results from the Holarctic sampling effort showed that S. magellanicum s.l. – relatively large, loose and wet growing compared to S. fuscum – had a stronger response to climatic variation than S. fuscum. This implies faster length growth in S. magellanicum in a warming climate as long as precipitation is maintained. However, S. magellanicum with its high water-loss resistance, can also grow dry under a canopy, and I speculate it has an advantage in relation to other sphagna also in warmer and drier scenarios, as drier mires will result in more wooded peatlands.
Heterosis as a possible explanation of successful niche occupation in allodiploid Sphagnum species
* Paul Lamkowski, Ernst Moritz Arndt University Greifswald, Germany
The genus of peatmosses (Sphagnum) is known for its comparably high number of diploid and triploid species within the class of Bryophyta. Most of these species seem to be of allopolyploid origins caused by hybridization. This study aims at the questions whether allodiploid Sphagna show better growth performance caused by heterosis effect and which ecological drivers might cause the successful establishment of those hybrids in their natural habitats. In total 13 species of 5 hybrid complexes (including the diploid S. majus, S. jensenii, S. troendelagicum, S. russowii and S. skyense plus the respective parental species) collected from at least three regions (Ireland, Scotland, Germany, Norway, Western and Eastern Siberia) have been included in a newly developed “single head approach”-growth experiment under controlled climate and nutrient conditions. Productivity has been used as a measure of competitional strength. The results showed that the diploids S. majus and S. jensenii surpassed their respective parental species in terms of productivity and display clear effects of heterosis. The other diploid mosses showed intermediate to slightly improved productivities in comparison to their parental species. In addition, allodiploid Sphagna tend to have an expected growth advantage under more nutrient-rich conditions, which corresponds to their naturally occupied habitats. This way diploid species are able to compete against or even outcompete the parental species in their natural habitat despite an often assumed reproductive disadvantage caused by the hybrid origin.
Nitrogen in Bogs It's Complicated
* R. Kelman Wieder, Villanova University, United States
Melanie A. Vile, West Chester University
Kimberli D. Scott, Villanova University
Dale H. Vitt, Southern Illinois University
Kimberli D. Scott, Villanova University
Jeremy A. Hartsock, University of Wisconsin - Superior
Jeremy A. Graham, Michigan Tech Research Institute
Hope Fillimgim, University of Missouri
James C. Quinn, Villanova University
Julia E.M. Stuart, Northern Arizona University
New insights into N cycling processes in bogs derives from research in bogs of northern Alberta, Canada, where background bulk N deposition is <2 kg/ha/yr. In these bogs, net N accumulation rates in peat exceed N deposition inputs. Biological N2-fixation, mainly by methanotrophs associated with surface Sphagnum, is by far the major source of new N, and is sufficient to support annual net primary production (NPP) of Sphagnum and vascular plants combined. Net N mineralization rates in surface peat, are quite low, with net dissolved organic N production dominating over net NH4+-N and NO3--N production. Field and laboratory N fertilization experiments have shown little evidence that Sphagnum (NPP) is N-limited, while shrub NPP (above and belowground) is stimulated by N addition. Surface peat has a remarkable ability to retain atmospherically deposited N, even at high deposition rates. As experimental N addition increases, N2-fixation is inhibited. N2-fixation incorporates N into microbial biomass as organic N; for this N to become available for Sphagnum or vascular plants, it must be mineralized, with Sphagnum growth likely taking up most of this mineralized N. As N addition increases, the ratio of organic N inputs (products of N2-fixation) to inorganic N inputs (from deposition) progressively decreases. Pulses of inorganic N inputs in sporadic rain events may deliver inorganic N into the rooting zone of vascular plants, stimulating shrub NPP. A major consequence of stimulated shrub NPP is an increase in shrub cover, which may lead to a decrease in Sphagnum cover resulting from shading.
Sphagnum peat moss thermotolerance is modulated by the microbiome
* Alyssa Carrell, Oak Ridge National Laboratory, United States
Tanja ivkovi, Oak Ridge National Laboratory
Dana Carper, Oak Ridge National Laboratory
Dale Pelletier, Oak Ridge National Laboratory
Jon Shaw, Oak Ridge National Laboratory
David Weston, Oak Ridge National Laboratory
Climate warming is expected to negatively impact carbon accumulation in peatlands and alter nutrient cycling, however peatland resilience to climate warming may depend, in part, on Sphagnum-microbiome associations. The ability of the microbiome to rapidly acclimatize to warming may aid Sphagnum exposed to elevated temperatures through host-microbiome acquired thermotolerance. Here we first examined the role of field warming in conditioning the Sphagnum microbiome and then the ability of the thermally conditioned microbiome to influence acclimation of Sphagnum growth to elevated temperatures. We first isolated microbiomes from Sphagnum within the Spruce and Peatland Responses Under Changing Environments (SPRUCE) warming experiment, inoculated germ-free Sphagnum, and then exposed the inoculated plants to temperature stress. Elevated temperature decreased growth of plants without added microbiomes while the addition of a microbiome from a thermal origin that matched experimental temperature resulted in similar growth to pre-warming growth rates. Metagenome and metatranscriptome analyses demonstrated warming changed microbiome structure and induced the plant heat shock response, suggesting that thermally conditioned microbiomes provided the host plant with thermal conditioning. We next repeated the experiment with microbiomes isolated from Sphagnum warming experiments in Iceland, Sweden, and France. Again, we found that Sphagnum growth rates were maximized when the experimental temperature treatment matched the inoculum origin temperature. Our findings show that Sphagnum temperature acclimation can be modulated by microbial interactions and may provide a valuable strategy for rapid response to environmental change.
Patterns of between species and within species gene flow and demographic history in Sphagnum flexuosum and Sphagnum recurvum
* Karn Imwattana, Duke University, United States
Jonathan Shaw, Duke University
Peatmosses (Sphagnum spp.) are spore producing plants capable of long-distance dispersal, which allows them to have wide geographic range and enables populations in different geographic regions to remain connected by gene flow. Also, several Sphagnum species can have between species gene flow through hybridization. The aim of this study is to investigate the role of geography in determining the patterns of within and between species gene flow in Sphagnum. A pair of sister species were studied: S. recurvum and S. flexuosum. Both species occur in eastern North America, and S. flexuosum have a separate population in Europe. The analysis of migration models was done using RAD-seq data and coalescent simulations of site frequency spectrum (SFS). The results showed that within S. flexuosum, there is an asymmetric gene flow from eastern North America to Europe, suggesting that Europe might have been colonized by plants from eastern North America after the last glacial maximum. The rate of gene flow between S. flexuosum and S. recurvum is significantly lower than gene flow among S. flexuosum populations, suggesting some level of reproductive isolation between the species. The rate of between species gene flow is higher in sympatric populations than in allopatric populations, indicating that hybridization is more likely when both parents have overlapping distribution. Interestingly, there is a significant amount of gene flow from S. recurvum to the ancestor of both S. flexuosum populations, suggesting that the two species might have diverged while still partially connected (parapatry), by specializing in different ecological niches.
Genomic diversity of keystone peat bog moss Sphagnum
* Adam Healey, HudsonAlpha Institute for Biotechnology, United States
Avinash Sreedasyam, HudsonAlpha Institute for Biotechnology
John Lovell, HudsonAlpha Institute for Biotechnology
Sujan Mamidi, HudsonAlpha Institute for Biotechnology
Bryan Piatkowski, Duke University
Aaron Duffy, Duke University
Jerry Jenkins, HudsonAlpha Institute for Biotechnology
Chris Plott, HudsonAlpha Institute for Biotechnology
Kerrie Barry, Joint Genome Institute
Shengqiang Shu, Joint Genome Institute
Anna Lipzen, Joint Genome Institute
Jane Grimwood, HudsonAlpha Institute for Biotechnology
Jeremy Schmutz, HudsonAlpha Institute for Biotechnology
Dave Weston, Oakridge National Lab
Jon Shaw, Duke University
Peat bogs represent important ecosystems in Northern habitats and play a crucial role in the global carbon cycle through sequestration of carbon as un-decomposed peat. The dominant taxa within most bogs is Sphagnum, which engineers its environment through acidification and creation of anoxic conditions to suppress growth of competing plants and microbes. Sphagnum species live in sympatry, occupying various niche habitats in relation to the water table, with some species growing strictly in low valleys (hollows), high mounds (hummocks), or large lawns. To understand the biology of this organism and how it dominates these ecosystems despite harsh conditions, we have generated two high-quality reference genomes for S. angustifolium (Hollow-lawn species; 395 Mb; Scaffold N50: 21 Mb) and S. magellanicum (Hummock species; 439 Mb; Scaffold N50: 17 Mb), accompanied by transcriptome data under various conditions (drought, dark, high/low pH and high/low temperature) and Illumina re-sequencing of 35 samples representing 15 taxa across the 5 major subsections of Sphagnum. Our results show that Sphagnum is truly a unique organism, with strong genome collinearity among species that does not extend any other plant genome queried thus far. Analysis of transcription factor response to environmental conditions by S. magellanicum and S. angustifolium shows tight regulation of genes related to secondary metabolism, cell wall catabolism, ion exchange, and response to light, a result mirrored by signatures of selection among hummock and hollow taxonomic clades that diverged more than 5 million years ago. These high-quality genomes help shed light on the ways in which Sphagnum has become the dominant carbon sink in Northern peatlands.