Contrasting sensitivity to extreme winter warming events of dominant sub-Arctic heathland bryophyte and lichen species

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Journal of Ecology 99 (2011): 1481-1488, doi:10.1111/j.1365-2745.2011.01859.x.Climate change in northern high latitudes is predicted to be greater in winter rather than summer, yet little is known about the effects of winter climate change on northern ecosystems. Among the unknowns are the effects of an increasing frequency of acute, short-lasting winter warming events. Such events can damage higher plants exposed to warm, then returning cold, temperatures after snow melt and it is not known how bryophytes and lichens, which are of considerable ecological importance in high-latitude ecosystems, are affected by such warming events. However, even physiological adaptations of these cryptogams to winter environments in general are poorly understood. Here we describe findings from a novel field experiment that uses heating from infrared lamps and soil warming cables to simulate acute mid-winter warming events in a sub-Arctic heath. In particular, we report the growing season responses of the dominant lichen, Peltigera aphthosa, and bryophyte, Hylocomium splendens, to warming events in three consecutive winters. While summertime photosynthetic performance of P. aphthosa was unaffected by the winter warming treatments, H. splendens showed significant reductions of net photosynthetic rates and growth rates (of up to 48% and 52% respectively). Negative effects were evident already during the summer following the first winter warming event. While the lichen develops without going through critical phenological stages during which vulnerable organs are produced, the moss has a seasonal rhythm, which includes initiation of growth of young, freeze-susceptible shoot apices in the early growing season; these might be damaged by breaking of dormancy during warm winter events. Synthesis. Different sensitivities of the bryophyte and lichen species were unexpected, and illustrate that very little is known about the winter ecology of bryophytes and lichens from cold biomes in general. In sharp contrast to summer warming experiments that show increased vascular plant biomass and reduced lichen biomass, these results demonstrate that acute climate events in mid-winter may be readily tolerated by lichens, in contrast to previously observed sensitivity of co-occurring dwarf shrubs, suggesting winter climate change may compensate for (or even reverse) predicted lichen declines resulting from summer warming.This research was supported by a grant from the Research Council of Norway (project no. 171542/V10) awarded to J.W.B., by a Leverhulme Trust (UK) grant to G.K.P. and T.V.C. (grant F/00 118/AV), by ATANS grants (EU Transnational Access Program, FP6 Contract no. 506004) to J.W.B., S.B., M.Z. and G.K.P., and by the Norwegian Institute for Nature Research. J.W.B.’s position at the Tromsø University Museum was financed by the Norwegian-Swedish Research School in Biosystematics, which received funding from the Research Council of Norway and the Norwegian Biodiversity Information Centre

Three ancient hormonal cues co-ordinate shoot branching in a moss.

Shoot branching is a primary contributor to plant architecture, evolving independently in flowering plant sporophytes and moss gametophytes. Mechanistic understanding of branching is largely limited to flowering plants such as Arabidopsis, which have a recent evolutionary origin. We show that in gametophytic shoots of Physcomitrella, lateral branches arise by re-specification of epidermal cells into branch initials. A simple model co-ordinating the activity of leafy shoot tips can account for branching patterns, and three known and ancient hormonal regulators of sporophytic branching interact to generate the branching pattern- auxin, cytokinin and strigolactone. The mode of auxin transport required in branch patterning is a key divergence point from known sporophytic pathways. Although PIN-mediated basipetal auxin transport regulates branching patterns in flowering plants, this is not so in Physcomitrella, where bi-directional transport is required to generate realistic branching patterns. Experiments with callose synthesis inhibitors suggest plasmodesmal connectivity as a potential mechanism for transport.We thank Catherine Rameau, Eva Sundberg and Klaus von Schwartzenberg for giving us mutant lines, Nik Cunniffe for his support with statistical analyses and Siobhan Braybrook for help with the scanning electron microscope. We thank our funding bodies for financial support. Yoan Coudert and Jill Harrison are funded by a BBSRC grant ‘PIN proteins and architectural diversification in plants’ (Grant BB/L00224811) and fellowships from the Gatsby Charitable Foundation (GAT2962) and Royal Society. Ottoline Leyser and Wojtek Palubicki are funded by the Gatsby Charitable Foundation (Grant GAT3272C) and by the European Research Council (Grant N° 294514—EnCoDe). Karin Ljung is funded by the Swedish Governmental Agency for Innovation Systems (VINNOVA) and the Swedish Research Council (VR) and thanks Roger Granbom for excellent technical assistance. Ondrej Novak is funded by a Czech Ministry of Education grant from the National Program for Sustainability I (LO1204).This is the final published version of the article. It was originally published in eLIFE (Coudert Y, Palubicki W, Ljung K, Novak O, Leyser O, Harrison CJ, eLIFE, 2015, 4:e06808, doi:10.7554/eLife.06808). The final version is available at http://dx.doi.org/10.7554/eLife.0680

Multiple innovations underpinned branching form diversification in mosses

International audienceBroad-scale evolutionary comparisons have shown that branching forms arose by convergencein vascular plants and bryophytes, but the trajectory of branching form diversificationin bryophytes is unclear. Mosses are the most species-rich bryophyte lineage andtwo sub-groups are circumscribed by alternative reproductive organ placements. In one,reproductive organs form apically, terminating growth of the primary shoot (gametophore)axis. In the other, reproductive organs develop on very short lateral branches. Aswitch from apical to lateral reproductive organ development is proposed to have primedbranching form diversification. Moss gametophores have modular development and each module develops from a singleapical cell. Here we define the architectures of 175 mosses by the number of module classes,branching patterns and the pattern in which similar modules repeat. Using ancestral characterstate reconstruction we identify two stages of architectural diversification. During a first stage there were sequential changes in the module repetition pattern, reproductiveorgan position, branching pattern and the number of module classes. During a secondstage, vegetative changes occurred independently of reproductive fate. The results pinpoint the nature of developmental change priming branching form diversificationin mosses and provide a framework for mechanistic studies of architectural diversificatio