Publications - SOMMARUGA Ruben Dr., Univ.-Prof.
161) Catalán, N., Rofner, C., Verpoorter, C., Pérez, M.-T., Dittmar, T., Tranvik, L., Sommaruga, R., and Peter, H. (2024) Treeline displacement may affect lake dissolved organic matter processing at high latitudes and altitudes. Nature Communications
160) Piccini, C., Bertoglio, F., Sommaruga, R., Martínez de La Escalera, G., Perez, L., Bugoni, L., Bergamino, L., Evangelista, H., and Garcia-Rodriguez, F. (2024) Prokaryotic richness and diversity increased during Holocene glacier retreat and onset of an Antarctic Lake. Communications Earth & Environment
159) Lewis, A. S. L., Lau, M. P., Jane, S. F., Rose, K.C., Be’eri-Shlevin, Y., Burnet, S. H., Clayer, F., Feuchtmayr, H., Grossart, H.P., Howard, D. W., Mariash, H., Delgado, J., North, R. L., Oleksy, I., Pilla, R.M., Smagula, A. P., Sommaruga, R., Steiner, S. E., Verburg, P., Wain, D., Weyhenmeyer, G. A., and Carey, C.C. (2024) Anoxia Begets Anoxia: a positive feedback to the deoxygenation of temperate lakes. Global Change Biology 30 (1): e17046. Open Access
158) Bellas, C., Hackl, T., Plakolb, M.-S., Koslová, A., Fischer, M.G., and Sommaruga, R. (2023) Large-scale invasion of unicellular eukaryotic genomes by integrating DNA viruses. Proceedings of the National Academy of Sciences, USA, 120(16): e2300465120. Open access
157) Schreder, S., Sommaruga, R., Psenner, R., Chimani, B., Ganekind, M. and Koinig, K.A. (2023) Changes in air temperature, but not in precipitation, determine long-term trends in water chemistry of high mountain lakes of the Alps with and without rock glacier influence. Science of the Total Environment 905: 167750. Open access
156) Jeppesen, E., Davidson, T. A., Meerhoff, M., DeMeester, L., González-Bergonzoni, I., Vidal, N., Arndt, H., Jürgens, K., Sommaruga, R., Özkan, K., Lauridsen, T.L., and Sh, T. (2023). Differences in food web structure and composition between new and nearby older lakes in West Greenland suggest succession trajectories driven by glacier retreat. Hydrobiologia 850: 4745–4761. Link to publication
155) Kopejtka, K., Tomasch, J., Kaftan, D., Gardiner, A.T., Bína, D., Gardian, Z., Bellas, C.M., Dröge, A., Geffers, R., Sommaruga, R. and Koblízek, M. (2022) A bacterium from a mountain lake harvests light using both proton-pumping xanthorhodopsins and bacteriochlorophyll-based photosystems. Proceedings of the National Academy of Sciences, USA, 119 (50): e2211018119. DOI: 10.1073/pnas.2211018119
154) Eisendle, D., Medgyesy, N., Niedrist, G.H., Kainz, M.J. and Sommaruga, R. (2022) Diet composition and quality of a Salmo trutta (L.) population stocked in a high mountain lake since the Middle Ages. Science of the Total Environment 853: 158415. Open access
153) Schmeller, D.S., Urbach, D., Bates, K., Catalan, J., Cogălniceanu, D., Fisher, M.C., Friesen, J., Füreder, L., Gaube, V., Haver, M., Jacobsen, D., Le Roux, G., Lin, Y.-P., Loyau, A., Machate, O., Mayer, A., Palomo, I., Plutzar, C., Sentenac, H., Sommaruga, R., Tiberti, R., Ripple, W.J. (2022). Scientists' warning of threats to mountains. Science of the Total Environment 853: 158611.
152) Templer, P.H., J.L. Harrison, F. Pilotto, A. Flores-Díaz, P. Haase, W.H. McDowell, R. Sharif, H. Shibata, D. Blankman, A. Avila, U. Baatar, H.R. Bogena, I. Bourgeois, J. Campbell, T. Dirnböck, W.K. Dodds, M. Hauken, I. Kokorite, K. Lajtha, I. Lai, H. Laudon, T.C. Lin, S. Lins, H. Meesenburg, P. Pinho, A. Robison, M. Rogora, B. Scheler, P. Schleppi, R. Sommaruga, T. Staszewski, and M. Taka. (2022) Atmospheric Deposition and Precipitation are Important Predictors of Inorganic Nitrogen Export to Streams from Forest and Grassland Watersheds: A Large-Scale Data Synthesis. Biogeochemistry 160: 219–241. https://doi.org/10.1007/s10533-022-00951-7
151) Tartarotti, B., Sommaruga, R. and Saul, N. (2022) Phenotypic and molecular responses of copepods to UV radiation stress in a clear vs. a glacially turbid lake. Freshwater Biology 67: 1456-1467. Open Access
150) Oester, R., Greenway, R., Moosmann, M., Sommaruga, R., Tartarotti, B., Brodersen, J. and Matthews, B. (2022) The influence of predator community composition on photoprotective traits of copepods. Ecology and Evolution 12(4): e8862. Open Access
149) Aguilar, P., Vila, I. and Sommaruga, R. (2022) Bacterioplankton zonation does exist in high elevation, polymictic lakes. Frontiers in Microbiology 13:764566. Open Access
148) Burpee, B.T., Saros, J.E., Nanus, L., Baron, J., Brahney, J., Christianson, K.R., Ganz, T., Heard, A., Hundey, B., Koinig, K.A., Koṕacek, Moser, J.K., Nydick, K., Oleksy, I., Sadro, S., Sommaruga, R., Vinebrooke, R., and Williams, J. (2022) Identifying factors that affect mountain lake sensistivity to atmospheric nitrogen deposition across multiple scales. Water Research, 209:117883 https://doi.org/10.1016/j.watres.2021.117883
147) Jane, S.F., Hansen, G.J.A., Kraemer, B., Leavitt, P.R., Mincer, J.L., North, R.L., Pilla, R.M., Stetler, J.T., Williamson, C.E., Woolway, R.I., Arvola, L., Chandra, S., DeGasperi, C.L., Diemer, L., Dunalska, J., Erina, O., Flaim, G., Grossart, H.-P., Hambright, K.D., Hein, C., Hejzlar, J., Janus, L.L., Jenny, J-P., Jones, J.R., Knoll, L.B., Leoni, B., Mackay, E., Matsuzaki, S.-I. S., McBride, C., Müller-Navarra, D.C., Paterson, A.M., Pierson, D., Rogora, M., Rusak, J.A., Sadro, S., Saulnier-Talbot, E., Schmid, M., Sommaruga, R., Thiery, W., Verburg, P., Weathers, K.C., Weyhenmeyer, G.A., Yokota, K. and Rose, K.C. (2021) Widespread deoxygenation of temperate lakes. Nature 594: 66–70. https://doi.org/10.1038/s41586-021-03550-y
146) Kraemer, B., R. M. Pilla, R. I. Woolway, O. Anneville, S Ban, W. Colom-Montero, S.P. Devlin, M. T. Dokulil, E. E. Gaiser, K. D. Hambright, D. O. Hessen, S. N. Higgins, K.D. Jöhnk, W. Keller, L. B. Knoll, P. R. Leavitt, F. Lepori, M. S. Luger, S. C. Maberly, D. C. Müller-Navarra, A.A. Paterson, D. C. Pierson, D.C. Richardson, M. Rogora, J.A. Rusak, S. Sadro, N. Salmaso, M. Schmid, E. A. Silow, R. Sommaruga, J. A.A. Stelzer, D. Straile, W.Thiery, P. Verburg, G.A. Weyhenmeyer, and R. Adrian (2021) Climate change drives widespread shifts in lake thermal habitat. Nature Climate Change 11: 521–529. Open access
145) Pilla, R. Elizabeth Mette, Craig Williamson, Boris Adamovich, Rita Adrian, Orlane Anneville, Esteban G. Balseiro, Syuhei Ban, Sudeep Chandra, William Colom-Montero, Shawn Devlin, Margaret Dix, Martin Dokulil, Natalie Feldsine, Heidrun Feuchtmayr, Natalie Fogarty, Evelyn Gaiser, Scott Girdner, María González, K. David Hambright, David Hamilton, Karl Havens, Dag Hessen, Harald Hetzenauer, Scott Higgins, Timo Huttula, Hannu Huuskonen, Peter Isles, Klaus Jöhnk, Wendel Keller, Jennifer Klug, Lesley Knoll, Johanna Korhonen, Nikolai Korovchinsky, Oliver Köster, Benjamin Kraemer, Peter Leavitt, Barbara Leoni, Fabio Lepori, Ekaterina Lepskaya, Noah Lottig, Martin Luger, Stephen Maberly, Sally Macintyre, Chris McBride, Peter McIntyre, Stephanie Melles, Beatriz E. Modenutti, Dörthe Müller-Navarra, Laura Pacholski, Andrew Paterson, Don Pierson, Helen Pislegina, Pierre-Denis Plisnier, David Richardson, Alon Rimmer, Michela Rogora, Denis Rogozin, James Rusak, Olga Rusanovskaya, Steven Sadro, Nico Salmaso, Jasmine Saros, Jouko Sarvala, Émilie Saulnier-Talbot, Daniel Schindler, Svetlana Shimaraeva, Eugene Silow, Lewis Sitoki, Ruben Sommaruga, Dietmar Straile, Kristin Strock, Hilary Swain, Jason Tallant, Wim Thiery, Maxim Timofeyev, Alexander Tolomeev, Koji Tominaga, Mike Vanni, Piet Verburg, Rolf Vinebrooke, Josef Wanzenböck, Kathleen Weathers, Gesa Weyhenmeyer, Egor Zadereev, and Tatyana Zhukova (2021). Global data set of long-term summertime vertical temperature profiles in 153 lakes. Scientific Data 8: 200. Open access
144) Kopejtka, K. Zeng, Y. Kaftan, D., Selyanin, V., Gardian, Z., Tomasch, J., Sommaruga, R., Koblížek, M. (2021) Characterization of the Aerobic Anoxygenic Phototrophic Bacterium Sphingomonas sp. AAP5. Microorganisms 9: 768. Open access
143) Bellas, C.M. and Sommaruga, R. (2021) Polinton-like viruses are abundant in aquatic ecosystems. Microbiome 9: 13 Open access
142) Werner, N., Orfanoudaki, M., Hartmann, A., Ganzera, M., and Sommaruga, R. (2021) Low temporal dynamics of mycosporine-like amino acids in benthic cyanobacteria from an alpine lake. Freshwater Biology 66: 169 - 176 Open access
141) Sommaruga, R. and Eldridge, H.M. (2021) Avocado production: Water footprint and socio-economic implications. EuroChoices 20: 46-53. Open access
140) Kopejtka, K., Tomasch, J., Zeng, Y., Selyanin, V., Dachev, M., Piwosz, K., Tichy, M., Bunk, B., Brinkmann, H., Gardian, Z., Geffers, R., Sommaruga, R. and Koblizek, M. (2020) Simultaneous presence of bacteriochlorophyll and xanthorhodopsin genes in a freshwater bacterium. mSystems 5:e01044-20. Open access
139) Pilla, R.M., Williamson, C.E., Adamovich, B.V., Adrian, R., Anneville, O., Chandra, S., Colom-Montero, W., Devlin, S.P., Dix, M.A., Dokulil, M.T., Gaiser, E.E., Girdner, S.F., Hambright, K.D., Hamilton, D.P., Havens, K., Hessen, D.O., Higgins, S.N., Huttula, T.M., Huuskonen, H., Isles, P.D.F., Joehnk, K.D., Jones, I.D., Keller, W.B., Knoll, L.B., Korhonen, J., Kraemer, B.M., Leavitt, P.R., Lepori, F., Luger, M.S.,. Maberly, S.C., Melack, J.M., Melles,S.J., Müller-Navarra, D.C., Pierson, D.C., Pislegina, H.V., Plisnier, P.-D., Richardson, D.C., Rimmer, A., Rogora, M., Rusak, J.A., Sadro, S., Salmaso, N., Saros, J.E., Saulnier-Talbot, É., Schindler, D.E., Schmid, M., Shimaraeva, S.V., Silow, E.A., Sitoki, L.M., Sommaruga, R., Straile, D., Strock, K.E., Thiery, W., Timofeyev, M.A., Verburg, P., Vinebrooke, R.D., Weyhenmeyer, G.A., and Zadereev, E. (2020) Deeper waters are changing less consistently than surface waters in a global analysis of 102 lakes. Scientific Reports 10: 20514 Open access
138) Elser, J.J., Wu, C., González, A.L: Shain, D.H., Smith, H.J., Sommaruga. R. et al. (2020) Key rules of life and the fading cryosphere: impacts in alpine lakes and streams. Global Change Biology 26: 6644–6656. Open access
137) Aguilar, P. and Sommaruga, R. (2020) The balance between deterministic and stochastic processes in structuring lake bacterioplankton over time. Molecular Ecology 29: 3117-3130 Open access
136) Barth, J.M.I., Gubili, C., Matschiner, M., Tørresen, O., Watanabe, S., Egger, B., Han, Y-S., Feunteun, E., Sommaruga, R., Jehle, R., and Schabetsberger, R. (2020) Stable species boundaries despite ten million years of hybridization in tropical eels. Nature Communications 11: 1433 Open access
135) Sonntag, B. and Sommaruga, R. (2020) Effectiveness of photoprotective strategies in three mixotrophic planktonic ciliate species. Diversity 12: 252 Open access
134) Alcocer, J., Delgado, C.N. and Sommaruga, R. (2020) Photoprotective compounds in zooplankton of two adjacent tropical high mountain lakes with contrasting underwater light climate and fish occurrence. Journal of Plankton Research 42: 105–118 Open access
133) Tiberti, R., Buscaglia, F., Callieri, C., Rogora, M., Tartari, G., and Sommaruga, R. (2020) Food web complexity of high-mountain lakes is largely affected by glacial retreat. Ecosystems 23: 1093–1106. Link to journal
132) Tartarotti, B., Sommaruga, R. and Saul, N. (2019) Contrasting diurnal patterns in antioxidant capacities but not in expression of stress protein genes among copepod populations from clear versus glacially-fed alpine and subalpine lakes. Journal of Plankton Research 41: 897-908, https://doi.org/10.1093/plankt/fbz061
131) Zocchi, M. and Sommaruga, R. (2019). Microplastics modify the toxicity of glyphosate on Daphnia magna. Science of the Total Environment, 697: 134194. DOI. https://doi.org/10.1016/j.scitotenv.2019.134194
130) Waibel, A., Peter, H. and Sommaruga, R. (2019) Importance of mixotrophic flagellates during the ice-free season in lakes located along an elevational gradient. Aquatic Sciences 81:45 Open access
129) Moser, K.A., Baron, J. S., Brahney, J., Oleksy, I., Saros, J.E., Hundey, E.J., Sadro, S.A., Kopáček, J., Sommaruga, R., Kainz, M.J., Strecker, A.L., Chandra, S., Walters, D.M., Preston, D.L., Michelutti, N., Lepori, F., Spaulding, S.A., Christianson, K., Melack, J.M., and Smol, J.P. (2019) Mountain Lakes: Eyes on Global Environmental Change. Global and Planetary Change 178: 77-95 https://doi.org/10.1016/j.gloplacha.2019.04.001
128) Aguilar, P., Dorador, C., Vila, I. and Sommaruga, R. (2019) Bacterial communities associated with spherical Nostoc macrocolonies. Frontiers in Microbiology 10: 483. DOI: 10.3389/fmicb.2019.00483. Open access
127) Niedrist G. H., Psenner, R., and Sommaruga, R. (2018) Climate warming increases vertical and seasonal water temperature differences, and inter-annual variability in a mountain lake. Climatic Change 151: 473–490. Open access
126) Tartarotti, B., Alfreider, A., Egg, M., Saul, N., Schneider, T., Sommaruga, R., Tischler A., and Vetter J. (2018) Seasonal plasticity in photoprotection modulates UV-induced hsp gene expression in copepods from a clear lake. Limnology and Oceanography 63: 1579-1592. Open access
125) Caputo, L., Huovinen, P., Sommaruga, R., and Gómez, I. (2018) Water transparency affects the survival of the the medusa stage of the invasive freshwater jellyfish Craspedacusta sowerbii (Hydrozoa, Lankester 1880). Hydrobiologia 817: 179–191. DOI: 10.1007/s10750-018-3520-4
124) Aguilar, P., Dorador, C., Vila, I. and Sommaruga, R. (2018) Bacterioplankton composition in tropical high-elevation lakes of the Andean plateau. FEMS Microbiology Ecology 94 (3), fiy004. Open access
123) Rogora, M., Frate L., Carranza ML, Freppaz M., Stanisci A., Bertani, I., Bottarin R., Brambilla A., Canullo R., Carbognani M., Cerrato C., Chelli, S., Cremonese E., Cutini, M., Di Musciano M., Erschbamer, B., Godone, D., Iocchi M., Isabellon, M., Magnani A., Mazzola L., Morra di Cella U., Pauli H., Petey M., Petriccione B., Porro F., Psenner R., Rossetti G., Scotti A., Sommaruga R., Tappeiner U., Theurillat, J.-P., Tomaselli M., Viglietti D., Viterbi R., Vittoz, P., Winkler M., Matteucci G. (2018) Assessment of climate change effects on mountain ecosystems through a cross-site analysis in the Alps and Apennines. Science of the Total Environment 624: 1429-1442.
122) Peter, H., De Meester, L., Jeppesen, E. and Sommaruga, R. (2018) Changes in bacterioplankton community structure during early lake ontogeny resulting from the retreat of the Greenland Ice Sheet. The ISME Journal 12: 544-555. Open access
121) Stenzel, B., Rofner, C., Pérez, M.T. and Sommaruga, R. (2017) Stoichiometry of natural bacterial assemblages from lakes located across an elevational gradient. Scientific Reports 7:5875 Open access
120) Tartarotti, B., Trattner, F., Remias, D., Saul, N., Steinberg, C.E.W., and Sommaruga, R. (2017) Distribution and UV protection strategies of zooplankton in clear and glacier-fed alpine lakes. Scientific Reports 7: 4487 Open access
119) Rofner, C., Peter, H., Catalán, N., Drewes, F., Sommaruga, R. and Pérez, M.T. (2017) Climate-related changes of soil characteristics affect bacterial community composition and function of high altitude and latitude lakes. Global Change Biology 23: 2331-2344. Open access
118) Major, Y., Kifle, D., Niedrist, G. H., and Sommaruga, R. (2017) An isotopic analysis of the phytoplankton-zooplankton link in a highly eutrophic tropical reservoir dominated by cyanobacteria. Journal of Plankton Research 39: 220-231. Link to pdf
117) Peter, H. and R. Sommaruga (2017) Alpine glacier-fed turbid lakes are discontinuous cold polymictic rather than dimictic. Inland Waters 7: 45-54. Open access
116) Haileselasie, T. H., Mergeay, J., Weider, L. J., Sommaruga, R., Davidson, T. A., Meerhoff, M., Arndt, H., Jürgens, K., Jeppesen, E. and De Meester, L. (2016) Environment not dispersal limitation drives clonal composition of arctic Daphnia in a recently deglaciated area. Molecular Ecology 25:5830–5842. Link to pdf
115) Kammerlander, S., Koinig, K., Rott, E., Sommaruga, R., Tartarotti, B., Trattner, F., and Sonntag, B. (2016) Ciliate community structure and interactions within the planktonic food web in two alpine lakes of contrasting transparency. Freshwater Biology 61: 1950-1965. doi:10.1111/fwb.12828 Open access
114) Rofner, C., Sommaruga, R. and Pérez, M.T. (2016) Differential utilization patterns of dissolved organic phosphorus compounds by heterotrophic bacteria in two mountain lakes. FEMS Microbiology Ecology 92, fiw139. Open access
113) Aguilar, P., Acosta, E., Dorador, C. and Sommaruga, R. (2016) Large differences in bacterial community composition among three nearby extreme waterbodies of the high Andean plateau. Frontiers in Microbiology 7:976 Open access
112) Krajíček, M., Fott, J., Miracle, M.R., Ventura, M., Sommaruga, R., Kirschner, P. and Černý, M. (2016) The genus Cyclops (Copepoda, Cyclopoida) in Europe. Zoologica Scripta 6: 671-682. Link to pdf
111) Rofner, C., Sommaruga, R. and Pérez, M.T. (2016) Phosphate and ATP uptake by lake bacteria: Does taxonomical identity matter? Environmental Microbiology 18: 4782-4793. Open access
110) Drewes, F., Peter, H., and Sommaruga, R. (2016). Are viruses important in the plankton of highly turbid glacier-fed lakes? Scientific Reports 6, 24608; doi: 10.1038/srep24608 Open access
109) Filker, S., Sommaruga, R., Vila, I. and Stoeck, T. (2016) Microbial eukaryote plankton communities of high-mountain lakes from three continents exhibit strong biogeographic patterns. Molecular Ecology 25: 2286–2301. Link to pdf
108) Oexle, S., Jansen, M., Pauwels, K., Sommaruga, R., De Meester, L. and Stoks, R. (2016) Rapid evolution of antioxidant defense in a natural population of Daphnia magna. Journal of Evolutionary Biology 29: 1328-1337. doi: 10.1111/jeb.12873 Open access
107) Peter, H. and R. Sommaruga (2016) Shifts in diversity and function of lake bacterial communities upon glacier retreat. The ISME Journal 10: 1545-1554. doi:10.1038/ismej.2015.2 Open access
106) Minella, M. Leoni, B., Salmaso, N., Savoye, L., Sommaruga, R., and Vione, D. (2016) Long-term trends of chemical and modelled photochemical parameters in four Alpine lakes. Science of the Total Environment 541: 247-256. Open access
105) Durif, C.M.F., Fields, D. M., Browman, H. I., Shema, S. D., Enoae, J. R., Skiftesvik, A. B., Bjelland, R., Sommaruga, R., and Arts, M. T. (2015) UV radiation changes algal stoichiometry but does not have cascading effects on a marine food chain. Journal of Plankton Research 37: 1120-1136. Featured article. Open access
104) Hylander, S., Kiørboe, T., Snoeijs, P., Sommaruga, R., and Nielsen, T.G. (2015). Concentrations of sunscreens and antioxidant pigments in Arctic Calanus spp. in relation to ice cover, ultraviolet radiation, and the phytoplankton spring bloom. Limnology & Oceanography 60: 2197–2206. Open access
103) Sommaruga, R. (2015) When glaciers and ice sheets melt: consequences for planktonic organisms. Journal of Plankton Research 37: 509-518. Open access
102) Piiparinen, J., Enberg, S., Rintala, J-M., Sommaruga, R., Majaneva, M, Autio, R., and Vähätalo, A. (2015) The contribution of mycosporine-like amino acids, chromophoric dissolved organic matter and particles to the UV protection of sea-ice organisms in the Baltic Sea. Photochemical & Photobiological Sciences 14: 1025-1038 Link to pdf
101) Debecker, S., Sommaruga, R., Maes, T. and Stoks, R. (2015) Larval UV exposure impairs adult immune function through a trade-off with larval investment in cuticular melanin. Functional Ecology 29: 1292-1299. Link to pdf
100) Farkas, J., Peter, H., Ciesielski, T.M., Thomas, K.V., Sommaruga, R., Salvenmoser, W., Weyhenmeyer, G.A., Tranvik, L.J. and Jenssen, B.M. (2015) Impact of TiO2 nanoparticles on freshwater bacteria from three Swedish lakes. Science of the Total Environment 535: 85-93. Link to pdf
99) Kammerlander, B., Breiner, H-W, Filker, S., Sommaruga, R. Sonntag, B. and Stoeck, T. (2015) High diversity of protistan plankton communities in remote high mountain lakes in the European Alps and the Himalaya mountains. FEMS Microbiology Ecology 91 (4): fiv010 Link to pdf
98) Pérez, M. T., Rofner, C., and Sommaruga, R. (2015) Dissolved organic monomer partitioning among bacterial groups in two oligotrophic lakes. Environmental Microbiology Reports 7: 265-272. Open access
97) Peter, H., Hörtnagl, P., Reche, I., and Sommaruga, R. (2014) Bacterial diversity and composition during rain events with and without Saharan dust influence reaching a high mountain lake in the Alps. Environmental Microbiology Reports 6: 619-624. Open access
96) Sommaruga, R. and Kandolf, G. (2014) Negative consequences of glacial turbidity for the survival of freshwater planktonic heterotrophic flagellates. Scientific Reports 4 : 4113 | DOI: 10.1038/srep04113. Open access
95) Tartarotti, B., Saul, N., Chakrabarti, S., Trattner, F., Steinberg C.E.W., and Sommaruga, R. (2014) UV-induced DNA damage in Cyclops abyssorum tatricus populations from clear and turbid alpine lakes. Journal of Plankton Research 36: 557-566 doi:10.1093/plankt/fbt109 Open access
94) Čuperová, Z., Holzer, E., Salka, I. Sommaruga, R, and Koblížek, M. (2013) Temporal changes and altitudinal distribution of aerobic anoxygenic phototrophs in mountain lakes. Applied and Environmental Microbiology 79: 6439-6446. Open access
93) Piccini, C., Conde, D., Pernthaler, J. and Sommaruga, R. (2013) Photoalteration of macrophyte-derived chromophoric dissolved organic matter induces growth of single bacterial populations in a coastal lagoon. Journal of Limnology 72: 582-591. Link to pdf
92) Ruiz-González, C., Simó, R., Sommaruga, R., and Gasol, J.M. (2013) Away from darkness: A review on the effects of solar radiation on heterotrophic bacterioplankton activity. Frontiers in Microbiology 4:131.doi: 10.3389/fmicb.2013.00131. Open access
91) Möst, M., A. Petrusek, R. Sommaruga, P. J. Juračka, M. Slusarczyk, M. Manca, and P. Spaak (2013) At the edge and on the top: molecular identification and ecology of Daphnia dentifera and D. longispina in high-altitude Asian lakes. In: Special Issue on Cladocera, Hydrobiologia 715: 51-62. Link to pdf
90) Schneider, T., A. Herzig, K. A. Koinig, and R. Sommaruga (2012) Copepods in turbid shallow soda lakes accumulate unexpected high levels of carotenoids. PLoS ONE 7(8): e43063. Open access
89) Ruiz-González, C., Lefort, T., Galí, M., Sala, M., Sommaruga, R., Simó, R., and Gasol, J.M. (2012) Seasonal patterns in the sunlight sensitivity of bacterioplankton from Mediterranean surface coastal waters. FEMS Microbiology Ecology 79:661-674. Open access
88) Comont, D., J. Martinez Abaigar, A. Albert, P. Aphalo, D. R. Causton, F. López Figueroa, A. Gaberscik, L. Llorens, M.-T. Hauser, M. A. K. Jansen, M. Kardefelt, P. Coba Luque, S. Neubert, E. Núñez-Olivera, J. Olsen, M. Robson, M. Schreiner, R. Sommaruga, Å. Strid, S. Torre, M. Turunen, S.Veljovic-Jovanovic, D. Verdaguer, M. Vidovic, J. Wagner, J.Barbro Winkler, G.Zipoli and D. Gwynn-Jones (2012) UV responses of Lolium perenne raised along a latitudinal gradient across Europe: a filtration study. Physiologia Plantarum 145: 604-618. Link to pdf
87) Ruiz-González, C., Simó, R., Vila-Costa, M, Sommaruga, R. and Gasol, J.M. (2012) Sunlight modulates the relative importance of heterotrophic bacteria and picophytoplankton in DMSP-sulphur uptake. ISME Journal 6: 650-659 DOI:10.1038/ismej.2011.118 Link to pdf
86) Mladenov, N., Sommaruga, R., Morales-Baquero, R., Laurion, I., Camarero, L., Diéguez, M., Camacho, A., Delgado, A., Torres, O., Chen, Z., Felip, M. and Reche I. (2011) Dust inputs and bacteria influence dissolved organic matter in clear alpine lakes. Nature Communications 2: 405| DOI: 10.1038/ncomms1411. Open access
85) Orfeo, M. Ventura, M., Tartarotti, B. and Sommaruga, R. (2011) Body distribution and source of mycosporine-like amino acids in the cyclopoid copepod Cyclops abyssorum tatricus. Journal of Plankton Research 33: 1430-1444.Open access, Journal's cover
84) Sonntag, B., Summerer, M., and Sommaruga, R. (2011) Are freshwater mixotrophic ciliates less sensitive to solar UV radiation than heterotrophic ones? Journal of Eukaryotic Microbiology 58: 196-202 Open access
83) Libkind, D., Moliné, M., Sommaruga, R., Sampaio, J.P. and van Broock, M. (2011) Phylogenetic distribution of fungal mycosporines within Pucciniomycotina (Basidiomycota). Yeast 28: 619-627. Open access
82) Pérez, M. T. and Sommaruga, R. (2011) Temporal changes in the dominance of major planktonic bacterial groups in an alpine lake: discrepancy with their contribution to bacterial production. Aquatic Microbial Ecology 63: 161-170. Open access
81) Hörtnagl, P., M. T. Pérez, and R. Sommaruga (2011) Contrasting effects of ultraviolet radiation on the growth efficiency of freshwater bacteria. Aquatic Ecology 45: 125-136. Link to pdf, Journals's cover
80) Sonntag, B., Summerer, M., and Sommaruga, R. (2011) Factors involved in the distribution pattern of ciliates in the water column of a transparent alpine lake. Journal of Plankton Research 33: 541-546. Link to pdf, Journals's cover
79) Hörtnagl, P., M. T. Pérez, M. Zeder, and Sommaruga, R. (2010) The bacterial community composition of the surface microlayer in a high mountain lake. FEMS Microbiology and Ecology 73: 458-467. Link to pdf
78) Sommaruga, R. (2010) Preferential accumulation of carotenoids rather than of mycosporine-like amino acids in copepods from high altitude Himalayan lakes. In: Eggermont, H., M. Kernan & K. Martens (eds.). Global Change Impacts on Mountain Lakes. Hydrobiologia 648:143–156. Link to pdf
77) Hörtnagl, P., M. T. Pérez, and R. Sommaruga (2010) Living at the border: a community and single-cell assessment of lake bacterioneuston activity. Limnology and Oceanography 55: 1134-1144. Link to pdf
76) Uusikivi, J.., Vähätalo, A. V., Granskog, M. A., and Sommaruga, R. (2010) Contribution of mycosporine-like amino acids, colored dissolved and particulate matter to sea ice optical properties and ultraviolet attenuation. Limnology and Oceanography 55: 703-713. Link to pdf
75) Pérez, M. T., Hörtnagl, P., and Sommaruga, R. (2010) Contrasting ability to take up leucine and thymidine among freshwater bacterial groups: implications for bacterial production measurements. Environmental Microbiology 12: 74-82. Link to pdf
74) Adrian, R., O’Reilly, C. M., Zagarese, H., Baines, S. B., Hessen, D.O., Keller, W., Livingstone, D. M., Sommaruga, R., Straile, D., Van Donk, E., Weyhenmeyer, G.A., and Winder, M. (2009) Lakes as sentinels of climate change. Limnology and Oceanography 54: 2283-2297. Link to pdf
73) Rose, K. C., Williamson, C. E., Saros, J. E., Sommaruga, R. and Fischer, J. M. (2009) Differences in UV transparency and thermal structure between alpine and subalpine lakes: Implications for organisms. Photochemical and Photobiological Sciences, 8: 1244–1256. Link to pdf
72) Piccini, C., Conde, D., Pernthaler, J. and Sommaruga, R. (2009) Alteration of chromophoric dissolved organic matter by solar UV radiation causes rapid changes in bacterial community composition. Photochemical and Photobiological Sciences 8: 1321–1328. Link to pdf
71) Sommaruga, R. and Sonntag, B. (2009) Photobiological aspects of the mutualistic association between Paramecium bursaria and Chlorella. In: Endosymbionts in Paramecium. M. Fujishima (Ed.). Microbiology Monographs 12, Springer-Verlag, Berlin, p. 111-130. Link to pdf
70) Nagiller, K. and Sommaruga, R. (2009) Differential tolerance of UV radiation between Chaoborus species and role of photoprotective compounds. Journal of Plankton Research 31: 503-513. Link to pdf
69) Summerer, M., Sonntag, B., Hoertnagl, P., and Sommaruga, R. (2009) Symbiotic ciliates receive protection against UV damage from their algae: A test with Paramecium bursaria and Chlorella. Protist 160: 233-243. Link to pdf
68) Sommaruga, R. and Casamayor, E. (2009) Bacterial 'cosmopolitanism' and importance of local environmental factors for community composition in remote high-altitude lakes. Freshwater Biology 54: 994-1005. Link to pdf
67) Sommaruga, R., Chen, Y., and Liu, Z. (2009) Multiple strategies of bloom-forming Microcystis to minimize damage by solar ultraviolet radiation in surface waters. Microbial Ecology 57: 667–674. Link to pdf
66) Mladenov, N., Pulido-Villena, E. Morales-Baquero, R. Ortega-Retuerta, E., Sommaruga, R. and Reche, I. (2008) Spatiotemporal drivers of dissolved organic matter in high alpine lakes: the role of Saharan dust inputs and bacterial activity. Journal of Geophysical Research 113, G00D01, DOI:10.1029/2008JG000699. Link to pdf
65) Sterr, B., and Sommaruga, R. (2008) Does ultraviolet radiation alter kairomones? An experimental test with Chaoborus obscuripes and Daphnia pulex. Journal of Plankton Research 30: 1343-1350. Link to pdf
64) Peter, H., and Sommaruga, R. (2008) An evaluation of methods to study the gut bacterial community composition of freshwater zooplankton. Journal of Plankton Research 30: 997-1006. Link to pdf
63) Obertegger, U., Flaim, G., and Sommaruga, R. (2008) Multifactorial nature of rotifer water layer preferences in an oligotrophic lake. Journal of Plankton Research 30: 633-643. Link to pdf
62) Summerer, M., Sonntag, B., and Sommaruga, R. (2008) Ciliate-symbiont specificity of freshwater endosymbiotic Chlorella (Trebouxiophyceae, Chlorophyta). Journal of Phycology 44: 77-84. Link to pdf
61) Obertegger, U., Flaim, G., Braioni, M.G., Sommaruga, R., Corradini, F., and Borsato, A. (2007) Water residence time as a driving force of zooplankton structure and succession. Aquatic Sciences 69: 575-583. Link to pdf
60) Hoertnagl, P. and Sommaruga, R. (2007) Photo-oxidative stress in symbiotic and aposymbiotic strains of the ciliate Paramecium bursaria. Photochemical and Photobiological Sciences 6: 842-847. Link to pdf
59) Felip, M., Andreatta, S., Sommaruga, R., Straskrábová, V., and Catalan, J. (2007) Suitability of flow cytometry for estimating bacterial biovolume in natural plankton samples: A comparison with microscopy data. Applied and Environmental Microbiology 73: 4508-4514. Link to pdf
58) Massana, R., del Campo, J., Dinter, C., and Sommaruga, R. (2007) Crash of a population of the marine heterotrophic flagellate Cafeteria roenbergensis by viral infection. Environmental Microbiology 9: 2660-2669. Link to pdf
57) Pérez, M. and Sommaruga, R. (2007) Interactive effects of solar radiation and dissolved organic matter on bacterial activity and community structure. Environmental Microbiology 9: 2200-2210. Open access
56) Hansson, L.-A., Hylander, S., and Sommaruga, R. (2007) Escape from UV threats in zooplankton: a cocktail of behavior and protective pigmentation. Ecology 88: 1932-1939. Open access
55) Summerer, M., Sonntag, B., and Sommaruga, R. (2007) An experimental test of the symbiosis specificity between the ciliate Paramecium bursaria and strains of the unicellular green alga Chlorella. Environmental Microbiology 9: 2117-2122. Open access
54) Sonntag, B., Summerer, M., and Sommaruga, R. (2007) Sources of mycosporine-like amino acids in planktonic Chlorella-bearing ciliates (Ciliophora). Freshwater Biology 52: 1476-1485. Open access
53) Mindl, B., Anesio A.M., Meirer, K., Hodson, A.H., Laybourn-Parry, J., Sommaruga, R. and Sattler, B. (2007) Factors influencing bacterial dynamics along a transect from supraglacial runoff to proglacial lakes of a high Arctic glacier. FEMS Microbiology Ecology 59: 307-317. Link to pdf
52) Guang, G., Q. Boqiang, R. Sommaruga, and R. Psenner (2007) The bacterioplankton of Lake Taihu: abundance, biomass, and production. Hydrobiologia 581: 177-188. Link to pdf
51) Pérez, M. T. and R. Sommaruga (2006) Differential effect of algal- and soil-derived dissolved organic matter on alpine lake bacterial community composition and activity. Limnology and Oceanography 51: 2527-2537. Link to pdf
50) Piccini, C., D. Conde, C. Alonso, R. Sommaruga, and J. Pernthaler (2006) Blooms of single bacterial species in a coastal lagoon of the South-western Atlantic Ocean. Applied and Environmental Microbiology 72: 6560-6568. Link to pdf
49) Alonso-Sáez, L., J.M Gasol, T. Lefort, J.Hofer and R. Sommaruga (2006) Effect of natural sunlight on bacterial activity and differential sensitivity of natural bacterioplankton groups in NW Mediterranean coastal waters. Applied and Environmental Microbiology 72: 5806-5813. Link to pdf
48) Sommaruga, R., and G. Augustin (2006) Seasonality in UV transparency of an alpine lake is associated to changes in phytoplankton biomass. Aquatic Sciences 68: 129-141. Link to pdf
47) Sommaruga, R., K. Whitehead, J. M. Shick, and C. S. Lobban (2006) Mycosporine-like amino acids in the zooxanthella-ciliate symbiosis Maristentor dinoferus. Protist 157: 185-191. Link to pdf
46) Tartarotti B. and R. Sommaruga (2006) Seasonal dynamics of photoprotective mycosporine-like amino acids in phytoplankton and zooplankton from a high mountain lake. Limnology and Oceanography 51: 1530-1541. Link to pdf
45) Pérez, P., D. Libkind, M.C. Diéguez, M. Summerer, B. Sonntag, R. Sommaruga, M. van Broock, and H.E. Zagarese (2006) Mycosporines from freshwater yeasts: a trophic cul-de-sac. Photochemical and Photobiological Sciences 5: 25-30. Link to pdf
44) Sommaruga, R., J. Hofer, L. Alonso-Sáez, and J. M. Gasol (2005) Differential sensitivity to sunlight of picophytoplankton from surface Mediterranean coastal waters. Applied and Environmental Microbiology 71: 2154-2157. Link to pdf
43) Warnecke, F., R. Sommaruga, R. Sekar, J. S. Hofer, and J. Pernthaler (2005) Abundances, identity and growth state of Actinobacteria in mountain lakes with different UV transparency. Applied and Environmental Microbiology 71: 5551-5559. Link to pdf
42) Moeller, R. E., S. Gilroy, C. E. Williamson, G. Dee, and R. Sommaruga (2005) Dietary acquisition of photoprotective compounds (mycosporine-like amino acids, carotenoids) and acclimation to ultraviolet radiation in a freshwater copepod. Limnology and Oceanography 50: 427-439. Open access
41) Libkind, D., R. Sommaruga, H. Zagarese, M. C. Diéguez, and M. van Broock (2005) Mycosporines in carotenogenic yeasts. Systematic and Applied Microbiology 28: 749-754. Link to pdf
40) Liu, Z., D.-P. Häder, and R. Sommaruga (2004). Occurrence of mycosporine-like amino acids (MAAs) in the bloom-forming cyanobacterium Microcystis aeruginosa. Journal of Plankton Research 26(8): 963-966. Link to pdf
39) Andreatta, S., M. Wallinger, J. Catalan, J. Piera, R. Psenner, J.S. Hofer, and R. Sommaruga (2004) Tools for the discrimination and analysis of lake bacterioplankton subgroups measured by flow cytometry in a high-resolution depth profile. Aquatic Microbial Ecology 36: 107-115. Link to pdf
38) Aubriot, L., Conde, D., Bonilla, S., and R. Sommaruga (2004) Phosphate uptake behavior of natural phytoplankton during exposure to solar ultraviolet radiation in a shallow coastal lagoon. Marine Biology 144: 623-631. Link to pdf
37) Libkind, D., P. Pérez, R. Sommaruga, M. C. Diéguez, M. Ferraro, S. Brizzio, H. Zagarese, and M. van Broock (2004) Constitutive and UV-inducible synthesis of photoprotective compounds (carotenoids and mycosporines) by freshwater yeasts. Photochemical and Photobiological Sciences 3: 281-286. Link to pdf
36) Sommaruga, R., D. Libkind, M. van Broock, and K. Whitehead (2004) Mycosporine-glutaminol-glucoside, a UV-absorbing compound of two Rhodotorula yeast species. Yeast 21: 1077-1081. Link to pdf Erratum
35) Sommaruga, R. (2003) Ultraviolet radiation and its effects on species interactions. In: UV effects in aquatic organisms and ecosystems (W. Helbling & H. Zagarese, eds.), Comprehensive Series in Photosciences, ESP, Royal Society of Chemistry, London, pp. 485-508. Link to pdf
34) Conde, D., Aubriot, L., Bonilla, S. and R. Sommaruga (2002) Marine intrusions in a coastal lagoon enhance the negative effect of solar UV radiation on phytoplankton photosynthetic rates. Marine Ecology Progress Series 240: 57-70. Link to pdf
33) Tartarotti, B. and R. Sommaruga (2002) The effect of different methanol concentrations and temperatures on the extraction of mycosporine-like amino acids (MAAs) in algae and zooplankton. Archiv für Hydrobiologie 154: 691-703. Link to pdf
32) Rocco, V.E., O. Oppezzo, R. Pizarro, R. Sommaruga, M. Ferraro, and H.E. Zagarese (2002) Ultraviolet damage and counteracting mechanisms in the copepod Boeckella poppei from Antarctic freshwater lakes. Limnology and Oceanography 47: 837-847. Link to pdf
31) Laurion, I., A. Lami, and R. Sommaruga (2002) Distribution of mycosporine-like amino acids and photoprotective carotenoids among freshwater phytoplankton assemblages. Aquatic Microbial Ecology 26: 283-294. Link to pdf
30) Neale, P.J., P. Bossard, Y. Huot, and R. Sommaruga (2001) Incident and in situ irradiance in Lakes Cadagno and Lucerne: A comparison of methods and models. Aquatic Sciences 63: 250-264. Link to pdf
29) Hofer, J. and R. Sommaruga (2001) Seasonal dynamics of viruses in an alpine lake: importance of filamentous forms. Aquatic Microbial Ecology 26: 1-11. Link to pdf
28) Sommaruga, R. (2001) Die Rolle der UV-Strahlung in Binnengewässern. In: Ökologie und Schutz von Seen (M. Dokulil, A. Hamm, J.-G- Kohl, Hrsg.), Facultas, UTB, Wien, p. 341-360.
27) Laybourn-Parry, J., J. S. Hofer, and R. Sommaruga (2001) Viruses in the plankton of freshwater and saline Antarctic lakes. Freshwater Biology 46: 1279-1287. Link to pdf
26) Tartarotti, B., I. Laurion, and R. Sommaruga (2001) Large variability in the concentration of mycosporine-like amino acids among zooplankton from lakes located across an altitude gradient. Limnology and Oceanography 46: 1546-1552. Link to pdf
25) Sommaruga, R. (2001) The role of UV radiation in the ecology of alpine lakes. Journal of Photochemistry and Photobiology B: Biology 62: 35-42. Link to pdf
24) Conde, D., L. Aubriot and R. Sommaruga (2000) Changes in UV penetration associated with marine intrusions and the freshwater discharge in a shallow coastal lagoon of the Southern Atlantic Ocean. Marine Ecology Progress Series 207: 19-31. Link to pdf
23) Siebeck, O., R. Sommaruga and B. Tartarotti (2000) Auswirkungen der UV-Strahlung auf heterotrophe aquatische Organismen. In: Handbuch der Umweltveränderungen und Ökotoxikologie, Band 3A, Aquatische Systeme (R. Guderian and G. Gunkel, Hrsg.), Springer-Verlag, Berlin, p. 243-264.
22) Laurion, I., M. Ventura, J. Catalan, R. Psenner, and R. Sommaruga (2000) Attenuation of ultraviolet radiation in mountain lakes: Factors controlling the among- and within-lake variability. Limnology and Oceanography 45: 1274-1288. Link to pdf
21) Sommaruga, R. and A. Buma (2000) UV-induced cell damage is species-specific among aquatic phagotrophic protozoans. Journal of Eukaryotic Microbiology 47: 450-455. Link to pdf
20) Sommaruga, R., R. Psenner, E. Schaferer, K. Koinig, S. Sommaruga-Wögrath (1999) Dissolved organic carbon concentration and phytoplankton biomass in high-mountain lakes of the Austrian Alps: potential effect of climatic warming on UV underwater attenuation. Arctic Antarctic and Alpine Research 31: 247-254. Link to JSTOR pdf
19) Sommaruga, R., B. Sattler, A. Oberleiter, A. Wille, S. Sommaruga-Wögrath, R. Psenner, M. Felip, L. Camarero, S. Pina, R. Gironés, and J. Catalán (1999) An in situ enclosure experiment to test the solar UVB impact on plankton in a high altitude mountain lake: Effects on the microbial food web. Journal of Plankton Research 21: 859-876. Link to pdf
18) Sommaruga, R. and F. Garcia-Pichel (1999) UV-absorbing mycosporine-like compounds in planktonic and benthic organisms from a high-mountain lake. Archiv für Hydrobiologie 144: 255-269. Link to pdf
17) Tartarotti, R., S. Cabrera, R. Psenner, and R. Sommaruga (1999) Survivorship of Cyclops abyssorum tatricus (Cyclopoida, Copepoda) and Boeckella gracilipes (Calanoida, Copepoda) under ambient levels of solar UV radiation in two high mountain lakes. Journal of Plankton Research 21: 549-560. Link to pdf
16) Pina, S, A. Creus, N. González, R. Gironés, M. Felip, and R. Sommaruga (1998) Abundance, morphology and distribution of planktonic virus-like particles in two high-mountain lakes. Journal of Plankton Research 20: 2413-2421. Link to pdf
15) Sommaruga, R., Obernosterer, I., Herndl, G. J. and Psenner, R. (1997) Inhibitory effect of solar radiation on thymidine and leucine incorporation by freshwater and marine bacterioplankton. Applied and Environmental Microbiology 63: 4178-4184. Link to pdf
14) Halac, S., Felip, M., Camarero, L., Sommaruga-Wögrath, S., Psenner, R., Catalan, J. and R. Sommaruga (1997) An in situ enclosure experiment to test the solar UV-B impact on microplankton in a high altitude mountain lake: Lack of effect on phytoplankton species composition and growth. Journal of Plankton Research 11: 1671-1687. Link to pdf
13) Sommaruga, R. and R. Robarts (1997) The significance of autotrophic and heterotrophic picoplankton in hypertrophic lakes. FEMS Microbiology Ecology 24: 187-200. Link to pdf
12) Sommaruga, R. and D. Conde (1997) Seasonal variability of metabolically active bacterioplankton in the euphotic zone of a hypertrophic lake. Aquatic Microbial Ecology 13: 241-248. Link to pdf
11) Sommaruga, R. and R. Psenner (1997) Ultraviolet radiation in a high mountain lake of the Austrian Alps: air and underwater measurements. Photochemistry and Photobiology 65: 957-963. Link to pdf
10) Sommaruga-Wögrath, S., Koinig, K, Schmidt, R., R. Tessadri, Sommaruga, R., and R. Psenner (1997) Temperature effects on the acidity of remote alpine lakes. Nature 387: 64-67. Link to pdf
9) Sommaruga, R, Oberleiter, A., and R. Psenner (1996) Effect of UV radiation on the bacterivory of a heterotrophic nanoflagellate. Applied and Environmental Microbiology 62: 4395-4400. Link to pdf, Erratum
8) Sommaruga, R., Krössbacher, M., Salvenmoser, W. Catalan, J. and R. Psenner (1995) Presence of large virus-like particles in a eutrophic reservoir. Aquatic Microbial Ecology 9: 305-308. Link to pdf
7) Sommaruga, R. and R. Psenner (1995) Permanent presence of grazing-resistant bacteria in a hypertrophic lake. Applied and Environmental Microbiology 61: 3457-3459. Link to pdf
6) Sommaruga, R. (1995). Microbial and classical food webs: a visit to a hypertrophic lake. FEMS Microbiology Ecology 17: 257-270. Link to pdf
5) Sommaruga, R. and R. Psenner (1995) Trophic interactions within the microbial food web in Piburger See (Austria). Archiv für Hydrobiologie 132: 257-278. Link to pdf
4) Sommaruga, R. and R. Psenner (1993) Nanociliates from a mesotrophic lake: The order Prostomatida and its relevance in the microbial food web. Aquatic Sciences 55: 179-187. Link to pdf
3) Sommaruga, R., N. Mazzeo, and D. Crosa (1993) The decomposition of Pistia stratiotes L. (Araceae). Internationale Revue der gesamten Hydrobiologie 78: 263-272. Link to pdf
2) Psenner, R. and R. Sommaruga (1992) Are rapid changes in bacterial biomass caused by shifts from top-down to bottom-up control? Limnology and Oceanography 37: 1092-1100. Link to pdf
1) Sommaruga, R.(1991) Sediment oxygen demand in a man-made lake Ton-Ton (Uruguay). Hydrobiologia 215: 215-221. Link to pdf