BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-10-8223-2013 Effects of nitrogen fertilization on the forest floor carbon balance over the growing season in a boreal pine forest Metcalfe D. B. 1 Eisele B. 2 Hasselquist N. J. 1 Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83, Umeå, Sweden Institute of Hydrology, University of Freiburg, Fahnenbergplatz, 79098, Freiburg, Germany 12 12 2013 10 12 8223 8231 Copyright: © 2013 D. B. Metcalfe et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/10/8223/2013/bg-10-8223-2013.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/10/8223/2013/bg-10-8223-2013.pdf

Boreal forests play a key role in the global carbon cycle and are facing rapid shifts in nitrogen availability with poorly understood consequences for ecosystem function and global climate change. We quantified the effects of increasing nitrogen availability on carbon fluxes from a relatively understudied component of these forests – the forest floor – at three intervals over the summer growing period in a northern Swedish Scots pine stand. Nitrogen addition altered both the uptake and release of carbon dioxide from the forest floor, but the magnitude and direction of this effect depended on the time during the growing season and the amount of nitrogen added. Specifically, nitrogen addition stimulated net forest floor carbon uptake only in the late growing season. We find evidence for species-specific control of forest floor carbon sink strength, as photosynthesis per unit ground area was positively correlated only with the abundance of the vascular plant <i>Vaccinium myrtillus</i> and no others. Comparison of understorey vegetation photosynthesis and respiration from the study site indicates that understorey vegetation photosynthate was mainly supplying respiratory demands for much of the year. Only in the late season with nitrogen addition did understorey vegetation appear to experience a large surplus of carbon in excess of respiratory requirements. Further work, simultaneously comparing all major biomass and respiratory carbon fluxes in forest floor and tree vegetation, is required to resolve the likely impacts of environmental changes on whole-ecosystem carbon sequestration in boreal forests.

 References Ågren, G. I., Bosatta, E., and Magill, A. H.: Combining theory and experiment to understand effects of inorganic nitrogen on litter decomposition, Oecologia, 128, 94–98, 2001. Allison, S. D., Czimzik, C. I., and Treseder, K. K.: Microbial activity and soil respiration under nitrogen addition in Alaskan boreal forest, Glob. Change Biol., 14, 1156–1168, 2008. Berg, B. and Matzner, E.: Effect of N deposition on decomposition of plant litter and soil organic matter in forest systems, Environ. Rev., 5, 1–25, 1997. Bobbink, R., Hicks, K., Galloway, J., Spranger, T., Alkemade, R., Ashmore, M., Bustamante, M., Cinderby, S., Davidson, E., Dentener, F., Emmett, B., Erisman, J-W., Fenn, M., Gilliam, F., Nordin, A., Pardo, L., and De Vries, W.: Global assessment of nitrogen deposition effects on terrestrial plant diversity: a synthesis, Ecol. App., 20, 30–59, 2010. Bond-Lamberty, B. and Thomson, A.: A global database of soil respiration data, Biogeosciences, 7, 1915–1926, <a href="http://dx.doi.org/10.5194/bg-7-1915-2010">https://doi.org/10.5194/bg-7-1915-2010</a>, 2010. Carpenter, S. R:. Microcosm experiments have limited relevance for community and ecosystem ecology, Ecology, 77, 677–680, 1996. Carpenter, S. R: The need for large-scale experiments to assess and predict the response of ecosystems to perturbation, in: Successes, limitations and frontiers in ecosystem science, edited by: Pace, M. L. and Groffman, P. M., 287–312, Springer-Verlag, New York, 1998. Chapin III, F. S.: Nitrogen and phosphorus nutrition and nutrient cycling by evergreen and deciduous understory shrubs in an Alaskan black spruce forest, Can. J. For. Res., 13, 773–781, 1983. De Vries, W., Reinds, G. J., Gundersen, P., and Sterba, H.: The impact of nitrogen deposition on carbon sequestration in European forests and forest soils. Glob. Change Biol., 12, 1151–1173, 2006. Eckstein, R. L., Karlsson, P. S., and Weih, M.: Leaf life span and nutrient resorption as determinants of plant nutrient conservation in temperate-arctic regions, New Phyt., 143, 177–189, 1999. Gamfeldt, L., Snäll, T., Bagchi, R., Jonsson, M., Gustafsson, L., Kjellander, P., Ruiz-Jaen, M. C., Fröberg, M., Stendahl, J., Philipson, C. D., Mikusi\'nski, G., Andersson, E., Westerlund, B., Andrén, H., Moberg, F., Moen, J., and Bengtsson, J.: Higher levels of multiple ecosystem services are found in forests with more tree species, Nature Comm., 4, 1340, <a href="http://dx.doi.org/10.1038/ncomms2328">https://doi.org/10.1038/ncomms2328</a>, 2013. Gärdenäs, A. I.: Soil respiration fluxes measured along a hydrological gradient in a Norway spruce stand in south Sweden (Skogaby), Plant Soil, 221, 273–280, 2000. Galloway, J. N., Townsend, A. R., Erisman, J. W., Bekunda, M., Zucong, C., Freney, J. R., Martinelli, L. A., Seitzinger, S. P., and Sutton, M. A.: Transformation of the nitrogen cycle: recent trends, questions, and potential solutions, Science, 320, 889–892, 2008. Goulden, M. L. and Crill P. M.: Automated measurements of CO<sub>2</sub> exchange at the moss surface of a black spruce forest, Tree Phys., 17, 537–542, 1997. Gower, S. T., Krankina, O., Olson, R. J., Apps, M., Linder, S., and Wang, C.: Net primary production and carbon allocation patterns of boreal forest ecosystems, Ecol. App., 11, 1395–1411, 2001. Hasselquist, N. J., Metcalfe, D. B., and Högberg, P.: Contrasting effects of low and high nitrogen additions on soil CO<sub>2</sub> flux components and ectomycorrhizal fungal sporocarp production in a boreal forest, Glob. Change Biol., 18, 3596–3605, 2012. Heijmans, M. M. P. D., Arp W. J., and Stuart Chapin III, F.: Carbon dioxide and water vapour exchange from understory species in boreal forest, Agric. For. Met., 123, 135–147, 2004. Högberg, M. N., Briones, M. J. I., Keel, S. G., Metcalfe, D. B., Campbell, C., Midwood, A. J., Thornton, B., Hurry, V., Linder, S., Näsholm, T., and Högberg, P.: Quantification of effects of season and nitrogen supply on tree below-ground carbon transfer to ectomycorrhizal fungi and other soil organisms in a boreal pine forest, New Phyt., 187, 485–493, 2010. Hurlbert, S. H: Pseudoreplication and the design of ecological field experiments, Ecol. Mono., 54, 187–211, 1984. Janssens, I. A., Dieleman, W., Luyssaert, S., Subke, J.-A., Reichstein, M., Ceulemans, R., Ciais, P., Dolman, A. J., Grace, J., Matteucci, G., Papale, D., Piao, S. L., Schulze, E.-D., Tang, J., and Law, B. E.: Reduction of forest soil respiration in response to nitrogen deposition, Nature Geo., 3, 315–322, 2010. Knorr, M., Frey, S. D., and Curtis, P. S.: Nitrogen additions and litter decomposition: a meta-analysis, Ecology, 86, 3252–3257, 2005. Kolari, P., Pumpanen, J., Kulmala, L., Ilvesniemi, H., Nikinmaa, E., Grönholm, T., and Hari, P.: Forest floor vegetation plays an important role in photosynthetic production of boreal forests, For. Ecol. Manag., 221, 241–248, 2006. Lamarque, J.-F., Kiehl, J. T., Brasseur, G. P., Butler, T., Cameron-Smith, P., Collins, W. D., Collins, W. J., Granier, C., Hauglustaine, D., Hess, P. G., Holland, E. A., Horowitz, L., Lawrence, M. G., McKenna, D., Merilees, P., Prather, M. J., Rasch, P. J., Rotman, D., Shindell, D., and Thornton, P.: Assessing future nitrogen deposition and carbon cycle feedback using a multimodel approach: Analysis of nitrogen deposition, J. Geophys. Res., 110, D19303, <a href="http://dx.doi.org/10.1029/2005JD005825">https://doi.org/10.1029/2005JD005825</a>, 2005. Lieffers, V. J., Messier, C., Stadt, K. J., Gendron, F., and Comeau, P. G.: Predicting and managing light in the understory of boreal forests, Can. J. For. Res., 29, 796–811, 1999. Mencuccini, M. and Grace, J.: Hydraulic conductance, light interception and needle nutrient concentration in Scots pine stands and their relations with net primary productivity, Tree Phys., 16, 459–468, 1996. Metcalfe, D. B., Fisher, R. A., and Wardle, D. A.: Plant communities as drivers of soil respiration: pathways, mechanisms, and significance for global change, Biogeosciences, 8, 2047–2061, <a href="http://dx.doi.org/10.5194/bg-8-2047-2011">https://doi.org/10.5194/bg-8-2047-2011</a>, 2011. Myneni, R. B., Dong, J., Tucker, C. J., Kaufmann, R. K., Kauppi, P. E., Liski, J., Zhou, L., Alexeyev, V., and Hughes, M. K.: A large carbon sink in the woody biomass of Northern forests, PNAS-USA, 98, 14784–14789, 2001. Nilsson, L. O. and Wallander, H.: Production of external mycelium by ectomycorrhizal fungi in a Norway spruce forest was reduced in response to nitrogen fertilization, New Phyt., 158, 409–416, 2003. Nilsson, M.-C., and Wardle, D. A.: Understory vegetation as a forest ecosystem driver: evidence from the northern Swedish boreal forest, Front. Ecol. Environ., 3, 421–428, 2005. Nordin, A., Strengbom, J., Witzell, J., Näsholm, T., and Ericson, L.: Nitrogen deposition and the biodiversity of boreal forests: implications for the nitrogen critical load, Ambio, 34, 20–24, 2005. Olsson, P., Linder, S., Giesler, R., and Högberg, P.: Fertilization of boreal forest reduces both autotrophic and heterotrophic soil respiration, Glob. Change Biol., 11, 1745–1753, 2005. Osmond, B., Ananyev, G., Berry, J., Langdon, C., Kolber, Z., Lin, G., Monson, R., Nichol, C., Rascher, U., Schurr, U., Smith, S. and Yakir, D: Changing the way we think about global change research: scaling up in experimental ecosystem science, Glob. Change Biol., 10, 393–407, 2004. Ostle, N. J., Smith, P., Fisher, R., Ian Woodward, F., Fisher, J. B., Smith, J. U., Galbraith, D., Levy, P., Meir, P., McNamara, N. P., and Bardgett, R. D.: Integrating plant–soil interactions into global carbon cycle models, J. Ecol., 97, 851–863, 2009. Pan, Y, Birdsey, R. A., Fang, J., Houghton, R., Kauppi, P. E., Kurz, W. A., Phillips, O. L., Shvidenko, A., Lewis, S. L., Canadell, J. G., Ciais, P., Jackson, R. B, Pacala, S. W., McGuire, A. D., Piao S., Rautiainen, A., Sitch, S., and Hayes, D. A.: A large and persistent carbon sink in the world's forests, Science, 333, 988–993, 2011. Reay, D. S., Dentener, F., Smith, P., Grace, J., and Feely, R. A.: Global nitrogen deposition and carbon sinks, Nature Geo., 1, 430–437, 2008. Richardson, A. D., Jenkins, J. P., Braswell, B. H., Hollinger, D. Y., Ollinger, S. V., and Smith, M.-L.:. Use of digital webcam images to track spring green-up in a deciduous broadleaf forest, Oecologia, 152, 323–334, 2007. Shaver, G., Rastetter, E. B., Salmon, V., Street, L. E., van de Weg, M. J., Rocha, A., van Wijk, M. T., and Williams, M:. Pan-Arctic modeling of net ecosystem exchange of CO<sub>2</sub>, Phil. Trans. Royal Soc. Lond. B., 368, 1624, https://doi.org/10.1098/rstb.2012.048. 2013. Strengbom, J. and Nordin, A.: Commercial forest fertilization causes long-term residual effects in ground vegetation of boreal forests, For. Ecol. Manag., 256, 2175–2181, 2008. Strengbom, J., Nordin, A., Näsholm, T., and Ericson, L.: Slow recovery of boreal forest ecosystem following decreased nitrogen input, Funct. Ecol., 15, 451–457, 2001. Sullivan, T. J: Ecosystem manipulation experimentation as a means of testing a biogeochemical model, Environ. Manage., 21, 15–21, 1997. Svensson, B. M., Rydin, H., and Carlsson, B. Å.: Clonal plants in the community, in: Vegetation ecology, edited by: Van der Maarel, E. and Bakker, J. P., 129–146, Wiley-Blackwell, Hoboken, 2009. Tamm, C. O.: Nitrogen in terrestrial ecosystems: questions of productivity, vegetational changes, and ecosystem stability, Springer-Verlag, Berlin, 1991. Vallack, H. W., Leronni, V., Metcalfe, D. B., Högberg, P., Ineson, P., and Subke, J. A.: Application of nitrogen fertilizer to a boreal pine forest has a negative impact on the respiration of ectomycorrhizal hyphae, Plant Soil, 352, 405–417, 2012. Vicca, S., Luyssaert, S., Peñuelas, J., Campioli, M., Chapin, F. S., Ciais, P., Heinemeyer, A., Högberg, P., Kutsch, W. L., Law, B. E., Malhi, Y., Papale, D., Piao, S. L., Reichstein, M., Schulze, E. D., and Janssens, I. A.: Fertile forests produce biomass more efficiently, Ecol. Lett., 15, 520–526, 2012. Vitousek, P. M. and Howarth, R. W.: Nitrogen limitation on land and in the sea: how can it occur?, Biogeochemistry, 13, 87–115, 1991. Vitousek, P. M., Aber, J. D., Howarth, R. W., Likens, G. E., Matson, P. A., Schindler, D. W., Schlesinger, W. H., and Tilman, D. G.: Human alteration of the global nitrogen cycle: sources and consequences, Ecol. App., 7, 737–750, 1997. Wardle, D. A., Hörnberg, G., Zackrisson, O., Kalela-Brundin, M., Coomes, D. A.: Long-term effects of wildfire on ecosystem properties across an island area gradient, Science, 300, 972–75, 2003. Wardle, D. A. and Zackrisson, O.: Effects of species and functional group loss on island ecosystem properties, Nature, 435, 806–810, 2005. Wardle, D. A., Nilsson, M.-C., Gallet, C., and Zackrisson, O.: An ecosystem-level perspective of allelopathy, Biol. Rev., 73, 305–319, 1998. Whitehead, D. and Gower S. T.: Photosynthesis and light-use efficiency by plants in a Canadian boreal forest ecosystem, Tree Phys., 21, 925–929, 2001.