Relating N transformation and transport to microbial activities in forest soils
Final Report Abstract
Global nitrogen deposition rates have quadrupled since pre-industrial times, causing structural and functional changes of terrestrial ecosystems. Therefore, different emission reduction policies were devised. The aim of this project was to investigate whether and how organic matter (OM) and nitrogen processing in soils respond to a decline in atmospheric N deposition, as proposed by the ‘Gothenburg Protocol’. The research was conducted at a N-saturated spruce forest (current N deposition: 34 kg ha-1 yr-1; critical N load: 14 ha-1 yr-1), where N deposition has been reduced to 11.5 kg ha-1 yr-1 since 1991 at one of the experimental plots. Within the application package, five subprojects investigated changes of biogeochemical processes and microbial communities throughout the soil profiles at three plots on which the entire throughfall water is permanently collected, filtered to remove the organic debris and immediately resprinkled onto the plots either without deionization or after partly deionization ( reduced N deposition). An unroofed plot was also considered to evaluate the impact of the roof constructions on the studied processes. The five subprojects were respectively dealing with: a) characterizing different soil compounds, their degradation and/or their distribution, b) tracing fungal genes encoding laccases, oxidative exoenzymes modifying complex soil organic compounds, c) monitoring enzymes and soil microorganisms (bacteria) involved in N cycling and the strongly interconnected C cycling, d) implementing a microarray to trace the diversity and community composition of soil fungi and e) studying the diversity of nitrogen fixing bacteria with molecular tools. In general significant effects of the N deposition manipulation were not observed, because of an ongoing N saturation in the soil despite 14.5 years of N input reduction. Effects were mainly detected at the most superficial horizons. Ecological factor such as the substrate availability within the soil profile, seasonal variations or effects of the roof construction (changed temperature and/or light regimes) appeared to have more prominent effects on many of the investigated subjects than the reduction of the N deposition. The detected effects were not sensitive at all investigated levels. While microbial communities reacted sensitive, the enzymatic activities appeared to be more stable. In general the results of all five research subprojects pin point a high resilience of element saturation in soils resulting from more than a century of atmospheric depositions. Therefore future investigations should in addition consider virgin sites that have not been exposed so long to anthropogenic impacts.
Publications
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(2008). Towards a universally adaptable method for quantitative extraction of high-purity nucleic acids from soil. Journal of Microbiological Methods 75: 19–24
Peršoh, D., Theuerl, S., Buscot, F. & Rambold, G.
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(2009). Microbial biomass and enzyme activities under reduced nitrogen deposition in a spruce forest soil. Applied Soil Ecology 43: 11–21
Enowashu E., Poll C., Lamersdorf N. & Kandeler E.
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(2009). New protocols for the extraction of nucleic acids from soil. Journal of Applied Microbiology 107, 2118
Peršoh, D., & Rambold, G.
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(2009). Response of total and nitrate-dissimilating bacteria to reduced N deposition in a spruce forest soil profile. FEMS Microbiology Ecology 67, 444-454
Kandeler, E., Brune, T., Enowashu, E., Dörr, N., Guggenberger, G., Lamersdorf, N. & Philipport, L.
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(2010). Response of fungal communities containing laccase encoding genes and lignin decomposition to reduced N deposition in a spruce forest soil. FEMS Microbiology Ecology 73: 166–177
Theuerl, S., Dörr, N., Guggenberger, G., Langer, U., Kaiser, K., Lamersdorf, N. & Buscot, F.
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(2010). Slow response of soil organic matter to the reduction in atmospheric nitrogen deposition in a Norway spruce forest. Global Change Biology 16: 2990–3003
Dörr, N., Kaiser, K., Mikutta, R. & Guggenberger, G.
