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Indications that long-term nitrogen loading limits carbon resources for soil microbes

Journal article
Authors M. O. Rappe-George
M. Choma
P. Čapek
G. Börjesson
E. Kaštovská
H. Šantrůčková
Annemieke I. Gärdenäs
Published in Soil Biology and Biochemistry
Volume 115
Pages 310-321
ISSN 0038-0717
Publication year 2017
Published at Department of Biological and Environmental Sciences
Pages 310-321
Language en
Links doi.org/10.1016/j.soilbio.2017.07.0...
Keywords Enzyme activity, Microbial biomass, Nitrogen addition, Nitrogen deposition, Nitrogen leaching, Bacteria, Biomass, Enzymes, Fatty acids, Forestry, Leaching, Microorganisms, Nitrogen, Phospholipids, Plants (botany), Soils, Hydrolytic enzyme activities, Microbial community composition, Nitrogen additions, Phospholipid fatty acids, Statistical significance, Loading, Negibacteria, Picea abies, Posibacteria
Subject categories Biological Sciences

Abstract

Microbial communities in the organic horizon (O-horizon) of forest soils play key roles in terrestrial nitrogen (N) cycling, but effects on them of long-term high N loading, by N deposition or experimental addition, are not fully understood. Thus, we investigated N-loading effects on soil microbial biomass N, carbon (C) and phosphorus stoichiometry, hydrolytic and oxidative enzymes, community composition (via phospholipid fatty acids, PLFA) and soil chemistry of the O-horizon in study plots of three well-studied experimental Norway spruce (Picea abies) forests in Sweden and the Czech Republic. These forests span substantial gradients in current N deposition, experimental N addition and nitrate (NO3 −) leaching. Current N deposition ranges from ∼3 kg ha−1 year−1 of N in central Sweden (Stråsan) to ∼15 kg ha−1 year−1 of N in SW Sweden (Skogaby) and Czech Republic (Čertovo). Furthermore, accumulated historical N loading during 1950–2000 (which include experimental N addition performed at Stråsan and Skogaby) ranged ∼200–∼2000 kg ha−1 of N. Across all sites and treatments, current NO3 − leaching ranged from low (∼0.1 kg ha−1 year−1 of N) at Stråsan, to high (∼15 kg ha−1 year−1 of N) at Skogaby and Čertovo. We found significantly lower C/N ratios and greater amounts of extractable inorganic N species in the forest soils’ O-horizons at the high N loading plots. Microbial biomass and basal respiration decreased under experimental N addition treatments and tended to decrease with increased N deposition. Similarly, activities of hydrolytic enzyme activity associated with N acquisition were lower, although differences in activities at specific sites with the highest and intermediate historical N deposition levels failed statistical significance. Conversely, activities of soil hydrolytic enzymes associated with C acquisition were greater in study plots exposed high N loading. PLFA profiles indicated shifts in microbial community composition induced by long-term N load, towards higher and lower relative abundance of Gram-positive and Gram-negative bacteria, respectively (but no changes in fungal relative abundance). Taken together, our results suggest that long-term N loading of N-limited Norway spruce forests aggravates limitation of other resources, likely of C, for soil microbial communities. Although microbial variables in the soil O-horizon differed between plots exposed to low and high current N loading, microbial variables in plots that leached small amounts and large amounts of NO3 − exposed to high N load were similar. © 2017

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