Fate and stabilization of labile carbon in a sandy boreal forest soil: A question of nitrogen availability?
Meyer, Nele; Sietiö, Outi-Maaria; Adamczyk, Sylwia; Ambus, Per; Biasi, Christina; Glaser, Bruno; Kalu, Subin; Martin, Angela; Mganga, Kevin Z.; Olin, Miikka; Seppänen, Aino; Shrestha, Rashmi; Karhu, Kristiina
(2023) Applied Soil Ecology, volume 191
(Article)
Abstract
Labile carbon (C) fractions, such as sugars, may persist in soil due to their incorporation into microbial biomass and are ultimately stabilized as microbial necromass as part of stable soil organic matter (SOM). However, the underlying factors and mechanisms are currently highly debated. To address this knowledge gap, we conducted
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a 1-year greenhouse experiment including four treatments: (1) bare soil, (2) bare soil and nitrogen (N) fertilization, (3) soil planted with a tree, and (4) tree and N. The boreal forest soil was a sandy and nutrient-poor Podzol taken from 0 to 20 cm depth and trees were Pinus sylvestris. We hypothesized that: (1) originally labile C does not accumulate under N-deficient conditions, as microbial residues may be intensely recycled for N acquisition and (2) differences in N supply and demand change the functionality and composition of the microbial community, which will be reflected in the stabilization of microbial C. We added 13C glucose to the soil and measured 13C recovery to trace the fate of added C in soil, microbial biomass (MBC), dissolved organic C (DOC), phospholipid fatty acids (PLFA), and amino sugars as biomarker for microbial necromass. We also analyzed microbial community structure and enzyme activities. Around 40 % of the added C was mineralized after one day. Mineralization of the added C continued for 6 months, but stabilized thereafter. After 1 year, the treatment with both tree and N fertilization had the highest amount of added 13C (34 %) remaining in soil compared to the other treatments (18 %). The recovery of 13C in DOC was <1 % from the 3rd day onwards, but remained higher in MBC (2 %) and microbial necromass (1.5 %) after 1 year. N fertilization increased bacterial growth on 13C-glucose and abundance of gram-positive bacteria, while trees increased the abundance of symbiotrophic fungi. The formation of more stable C in the treatment with both tree and N indicates that under those conditions, recycling of microbial necromass for N acquisition is lower and the changed microbial composition leaves behind more stable residues.
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Keywords: Microbial carbon pump, Microbial community, Microbial necromass, Microbial nitrogen mining, Nitrogen limitation, Pinus sylvestris, Agricultural and Biological Sciences (miscellaneous), Soil Science, Ecology
ISSN: 0929-1393
Publisher: Elsevier
Note: Funding Information: This research was supported by funds from the Academy of Finland (grant numbers 319952 , 316401 , 348824 ), Helsinki Institute of Life Science (HiLIFE) (a HiLIFE Fellow Grant to K.K. covering e.g. the salary of N.M.) and Maj and Tor Nessling Foundation (personal grant to O.-M.S.). We thank Marjut Wallner and Yi Xu for their assistance with laboratory analysis, Daniel Richterich for his support in the greenhouse, Marianne Benesch for conducting δ 13 C measurements of amino sugars, Gerhard Gebauer (BayCEER - Laboratory of Isotope Biogeochemistry, Bayreuth) for conducting δ 13 C measurements of charcoal, and Jussi Heinonsalo for providing the P. sylvestris seedlings. The CSC IT Center for Science, Finland is acknowledged for providing computational resources for processing the sequencing data. Funding Information: This research was supported by funds from the Academy of Finland (grant numbers 319952, 316401, 348824), Helsinki Institute of Life Science (HiLIFE) (a HiLIFE Fellow Grant to K.K. covering e.g. the salary of N.M.) and Maj and Tor Nessling Foundation (personal grant to O.-M.S.). We thank Marjut Wallner and Yi Xu for their assistance with laboratory analysis, Daniel Richterich for his support in the greenhouse, Marianne Benesch for conducting δ13C measurements of amino sugars, Gerhard Gebauer (BayCEER - Laboratory of Isotope Biogeochemistry, Bayreuth) for conducting δ13C measurements of charcoal, and Jussi Heinonsalo for providing the P. sylvestris seedlings. The CSC IT Center for Science, Finland is acknowledged for providing computational resources for processing the sequencing data. Publisher Copyright: © 2023 Elsevier B.V.
(Peer reviewed)