| 1. |
- Turner, Stephanie, et al.
(författare)
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Distinct pattern of nitrogen functional gene abundances in top- and subsoils along a 120,000-year ecosystem development gradient
- 2019
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Ingår i: Soil Biology and Biochemistry. - : Elsevier. - 0038-0717 .- 1879-3428. ; 132, s. 111-119
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Tidskriftsartikel (refereegranskat)abstract
- Soil microorganisms are key players of the nitrogen cycle and relevant for soil development. While the community structure of nitrogen-cycling microorganisms during initial soil development is already well investigated, knowledge about the patterns during long-term ecosystem development is limited. In this study, nitrogen functional genes of ammonia-oxidizers (amoA), nitrate-reducers (narG), and chitin-degraders (chiA) were determined via quantitative PCR and the functional community composition of archaeal ammonia-oxidizers was analyzed via clone libraries and DNA sequencing (amoA) in soil depth profiles along the 120,000-year Franz Josef chronosequence (New Zealand). The results show that absolute nitrogen functional gene abundances change significantly during long-term soil development. In organic layers, narG and chiA gene abundances were highest in young to intermediate-aged soils and then decreased following progressive and retrogressive development of the vegetation. While relative archaeal amoA gene abundance (proportional to total cell counts) decreased in the oldest phosphorus-limited topsoils, relative narG and chiA gene abundances remained constant. In subsoils, archaeal amoA and narG gene abundances also decreased with ecosystem retrogression that coincided with the increasing content of iron and aluminum oxides as well as other clay-sized minerals. In contrast, subsoil chiA gene abundances were hardly affected by soil age. The analysis of the archaeal amoA community revealed a compositional shift during long-term ecosystem development. Our study provides evidence that the community structure of nitrogen-cycling microorganisms in top- and subsoils is significantly affected by long-term ecosystem development and suggests an important role of the mineral phase in subsoils.
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| 2. |
- Turner, Stephanie, et al.
(författare)
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Microbial utilization of mineral-associated nitrogen in soils
- 2017
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 104, s. 185-196
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Tidskriftsartikel (refereegranskat)abstract
- In soils, a large portion of organic nitrogen (ON) is associated with minerals and thus, possibly stabilized against biological decay. We therefore tested if mineral-associated N is an important N source for soil microorganisms, and which soil parameters control its bioavailability. Microcosm experiments with mineral-associated organic matter, obtained as heavy fraction (HF) via density fractionation, and bulk soil from mineral topsoil of the Franz Josef chronosequence were conducted for 125 days. We examined the effects of O2 status, soil age (differences in mineralogical properties), as well as cellulose and phosphate additions on the turnover of mineral-associated N. Using a combination of activity measurements and quantitative PCR, microbial N transformation rates and abundances of N-related functional genes (amoA, narG, chiA) were determined. Similar or higher values for microbial N cycling rates and N-related functional abundances in the HF compared to bulk soil indicated that mineral-associated N provides an important bioavailable N source for soil microorganism. The turnover of mineral-associated N was mainly controlled by the O2 status. Besides, soil mineralogical properties significantly affected microbial N cycling and related gene abundances with the effect depending on the N substrate type (ON, NH4+ or NO3−). In contrast, cellulose or phosphate addition hardly enhanced microbial utilization of mineral-associated N. The results of our microcosm study indicate that mineral-associated N is highly bioavailable in mineral topsoils, but effects of the mineral phase differ between N cycling processes.
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