Abstract
We studied bacterial and fungal colonization of submerged plant litter, using a known Si-accumulator (Equisetum arvense), in experimental microcosms during one month. We specifically addressed the microbial decomposer role concerning biogenic silica (bSiO2) dissolution from the degrading litter. To vary the rates and level of microbial colonization, the litter was combined with a range of mineral nitrogen (N) and phosphorous (P) supplements. Overall microbial growth on plant litter increased with higher levels of N and P. There was a tendency for higher relative bacterial than fungal stimulation with higher nutrient levels. Differences in microbial colonization of litter between treatments allowed us to test how Si remineralization from plants was influenced by microbial litter decomposition. Contrary to previous results and expectations, we observed a general reduction in Si release from plant litter colonized by a microbial community, compared with sterile control treatments. This suggested that microbial growth resulted in a reduction of dissolved Si concentrations, and we discuss candidate mechanisms to explain this outcome. Hence, our results imply that the microbial role in plant litter associated Si turnover is different from that commonly assumed based on bSiO2 dissolution studies in aquatic ecosystems.
Highlights
Microorganisms are the principal regulators of biogeochemical cycles (Rousk and Bengtson 2014)
In microcosms amended with higher N and P amounts (C:N:P 50:1:1 and 25:1:1) bacterial growth rates increased to a maximum rate at about day 7 (∼17 and ∼32 pmol Leu h−1 g−1 dry litter, respectively)
Bacterial growth rates in treatment C:N:P 50:1:1 converged to levels similar to C:N:P 200:1:1 and 100:1:1, while bacterial growth in the C:N:P 25:1:1 treatment remained one order of magnitude higher for the duration of the experiment. This resulted in a cumulative bacterial growth that differed between treatments (C:N:P 25:1:1 > 50:1:1, 100:1:1, 200:1:1, C:N:P 50:1:1 > 100:1:1; ANOVA, P = < 0.0001; Fig. 2a)
Summary
Microorganisms are the principal regulators of biogeochemical cycles (Rousk and Bengtson 2014). Microbial colonization of plant litter and its decomposition rate is strongly influenced by nutrient availability (e.g. nitrogen (N) and phosphorous (P)) (Scheu 1993; Henriksen and Breland 1999; Alden, Demoling and Baa ̊ th 2001; Sistla, Shinichi and Schimel 2012) along with substrate carbon (C) quality (Hogberg, Hogberg and Myrold 2007; Strickland et al 2009; Rousk and Frey 2015). The same factors influence the balance between fungal and bacterial colonizers
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