Abstract
Along a long-term ecosystem development gradient, soil nutrient contents and mineralogical properties change, therefore probably altering soil microbial communities. However, knowledge about the dynamics of soil microbial communities during long-term ecosystem development including progressive and retrogressive stages is limited, especially in mineral soils. Therefore, microbial abundances (quantitative PCR) and community composition (pyrosequencing) as well as their controlling soil properties were investigated in soil depth profiles along the 120,000 years old Franz Josef chronosequence (New Zealand). Additionally, in a microcosm incubation experiment the effects of particular soil properties, i.e., soil age, soil organic matter fraction (mineral-associated vs. particulate), O2 status, and carbon and phosphorus additions, on microbial abundances (quantitative PCR) and community patterns (T-RFLP) were analyzed. The archaeal to bacterial abundance ratio not only increased with soil depth but also with soil age along the chronosequence, coinciding with mineralogical changes and increasing phosphorus limitation. Results of the incubation experiment indicated that archaeal abundances were less impacted by the tested soil parameters compared to Bacteria suggesting that Archaea may better cope with mineral-induced substrate restrictions in subsoils and older soils. Instead, archaeal communities showed a soil age-related compositional shift with the Bathyarchaeota, that were frequently detected in nutrient-poor, low-energy environments, being dominant at the oldest site. However, bacterial communities remained stable with ongoing soil development. In contrast to the abundances, the archaeal compositional shift was associated with the mineralogical gradient. Our study revealed, that archaeal and bacterial communities in whole soil profiles are differently affected by long-term soil development with archaeal communities probably being better adapted to subsoil conditions, especially in nutrient-depleted old soils.
Highlights
Soil microbial communities mediate key processes in soil ecosystem functioning including organic matter (OM) degradation, nutrient cycling, and mineral weathering
Our study provides first insights in patterns of microbial communities in soil depth profiles along the long-term ecosystem development gradient of the Franz Josef chronosequence
The archaeal to bacterial abundance ratio increased with soil depth, and with soil age with archaeal abundances being less impacted by the mineral-associated soil fraction and soil age than Bacteria
Summary
Soil microbial communities mediate key processes in soil ecosystem functioning including organic matter (OM) degradation, nutrient cycling, and mineral weathering. During the early stage of pedogenesis heterotrophic and phototrophic pioneer microorganisms are responsible for biological weathering of the bedrock material and create interfaces for OM and nutrient turnover, e.g., in biofilms (Tscherko et al, 2003; Nemergut et al, 2007; Schulz et al, 2013; Haynes, 2014). Thereby they provide favorable conditions for the colonization by plants (Schulz et al, 2013). Many studies reported that the bacterial community composition considerably changed during progression with highest bacterial species turnover rates during the first years (Nemergut et al, 2007; Schütte et al, 2009; Wu et al, 2012; Zumsteg et al, 2012; Jangid et al, 2013a,b)
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