Elevated Air Humidity Changes Soil Bacterial Community Structure in the Silver Birch Stand

Abstract

Soil microbes play a fundamental role in forest ecosystems and respond rapidly to changes in the environment. Simultaneously with the temperature increase the climate change scenarios also predict an intensified hydrological cycle for the Baltic Sea runoff region. The aim of this study was to assess the effect of elevated air humidity on the top soil microbial community structure of a silver birch (Betula pendula Roth.) stand by using a free air humidity manipulation facility (FAHM). The bacterial community structures of bulk soil and birch rhizosphere were analyzed using high-throughput sequencing of bacteria-specific16S rRNA gene fragments and quantification of denitrification related genes. The increased air humidity altered both bulk soil and rhizosphere bacterial community structures, and changes in the bacterial communities initiated by elevated air humidity were related to modified soil abiotic and biotic variables. Network analysis revealed that variation in soil bacterial community structural units is explained by altered abiotic conditions such as increased pH value in bulk soil, while in rhizosphere the change in absorptive root morphology had a higher effect. Among root morphological traits, the absorptive root diameter was strongest related to the bacterial community structure. The changes in bacterial community structures under elevated air humidity are associated with shifts in C, N, and P turnover as well as mineral weathering processes in soil. Increased air humidity decreased the nir and nosZ gene abundance in the rhizosphere bacterial community. The potential contribution of the denitrification to the N2O emission was not affected by the elevated air humidity in birch stand soil. In addition, the study revealed a strong link between the bacterial community structure, abundance of denitrification related genes, and birch absorptive root morphology in the ecosystem system adaptation to elevated air humidity.

Soil Bacterial and Archaeal Communities and Their Potential to Perform N-Cycling Processes in Soils of Boreal Forests Growing on Well-Drained Peat

“…The proportion of the genus Pseudolabrys, whose members metabolize organic acids (Kämpfer et al, 2006) and increase in response to N addition to soil (Eo and Park, 2016), was significantly higher in the birch forest soil communities than in those of the other two forest types and was related to the nirS and nosZII abundances in this study. Contrary to the silver birch stands grown on former agricultural land (Truu et al, 2017), the results of this study suggest that there were more complete denitrifiers among the nirS-type denitrifiers because the demands for environmental conditions (pattern of significant factors) of these organisms more closely resembled those of nosZ-possessing organisms in the studied soils.…”

“…The share of FRBt increased in the total FRB with increasing distance from the drainage ditch in the pine and birch forests and strongly affected the prokaryotic community structure of all the studied stands. Although this relationship was not evident in the birch forests of this study, probably because of the almost two-fold lower variation of the FRBt value in these soils relative to the coniferous forest soils, the complementarity of the bacterial community and absorptive roots (evaluated by morphological traits) to the changes in environmental conditions have previously been shown in silver birch forests (Truu et al, 2017). Furthermore, multilateral relationships between the absorptive roots, ectomycorrhizal fungi, and both soil bacterial communities (bulk soil and rhizosphere) across 10 silver birch stands indicated a significant role of each organism group, although the role of each associated partner was affected by environmental conditions such as the N and C/N status of the soil (Ostonen et al, 2017).…”

“…Similar to some other forest soils (Truu et al, 2017), the soils of drained peatland forests favored nirK-type denitrifiers that dominated over the nirS-type organisms. However, the abundance and proportion of nirK-type organisms in the soils of coniferous forests considerably exceeded those of birch forest soils.…”

“…Biogeochemical cycles in forest soils are mediated by microbial communities and the quantity and quality of soil organic matter significantly affect the abundance, structure, and activity of bacterial and archaeal communities in these heterogeneous habitats ( Norman and Barrett, 2016 ). Compared to fungi, there is limited research on bacteria and archaea in the soils of temperate and boreal forests ( Sun et al, 2014 ; Baldrian, 2016 ; Ostonen et al, 2017 ; Truu et al, 2017 ). These studies are scarce also in the drained peatland forests.…”

Contribution of organic amendments to soil properties and survival of Stenocarpella on maize stalk

“…Moreover, the increase of stalk contact reduces temperature and humidity fluctuations, favoring microbial activity. However, soil available water and air humidity are of utmost importance for microbial activity (De Leij et al, 1993;Truu et al, 2017). In this study, both assays were carried out in the period with lower humidity (Table 4), which may have impaired the microbial activity (Table 2) and thus, pathogen displacement from stalks.…”