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.
Highlights
Soil microbes play a fundamental role in forest ecosystems by stabilizing soil particles, performing organic matter decomposition, and mediating nutrient cycling and energy flow (Doran and Zeiss, 2000)
Even though the onsite measurements showed higher relative air humidity (RH), soil water potential (SWP) and soil temperature (ST; differences on average of 1.5%, 36.2 kPa and 0.2◦C, respectively), and about 0.1◦C lower air temperature (AT) was measured in humidified (H) plots compared to the control (C) plots during all vegetation periods of the experimental years (Supplementary Table 1); the statistical analyses did not confirm the significance of these differences (p > 0.05 in all cases)
The analysis revealed that the whole bacterial community structure as well as the structure of the three most dominant phyla was significantly different between C and H plots
Summary
Soil microbes play a fundamental role in forest ecosystems by stabilizing soil particles, performing organic matter decomposition, and mediating nutrient cycling and energy flow (Doran and Zeiss, 2000). Microbial activity is strongly dependent on nutritional, chemical, and physical conditions in the soil, and microorganisms respond rapidly to changes in soil properties caused by land. The global climate change is an unequivocal process (IPCC, 2007, 2013) that is accompanied by changes in the hydrological cycle (Held and Soden, 2006). The global annual evapotranspiration has increased on average by 7.1 mm per year during the period of 1982 to 1997 (Jung et al, 2010), and the climate change scenarios predict further increase in air temperature (by 2.3–4.5◦C) and in precipitation (by 5–30%) in Northern Europe for year 2100 (IPCC, 2007). Climate change is driven by external forcing mechanisms (i.e., greenhouse gases) and natural variability of ecosystems (IPCC, 2007). Boreal forests are predicted to be more affected by the changed climatic conditions. An understanding of how these systems react to the changing environment is crucial for possible mitigation actions (IPCC, 2007; Poulter et al, 2013)
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