Soil Bacterial Community Structure Responses to Precipitation Reduction and Forest Management in Forest Ecosystems across Germany

Abstract

Soil microbial communities play an important role in forest ecosystem functioning, but how climate change will affect the community composition and consequently bacterial functions is poorly understood. We assessed the effects of reduced precipitation with the aim of simulating realistic future drought conditions for one growing season on the bacterial community and its relation to soil properties and forest management. We manipulated precipitation in beech and conifer forest plots managed at different levels of intensity in three different regions across Germany. The precipitation reduction decreased soil water content across the growing season by between 2 to 8% depending on plot and region. T-RFLP analysis and pyrosequencing of the 16S rRNA gene were used to study the total soil bacterial community and its active members after six months of precipitation reduction. The effect of reduced precipitation on the total bacterial community structure was negligible while significant effects could be observed for the active bacteria. However, the effect was secondary to the stronger influence of specific soil characteristics across the three regions and management selection of overstorey tree species and their respective understorey vegetation. The impact of reduced precipitation differed between the studied plots; however, we could not determine the particular parameters being able to modify the response of the active bacterial community among plots. We conclude that the moderate drought induced by the precipitation manipulation treatment started to affect the active but not the total bacterial community, which points to an adequate resistance of the soil microbial system over one growing season.

Responses of the structure and function of the understory plant communities to precipitation reduction across forest ecosystems in Germany

“…We aimed to test if such a relationship could also be observed for the understory of beech dominated forests and conifer replacement stands. We found that understory Shannon diversity was, in fact, lower in the unmanaged beech stands compared to the other two management intensities and significantly higher at the Schwäbische Alb exploratory compared to the other two exploratories (Felsmann et al 2015). Plotting Shannon diversity against the impact of the drought treatment on community transpiration or community Δ 13 C, however, showed that understory diversity had no influence on the strength of the responses to drought (see Fig.…”

“…The study was carried out at the three regions of the Biodiversity Exploratories (http://www.biodiversityexploratories.de; for details, see Fischer et al 2010): Schorfheide-Chorin (S) in the north-east, Hainich Dün (H) in the middle, and Schwäbische Alb (A) in the south-west of Germany as described recently by Felsmann et al (2015). In each of the Exploratories, we selected three forest stands, which represent different forest types, management intensities and comprise different vegetation communities (see table 1 in Gimbel et al 2015), but are similar with respect to topography and soil type within each exploratory (Table 1).…”

“…The necessary climate data were obtained for the period 2010-2013 from near-by stations of the German weather service (DWD). For further details, we refer to Felsmann et al (2015). In addition to the simulated values, volumetric soil water contents (%) as an average of the upper 10 cm of the soil were determined in spring or early summer, and in late summer in 2012 and 2013.…”

“…Species composition (Table S2), LAI, species richness and diversity (Shannon's diversity index) of the understory were determined according to Felsmann et al (2015) during field campaigns in 2012 and 2013 (for dates, see Table S1). Species composition and richness were determined in field surveys.…”

Impact of interspecific competition and drought on the allocation of new assimilates in trees

“…In contrast to the abovementioned studies, the drought intensity in our study was rather moderate as we aimed to simulate the conditions in the forest understorey where extreme environmental amplitudes are buffered by the sheltering canopy (Hommel et al 2014;Felsmann et al 2015;Gimbel et al 2015), and thus we kept soil moisture tension close to but above the root water uptake thresholds.…”