Changes in SOM under short-rotation forestry with fast-growing tree species

Soil carbon storage is strongly affected by land use and land use change. Afforestation with fast growing tree species on former arable soils may increase soil organic carbon (SOC) contents due to the reduction in soil cultivation frequency. The DFG-funded project „The mycorrhiza-mediated pathway for soil organic matter (SOM) formation and consequences for the SOM turnover under short rotation forestry“ investigates two major types of mycorrhiza formation as a function of land use and the importance of composition, stability and storage of SOM. In our subproject we compared SOC stocks of ongoing short rotation forestry (SRF) and former forestry fields (f-SRF). This leads to the following questions: i) Is there a long-term increase in carbon storage under current SRF schemes; and ii) Is this carbon storage under SRF sustainable; what are the consequences of transforming forest soils back into arable land? Two current (SRF) and two former (f-SRF) (Populus nigra x P. maximowiczii) test sites in different temporal stages of change were selected, with corresponding reference sites (REF)in each case. We found an accumulation of SOC in topsoil of current long-term SRF in comparison to REF, but lower carbon content in the subsoil. In former SRF sites accumulation of SOC was not detectable and we found no increase in the total SOC stocks per site. Effects are marked by soil treatment. Variance in total accumulation of SOC occurs in spatial distribution of investigated areas and was effected by its annual variabilities. Combined, the investigations results in following: i) SRF changes the carbon distribution in the anthric horizon. However, a total carbon storage change could not be detected. ii) The differences in carbon distribution were quickly removed by planting

Tree mycorrhizal type regulates leaf and needle microbial communities, affects microbial assembly and co-occurrence network patterns, and influences litter decomposition rates in temperate forest

BackgroundTree mycorrhizal types (arbuscular mycorrhizal fungi and ectomycorrhizal fungi) alter nutrient use traits and leaf physicochemical properties and, thus, affect leaf litter decomposition. However, little is known about how different tree mycorrhizal species affect the microbial diversity, community composition, function, and community assembly processes that govern leaf litter-dwelling microbes during leaf litter decomposition. MethodsIn this study, we investigated the microbial diversity, community dynamics, and community assembly processes of nine temperate tree species using high-resolution molecular technique (Illumina sequencing), including broadleaved arbuscular mycorrhizal, broadleaved ectomycorrhizal, and coniferous ectomycorrhizal tree types, during leaf litter decomposition.Results and discussionThe leaves and needles of different tree mycorrhizal types significantly affected the microbial richness and community composition during leaf litter decomposition. Leaf litter mass loss was related to higher sequence reads of a few bacterial functional groups, particularly N-fixing bacteria. Furthermore, a link between bacterial and fungal community composition and hydrolytic and/or oxidative enzyme activity was found. The microbial communities in the leaf litter of different tree mycorrhizal types were governed by different proportions of determinism and stochasticity, which changed throughout litter decomposition. Specifically, determinism (mainly variable selection) controlling bacterial community composition increased over time. In contrast, stochasticity (mainly ecological drift) increasingly governed fungal community composition. Finally, the co-occurrence network analysis showed greater competition between bacteria and fungi in the early stages of litter decomposition and revealed a contrasting pattern between mycorrhizal types.ConclusionOverall, we conclude that tree mycorrhizal types influence leaf litter quality, which affects microbial richness and community composition, and thus, leaf litter decomposition

Determination of trace amounts of nitrate in potassium chloride-extracts by HPLC with ultra-violet-detection

A method is presented that allows the determination of trace amounts of nitrate in I M potassium chloride extracts of environmental soil samples from Northern Europe. To avoid the interference of bromine ions on the evaluation of the nitrate peak, 50 muL of a 50mg/L nitrate standard solution are added to a 5mL soil extract. This makes sure that the overall nitrate concentration in the spike is >500 mug/L which allows an exact and reliable determination of the nitrate concentration. Analyses of the soil extracts are carried out by anion-exchange HPLC with ultra-violet detection at lambda = 210nm using 0.1 M KCl as eluent. Concentrations down to 25 mug/L of nitrate can be analyzed

Sustainability of Impacts of Poplar Growth on Soil Organic Matter in Eutric Cambisols

Short rotation coppices (SRC) with poplar on arable soils constitute no-till management in combination with a changed litter quality compared to annual crops. Both tillage and litter quality impact soil organic matter (SOM) composition, but little is known on the sustainability of this impact at the molecular level. We compared the microbial colonization and SOM quantity and quality of a young (4 years), old (17 years) and a former SRC with hybrid poplar (Populus maximoviczii × Populus nigra cv. Max) to adjacent arable sites with annual crops or grass. Total fungal and arbsucular mycorrhizal fungal phospholipid fatty acid (PLFA) markers were increased under no-till treatments with permanent crops (SRC and grass) compared to tilled cereals. Enrichments in fungal biomass coincided with C accumulation close to the soil surface (0−5 cm) but was abolished under former SRC after return to annual tillage. This management change altered the spatial distribution but not the accumulation of SOM within the topsoil (0−30 cm). However, lasting qualitative changes in SOM with increased proportions of lignin, lipids and sterols were found under current and former SRC. Increased colonization by arbuscular mycorrhizal fungi was correlated with increased invertase activity (R = 0.64; p < 0.05), carbohydrate consumption and a corresponding accumulation of lignins and lipids in the SOM. This link indicates a regulatory impact of mycorrhizal fungi on soil C dynamics by changing the quality of SOM. Increased stability of SOM to microbial degradation by higher portions of lipids and sterols in the SOM were assumed to be a sustainable effect of poplar growth at Eutric Cambisols

Thiosulfate- and hydrogen-driven autotrophic denitrification by a microbial consortium enriched from groundwater of an oligotrophic limestone aquifer

Despite its potentially high relevance for nitrate removal in freshwater environments limited in organic carbon, chemolithoautotrophic denitrification has rarely been studied in oligotrophic groundwater. Using thiosulfate and H2 as electron donors, we established a chemolithoautotrophic enrichment culture from groundwater of a carbonate-rock aquifer to get more insight into the metabolic repertoire, substrate turnover, and transcriptional activity of subsurface denitrifying consortia. The enriched consortium was dominated by representatives of the genus Thiobacillus along with denitrifiers related to Sulfuritalea hydrogenivorans, Sulfuricella denitrificans, Dechloromonas sp. and Hydrogenophaga sp., representing the consortium's capacity to use multiple inorganic electron donors. Microcosm experiments coupled with Raman gas spectroscopy demonstrated complete denitrification driven by reduced sulfur compounds and hydrogen without formation of N2O. The initial nitrate/thiosulfate ratio had a strong effect on nosZ transcriptional activity and on N2 formation, suggesting similar patterns of the regulation of gene expression as in heterotrophic denitrifiers. Sequence analysis targeting nirS and nosZ transcripts identified Thiobacillus denitrificans-related organisms as the dominant active nirS-type denitrifiers in the consortium. An additional assessment of the nirS-type denitrifier community in the groundwaterclearly confirmed the potential for sulfur- and hydrogen-dependent chemolithoautotrophic denitrification as important metabolic feature widely spread among subsurface denitrifiers at the Hainich Critical Zone Exploratory