engleski

Hotspots and Hot Moments: Effect of Plant Litter on the Formation of Biogeochemical Interfaces in Soil

Plant litter creates a large number of new biogeochemical interfaces (BGIs) in soil and increases soil heterogeneity. As a consequence, bulk soil habitats, with are low in microbial activities, are transformed into hotspots, with highly active microbial communities after litter fall. Over time microbial activities decreases at this BGIs as a result of reduced nutrient contents and soluble compounds of the plant litter leach to soil layers deeper than the litter–soil interface, changing also here temporally microbial community structure and function. This concept of hot spots and hot moments has been widely proposed in literature but rarely proven on the small scale, where microbes shape their environment. As plant litter material contains a large number of plant waxes, alkane degrading microbes are a highly important part of the litter degrading microbial communities. Thus in the frame of our project we focused on the effects of litter application on the abundance, diversity and activity of microbial communities involved in alkane degradation using the alkane monooxygenase gene alkB as a proxy in time and space. We performed several microcosm experiments addressing questions on the role of the litter material as well as of the soil type for the formation of characteristic BGIs mainly at the border of litter and soil, but also in deeper soil layers. Therefore we used soils, which were under agricultural use with different soil texture. In addition we performed studies using mixtures of inorganic materials, which form the soil matrix, which had been inoculated with microbes from a “natural soil” together with sterile manure to stimulate soil formation (“artificial soils”) at different maturation stages. For the “natural” soils our results indicate a clear response pattern of all investigated biotic and abiotic parameters depending on the applied litter material, the type of soil used, the time point of sampling and the soil compartment studied. As expected the distribution of alkanes of different chain length formed a steep gradient from the litter layer to the bulk soil. At the litter–soil interface the community structure and abundance patterns of alkB were driven by the applied litter type and its degradation. Surprisingly, the differences between the different compartments in one soil were more pronounced than the differences between similar compartments in the soils studied. For the “artificial” soils we observed an overall increasing divergence in community composition of alkB harbouring microbes during maturation, without litter application. The impact of metal oxides on alkane degrading communities increased during soil maturation whereas the charcoal impact decreased over time of maturation. Amongst the clay minerals illite influenced the alkB harbouring bacteria significantly, but not montmorillonite. The litter application induced strong community shifts in soils for those sols that have been maturated for a longer time period towards functional guilds typical for younger maturation stages pointing to a resilience of the alkane degradation function fostered by a potential ‘seed bank’ formation. Overall our data clearly indicates the importance of plant litter for the formation of BGIs in soil. The effects observed however vary strongly on the soil type and the soil development stage.

Biogeochemical interfaces ; clay minerals ; charcoal ; metal-oxides ; plant litter ; alkB, microbial communities

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