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Additional file 1. The file contains all supplementary tables and figures listed below. Table S1. Shannon and Simpson diversity indices on different sampling times. Table S2. Chemical sampling, measured parameters, sample preparation and further analysis. Table S3. Microbial biofilm sampling and used material at the sampling and further sample preparation. Table S4. Primers used for the microbial analysis. Figure S1. Non-metric multidimensional scaling plot of bacterial and archaeal communities with 95% confidence eclipses in different compartments of the aquaponic system. Figure S2. Principal component analysis (PCA) with 95% confidence eclipses of measured environmental parameters. Figure S3. Non-metric multidimensional scaling plot of bacterial community with generalized additive models (gray lines) of fitted environmental variables. Figure S4. Non-metric multidimensional scaling plot of archaeal community with generalized additive models (gray lines) of fitted environmental variables. Figure S5. Redundancy analysis (RDA) of the bacterial (A) and archaeal (B) community in different compartments of the aquaponic system.

Due to increasing nitrogen (N) deposition from the atmosphere, temperate forests are progressively becoming phosphorus (P) limited. Trees take up P mainly from the soil solution, which soil microorganisms can replenish by mineralizing organic P through enzymatic hydrolysis (e.g. using phosphatases). We investigated how bacterial (including phosphatase harboring bacteria) and fungal communities in organic horizons with contrasting nutrient status respond within months to changes in soil N and P concentrations. A field experiment with water-soluble N (NH4NO3) and P (KH2PO4) additions was conducted at a high-P and a low-P beech (Fagus sylvatica L.) forest site in Germany. Bacterial (16S rRNA), fungal (ITS), and alkaline (phoD) and acid (acpA) phosphatase harboring community structure was investigated by molecular fingerprinting. Bacterial and fungal community structure was mainly related to available P (resin P) in the high-P site but related to more stable P pools (sequentially extracted NaOH/EDTA P) and total P in the low-P site. The increased importance of strategies to access more stable P forms in the low-P site was reflected by a higher relative abundance of some dominant alkaline phosphatase harboring taxa. In the high-P site, increased available P following P addition was the main influencing factor on community structure. By contrast, in the low-P site predominantly N addition induced differences in the microbial communities, which was linked to decreased P concentrations in several soil pools. Increasing N deposition might thus pose greater impacts on microbial communities in low-P compared to high-P sites, by further increasing the already high competition for P. Our findings illustrate that the soil P status in the organic horizon can shape the structure of microbial communities and their roles in the P cycle., Applied Soil Ecology, 172, ISSN:0929-1393, ISSN:1873-0272

Gross phosphorus (P) fluxes measured in isotopic dilution studies with 33P labeled soils include the biological processes of microbial P immobilization remineralization of immobilized P and mineralization of non microbial soil organic P. In this approach isotopic dilution due to physicochemical processes is taken into account. Our objectives were to assess the effect of inorganic P availability on gross P mineralization and immobilization in soil under permanent grassland and to relate these fluxes to soil respiration phosphatase activity and substrate availability as assessed by an enzyme addition method. We used soils from an 18 year old grassland fertilization experiment near Zurich Switzerland that were collected in two treatments which differed only in the amount of mineral P applied (0 and 17 kg P ha-1 yr-1 in NK and NPK respectively). Water extractable phosphate was low (0.1 and 0.4 mg P kg-1 soil in NK and NPK while hexanol labile (microbial) P was high (36 and 54 mg P kg-1 soil in NK and NPK). Extremely fast microbial P uptake under P limited conditions in NK necessitated the use of a microbial inhibitor when determining isotopic dilution due to physicochemical processes. At the higher inorganic P availability in NPK however isotopic exchange parameters were similar in the presence and absence of a microbial inhibitor. Phosphatase activity was higher in NK than in NPK while soil respiration water extractable organic P and its enzyme labile fraction were not affected by P status. Together the results showed that inorganic P availability primarily affected microbial P immobilization which was the main component of gross P fluxes in both treatments. Gross P mineralization rates (8.2 and 3.1 mg P kg-1 d-1 for NK and NPK) during the first week were higher than reported in other studies on arable and forest soils and at least equal to isotopically exchangeable P due to physicochemical processes confirming the importance of microbial processes in grassland soils.