Interactions between root C, microbial activity and turnover, and food web complexity
Zusammenfassung der Projektergebnisse
The main aims of the SP ROOT-C were: i) to assess the input by roots into the soil including rhizodeposition, ii) to estimate the first steps of the soil food-web - the incorporation of root C into microbial biomass including their functional groups, iii) to identify sources of CO2 fluxes from soil and to link them with microbial decomposition of rhizodeposits and SOM, and iv) to analyze the changes of microbial activities in the rhizosphere (broad range of enzyme activities, respiratory activities). The input of root C including rhizodeposition was measured in field and lab experiments. Based on the 13C or 14C in roots and root/rhizodeposition ratio, a new approach to estimate rhizodeposition under field conditions was suggested and applied on the plots of the FOR Food-Webs in Holtensen. 13C in PLFA revealed that root-derived C was incorporated into the soil food web mainly via saprotrophic fungi rather than via bacteria. Only small 13C amounts from rhizodeposition were transferred to higher trophic levels, mainly into fungal-feeding nematodes and macrofauna decomposers. 13C incorporation did not match pool size - this challenges previous views on the dominance of bacteria in root C dynamics and suggests saprotrophic fungi to function as major agents channeling recent photoassimilates into the soil food web. Full C budget and C fluxes of food web were calculated. Based on the δ13C of CO2 purified from the atmospheric CO2 by the Miller/Tans model and on the δ13C of SOM, the contributions of younger and older C to CO2 and SOM were assessed. Depending on the soil depth and the presence of living roots, the contribution of younger C to soil CO2 ranged from 16 to 50%. The relative availability of organics recently introduced into the soil (C4-derived) was about 7 times higher than the availability of C stabilized in soil for longer than one year (C3-derived). Simultaneous analysis of the δ13C values of SOM and of CO2 allows for the quantification of the CO2 sources and of the availability of soil C pools of different age for microorganisms. Binary links for bacterial and fungal feeders were investigated by Collembola grazing based on δ13C of microbial biomass, DOC, SOM and CO2. Fungi had the lowest CO2 production and the highest C use efficiency, but it decreased in the presence of Collembola. The `microbial loop` - effects of fauna on N release by feeding on microorganisms and consequently positive effects on plants - were investigated by 14C labelled root exudates under maize with an added model protist (Acanthamoebae castellani). The presence of Acanthamoeba increased the activity of C-cycling enzymes, especially β-glucosidase by 9-fold. 15N uptake from litter into the shoots increased by 24% by protozoan predation and stimulated rhizodeposition. So, microfaunal grazing induced process chains between benefiting plants and microorganisms, caused by proliferation of N. Microbial growth rates were compared with kinetics of six hydrolytic enzymes: β-glucosidase, β-cellobiohydrolase, β-xylosidase, acid phosphatase, leucine- and tyrosine-aminopeptidase. Shifts in microbial growth strategy, upregulation of enzyme production and increased microbial respiration indicated strong root effects in soil planted with maize. Kinetic parameters (Vmax and Km) of four hydrolytic enzymes in rhizosphere and detritusphere showed that catalytic properties of cellulolytic enzymes were much stronger affected by plants (substrate quality in the rhizosphere and detritusphere compared to bare fallow) than by soil depth (substrate content).
Projektbezogene Publikationen (Auswahl)
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(2012). Carbon flow into microbial and fungal biomass as basis for the belowground food web of agroecosystems. Pedobiologia 55, 111-119
Kramer S., Marhan S., Ruess L., Armbruster W., Butenschoen O., Haslwimmer H., Kuzyakov Y., Pausch J., Scheunemann N., Schoene J., Schmalwasser A., Totsche K.U., Walker F., Scheu S., Kandeler E.
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(2012). Soil organic carbon decomposition from recently added and older sources estimated by δ13C values of CO2 and organic matter. Soil Biology and Biochemistry, 55, 40−47
Pausch, J., Kuzyakov, Y.
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(2013). Estimation of rhizodeposition at field scale: upscaling of a 14C labeling study. Plant and Soil, 364(1-2), 273−285
Pausch, J., Tian, J., Riederer, M., Kuzyakov, Y.
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(2015). Small but active–pool size does not matter for carbon incorporation in below-ground food webs. Functional Ecology, 30, 479-489
Pausch, J., Kramer, S., Scharroba, A., Scheunemann, N., Butenschoen, O., Kandeler, E., Marhan, S., Riederer, M, Scheu, S., Kuzyakov, Y., Ruess, L.
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(2015). Substrate quality affects microbial and enzyme activities in rooted soil. Journal of Plant Nutrition and Soil Science 179, 39−47
Loeppmann, S., Semenov, M., Blagodatskaya, E., Kuzyakov, Y.
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(2016). Enzyme properties down the soil profile - A matter of substrate quality in rhizosphere and detritusphere. Soil Biology and Biochemistry, 103, 274−283
Loeppmann, S., Blagodatskaya, E., Pausch, J., Kuzyakov, Y.
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(2016). Fluxes of rootderived carbon into the nematode micro-food web of an arable soil. Food Webs
Pausch, J., Hofmann, S., Scharroba, A., Kuzyakov, Y., Ruess, L.
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(2016). Incorporation of root C and fertilizer N into the food web of an arable field: Variations with functional group and energy channel. Food Webs 9, 39-45
Scheunemann N., Scharroba A., Butenschoen O., Ruess L., Kandeler E., Kuzyakov Y., Kramer S., Digel C., Pausch J., Scheu S.
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(2016). Substrate quality affects kinetics and catalytic efficiency of exo-enzymes in rhizosphere and detritusphere. Soil Biology and Biochemistry, 92, 111−118
Loeppmann, S., Blagodatskaya, E., Pausch, J., Kuzyakov, Y.
