Browsing by Person "Uksa, Marie"

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Interactions between cover crops and soil microorganisms increase phosphorus availability in conservation agriculture
(2021) Hallama, Moritz; Pekrun, Carola; Pilz, Stefan; Jarosch, Klaus A.; Frąc, Magdalena; Uksa, Marie; Marhan, Sven; Kandeler, Ellen
Aims: An essential task of agricultural systems is to improve internal phosphorus (P) recycling. Cover crops and tillage reduction can increase sustainability, but it is not known whether stimulation of the soil microbial community can increase the availability of soil organic P pools. Methods: In a field experiment in southwest Germany, the effects of a winter cover crop mixture (vs. bare fallow) and no-till (vs. non-inversion tillage) on microbial P-cycling were assessed with soybean as the main crop. Microbial biomass, phospholipid fatty acids (PLFAs), P cycling enzymes, and carbon-substrate use capacity were linked for the first time with the lability of organic P pools measured by enzyme addition assays (using phosphodiesterase, non-phytase-phosphomonoesterase and fungal phytase). Results: Microbial phosphorus, phosphatase, and fatty acids increased under cover crops, indicating an enhanced potential for organic P cycling. Enzyme-stable organic P shifted towards enzyme-labile organic P pools. Effects of no-till were weaker, and a synergy with cover crops was not evident. Conclusions: In this experiment, cover crops were able to increase the microbially mediated internal P cycling in a non-P-limited, temperate agroecosystems.
The role of microbes in the increase of organic phosphorus availability in the rhizosheath of cover crops
(2022) Hallama, Moritz; Pekrun, Carola; Mayer-Gruner, Paula; Uksa, Marie; Abdullaeva, Yulduz; Pilz, Stefan; Schloter, Michael; Lambers, Hans; Kandeler, Ellen
Background and aims: The characterisation of plant-available phosphorus (P) pools and the assessment of the microbial community in the rhizosheath of cover crops can improve our understanding of plant–microbe interactions and P availability. Methods: Mustard (Sinapis alba), phacelia (Phacelia tanacetifolia) and buckwheat (Fagopyrum esculentum) were grown as cover crops before soybean (Glycine max) in an on-farm experiment on a soil low in available P in southwest Germany. The cycling of P through the cover crop biomass and the enzyme-availability of organic P (Porg) pools in the cover crop rhizosheath were characterised. The soil microbial community (PLFA), activity (acid and alkaline phosphomonoesterase, as well as phosphodiesterase), and microbial P were assessed. The abundance of 16S-rRNA and phoD, coding for alkaline phosphomonoesterase in bacteria, were quantified using real-time qPCR. Results: Mustard contained the greatest amount of P in its large biomass. In the rhizosheath of all cover crops, the concentration of enzyme-labile Porg was higher than that in the control bulk soil, along with substantial increases of microbial abundance and activity. There were little differences among cover crop species, few changes in the bulk soil and only a limited carryover effect to soybean, except for fungi. Conclusions: Turnover of microbial biomass, especially saprotrophic fungi, increased by rhizodeposition of cover crop roots; this was likely responsible for the observed increases in enzyme-available Porg. Microbial function was correlated linearly with microbial biomass, and the data of enzyme activity and phoD did not suggest a difference of their specific activity between bulk and rhizosheath soil.