TY - JOUR A1 - Attermeyer, Katrin A1 - Premke, Katrin A1 - Hornick, Thomas A1 - Hilt, Sabine A1 - Grossart, Hans-Peter T1 - Ecosystem-level studies of terrestrial carbon reveal contrasting bacterial metabolism in different aquatic habitats JF - Ecology : a publication of the Ecological Society of America N2 - In aquatic systems, terrestrial dissolved organic matter (t-DOM) is known to stimulate bacterial activities in the water column, but simultaneous effects of autumnal leaf input on water column and sediment microbial dynamics in littoral zones of lakes remain largely unknown. The study's objective was to determine the effects of leaf litter on bacterial metabolism in the littoral water and sediment, and subsequently, the consequences for carbon cycling and food web dynamics. Therefore, in late fall, we simultaneously measured water and sediment bacterial metabolism in the littoral zone of a temperate shallow lake after adding terrestrial particulate organic matter (t-POM), namely, maize leaves. To better evaluate bacterial production (BP) and community respiration (CR) in sediments, we incubated sediment cores with maize leaves of different quality (nonleached and leached) under controlled laboratory conditions. Additionally, to quantify the incorporated leaf carbon into microbial biomass, we determined carbon isotopic ratios of fatty acids from sediment and leaf-associated microbes from a laboratory experiment using C-13-enriched beech leaves. The concentrations of dissolved organic carbon (DOC) increased significantly in the lake after the addition of maize leaves, accompanied by a significant increase in water BP. In contrast, sediment BP declined after an initial peak, showing no positive response to t-POM addition. Sediment BP and CR were also not stimulated by t-POM in the laboratory experiment, either in short-term or in long-term incubations, except for a short increase in CR after 18 hours. However, this increase might have reflected the metabolism of leaf-associated microorganisms. We conclude that the leached t-DOM is actively incorporated into microbial biomass in the water column but that the settling leached t-POM (t-POML) does not enter the food web via sediment bacteria. Consequently, t-POML is either buried in the sediment or introduced into the aquatic food web via microorganisms (bacteria and fungi) directly associated with t-POML and via benthic macroinvertebrates by shredding of t-POML. The latter pathway represents a benthic shortcut which efficiently transfers t-POML to higher trophic levels. KW - bacterial production KW - carbon turnover KW - community respiration KW - leaf litter KW - phospholipid-derived fatty acid KW - PLFA KW - Schulzensee KW - Germany KW - sediments KW - shallow lakes KW - stable isotopes KW - terrestrial subsidies Y1 - 2013 U6 - https://doi.org/10.1890/13-0420.1 SN - 0012-9658 SN - 1939-9170 VL - 94 IS - 12 SP - 2754 EP - 2766 PB - Wiley CY - Washington ER - TY - JOUR A1 - Schaller, Jörg A1 - Puppe, Daniel A1 - Kaczorek, Danuta A1 - Ellerbrock, Ruth A1 - Sommer, Michael T1 - Silicon cycling in soils revisited JF - Plants : open access journal N2 - Silicon (Si) speciation and availability in soils is highly important for ecosystem functioning, because Si is a beneficial element for plant growth. Si chemistry is highly complex compared to other elements in soils, because Si reaction rates are relatively slow and dependent on Si species. Consequently, we review the occurrence of different Si species in soil solution and their changes by polymerization, depolymerization, and condensation in relation to important soil processes. We show that an argumentation based on thermodynamic endmembers of Si dependent processes, as currently done, is often difficult, because some reactions such as mineral crystallization require months to years (sometimes even centuries or millennia). Furthermore, we give an overview of Si reactions in soil solution and the predominance of certain solid compounds, which is a neglected but important parameter controlling the availability, reactivity, and function of Si in soils. We further discuss the drivers of soil Si cycling and how humans interfere with these processes. The soil Si cycle is of major importance for ecosystem functioning; therefore, a deeper understanding of drivers of Si cycling (e.g., predominant speciation), human disturbances and the implication for important soil properties (water storage, nutrient availability, and micro aggregate stability) is of fundamental relevance. KW - andosols KW - clay neoformation KW - crop yield KW - land use change KW - micro KW - aggregate stability KW - phytoliths KW - sediments KW - silicon cycling KW - silicon KW - extraction methods KW - silicon pore water speciation Y1 - 2021 U6 - https://doi.org/10.3390/plants10020295 SN - 2223-7747 VL - 10 IS - 2 PB - MDPI CY - Basel ER -