Browsing by Person "Brandt, Luise"

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Formation of mineral‐associated organic matter in temperate soils is primarily controlled by mineral type and modified by land use and management intensity
(2023) Bramble, De Shorn E.; Ulrich, Susanne; Schöning, Ingo; Mikutta, Robert; Brandt, Luise; Poll, Christian; Kandeler, Ellen; Mikutta, Christian; Konrad, Alexander; Siemens, Jan; Yang, Yang; Polle, Andrea; Schall, Peter; Ammer, Christian; Kaiser, Klaus; Schrumpf, Marion
Formation of mineral-associated organic matter (MAOM) supports the accumulation and stabilization of carbon (C) in soil, and thus, is a key factor in the global C cycle. Little is known about the interplay of mineral type, land use and management intensity in MAOM formation, especially on subdecadal time scales. We exposed mineral containers with goethite or illite, the most abundant iron oxide and phyllosilicate clay in temperate soils, for 5 years in topsoils of 150 forest and 150 grassland sites in three regions across Germany. Results show that irrespective of land use and management intensity, more C accumulated on goethite than illite (on average 0.23 ± 0.10 and 0.06 ± 0.03 mg m−2 mineral surface respectively). Carbon accumulation across regions was consistently higher in coniferous forests than in deciduous forests and grasslands. Structural equation models further showed that thinning and harvesting reduced MAOM formation in forests. Formation of MAOM in grasslands was not affected by grazing. Fertilization had opposite effects on MAOM formation, with the positive effect being mediated by enhanced plant productivity and the negative effect by reduced plant species richness. This highlights the caveat of applying fertilizers as a strategy to increase soil C stocks in temperate grasslands. Overall, we demonstrate that the rate and amount of MAOM formation in soil is primarily driven by mineral type, and can be modulated by land use and management intensity even on subdecadal time scales. Our results suggest that temperate soils dominated by oxides have a higher capacity to accumulate and store C than those dominated by phyllosilicate clays, even under circumneutral pH conditions. Therefore, adopting land use and management practices that increase C inputs into oxide-rich soils that are under their capacity to store C may offer great potential to enhance near-term soil C sequestration.
Release of glucose from dissolved and mineral‐bound organic matter by enzymatic hydrolysis
(2023) Lenhardt, Katharina R.; Brandt, Luise; Poll, Christian; Rennert, Thilo; Kandeler, Ellen
Sorption of dissolved organic matter (DOM) by poorly crystalline minerals during their formation may protect large amounts of carbon in soils from mineralization. We investigated the bioavailability of carbohydrates in DOM and after co-precipitation with short-range ordered aluminosilicates. Carbohydrates originated from soil solutions collected in situ at two depths of a Dystric Cambisol, and from litter extracts. Quantification of substrate-specific degradability was achieved by the addition of β-glucosidase at an optimal concentration and subsequent determination of glucose release. Depending on DOM composition, 0.6–41.4 mg g−1 C−1 of glucose was enzymatically released from dissolved carbohydrates. Co-precipitated carbohydrates were partially accessible, resulting in a glucose release of 0.7–5.2 mg g−1 C−1. Restricted enzymatic depolymerization due to co-precipitation may contribute to accumulation of easily degradable substrates in soils.
Soil water status shapes nutrient cycling in agroecosystems from micrometer to landscape scales
(2022) Bauke, Sara L.; Amelung, Wulf; Bol, Roland; Brandt, Luise; Brüggemann, Nicolas; Kandeler, Ellen; Meyer, Nele; Or, Dani; Schnepf, Andrea; Schloter, Michael; Schulz, Stefanie; Siebers, Nina; von Sperber, Christian; Vereecken, Harry
Soil water status, which refers to the wetness or dryness of soils, is crucial for the productivity of agroecosystems, as it determines nutrient cycling and uptake physically via transport, biologically via the moisture‐dependent activity of soil flora, fauna, and plants, and chemically via specific hydrolyses and redox reactions. Here, we focus on the dynamics of nitrogen (N), phosphorus (P), and sulfur (S) and review how soil water is coupled to the cycling of these elements and related stoichiometric controls across different scales within agroecosystems. These scales span processes at the molecular level, where nutrients and water are consumed, to processes in the soil pore system, within a soil profile and across the landscape. We highlight that with increasing mobility of the nutrients in water, water‐based nutrient flux may alleviate or even exacerbate imbalances in nutrient supply within soils, for example, by transport of mobile nutrients towards previously depleted microsites (alleviating imbalances), or by selective loss of mobile nutrients from microsites (increasing imbalances). These imbalances can be modulated by biological activity, especially by fungal hyphae and roots, which contribute to nutrient redistribution within soils, and which are themselves dependent on specific, optimal water availability. At larger scales, such small‐scale effects converge with nutrient inputs from atmospheric (wet deposition) or nonlocal sources and with nutrient losses from the soil system towards aquifers. Hence, water acts as a major control in nutrient cycling across scales in agroecosystems and may either exacerbate or remove spatial disparities in the availability of the individual nutrients (N, P, S) required for biological activity.
Unraveling the interplay of microorganisms, organic matter, and secondary minerals in the mineralosphere of grasslands and forests
(2024) Brandt, Luise; Kandeler, Ellen
Mineral surfaces within soil create a distinct microhabitat for microorganisms, known as the “mineralosphere”. In this habitat, the physicochemical properties of minerals play a crucial role for the establishment of mineral-associated microbial communities and their functionality. Secondary minerals, such as iron oxides and clay minerals, possess large surface areas and charge densities, allowing them to retain the majority of the soil’s carbon (C) as mineral-associated organic matter (MAOM). However, these two types of secondary minerals exhibit contrasting surface properties, which greatly influence their interactions with organic matter (OM). Consequently, specific interactions between mineral surfaces, microorganisms, and MAOM are likely to occur, resulting in variations in MAOM formation and microbial turnover processes across different minerals. However, our understanding of how specific secondary minerals impact the biomass, composition, and functions of microbial communities colonizing their surfaces, as well as their interactions with adsorbed MAOM, remains elusive. Moreover, the colonization of mineral surfaces by microorganisms is not solely determined by mineral properties but is further influenced by environmental factors. Different land uses and management practices in grasslands and forests can significantly alter the input of OM into the soil, thereby affecting the formation of MAOM, but possibly also the composition and functions of microbial communities within the mineralosphere. Knowledge of these complex interactions is limited but crucial for understanding the role of secondary mineral surfaces to serve as microbial habitats and stabilize OM in forest and grassland ecosystems. The objective of this thesis was therefore to unravel the complex interplay between microorganisms, organic matter, and secondary minerals within the mineralosphere under the influence of common anthropogenic land use practices in grasslands and forests. The first three studies of this dissertation aimed to move beyond laboratory-based investigations and consider the complex and dynamic nature of soils under field conditions. Over a five-year period, mineral containers containing either goethite (an iron oxide) or illite (a clay mineral) were buried at a depth of 5 cm in soil at 150 grassland and 150 forest sites across three regions of the Biodiversity Exploratories in Germany. This in situ approach enabled us to experimentally isolate the mineralosphere microhabitat within the soil and to examine its unique characteristics. Moreover, we were able to examine how mineral type as well as land use and management influence mineralosphere characteristics by comparing patterns of MAOM accumulation and microbial parameters between goethite and illite and between the different grassland and forest Management practices. Collectively, these three studies underscore the relevance of iron oxides and clay minerals as distinct microhabitats. The accumulation of MAOM played a pivotal role for microorganisms on both goethite and illite, as evidenced by the strong correlation between microbial biomass and MAOM-C contents in the mineralosphere. Microbial communitiesassociated with the minerals differed from those in the bulk soil, consistently showing relative enrichment in fungi and Gram-negative bacteria across grasslands and forests. Furthermore, the stoichiometry of enzyme activities involved in C, nitrogen (N), and phosphorus (P) cycling indicated an increased relative acquisition of nutrients (N and P) than C compared to the surrounding bulk soil. Mycorrhizal fungi likely played a pivotal role in the increased relative nutrient acquisition in the mineralosphere, as they are independent of the C availability in the microhabitat due to the C supply via their host plant. In contrast, saprotrophic fungi in particular showed limited competitiveness compared to other fungal taxa, as they are poorly adapted to the low-C conditions in the mineralosphere. Within the mineralosphere, the mineral type played a crucial role in shaping its characteristics. The consistently higher MAOM accumulation on the iron oxide goethite compared to the clay mineral illite emphasized the significance of the mineral type for the extent of MAOM formation. Goethite, with its higher OM sorption capacity and stronger bonds formed with OM via ligand exchange, contrasted with illite, which bound less OM through weaker cation bridges. These differences in sorption behavior also had implications for the accessibility of OM and enzymes, and ultimately, the microbial communities inhabiting the two minerals. The higher C-specific microbial biomass on illite compared to goethite suggested a greater availability of illite-associated OM for microbial utilization. Microorganisms on goethite likely needed to enhance enzyme production at the cost of biomass synthesis to counteract a reduced substrate availability. Conversely, microorganisms on illite could utilize acquired OM to synthesize relatively more biomass than on goethite. These mineral-specific interactions between mineral surfaces, OM, enzymes, and microbes likely modify microbial MAOM formation and turnover pathways on different mineral types. The consequences of the strong association between OM and certain minerals on enzymatic substrate turnover were also evident in a separate laboratory experiment in the fourth study of this thesis. By adding β-glucosidase to co-precipitates of litter- or soil-derived dissolved organic matter (DOM) and specific aluminosilicates, the amount of mineral-associated substrates available for enzymatic degradation was determined. In this experiment, the enzymatic degradation of mineral-associated OM was reduced compared to free OM in solution. This emphasizes how strong interactions between OM and mineral surfaces have the potential to protect MAOM from enzymatic degradation, reducing its bioavailability to microbes. Not only effects of the mineral type but, to a lower degree, also effects of land use and management on the interplay of microbes and MAOM were evident. Fertilization in grasslands as well as tree species selection, thinning, and harvesting in forests altered the quantity and quality of nutrient and OM inputs into the soil. Moreover, land use had an impact on soil pH, consequently modifying the sorption capacity of the minerals. These effects were also reflected in various microbial parameters within the mineralosphere, which in turn, likely affected microbially mediated pathways of MAOM formation and turnover. Overall, this dissertation reveals the intricate relationship between microorganisms, OM, and different secondary minerals within the mineralosphere microhabitat and the mineral-specific involvement of microorganisms in MAOM turnover. The gained insights enrich our understanding of the ability of soils with different mineral compositions and under different land use and management practices to stabilize C in the MAOM pool.