Marco Griepentrog

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Griepentrog

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Marco

ORCID

0000-0002-9452-9903

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09646 - Dötterl, Sebastian / Dötterl, Sebastian

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Publications1 - 10 of 29

Parent material geochemistry – and not plant biomass – as the key factor shaping soil organic carbon stocks in European alpine grasslands
Maier, Annina; Macfarlane, Maria E.; Griepentrog, Marco; et al. (2025)
Biogeosciences
Soils represent the largest terrestrial carbon (C) reservoir on Earth. Within terrestrial ecosystems, soil geochemistry can be a strong driver of plant-soil-carbon dynamics, especially in young, less weathered soils. Here, we investigate the impact of potential plant biomass input, soil fertility parameters, and soil organic carbon (SOC) stabilization mechanisms on the distribution of SOC in European alpine grasslands across gradients of geochemically distinct parent materials. We demonstrate that SOC stock accrual and persistence in geochemically young soils, with fraction modern (F14C) values ranging from 0.77–1.06, is heavily dependent on soil mineralogy as a result of parent material weathering, but is not strongly linked to plant biomass. We show potential differences in the importance of geochemical variables and SOC stabilization mechanisms, with the microaggregate soil fraction contributing ≥ 50 % to bulk SOC in the majority of cases. We further show that concentrations of Fe, Al and Mn pedogenic oxides coincide with SOC stock magnitude across an alpine soil geochemical gradient, where SOC stocks range between 8.1–23.2 kg C m−2. Our results highlight that soil fertility and soil mineralogical characteristics, which govern plant C inputs and control C stabilization respectively, play equally crucial roles in predicting SOC contents in alpine soils at an early development stage.
Soil chemistry effect on GDGT abundances and their proxies in soils of the Okavango Delta
Lattaud, Julie; Gondwe, Mangaliso J.; Griepentrog, Marco; et al. (2024)
Organic Geochemistry
Branched and isoprenoid glycerol dialkyl glycerol tetraethers (brGDGTs, and isoGDGTs) are two families of membrane lipids commonly used to reconstruct paleo-environmental parameters. Their use as a quantitative proxy for past temperatures has been hindered by the discovery of other environmental controls on their distribution in soils, such as changes in bacterial community composition, chemistry and aridity. To test for the impact of aridity-driven soil chemistry changes, GDGT concentrations and derived proxies were measured in 43 soils along a chemical gradient in the Okavango Delta. All brGDGT concentrations increase with decreasing pH. Alkalinity-promoted (6-methyl and cyclopentane-containing) brGDGTs show a secondary concentration increase in arid soils, characterized by a high pH>8 and cation exchange capacity (CEC>30 cmolc kg−1). The concentration of 5-methyl brGDGTs increases faster that of 6-methyl brGDGTs in arid compared with non-arid soils. Although limited variability in temperature is present (∼2 °C), significant variation in MBT′5ME values is observed (0.63–0.96) likely driven by the variation in CEC. IsoGDGTs are present in lower concentrations than brGDGTs, and Ri/b values, a potential proxy for paleohydrological reconstruction, correlating with soil water content (r = 0.45, p < 0.01). TEX86 values (0.57–0.97) correlate with pH across the aridity transect. In this region, where accurate proxies and quantitative paleostudies are scarce, the impact of aridity-driven chemistry changes on GDGT-proxies is shown, i.e., MBT′5ME is overall controlled by CEC, but correlates negatively with pH in non-arid soils and with IR6ME in arid alkaline soils. Furthermore, we propose GDGT-based proxies for concentration in exchangeable calcium, past hydrological changes and soil pH.
The role of geochemistry in organic carbon stabilization against microbial decomposition in tropical rainforest soils
Reichenbach, Mario; Fiener, Peter; Garland, Gina; et al. (2021)
Soil
Stabilization of soil organic carbon (SOC) against microbial decomposition depends on several soil properties, including the soil weathering stage and the mineralogy of parent material. As such, tropical SOC stabilization mechanisms likely differ from those in temperate soils due to contrasting soil development. To better understand these mechanisms, we investigated SOC dynamics at three soil depths under pristine tropical African mountain forest along a geochemical gradient from mafic to felsic and a topographic gradient covering plateau, slope and valley positions. To do so, we conducted a series of soil C fractionation experiments in combination with an analysis of the geochemical composition of soil and a sequential extraction of pedogenic oxides. Relationships between our target and predicting variables were investigated using a combination of regression analyses and dimension reduction. Here, we show that reactive secondary mineral phases drive SOC properties and stabilization mechanisms together with, and sometimes more strongly than, other mechanisms such as aggregation or C stabilization by clay content. Key mineral stabilization mechanisms for SOC were strongly related to soil geochemistry, differing across the study regions. These findings were independent of topography in the absence of detectable erosion processes. Instead, fluvial dynamics and changes in soil moisture conditions had a secondary control on SOC dynamics in valley positions, leading to higher SOC stocks there than at the non-valley positions. At several sites, we also detected fossil organic carbon (FOC), which is characterized by high C/N ratios and depletion of N. FOC constitutes up to 52.0 +/- 13.2 % of total SOC stock in the C-depleted subsoil. Interestingly, total SOC stocks for these soils did not exceed those of sites without FOC. Additionally, FOC decreased strongly towards more shallow soil depths, indicating decomposability of FOC by microbial communities under more fertile conditions. Regression models, considering depth intervals of 0-10, 30-10 and 60-70 cm, showed that variables affiliated with soil weathering, parent material geochemistry and soil fertility, together with soil depth, explained up to 75 % of the variability of SOC stocks and Delta C-14. Furthermore, the same variables explain 44 % of the variability in the relative abundance of C associated with microaggregates vs. free-silt- and-clay-associated C fractions. However, geochemical variables gained or retained importance for explaining SOC target variables when controlling for soil depth. We conclude that despite long-lasting weathering, geochemical properties of soil parent material leave a footprint in tropical soils that affects SOC stocks and mineral-related C stabilization mechanisms. While identified stabilization mechanisms and controls are similar to less weathered soils in other climate zones, their relative importance is markedly different in the tropical soils investigated.
The impact of soil chemistry, moisture and temperature on branched and isoprenoid GDGTs in soils: A study using six globally distributed elevation transects
De Jonge, Cindy; Guo, Jingjing; Hallberg, Petter; et al. (2024)
Organic Geochemistry
Glycerol dialkyl glycerol tetraethers (GDGTs) are microbial membrane-spanning lipids that are produced in a variety of environments. To better understand the potentially confounding effect of soil chemistry on the temperature relationship of branched GDGTs (brGDGTs), isoprenoid GDGTs (isoGDGTs) and GDGT-based proxies MBT’5ME and TEX86, soils from 6 elevation transects (mean annual air temperature 0 – 26 ℃, n = 74) were analyzed. Corroborating earlier work, the MBT’5ME index correlates well with mean annual air temperature in the low pH (pH < 7), non-arid soils under study (r = 0.87, p < 0.001). However, a clear over-estimation of reconstructed temperature in the lowest pH (<3.5) soils is observed, explained by the correlation between brGDGT Ia and free acidity. TEX86 also shows a significant correlation with mean annual air temperature (r = 0.45, p < 0.001), driven by temperature dependent concentration changes of isoGDGTs 3 and cren’. However, an overarching correlation with P/E values dominates concentration changes of all supposed Thaumarchaeotal isoGDGTs lipids (GDGT1-3, cren and cren’), implying a potential impact of soil moisture on TEX86 values. In addition to identifying the impact of these confounding factors on the temperature proxy, GDGT ratios that can be used to constrain changes in soil chemistry, specifically exchangeable Ca2+, sum of basic cations, exchangeable Fe3+ and sum of soil metals are proposed (0.53 < r2 < 0.68), while existing ratios for soil moisture availability are tested for the first time in a dataset of non-arid soils. While the impact of soil chemistry on GDGTs may complicate the interpretation of their temperature proxies, our proposed GDGT ratios can potentially be used to constrain a subset of soil chemistry changes through time.
Nutrient limitations regulate soil greenhouse gas fluxes from tropical forests: evidence from an ecosystem-scale nutrient manipulation experiment in Uganda
Tamale, Joseph; Hüppi, Roman; Griepentrog, Marco; et al. (2021)
Soil
Soil macronutrient availability is one of the abiotic controls that alters the exchange of greenhouse gases (GHGs) between the soil and the atmosphere in tropical forests. However, evidence on the macronutrient regulation of soil GHG fluxes from central African tropical forests is still lacking, limiting our understanding of how these biomes could respond to potential future increases in nitrogen (N) and phosphorus (P) deposition. The aim of this study was to disentangle the regulation effect of soil nutrients on soil GHG fluxes from a Ugandan tropical forest reserve in the context of increasing N and P deposition. Therefore, a large-scale nutrient manipulation experiment (NME), based on 40m x 40m plots with different nutrient addition treatments (N, P, N + P, and control), was established in the Budongo Central Forest Reserve. Soil carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes were measured monthly, using permanently installed static chambers, for 14 months. Total soil CO2 fluxes were partitioned into autotrophic and heterotrophic components through a root trenching treatment. In addition, soil temperature, soil water content, and nitrates were measured in parallel to GHG fluxes. N addition (N and N + P) resulted in significantly higher N2O fluxes in the transitory phase (0-28 d after fertilization; p < 0.01) because N fertilization likely increased soil N beyond the microbial immobilization and plant nutritional demands, leaving the excess to be nitrified or denitrified. Prolonged N fertilization, however, did not elicit a significant response in background (measured more than 28 d after fertilization) N2O fluxes. P fertilization marginally and significantly increased transitory (p = 0.05) and background (p = 0.01) CH4 consumption, probably because it enhanced methanotrophic activity. The addition of N and P (N + P) resulted in larger CO2 fluxes in the transitory phase (p = 0.01), suggesting a possible co-limitation of both N and P on soil respiration. Heterotrophic (microbial) CO2 effluxes were significantly higher than the autotrophic (root) CO2 effluxes (p < 0.01) across all treatment plots, with microbes contributing about two-thirds of the total soil CO2 effluxes. However, neither heterotrophic nor autotrophic respiration significantly differed between treatments. The results from this study suggest that the feedback of tropical forests to the global soil GHG budget could be disproportionately altered by increases in N and P availability over these biomes.
Drivers of the distribution of soil organic matter fractions along a geo-climatic gradient
Wasner, Daniel; Abramoff, Rose; Zagal, Erick; et al. (2022)
EGUsphere
The concept of distinct soil organic matter (SOM) fractions – with differing formation pathways, stabilization mechanisms and responses to change – is a promising avenue to improve our understanding of soil carbon (C) dynamics. While there is widespread consensus on the general usefulness of conceptual fractions with specific functional implications, there is still a lack of information on the patterns with which they contribute to bulk soil organic carbon (SOC) stock at larger scales and across climatic and soil physicochemical gradients. In this study, we aimed to assess first the quantitative importance of three key SOM fractions across a diverse range of 12 soil groups with global significance. Secondly, we wanted to gain insights on the environmental drivers that shape the contribution of these fractions to SOC stocks. Here we sampled a set of 35 grassland topsoils (0 – 10 cm) along a 3000 km north-south transect in Chile ranging from subpolar to Mediterranean climate, and covering 12 WRB major soil groups. Following a modified version of the protocol in Zimmermann et. al (2007), we partitioned the soils into three functional SOM fractions defined by particle size and density (free silt and clay, free particulate organic matter, stable microaggregates), enabling us to quantify SOC stocks and the relative contribution to SOC in these three fractions. In order to identify links between fractions and potential drivers of C stabilization, we further characterized extensively relevant physico-chemical properties of the soils, compiled climatic data of the sites and characterized OM maturity (DRIFT spectroscopy and Rock-Eval pyrolysis) as well as pedogenic, secondary Fe-, Al- and Mn-oxide concentrations through sequential extraction. We found that the contributions of mineral-associated SOM fractions to bulk SOC varied strongly across the soil gradient, while the contribution of free particulate organic matter was comparatively stable and low. SOM associated with free silt and clay sized particles are the most important C reservoir in soils with less than 4 % SOC, whereas in soils with higher SOC content, the majority of the SOC is contained in stable microaggregates. The SOC stock in various fractions was sensitive to changes in temperature, pedogenic oxides, and OM input vs. decomposition. Comparison of OM maturity showed that free particulate OM and free silt and clay associated OM can be clearly distinguished, while OM in microaggregates is likely a mixture of both. However, drivers of OM composition in microaggregates could not be identified. This study demonstrates that in SOC-rich soils, microaggregates represent a major fraction of bulk SOC, and that SOC stocks in key SOM fractions can be linked to distinct climatic and soil physicochemical factors.
Tropical wood stores substantial amounts of nutrients, but we have limited understanding why
Bauters, Marijn; Grau, Oriol; Doetterl, Sebastian; et al. (2022)
Biotropica
Rock-derived nutrients such as calcium (Ca), magnesium (Mg), phosphorus (P), and potassium (K) are essential plant resources, yet depleted in highly weathered tropical soils, leading to nutrient limitation of productivity or other ecosystem processes. Despite this, substantial amounts of rock-derived nutrients occur within wood, which raises questions about the role that wood nutrients play in the ecology of tropical forests. Using data from forests across the tropics, we quantify wood nutrient stocks at individual tree and ecosystem levels. At the ecosystem level, we show that tropical wood can store substantial amounts of rock-derived nutrients. Furthermore, on a tree level, tree species vary widely in woody nutrient concentrations. These observations raise important questions as to the biogeochemical or ecological drivers that lead to this variability, as well as the role that woody tissue plays in the buffering and cycling of nutrients. We offer some potential explanations and direction for future research to explore this under-appreciated but sizable store of inorganic nutrients in tropical biomass.
Increasing calcium scarcity along Afrotropical forest succession
Bauters, Marijn; Janssens, Ivan A.; Wasner, Daniel; et al. (2022)
Nature Ecology & Evolution
Secondary forests constitute an increasingly important component of tropical forests worldwide. Although cycling of essential nutrients affects recovery trajectories of secondary forests, the effect of nutrient limitation on forest regrowth is poorly constrained. Here we use three lines of evidence from secondary forest succession sequences in central Africa to identify potential nutrient limitation in regrowing forests. First, we show that atmospheric phosphorus supply exceeds demand along forest succession, whereas forests rely on soil stocks to meet their base cation demands. Second, soil nutrient metrics indicate that available phosphorus increases along the succession, whereas available cations decrease. Finally, fine root, foliar and litter stoichiometry show that tissue calcium concentrations decline relative to those of nitrogen and phosphorus during succession. Taken together, these observations suggest that calcium becomes an increasingly scarce resource in central African forests during secondary succession. Furthermore, ecosystem calcium storage shifts from soil to woody biomass over succession, making it a vulnerable nutrient in the wake of land-use change scenarios that involve woody biomass export. Our results thus call for a broadened focus on elements other than nitrogen and phosphorus regarding tropical forest biogeochemical cycles and identify calcium as a scarce and potentially limiting nutrient in an increasingly disturbed and dynamic tropical forest landscape.
Nutrient limitations regulate soil greenhouse gas fluxes from tropical forests: evidence from an ecosystem-scale nutrient manipulation experiment in Uganda
Tamale, Joseph; Hüppi, Roman; Griepentrog, Marco; et al. (2021)
Soil Discussions
Tropical forests contribute significantly to the emission and uptake of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). However, studies on the soil environmental controls of greenhouse gases (GHGs) from African tropical forest ecosystems are still rare. The aim of this study was to disentangle the regulation effect of soil nutrients on soil GHG fluxes in a tropical forest in northwestern Uganda. Therefore, a large-scale nutrient manipulation experiment (NME) based on 40 m × 40 m plots with different nutrient addition treatments (nitrogen (N), phosphorus (P), N + P, and control) was established. Soil CO2, CH4, and N2O fluxes were measured monthly using permanently installed static chambers for 14 months. Total soil CO2 fluxes were partitioned into autotrophic and heterotrophic components through a root trenching treatment. In addition, soil temperature, soil water content, and mineral N were measured in parallel to GHG fluxes. N addition (N, N + P) resulted in significantly higher N2O fluxes in the transitory phase (0–28 days after fertilization, p < 0.01), because N fertilization likely increased soil N beyond the microbial immobilization and plant nutritional demands leaving the excess to be nitrified or denitrified. Prolonged N fertilization however, did not elicit a significant response in background (measured more than 28 days after fertilization) N2O fluxes. P fertilization marginally and significantly increased transitory (p = 0.052) and background (p = 0.010) CH4 consumption, probably because it enhanced methanotrophic activity. Addition of N and P together (N + P) resulted in larger CO2 fluxes in the transitory phase (p = 0.010), suggesting a possible co-limitation of N and P on soil respiration. Heterotrophic (microbial) CO2 effluxes were significantly higher than the autotrophic (root) CO2 effluxes (p < 0.001) across all treatment plots with microbes contributing about three times more to the total soil CO2 effluxes compared to roots (p < 0.001). However, neither heterotrophic nor autotrophic respiration significantly differed between treatments. The results from this study suggest that the feedback of tropical forests to the global soil GHG budget could be disproportionately altered by changes in N and P availability in these biomes.
Influence of plant growth form, habitat and season on leaf-wax n-alkane hydrogen-isotopic signatures in equatorial East Africa
Griepentrog, Marco; De Wispelaere, Lien; Bauters, Marijn; et al. (2019)
EarthDoc ~ Conference Proceedings, 29th International Meeting on Organic Geochemistry, Sep 2019
Leaf-wax n-alkanes are produced by terrestrial plants, and through long-term preservation in sediments their stable hydrogen-isotopic signature (δ²Hwax) provides useful information on past hydrological variation for paleoclimate reconstructions. However, gaps remain in our understanding of the isotopic relationships between the leaf waxes and the plants' source water. In this study, we investigated the influence of plant growth form, habitat and season on the distribution patterns and δ²Hwax values of 14 plant species (among which are two grasses, five trees and seven shrubs) sampled during four successive dry and wet seasons in three distinct habitats around Lake Chala in equatorial East Africa. Variation in δ²Hwax was analyzed with linear mixed-effect models and compared with the associated values of xylem water (δ²Hxylem), leaf water (δ²Hleaf) and biosynthetic hydrogen fractionation (εbio) (Figure 1). Our results show that plant growth form was the most important driver of modern-day δ²Hwax variability in the study area, and that differences in δ²Hwax between habitats to a large extent reflect the representation of the three major growth forms in those habitats. Individual plant species appear to express substantial species-specific isotopic fractionation that cannot be attributed to the tested external factors but rather seem to depend on intrinsic (e.g., plant phenological and biosynthesis-related) factors. For the purpose of calibrating δ²Hwax signatures against vegetation types, it is thus crucial to analyze representative samples of the plant communities present in the study area. Our results further indicate that paleohydrological studies in regions receiving rain from multiple moisture sources must take into account possible seasonal bias in the δ²Hwax signature relative to annual rainfall (Figure 1), due to unequal use of those moisture sources by the plants (De Wispelaere et al., 2017). Finally, the strong influence of plant growth form on δ²Hwax values argues for systematic evaluation of δ²Hwax variation in paleo-records in conjunction with independent proxy data on changes in vegetation composition. Differences in n-alkane distribution patterns (average chain length, carbon preference index and C31/(C29+C31) ratio) among trees, shrubs and grasses may provide such a proxy, and can be produced from the same leaf-wax n-alkane dataset used to determine δ²Hwax.

Publications1 - 10 of 29

Marco Griepentrog

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