@article{SandhageHofmannLinstaedterKindermannetal.2021, author = {Sandhage-Hofmann, Alexandra and Linst{\"a}dter, Anja and Kindermann, Liana and Angombe, Simon and Amelung, Wulf}, title = {Conservation with elevated elephant densities sequesters carbon in soils despite losses of woody biomass}, series = {Global change biology}, volume = {27}, journal = {Global change biology}, number = {19}, publisher = {Blackwell Science}, address = {Oxford [u.a.]}, issn = {1354-1013}, doi = {10.1111/gcb.15779}, pages = {4601 -- 4614}, year = {2021}, abstract = {Nature conservation and restoration in terrestrial ecosystems is often focused on increasing the numbers of megafauna, expecting them to have positive impacts on ecological self-regulation processes and biodiversity. In sub-Saharan Africa, conservation efforts also aspire to protect and enhance biodiversity with particular focus on elephants. However, elephant browsing carries the risk of woody biomass losses. In this context, little is known about how increasing elephant numbers affects carbon stocks in soils, including the subsoils. We hypothesized that (1) increasing numbers of elephants reduce tree biomass, and thus the amount of C stored therein, resulting (2) in a loss of soil organic carbon (SOC). If true, a negative carbon footprint could limit the sustainability of elephant conservation from a global carbon perspective. To test these hypotheses, we selected plots of low, medium, and high elephant densities in two national parks and adjacent conservancies in the Namibian component of the Kavango Zambezi Transfrontier Area (KAZA), and quantified carbon storage in both woody vegetation and soils (1 m). Analyses were supplemented by the assessment of soil carbon isotopic composition. We found that increasing elephant densities resulted in a loss of tree carbon storage by 6.4 t ha(-1). However, and in contrast to our second hypothesis, SOC stocks increased by 4.7 t ha(-1) with increasing elephant densities. These higher SOC stocks were mainly found in the topsoil (0-30 cm) and were largely due to the formation of SOC from woody biomass. A second carbon input source into the soils was megaherbivore dung, which contributed with 0.02-0.323 t C ha(-1) year(-1) to ecosystem carbon storage in the low and high elephant density plots, respectively. Consequently, increasing elephant density does not necessarily lead to a negative C footprint, as soil carbon sequestration and transient C storage in dung almost compensate for losses in tree biomass.}, language = {en} } @article{PuppeLeueSommeretal.2022, author = {Puppe, Daniel and Leue, Martin and Sommer, Michael and Schaller, J{\"o}rg and Kaczorek, Danuta}, title = {Auto-fluorescence in phytoliths}, series = {Frontiers in Environmental Science}, volume = {10}, journal = {Frontiers in Environmental Science}, publisher = {Frontiers Media}, address = {Lausanne}, issn = {2296-665X}, doi = {10.3389/fenvs.2022.915947}, pages = {14}, year = {2022}, abstract = {The detection of auto-fluorescence in phytogenic, hydrated amorphous silica depositions (phytoliths) has been found to be a promising approach to verify if phytoliths were burnt or not, especially in archaeological contexts. However, it is unknown so far at what temperature and how auto-fluorescence is induced in phytoliths. We used fluorescence microscopy, scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX), and Fourier transform infrared spectroscopy to analyze auto-fluorescence in modern phytoliths extracted from plant samples or in intact leaves of winter wheat. Leaves and extracted phytoliths were heated at different temperatures up to 600 degrees C. The aims of our experiments were i) to find out what temperature is needed to induce auto-fluorescence in phytoliths, ii) to detect temperature-dependent changes in the molecular structure of phytoliths related to auto-fluorescence, and iii) to derive a mechanistic understanding of auto-fluorescence in phytoliths. We found organic compounds associated with phytoliths to cause auto-fluorescence in phytoliths treated at temperatures below approx. 400 degrees C. In phytoliths treated at higher temperatures, i.e., 450 and 600 degrees C, phytolith auto-fluorescence was mainly caused by molecular changes of phytolith silica. Based on our results we propose that auto-fluorescence in phytoliths is caused by clusterization-triggered emissions, which are caused by overlapping electron clouds forming non-conventional chromophores. In phytoliths heated at temperatures above about 400 degrees C dihydroxylation and the formation of siloxanes result in oxygen clusters that serve as non-conventional chromophores in fluorescence events. Furthermore, SEM-EDX analyses revealed that extractable phytoliths were dominated by lumen phytoliths (62\%) compared to cell wall phytoliths (38\%). Our findings might be not only relevant in archaeological phytolith-based examinations, but also for studies on the temperature-dependent release of silicon from phytoliths and the potential of long-term carbon sequestration in phytoliths.}, language = {en} } @article{LandholmPradhanWegmannetal.2019, author = {Landholm, David M. and Pradhan, Prajal and Wegmann, Peter and Romero Sanchez, Miguel Antonio and Suarez Salazar, Juan Carlos and Kropp, J{\"u}rgen}, title = {Reducing deforestation and improving livestock productivity: greenhouse gas mitigation potential of silvopastoral systems in Caqueta}, series = {Environmental research letters}, volume = {14}, journal = {Environmental research letters}, number = {11}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1748-9326}, doi = {10.1088/1748-9326/ab3db6}, pages = {12}, year = {2019}, abstract = {Colombia's agriculture, forestry and other land use sector accounts for nearly half of its total greenhouse gas (GHG) emissions. The importance of smallholder deforestation is comparatively high in relation to its regional counterparts, and livestock agriculture represents the largest driver of primary forest depletion. Silvopastoral systems (SPSs) are presented as agroecological solutions that synergistically enhance livestock productivity, improve local farmers' livelihoods and hold the potential to reduce pressure on forest conversion. The department of Caquet{\´a} represents Colombia's most important deforestation hotspot. Targeting smallholder livestock farms through survey data, in this work we investigate the GHG mitigation potential of implementing SPSs for smallholder farms in this region. Specifically, we assess whether the carbon sequestration taking place in the soil and biomass of SPSs is sufficient to offset the per-hectare increase in livestock GHG emissions resulting from higher stocking rates. To address these questions we use data on livestock population characteristics and historic land cover changes reported from a survey covering 158 farms and model the carbon sequestration occurring in three different scenarios of progressively-increased SPS complexity using the CO2 fix model. We find that, even with moderate tree planting densities, the implementation of SPSs can reduce GHG emissions by 2.6 Mg CO2e ha-1 yr-1 in relation to current practices, while increasing agriculture productivity and contributing to the restoration of severely degraded landscapes.}, language = {en} } @article{MilcuHeimEllisetal.2011, author = {Milcu, Alexandru and Heim, Angela and Ellis, Richard J. and Scheu, Stefan and Manning, Pete}, title = {Identification of general patterns of nutrient and labile carbon control on soil carbon dynamics across a successional gradient}, series = {Ecosystems}, volume = {14}, journal = {Ecosystems}, number = {5}, publisher = {Springer}, address = {New York}, issn = {1432-9840}, doi = {10.1007/s10021-011-9440-z}, pages = {710 -- 719}, year = {2011}, abstract = {Carbon (C) inputs and nutrient availability are known to affect soil organic carbon (SOC) stocks. However, general rules regarding the operation of these factors across a range of soil nutrient availabilities and substrate qualities are unidentified. "Priming" (stimulated decomposition by labile C inputs) and 'preferential substrate utilization' (retarded decomposition due to shifts in community composition towards microbes that do not mineralize SOC) are two hypotheses to explain effects of labile C additions on SOC dynamics. For effects of nutrient additions (nitrogen and phosphorus) on SOC dynamics, the stoichiometric (faster decomposition of materials of low carbon-to-nutrient ratios) and 'microbial mining' (that is, reduced breakdown of recalcitrant C forms for nutrients under fertile conditions) hypotheses have been proposed. Using the natural gradient of soil nutrient availability and substrate quality of a chronosequence, combined with labile C and nutrient amendments, we explored the support for these contrasting hypotheses. Additions of labile C, nitrogen (N), phosphorus (P), and combinations of C and N and C and P were applied to three sites: 2-year fallow grassland, mature grassland and forest, and the effects of site and nutrient additions on litter decomposition and soil C dynamics were assessed. The response to C addition supported the preferential substrate hypothesis for easily degradable litter C and the priming hypothesis for SOC, but only in nitrogen-enriched soils of the forest site. Responses to N addition supported the microbial mining hypothesis irrespective of C substrate (litter or SOC), but only in the forest site. Further, P addition effects on SOC support the stoichiometric hypothesis; P availability appeared key to soil C release (priming) in the forest site if labile C and N is available. These results clearly link previously contrasting hypotheses of the factors controlling SOC with the natural gradient in litter quality and nutrient availability that exists in ecosystems at different successional stages. A holistic theory that incorporates this variability of responses, due to different mechanisms, depending on nutrient availability and substrate quality is essential for devising management strategies to safeguard soil C stocks.}, language = {en} }