Reading tea leaves worldwide: decoupled drivers of initial litter decomposition mass-loss rate and stabilisation

The breakdown of plant material fuels soil functioning and biodiversity. Currently, process understanding of global decomposition patterns and the drivers of such patterns are hampered by the lack of coherent large-scale datasets. We buried 36,000 individual litterbags (tea bags) worldwide and found an overall negative correlation between initial mass-loss rates and stabilization factors of plant-derived carbon, using the Tea Bag Index (TBI). The stabilization factor quantifies the degree to which easy-to-degrade components accumulate during early-stage decomposition (e.g. by environmental limitations). However, agriculture and an interaction between moisture and temperature led to a decoupling between initial mass-loss rates and stabilization, notably in colder locations. Using TBI improved mass-loss estimates of natural litter compared to models that ignored stabilization. Ignoring the transformation of dead plant material to more recalcitrant substances during early-stage decomposition, and the environmental control of this transformation, could overestimate carbon losses during early decomposition in carbon cycle models

Decomposition and soil carbon sequestration in mangrove ecosystems

Joost Keuskamp keek naar de gevolgen van de toename van meststoffen op mangrovebossen in tropische gebieden. Meststoffen beïnvloeden de snelheid waarmee koolstof in mangroven wordt vastgelegd of afgebroken. Dit is van belang omdat deze snelheid de opwarming van de aarde kan versnellen of kan remmen. Mangrovebossen bestrijken grote delen van tropische en subtropische kusten en riviermondingen en leggen aanzienlijke hoeveelheden organische stof vast in de bodem. Dit proces speelt een grote rol bij oceanische mangrove-eilanden, omdat zij zo meestijgen met de zeespiegel. Omdat in kustgebieden steeds meer mensen wonen en het gebruik van deze gebieden dus intensiever is, komen ook steeds meer meststoffen in de bodem terecht. Keuskamp laat zien hoe deze eutrofiëring de afbraak van bodemorganische stof beïnvloedt en wat daarvan de mogelijke gevolgen zijn voor koolstofopslag in mangrovesystemen. Het onderzoek werd uitgevoerd in bodems onder standplaatsen van mangroven uit de genera Avicennia en Rhizophora in Saoedi-Arabië en Belize. De uitkomsten kunnen worden gebruikt om het risico van het wegzinken van mangrove-eilanden als gevolg van eutrofiëring van de zee beter in te schatten. Onderdeel van het proefschrift is een studie naar een goedkope, alternatieve manier om de afbraaksnelheid van organisch materiaal te meten door middel van de ‘Tea Bag Index’

Decomposition and soil carbon sequestration in mangrove ecosystems

Joost Keuskamp keek naar de gevolgen van de toename van meststoffen op mangrovebossen in tropische gebieden. Meststoffen beïnvloeden de snelheid waarmee koolstof in mangroven wordt vastgelegd of afgebroken. Dit is van belang omdat deze snelheid de opwarming van de aarde kan versnellen of kan remmen. Mangrovebossen bestrijken grote delen van tropische en subtropische kusten en riviermondingen en leggen aanzienlijke hoeveelheden organische stof vast in de bodem. Dit proces speelt een grote rol bij oceanische mangrove-eilanden, omdat zij zo meestijgen met de zeespiegel. Omdat in kustgebieden steeds meer mensen wonen en het gebruik van deze gebieden dus intensiever is, komen ook steeds meer meststoffen in de bodem terecht. Keuskamp laat zien hoe deze eutrofiëring de afbraak van bodemorganische stof beïnvloedt en wat daarvan de mogelijke gevolgen zijn voor koolstofopslag in mangrovesystemen. Het onderzoek werd uitgevoerd in bodems onder standplaatsen van mangroven uit de genera Avicennia en Rhizophora in Saoedi-Arabië en Belize. De uitkomsten kunnen worden gebruikt om het risico van het wegzinken van mangrove-eilanden als gevolg van eutrofiëring van de zee beter in te schatten. Onderdeel van het proefschrift is een studie naar een goedkope, alternatieve manier om de afbraaksnelheid van organisch materiaal te meten door middel van de ‘Tea Bag Index’

Potential for sulfate reduction in mangrove forest soils: Comparison between two dominant species of the Americas

Avicennia and Rhizophora are globally occurring mangrove genera with different traits that place them in different parts of the intertidal zone. It is generally accepted that the oxidizing capacity of Avicennia roots is larger than that of Rhizophora roots, which initiates more reduced conditions in the soil below the latter genus. We hypothesize that the more reduced conditions beneath Rhizophora stands lead to more active sulfate-reducing microbial communities compared to Avicennia stands. To test this hypothesis, we measured sulfate reduction traits in soil samples collected from neighboring Avicennia germinans and Rhizophora mangle stands at three different locations in southern Florida. The traits measured were sulfate reduction rates (SRR) in flow-through reactors containing undisturbed soil layers in the absence and presence of easily degradable carbon compounds, copy numbers of the dsrB gene, which is specific for sulfate-reducing microorganisms, and numbers of sulfate-reducing cells that are able to grow in liquid medium on a mixture of acetate, propionate and lactate as electron donors. At the tidal locations Port of the Islands and South Hutchinson Islands, steady state SRR, dsrB gene copy numbers and numbers of culturable cells were higher at the A. germinans than at the R. mangle stands, although not significantly for the numbers at Port of the Islands. At the non-tidal location North Hutchinson Island, results are mixed with respect to these sulfate reduction traits. At all locations, the fraction of culturable cells were significantly higher at the R. mangle than at the A. germinans stands. The dynamics of the initial SRR implied a more in situ active sulfate-reducing community at the intertidal R. mangle stands. It was concluded that in agreement with our hypothesis R. mangle stands accommodate a more active sulfate-reducing community than A. germinans stands, but only at the tidal locations. The differences between R. mangle and A. germinans stands were absent at the non-tidal, impounded location

European-scale modelling of groundwater denitrification and associated N2O production

This paper presents a spatially explicit model for simulating the fate of nitrogen (N) in soil andgroundwaterand nitrous oxide (N2O) production in groundwater with a 1 km resolution at the Europeanscale. The results show large heterogeneity of nitrate outflow from groundwater to surface water andproductionof N2O. This heterogeneity is the result of variability in agricultural and hydrological systems. Large parts of Europe have no groundwater aquifers and short travel times from soil to surface water. In these regions no groundwaterdenitrificationand N2O production is expected. Predicted N leaching (16% of the N inputs) and N2O emissions (0.014% of N leaching) are much less than the IPCC default leaching rate and combined emission factor for groundwaterand riparian zones, respectivel

Tea Bag Index: A novel approach to collect uniform decomposition data across ecosystems

1.Changes in the balance between soil carbon storage and release can significantly amplify or attenuate global warming. Although a lot of progress has been made in determining potential drivers of carbon release through large-scale decomposition experiments, climate predictions are still hampered by data limitation at a global scale as a result of high effort and measurement costs of comparative litter decomposition studies. 2.We introduce an innovative, cost-effective, well-standardised method to gather data on decomposition rate and litter stabilisation using commercially available tea bags as standardised test kits. By using two tea types with contrasting decomposability, we can construct a decomposition curve using a single measurement in time. The acquired Tea Bag Index (TBI) consists of two parameters describing decomposition rate (k) and litter stabilisation factor (S). 3.The method was tested for its sensitivity and robustness in contrasting ecosystems and biomes, confirming that the TBI is sensitive enough to discriminate between these systems. Within an ecosystem, TBI is responsive to differences in abiotic circumstances such as soil temperature and moisture content. The collected k and S values are in accordance with expectations based on decomposition process literature. They are therefore interpretable within the current knowledge framework. 4.Tea Bag Index is a unique, multifunctional method requiring few resources and minimal prior knowledge. The standardisation and simplicity of the method make it possible to collect comparable, globally distributed data through crowdsourcing. TBI can further provide an excellent decomposition reference and has the potential to increase reliability of soil carbon flux estimates based on extrapolations of decomposition data

Monitoring van methaan-, ammoniak- en lachgasemissies uit melkveestallen : Praktijkmetingen in de periode oktober 2018-oktober 2020

Between October 2018 and October 2020 measurements have taken place on 18 dairy farms in The Netherlands based on which their ammonia- (NH3) and methane (CH4) emissions were determined. With the measurement equipment, an emission estimation was made per day and compared with a reference measurement. The aim of this study was to determine the methane emissions and its variation from dairy houses in the Netherlands. Besides that, an aim was to find relations with farm management factors. Another aim was to investigate how such a measurement system could support farmers to apply measures in order to reduce ammonia- and methane emissions. The mean emission ± standard deviation was 13,8 ± 3,2 kg NH3 per animal place per year and 193 ± 56 kg CH4 per animal place per year based on the reference measurements. Based on thedaily averages (from the continuous measurements), the average ammonia emissions were 12,0 ±2,9 kg per animal place per year and the average methane emissions 184 ± 50 kg per animal place per year. Based on continuous measurements, the variation in methane emissions was 27% between farms and 29% within farms (i.e. the variation between days). The outside temperature is found to be a good predictor for the ammonia emissions pattern throughout the year. In addition to that, the CH4-CO 2 ratio at concentration level of house air can be used as a predictor for the total methane emission of a certain farm. Quantifying emission levels by a measurement system can help the farmer to implement farm specific measures