Quantification of methane oxidation in the rice rhizosphere using 13C-labelled methane

In this paper isotope ratio mass spectrometry is used to determine the methane (CH4) oxidation fraction in the rhizosphere of intact rice plant-soil systems. Earlier studies on quantification of the methane oxidation were based on inhibition or incubation procedures which strongly interfered with the plant-soil system and resulted in a large variability of the reported fractions, while other studies considered stable isotopes at natural abundance levels to investigate methanotrophy in the rhizosphere of rice. The current work is the first that used 13C-labelled CH4 as additive and calculated the oxidation fraction from the ratio between the added 13C-labelled CH4 and its oxidation product 13CO2. Both labelled gases could be distinguished from the natural abundance percentages. The oxidation fraction for methane was found to be smaller than 7%, suggesting that former approaches overestimate the methane oxidation fraction.

Tweerichtingsverkeer tussen mens en biodiversiteit

Oratie uitgesproken door Prof.dr.ir. P.M. van Bodegom bij de aanvaarding van het ambt van hoogleraar Environmental Biology aan de Universiteit Leiden op vrijdag 8 mei 2015Conservation Biolog

Methane emissions from rice paddies : experiments and modelling

This thesis describes model development and experimentation on the comprehension and prediction of methane (CH 4 ) emissions from rice paddies. The large spatial and temporal variability in CH 4 emissions and the dynamic non-linear relationships between processes underlying CH 4 emissions impairs the applicability of empirical relations. Mechanistic concepts are therefore starting point of analysis throughout the thesis.The process of CH 4 production was investigated by soil slurry incubation experiments at different temperatures and with additions of different electron donors and acceptors. Temperature influenced conversion rates and the competitiveness of microorganisms. The experiments were used to calibrate and validate a mechanistic model on CH 4 production that describes competition for acetate and H 2 /CO 2 , inhibition effects and chemolithotrophic reactions. The redox sequence leading eventually to CH 4 production was well predicted by the model, calibrating only the maximum conversion rates.Gas transport through paddy soil and rice plants was quantified by experiments in which the transport of SF 6 was monitored continuously by photoacoustics. A mechanistic model on gas transport in a flooded rice system based on diffusion equations was validated by these experiments and could explain why most gases are released via plant mediated transport. Variability in root distribution led to highly variable gas transport.Experiments showed that CH 4 oxidation in the rice rhizosphere was oxygen (O 2 ) limited. Rice rhizospheric O 2 consumption was dominated by chemical iron oxidation, and heterotrophic and methanotrophic respiration. The most abundant methanotrophs and heterotrophs were isolated and kinetically characterised. Based upon these experiments it was hypothesised that CH 4 oxidation mainly occurred at microaerophilic, low acetate conditions not very close to the root surface. A mechanistic rhizosphere model that combined production and consumption of O 2 , carbon and iron compounds with iron adsorption kinetics and diffusive transport in a rice plant and rhizosphere, confirmed this hypothesis. Oxidation of CH 4 depended on acetate and O 2 concentrations and on variables influencing competition between methanotrophs and chemical iron oxidation. Oxidation of CH 4 also depended on root growth dynamics and was intrinsically dynamic.The process-based concepts were simplified in a field scale model on CH 4 emissions by dividing a rice paddy into a rhizosphere compartment and a bulk soil compartment. The field scale model was validated by independent CH 4 emission measurements from fields in the Philippines, China and Indonesia in different seasons and with different inorganic and organic fertiliser additions. The model predicted CH 4 emissions well with only few generally available site-specific input parameters. A sensitivity analysis showed that the model was very sensitive to the description of substrate supply.The field scale model was coupled to a Geographic Information System to scale up regional CH 4 emissions from rice paddies, as was the aim of the overall project. Regional CH 4 emission estimates were however affected by the applied interpolation technique and by data resolution effects in a case study for the island of Java, Indonesia. The scaling effects were induced by the combination of a loss of information on heterogeneities and by non-linear model responses. Data availability and not model uncertainty, which was small for the field scale model developed in this thesis, limits upscaling of CH 4 emissions from rice paddies to regions.</p

Analysis of species attributes to determine dominant environmental drivers, illustrated by species decline in the Netherlands since the 1950s

The relative impact of climate change and land use change on biodiversity loss is still under discussion. To alleviate drawbacks related to the use of observed species distributions, we introduce a novel approach to separate the effects of climate change and land use change, the latter split into fragmentation, agricultural intensification and reforestation. This approach, coined the Attribute Importance Analysis (AIA), uses the ability of species attributes to explain population declines. Through the a priori association between attributes and individual drivers, the relative importance of the drivers in causing the species decline can be assessed. We tested this approach on the population decline of vertebrate, insect, vascular plant, and fungi species in the Netherlands since the 1950s. Fragmentation was clearly the strongest driver of species decline for vertebrates and plants, and this may also be true for insects. For fungi, climate change seems the only driver. We found a weak signal of the importance of agricultural intensification for the decline of vertebrates only. We ascribe this unexpected low importance of agricultural intensification to our partitioning of agricultural effects into fragmentation and intensification. Our generic approach can offer valuable quantitative information on the relative importance of drivers that change local community composition without the need for spatial explicit information. Without data on temporal trends in drivers, including local climate and land use change, accurate information on species decline, species attribute values and association of attributes with drivers can give insights into the causes of species decline, which, in turn, can be used to adapt nature management accordingly.Conservation Biolog

A multi-metric assessment of drought vulnerability across different vegetation types using high resolution remote sensing

Drought impact monitoring is of crucial importance in light of climate change. However, we lack an understanding of the concomitant responses of ecosystems to a variety of drought characteristics and the links between drought and ecosystem anomaly characteristics for a comprehensive set of vegetation types to provide needed information for water management. In response, this study presents a new framework that allows us to explore the relationship between drought and its impact on ecosystems in greater detail. Specifically, our framework focuses on estimating jointly the hydrological and ecosystem temporal evolution and anomalies around a drought event using four pairs of metrics: onset-onset, duration-duration, intensity-intensity, and severity-severity of drought and vegetation damage. Additionally, we incorporated a metric on vegetation vulnerability based on changes in damage severity along a gradient of increasing drought severity. Based on this framework, we evaluated drought vulnerability patterns of various vegetation types across the Netherlands and Belgium in 2018 at high spatiotemporal resolution. Our results reveal a differential vulnerability of vegetation between ecosystems with increasing drought severity, which could aid future drought impact predictions. In particular, mosaic grasslands and tree/shrub croplands are highly sensitive to increasing drought severity. Individual characteristics (onset, duration, intensity and severity) of drought and vegetation damage behave differently in various vegetation types. For instance, broadleaved forests respond faster than other forests, while mixed forests suffer less damage than other types. The early warning threshold to drought for most vegetation types is around a Standardized Precipitation Evapotranspiration Index (SPEI) value of -1. The characterization of a suite of drought response characteristics through our impact analysis framework can be used in a wide variety of regions to understand current and possible future responses to drought.Environmental Biolog

Microbial processes of CH4 production in a rice paddy soil: model and experimental validation.

The importance of different anaerobic processes leading to CH4 production in rice paddies is quantified by a combination of experiments and model. A mechanistic model is presented that describes competition for acetate and H2/CO2, inhibition effects and chemolithotrophic redox reactions. The model is calibrated with anaerobic incubation experiments with slurried rice soil, monitoring electron donors and electron acceptors influencing CH4 production. Only the values for maximum conversion rates (Vmax) for sulphate and iron reduction and CH4 production are tuned. The model is validated with similar experiments in which extra electron donors or electron acceptors had been added. The differences between model estimates without kinetic parameter adjustments and experiment were not significant, showing that the model contains adequate process descriptions. The model is sensitive to the estimates of Vmax, that are site dependent and to the description of substrate release, that drives all competition processes. For well-shaken systems, the model is less sensitive to chemolithotrophic reactions and inhibitions. Inhibition of sulphate reduction and methanogenesis during iron reduction can however explain acetate accumulation at the start of the incubations. Iron reduction itself is most probably retarded due to manganese reductio

Nieuwe maat voor bodemvochtregime ook geschikt onder toekomstig klimaat

Huidige maten voor zuurstofstress in het wortelmilieu van planten, zoals de gemiddelde voorjaarsgrondwaterstand en het percentage luchtgevulde poriën, zijn niet geschikt voor klimaatprojecties. Dat komt doordat ze correlatief en indirect zijn en geen rekening houden met veranderingen in temperatuur en neerslagpatronen. In natte omstandigheden is de respiratiestress wel een geschikte maat. Met een nieuw model is die nu voor alle locaties in Nederland te berekenen. In de nieuwe maat komen zowel de effecten op de vegetatie van extreme neerslag tot uitdrukking als die van hoge temperaturen. Zuurstofstress door een hevige regenbui op een warme zomerdag zal onder het toekomstige klimaat veel vaker voorkomen. De door het nieuwe model berekende hoge respiratiestress van een dergelijke gebeurtenis zal leiden tot natuurlijke vegetaties van nattere bodems dan de huidige, niet klimaatbestendige maten voorzie