Thematic session 10 – Nitrogen Cycling Research

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Thematic Session 10

Nitrogen Cycling Research

Wednesday 10 February 2021 | 10:00-12:00 hrs


LINK TO ZOOM MEETING: Will Follow soon.


10:00 – 10:05 Introduction by the session chairs - Dr Annelies Veraart & Dr Bjorn Robroek (Assistant Professors Aquatic Ecology and Environmental Biology @ Radboud University)
10:05 – 10:20 KEYNOTE LECTURE | Nitrogen cycling in pristine ecosystems. Spotlight: Nitrogen fixation
Kathrin Rousk @ University of Copenhagen

Nitrogen (N2) fixation performed by moss-associated cyanobacteria is one of the main sources of new N input in pristine ecosystems like boreal forests and arctic tundra. Here, moss-cyanobacteria associations can contribute more than 50% to total ecosystem N input, thereby sustaining plant productivity in these pristine systems. However, N2 fixation in mosses is strongly influenced by abiotic factors. Here, I will present results from field and laboratory assessments on the controls of moss-associated N2 fixation, focussing on global change effects such as increased temperature, moisture availability and nitrogen deposition.
10:20 – 10:30 Dynamics of nutrients, soil biology and agricultural management within a cropping cycle
Kyle Mason-Jones @ Terrestrial Ecology, Netherlands Institute of Ecology

Organic management is expected to enhance the sustainability of agricultural C and N cycles. Past research has either examined multiple functions from long-term experiments, or tested specific functions at the seasonal level (e.g., N mineralization). However, few studies examine multiple parameters over a single season, though this is a relevant timescale for C and N cycles. We present a year of soil chemical and biological data from an experimental comparison of organic and conventional cropping. This reveals how management (including fertilization) and environmental drivers relate to C and N dynamics, and provides new hypotheses for agro-ecosystem function.
10:30 – 10:40 Optimizing fertilization policies for crop growth with reinforcement learning
Hiske Overweg @ Geo-Information and Remote Sensing Group, Wageningen University

To reduce the detrimental effects of nitrogen fertilizers on the environment, optimizing management policies in terms of application rates, dates and location is essential. In recent years, reinforcement learning has been employed successfully to learn state of the art policies in a wide range of applications, from games like chess and Go, to trading strategies. We propose to train reinforcement learning agents on process-based crop growth models to efficiently explore the space of possible fertilizer management policies and to identify those with reduced environmental impact.
10:40 – 10:50 Assessing the potential of (a)biotic interactions to conserve and restore Zostera marina communities
Yvet Telgenkamp @
Aquatic Ecology and Environmental Biology, Radboud University
Globally, seagrass ecosystems are declining with ever-increasing numbers. Therefore, conservation and restoration practices are often needed to restore and preserve these systems. In the Netherlands, researchers observed that juvenile Platynereis dumerilii ragworms tangled leaf blades of the seagrass Zostera marina by jointly ‘gluing’ them with their dwelling tube constructions. This ‘gluing’ is a so-far undescribed phenomenon in seagrass meadows. We theorized that the presence of the common periwinkle Littorina littorea could reduce leaf gluing due grazing on epiphytes that are used by the ragworms as building material for their dwelling tubes. We tested these hypothesized interactions and investigated how eutrophication influences this mechanism.
10:50 – 11:10 Joint coffee / tea break and time to socialise within your breakout room
11:10 – 11:20 Connecting the nitrogen and methane cycle: how does nitrate stimulate methane consumption?
Sigrid van Grinsven @ Microbiology and Biogeochemistry, Royal Netherlands Institute for Sea Research (NIOZ) & Biogeochemistry, Eawag - Swiss Federal Institute of Aquatic Science and Technology

Eutrophication is known to stimulate methane production in lakes. Our research has, however, shown that nitrate may also enhance methane consumption in lakes, reducing methane emissions. In this talk, I will highlight the effects of nitrate we observed under natural water column conditions, followed by an overview of our enrichment culture experiments. These experiments aimed to unravel how nitrate can stimulate methane consumption and which conditions may stimulate this process. We showed that nitrate-coupled methane oxidation may depend on a syntrophic interaction between two species, a theory that was supported by our metagenomic analysis of the methanotroph and its partner.
11:20 – 11:30 Drivers of temperature sensitivity of lake denitrification and N2O emission - a meta-analysis
Mandy Velthuis @ Aquatic Ecology and Environmental Biology, Radboud University

Temperature affects freshwater denitrification rates, a microbial process which removes reactive nitrogen from these ecosystems. However, incomplete denitrification can enhance nitrous oxide (N2O) emissions, a potent greenhouse gas. Using a meta-analytic approach, we investigated the temperature sensitivity of denitrification rates in and N2O emissions from lakes worldwide. Our results show that temperature sensitivity of denitrification increased with nitrogen availability and the distance from the equator. Contrastingly, temperature sensitivity of N2O emissions decreased with distance from the equator. As global temperatures are currently increasing, especially in higher latitudes, our data suggests overall enhanced denitrification and N2O emissions from freshwater ecosystems.
11:30 – 11:40 Statistical analysis of nitrogen use efficiency using multiple linear regression and random forest in northeast China
Yingxia Liu @ Soil Geography and Landscape group, Wageningen University

This study aims to evaluate spatial-temporal variations of county-scale PFPN (the Partial factor productivity of nitrogen) and PNBN (the Partial nutrient balance of nitrogen) in northeast China from 1990 to 2015. Results revealed the R-square in SMLR and RF models were 0.45 and 0.81 for PFPN, and 0.70 and 0.88 for PNBN. The planting area index of vegetables, agricultural GDP available, soil water capacity, coarse fragments, CEC and temperature are main covariates for NUE. The study provide scientific insights and support for the development of sustainable agriculture in China and could provide a reference for formulating scientific agricultural policies.
11:40 – 11:55 General discussion and wrap up of the session