BECC Action group: Nutrient weathering from rocks

In this action group we seek to bridge the theoretical concepts of long-term (geological) and short-term (ecosystem) N and P dynamics by an ambitious cross-disciplinary knowledge exchange.

Understanding the production and consumption of available nutrients is paramount for predicting ecosystem responses to climate change factors. Available nutrients define the potential of the vegetation to grow and their response potential to global change. Stimulation of physical and biological processes by future – and ongoing - warming and acidification, caused by elevated atmospheric CO2 or acidified rainfall, can lead to increased availability of nutrients released from SOM and soil minerals. Any nutrient such as nitrogen (N) might become limiting for plants under climate change, leading to slowed or even stopped plant growth stimulation under future eCO2. Missing link in this concept is the importance of nutrients other than N, such as phosphorous (P). For example, co-limitation by phosphorus (P) or solely P limitation is only sparsely considered in climate change manipulation studies.

Input to ecosystem cycling of essential nutrients from bed-rocks is well-known for P as this is the only source of new P to the biosphere. Till recently, N input to terrestrial ecosystems was thought to come mainly from N2 fixation, however new evidence of input of N from bed-rock material to ecosystem N cycling is accumulating. The possibility of significant N input directly from minerals of soil and underlying rocks is potentially highly relevant for understanding ecosystem P and N budgets. Sedimentary (e.g., mudstones), magmatic (e.g., granites) and metamorphic rocks (e.g., schists) contain micas (predominantly biotite and muscovite) as major mineral that can have substantial concentrations of N. This N can be available for plant uptake upon weathering of the rock or leak into streams.

Planned actions through 2016: i) Synthetize current conceptual and methodological advances of rock-nitrogen within ecosystems in a future changed environment; ii) Develop a conceptual model for rock-nitrogen (N) and -phosphor (P) input to the ecosystem dynamics, in a rock- soil-plant-ecosystem scenario, with the aim of determining transit from ecosystem N to P limitation, and assessing if N and P dynamics are coupled or un-coupled; iii) Stratify the requirements of a needed database from a specific geological area to give data input to the model, and identification of a relevant location to test the concept. iv) initiate a scheme for inter-calibration of analysis methodology (IRMS) with international collaborating expert laboratories.

Activities:
13-18/8 Seminar at ‘Goldschmidt’ Paris 2017

This action group is convening a session (09K) at the conference: ‘Goldschmidt’ Paris 2017, August 13 to 18 under the Theme: Weathering, erosion and climate (past, present and future)

The feedbacks among tectonics, weathering, erosion, rainfall, temperature and terrestrial life play an important role in stabilizing climate and thus ensuring planetary habitability on geologic time scales. Despite decades of work, a comprehensive understanding of the nature and strength of the feedbacks, and how they work together to regulate climate, remain elusive. Sessions under this theme will explore new approaches to this old problem, with a focus on innovations in observation and modelling of chemical weathering, physical erosion, and the factors that control these processes, in the past, present, and future.

The session 09K is titled Rock Nitrogen: From Early Earth History to Modern Sustainable Ecosystem Services. Convenors are Benjamin Houlton and Louise C. Andresen with the invited keynote: Randy Dahlgren (University of California - Davis).

Rock nitrogen (N) is becoming a dynamic new area of research that connects biological and geological disciplines, both over deep to modern time periods, with important implications for Earth’s climate system and the sustainability of ecosystem services. The purpose of this session is to bring together a vibrant leading community of scientists across disparate fields to understand rock N from multi-disciplinary perspective. The planetary N cycle, initiated via the evolution of biological N2 fixation c. 3.5 billion years ago, has resulted in substantial quantities of fixed N burial, such that ~20% of all of Earth’s N is found in rock today. The physical and chemical weathering of this N is critical to understanding limitation of plant productivity and the terrestrial CO2 sink; and geobiological controls on rock weathering and the importance of the “critical zone”. We aim to cover the following research questions, concerning N and the role of life on Earth: 1. How can we constrain the bioavailability and weathering of rock N through models and geochemical proxies? 2. Can rock N constitute a missing pool that potentially enhances the carbon sink in vegetation globally? 3. Will climate change accelerate weathering rates? 4. What organisms (plants, bacteria, fungi, mycorrhiza) can directly attack minerals and relic organic N to gain N? 5. Can regional (lateral) and global (vertical) rock N content, δ15N signature, transport rates and isotope fractionation inform models? 6. In what way are tectonic, subduction and long term transfer to the crust relevant for contemporary N cycling?