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RACe Report Summary

Project ID: 661674
Funded under: H2020-EU.1.3.2.

Periodic Reporting for period 1 - RACe (The impact of climate change on the uptake of arsenic into rice)

Reporting period: 2016-03-30 to 2018-03-29

Summary of the context and overall objectives of the project

Rice is the staple food worldwide. Unfortunately, global rice yield is already falling behind population growth. With more than half of the world’s population consuming rice daily, it is crucial to ensure future rice productivity and quality for a growing population. Most crucial constraints to future rice production in Asia and the US are climate change and the contaminant arsenic that is enriching in paddy soils. According to the highest emission scenario for greenhouse gases presented in the 5th assessment report of the IPCC, global annual temperatures could rise by more than 5°C by the year 2100. Thus, the objective for the RACe-MSC-action was to investigate whether a changing climate combined with rising arsenic levels in the soil affect the grain yield and quality of rice. To better understand the uptake of arsenic into the plant, changes in soil geochemistry and arsenic dynamics in the bulk soil compared to the rhizosphere soil were assessed using classic geochemical approaches combined with high resolution, synchrotron-based mineralogical analysis. Furthermore, omics-based sequencing of the soil microbial community in proximity to rice roots serve to mechanistically explain the observed changes in soil geochemistry.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Fully climate controlled growth chambers were constructed in large greenhouses at the Global Ecology Department of the Carnegie Institution for Science, which is located on Stanford University grounds. The Californian rice variety M206 was grown on Californian paddy soil under fully controlled climate conditions and two different soil arsenic levels for a total of two generations. Rice plants were either grown under today's climate (33°C, 415 ppmv CO2) or the IPCC-worst case postulated climate of the year 2100 (38°C, 850 ppmv CO2). Additionally, climates varied only in temperature or atmospheric CO2 were also investigated to tease apart the effect of each individual climate parameters on arsenic uptake by rice and its productivity. Productivity loss under a future climate with low soil arsenic levels support previous literature findings. However, when investigating the effect of climate change and elevated soil arsenic combined on rice production, the amount of arsenic present in pore water increased. This increased arsenic bioavailability to the plant resulted in higher loss of produced grain, which is currently not accounted for. Additionally, a loss in grain quality is observed as more arsenic is accumulated in the grain. Time-resolved quantification of iron, sulfur and manganese in the pore water showed that reducing conditions were faster achieved under hotter climatic conditions. Geochemical modelling further proved that secondary mineral precipitation slowed down under hotter conditions, not allowing arsenic to be removed from the bioavailable fraction and associating with soil minerals as much as under today's climatic conditions. Samples for soil microbial community profiling were collected and are currently being processed.
The data was presented at several conferences and invited talks and a few manuscripts are in preparation.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We expect to find differences in the microbial community composition in the bulk soil and rhizosphere of rice plants exposed to different climates and soil arsenic conditions. These differences might include functional microbial guilds involved in arsenic, iron and sulfur cycling. We hope to link climate induced changes in soil geochemistry and mineralogy to microbial community dynamics in the rhizosphere to identify rhizosphere limitations causing macroscopic grain yield and quality outcomes. Additionally we have started to contact different agencies and research institutes working on food security in general and rice production specifically to talk about the impact of our obtained data for rice growing regions in the world and for including our findings in global rice models.
Furthermore, the current data presented two intriguing observations that led us to start two originally not planned projects. First, when tracking the dynamics of arsenic in the pore water, it was imminent that the first eight weeks of plant growth are important for later arsenic impacts on yield and quality. Thus, we constructed rhizobox experiments to better understand and spatially resolve what happens geochemically and microbially in the rhizospheres of rice plants exposed to different climates and arsenic conditions. Second, we observed differences in greenhouse gas emissions due to the presence of arsenic in the soil under different climatic conditions. We are currently investigating this relationship in detail.

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