Periodic Reporting for period 2 - RACe (The impact of climate change on the uptake of arsenic into rice)
Okres sprawozdawczy: 2018-03-30 do 2019-03-29
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. Overall, climate-induced changes of the fate of arsenic in the soil and the response of the plant will lead to unpredictable losses in rice grain productivity and quality at this point. Global models of rice production need to include contaminant dynamics in order to not overestimate rice production in the future.
The main results of the project were:
- The availability of arsenic in the soil increased due to future climatic conditions.
- Iron(III) and arsenate(V) reducing microbial communities are responsible for shifts in arsenic mobility in the soil.
- M206 grain yields decrease by 42% due to combined climate and soil arsenic stress compared to yields at today’s climate and arsenic soil concentrations.
- Future climatic conditions cause a nearly twofold increase of grain inorganic arsenic concentrations compared to today's climatic conditions.
- Soil arsenic is the stronger determinant of rice yield compared to climatic condition.
- A shift to future climatic conditions adversely affect grain arsenic levels even at low soil arsenic concentrations.
- Temperature increases soil arsenic bioavailability, elevated CO2 as well, though combined they increase arsenic bioavailability in between.
- Temperature decreases grain yields, elevated CO2 increases grain yield, jointly they decrease grain yield.
The main results of the project were:
- The availability of arsenic in the soil increased due to future climatic conditions.
- Iron(III) and arsenate(V) reducing microbial communities are responsible for shifts in arsenic mobility in the soil.
- M206 grain yields decrease by 42% due to combined climate and soil arsenic stress compared to yields at today’s climate and arsenic soil concentrations.
- Future climatic conditions cause a nearly twofold increase of grain inorganic arsenic concentrations compared to today's climatic conditions.
- Soil arsenic is the stronger determinant of rice yield compared to climatic condition.
- A shift to future climatic conditions adversely affect grain arsenic levels even at low soil arsenic concentrations.
- Temperature increases soil arsenic bioavailability, elevated CO2 as well, though combined they increase arsenic bioavailability in between.
- Temperature decreases grain yields, elevated CO2 increases grain yield, jointly they decrease grain yield.
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. Soil microbial community profiling proved that iron(III)-reducing and arsenic(V)-reducing microbial functional groups were responsible for the release of arsenic into soil solution.
Part of the data was published (Muehe et al., Rice production threatened by coupled stresses of climate and soil arsenic, Nature Communications, 2019) and more manuscripts are in preparation. The data was also presented at several conferences, and invited scientific and general audience talks.
Part of the data was published (Muehe et al., Rice production threatened by coupled stresses of climate and soil arsenic, Nature Communications, 2019) and more manuscripts are in preparation. The data was also presented at several conferences, and invited scientific and general audience talks.
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. This work has shown interesting results, indicating that the mineralogy of formed iron plaque around rice roots and the type of arsenic that is retain differs under different climatic conditions. We are currently writing up these results for publication.
Second, we observed differences in greenhouse gas emissions due to the presence of arsenic in the soil under different climatic conditions. Also here, we are currently preparing manuscripts.
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. This work has shown interesting results, indicating that the mineralogy of formed iron plaque around rice roots and the type of arsenic that is retain differs under different climatic conditions. We are currently writing up these results for publication.
Second, we observed differences in greenhouse gas emissions due to the presence of arsenic in the soil under different climatic conditions. Also here, we are currently preparing manuscripts.