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2023

Genotypic responses of rice to alternate wetting and drying irrigation in the Mekong Delta
Kristian Johnson, Thuong Ti Bach Vo, Duong Van Nha, Folkard Asch

Abstract

Journal: Journal of Agronomy and Crop Science

Title: Genotypic responses of rice to alternate wetting and drying irrigation in the Mekong Delta

Authors: Folkard Asch, Kristian Johnson, Thuong Ti Bach Vo, Bjorn Ole Sander, Van Nha Duong, Reiner Wassmann

University of Hohenheim, Inst. of Agric. Sci. in the Tropics (Hans-Ruthenberg-Institute), Germany

International Rice Research Institute, Los Banos, Philippines

Karlsruhe Institute of Technology, Campus Alpin, Garmisch-Partenkirchen, Germany

Kien Giang University, Kien Giang, Vietnam

Abstract:

Alternate wetting and drying irrigation (AWD) has been shown to decrease water use and trace gas emissions from paddy fields. Whereas genotypic water use shows little variation, it has been shown that rice varieties differ in the magnitude of their methane emissions. Management and variety-related emission factors have been proposed for modelling the impact of paddy production on climate change; however, the magnitude of a potential reduction in greenhouse gas emissions by changing varieties has not yet been fully assessed. AWD has been shown to affect genotypic yields and high-yielding varieties suffer the greatest loss when grown under AWD. The highest yielding varieties may not have the highest methane emissions; thus, a potential yield loss could be compensated by a larger reduction in methane emissions. However, AWD can only be implemented under full control of irrigation water, leaving the rainy seasons with little scope to reduce methane emissions from paddy fields. Employing low-emitting varieties during the rainy season may be an option to reduce methane emissions but may compromise farmers’ income if such varieties perform less well than the current standard. Methane emissions and rice yields were determined in field trials over two consecutive winter/spring seasons with continuously flooded and AWD irrigation treatments for 20 lowland rice varieties in the Mekong Delta of Vietnam. Based on the results, this paper investigates the magnitude of methane savings through varietal choice for both AWD and continuous flooding in relation to genotypic yields and explores potential options for compensating farmers’ mitigation efforts.

Journal: Plant-Environment Interactions

Title: Chamber-based system for measuring whole-plant transpiration dynamics

Authors: Alejandro Pieters, Marcus Giese, Marc Schmierer, Kristian Johnson, Folkard Asch

University of Hohenheim, Inst. of Agric. Sci. in the Tropics (Hans-Ruthenberg-Institute), Germany

Abstract:

Most of our insights on whole-plant transpiration (E) are based on leaf-chamber measurements using water vapor porometers, IRGAs, or flux measurements. Gravimetric methods are integrative, accurate, and a clear differentiation between evaporation and Ecan be made. Water vapor pressure deficit (VPD) is the driving force for E but assessing its impact has been evasive, due to confounding effects of other climate drivers. We developed a chamber-based gravimetric method, in which whole plant response of E to VPD could be assessed, while keeping other environmental parameters at predetermined values. Stable VPD values (0.5–3.7 kPa) were attained within 5 min after changing flow settings and maintained for at least 45 min. Species differing in life form and photosynthetic metabolism were used. Typical runs covering the range of VPDs lasted up to 4 h, preventing acclimation responses or soilborne water deficit. Species-specific responses of E to VPD could be identified, as well as differences in leaf conductance. The combined gravimetric-chamber-based system presented overcomes several limitations of previous gravimetric set ups in terms of replicability, time, and elucidation of the impact of specific environmental drivers on E, filling a methodological gap and widening our phenotyping capabilities.

Journal: Journal of Plant Nutrition and Soil Science

Title: Comprehensive assessment of extraction methods for plant tissue samples for determining sodium and potassium via flame photometer and chloride via automated flow analysis

Authors: Julia Asch, Kristian Johnson, Shimul Mondal, Folkard Asch

University of Hohenheim, Inst. of Agric. Sci. in the Tropics (Hans-Ruthenberg-Institute), Germany

Abstract:

Background and aims

Determination of sodium (Na), potassium (K), and chloride (Cl) content in plant tissue is required for research related to salinity resistance in plants. Standard methods are available to extract these elements from dried plant material, but these methods are often costly, relatively dangerous, or time consuming. Many authors modify extraction methods substantially without proof of comparability across methods.

Methods

Here, dried tissues of two varieties of rice and three varieties of sweet potato subjected to salt stress were extracted for Na and K using six different extraction methods (1–6) and for Cl using three Cl-free extraction methods (2, 4, 5) for Cl: (1) the VDLUFA standard method, consisting of ashing, and heat extraction in hydrochloric acid (HCl), (2) hot water pressure extraction via autoclave, (3) extraction with 1 M HCl overnight, (4) hot water extraction at 90°C for 1 h, (5) acetic acid extraction in hot 1 M acetic acid for 2 h, and (6) extraction with a microwave using nitric acid. Na and K were determined via flame photometer and Cl via automated flow analysis.

Results

Na and K concentrations varied little among different extraction methods as compared to the VDLUFA standard method, and for Cl, all extractions resulted in similar tissue Cl concentrations.

Conclusions

Ultimately, the choice of extraction method depends on the instrumentation and lab equipment necessary, available budget, the available amount of sample, and time constraints which should be decided according to the experiment. For reasons of comparability among publications, methods applied should be clearly described since results vary depending on the method chosen.

Conference: Tropentag, September 14-16, 2022, hybrid conference
“Can agroecological farming feed the world? Farmers’ and academia’s views”

Title: The effect of alternate-wetting-and-drying irrigation (AWD) on rice
phenology and yield

Authors: Kristian Johnson, Thi Bach Thuong Vo, Folkard Asch

University of Hohenheim, Inst. of Agric. Sci. in the Tropics (Hans-Ruthenberg-Institute), Germany

Abstract:
In the Vietnamese Mekong Delta, an alternative water management strategy is needed to maintain the productivity and sustainability of triple cropping rice (Oryza sativa) systems. During the dry season, water saving irrigation technologies, such as alternate wetting and drying (AWD), reduce methane (CH₄) and nitrous oxide (N₂O) emissions due to periodic soil aeration while reducing freshwater use. To evaluate potential yield penalties caused by AWD, field trials were established over two years in the Mekong Delta, Vietnam, in which 20 rice varieties were grown under fully irrigated and ‘safe’ AWD conditions and yield and yield components were determined. The varieties comprised a selection of twenty commonly cultivated and soon to be released Vietnamese rice varieties and were grown for two successive dry seasons at the Loc Troi agricultural research station in collaboration with the BMBF project, RiSaWa. During both seasons we measured yield components, yield, and water level. We observed a slight, but significant (p < 0.001), yield reduction, 7 % on average, across all varieties grown under AWD. Analysis of yield components showed that across all varieties under AWD, rice plants grew more tillers, produced fewer panicles and spikelets, suffered greater sterility, and had a lower 1000 grain weight. Varietal difference could in part be attributed to varying development rates, which exposed certain varieties to a more severe water deficit during key phenological stages. Based on the number of days that overlapped with a phenological stage of a variety, we found that there was a significant (p < 0.05) relationship between the number of days exposed to the dry down period during panicle initiation and the spikelet number. Considering the field is already kept flooded during flowering, practitioners of AWD should take other phenological stages into account when scheduling irrigation events. Potentially under ‘safe’ AWD’, the start of AWD could be delayed until after panicle initiation, and the field could be allowed to dry during flowering.

Conference: Tropentag, September 9-11, 2020, virtual conference
“Food and nutrition security and its resilience to global crises”

Title: Reserve Mobilisation, Dry Matter Partitioning, and K/Na Ratio of
Rice (Oryza sativa) Seedlings in Response to Varying Levels of Salt
Stress

Authors: Kristian Johnson, Folkard Asch

University of Hohenheim, Inst. of Agric. Sci. in the Tropics (Hans-Ruthenberg-Institute), Germany

Abstract:
Across South and Southeast Asia millions of hectares of arable land are left uncultivated or only support low yields due to salinity. This will likely worsen through a combination of changes in land use and climate, such as urbanisation, intensification of agriculture, unpredictable wet seasons, irregular rainfall, and rising sea levels. Greater insight into the underlying physiological mechanisms of varietal tolerance in rice (Oryza sativa) to salt stress across development stages, in particular germination and early seedling stages, will
improve management practices and varietal screening, ultimately leading to more targeted breeding. This study investigates morphophysiological characteristics related to rice seedling vigour and salt stress tolerance, such as the kinetics of reserve mobilisation, dry matter partitioning among organs, the K/Na ratio, and early seedling growth in seedlings subjected to salt stress . Five rice cultivars ranging in their sensitivity to salt stress (I Kong Pao, IR4630–22-2–5-1–3, OM5451, IR31785–58-2–3-3, and IR64) were germinated in sand and subjected to three levels of salinity (0, 50, 100 mM) over the course of 17 days in a greenhouse. Dry matter fractions were measured from samples taken every other day. Sodium and potassium concentrations within the seedling biomass were determined on a whole seedling basis for each sampling period, except for the final sampling date, during which above and below-ground biomass were analysed separately. Varietal differences in
early growth vigour across salt stress treatments will be discussed in relation to genotypic partitioning strategies among organs, growth respiration, transition to autotrophy, and the sodium and potassium concentrations within the seedling biomass.

Conference: Tropentag, September 15-17, 2021, hybrid conference
“Towards shifting paradigms in agriculture for a healthy and sustainable future”

Title: Effects of Halo- and Hydropriming on Early Rice Seedling Vigour
under Salinity

Authors: Anna Tabea Mengen, Kristian Johnson, Folkard Asch

University of Hohenheim, Inst. of Agric. Sci. in the Tropics (Hans-Ruthenberg-Institute), Germany

Abstract:
For the food security of a growing world population, rice production needs to increase significantly. Therefore, current production will need to be maintained, intensified, and in some cases expanded to include less suitable areas. Meanwhile a rising sea level, linked to climate change, leads to impaired field emergence and salt stress from tidal flooding and saline groundwater. Priming as a seed pre-treatment, which includes soaking of the seed in a solution and subsequent redrying, has been reported to improve field establishment and plant stress tolerance in diverse species under a variety of abiotic stresses. Here, the effect of Hydro- and Halopriming on germination under saline conditions was tested in a blind test of three varieties. First, the moisture uptake pattern of the seeds during priming was assessed under three NaCl-concentrations (0,50,100mM). Afterwards, seeds were primed in these solutions, followed by a germination test under the three levels of salinity. It was found that the NaCl-concentration of the priming solution has no significant effect on moisture uptake. Furthermore, priming treatments were able to accelerate germination speed, with hydropriming showing the best results. In contrast, halopriming improved endosperm use efficiency depending on the variety.. These results suggest that priming can have a beneficial effect on germination, supporting rapid field emergence and field establishment under adverse conditions. Nevertheless, the underlying mechanisms have yet to be investigated and treatment×variety interactions, as well as the effect of different treatments on different germination parameters, need to be further evaluated to develop suitable priming methods applicable on a large scale. Priming has the potential to be a cheap and easy way to increase the productivity of rice production under unfavourable conditions and to help mitigate the effects of climate change.

Conference: Tropentag, September 17-19, 2018, Ghent
“Global food security and food safety: The role of universities”

Title: Effects of Day and Night Temperature on Rice Photosynthesis

Authors: Kristian Johnson, Sabine Stürz, Marc Schmierer, Folkard Asch

University of Hohenheim, Inst. of Agric. Sci. in the Tropics (Hans-Ruthenberg-Institute), Germany

Abstract:
It has been shown that the yield of rice (Oryza sativa) decreases in response to higher night temperatures. Projected temperature increases due to climate change are expected to be more pronounced at night. As the primary staple for more than half of the world’s population, a decrease in rice yield could pose a serious threat to food security. However, the physiological response of rice to night temperature is not yet fully understood. Studies indicate both positive and negative effects of high night temperatures on CO₂ assimilation and growth in rice. It has also been shown that the physiology of rice during the day is also affected, as warmer nights lead to higher leaf conductance and net assimilation rates during the day. It is unclear if the day response is part of a mechanism to compensate for depleted carbohydrate pools within the leaves from night-time respiratory CO₂ losses. A day-time increase in net assimilation, comprised of assimilation, day respiration, and photorespiration, implies changes in the photosynthetic complex to either reduce CO2 releasing processes or an increase in assimilation.
In the presented study, groups of 5-week-old IR64 rice plants were exposed to six different two-week long day and night temperature treatments in a growth chamber. After one week of adjustment to the temperature treatment, photosynthetic parameters, such as assimilation rate, stomatal and mesophyll conductance, and respiration and growth parameters, such as leaf area, biomass, tiller number were measured among sampled plants. During
the temperature treatment, the youngest developed leaf on the main tiller was shaded for 40 hours, and on re-exposure to light assimilation was measured. In both temperature and shade treatments, leaf samples were taken to determine levels of non-structural carbohydrates and active Rubisco content.