Combinations of cultivar selection and management practices are used to maximize soybean yields in Japan. High plant density could increase the amount of solar radiation intercepted by the canopy and ...thereby increase growth and yield, but both cultivar and environment affect the response to plant density. The mechanisms underlying responses of soybean to high plant density are not fully understood. This study tested the effects of high plant density by narrow intra-row spacing on agronomic traits in 2 years using three cultivars (Ryuhou, Okushirome, and Fukuibuki) in Morioka, Iwate, in the Tohoku region of Japan. Averaged across years and cultivars, narrow intra-row spacing increased seed yield. Interestingly, there was a significant year × intra-row spacing × cultivar interaction: In the first year, narrow intra-row spacing increased yield of Ryuhou and Fukuibuki but not of Okushirome; in the second year, however, it increased yield of all cultivars similarly. The lack of yield response of Okushirome to narrow intra-row spacing in the first year presumably resulted from an excessive leaf area index (LAI) and a higher lodging score. The results suggest that high plant density by narrow intra-row spacing is an effective option for increasing soybean yields in the Tohoku region, although agronomic traits such as LAI and susceptibility to lodging should be considered.
Selection for cultivars with superior responsiveness to elevated atmospheric CO₂ concentrations (eCO₂) is a powerful option for boosting crop productivity under future eCO₂. However, neither criteria ...for eCO₂ responsiveness nor prescreening methods have been established. The purpose of this study was to identify traits responsible for eCO₂ responsiveness of soybean (Glycine max). We grew 12 Japanese and U.S. soybean cultivars that differed in their maturity group and determinacy under ambient CO₂ and eCO₂ for 2 years in temperature gradient chambers. CO₂ elevation significantly increased seed yield per plant, and the magnitude varied widely among the cultivars (from 0% to 62%). The yield increase was best explained by increased aboveground biomass and pod number per plant. These results suggest that the plasticity of pod production under eCO₂ results from biomass enhancement, and would therefore be a key factor in the yield response to eCO₂, a resource-rich environment. To test this hypothesis, we grew the same cultivars at low planting density, a resource-rich environment that improved the light and nutrient supplies by minimizing competition. Low planting density significantly increased seed yield per plant, and the magnitude ranged from 5% to 105% among the cultivars owing to increased biomass and pod number per plant. The yield increase due to low-density planting was significantly positively correlated with the eCO₂ response in both years. These results confirm our hypothesis and suggest that high plasticity of biomass and pod production at a low planting density reveals suitable parameters for breeding to maximize soybean yield under eCO₂.
Traditional gas exchange measurements are cumbersome, which makes it difficult to capture variation in biochemical parameters, namely the maximum rate of carboxylation measured at a reference ...temperature (Vcmax25) and the maximum electron transport at a reference temperature (Jmax25), in response to growth temperature over time from days to weeks. Hyperspectral reflectance provides reliable measures of Vcmax25 and Jmax25; however, the capability of this method to capture biochemical acclimations of the two parameters to high growth temperature over time has not been demonstrated. In this study, Vcmax25 and Jmax25 were measured over multiple growth stages during two growing seasons for field‐grown soybeans using both gas exchange techniques and leaf spectral reflectance under ambient and four elevated canopy temperature treatments (ambient+1.5, +3, +4.5, and +6°C). Spectral vegetation indices and machine learning methods were used to build predictive models for Vcmax25 and Jmax25, based on the leaf reflectance. Results showed that these models yielded an R2 of 0.57–0.65 and 0.48–0.58 for Vcmax25 and Jmax25, respectively. Hyperspectral reflectance captured biochemical acclimation of leaf photosynthesis to high temperature in the field, improving spatial and temporal resolution in the ability to assess the impact of future warming on crop productivity.
Seasonally dependent acclimation of leaf photosynthetic biochemistry was found in field‐grown soybean under full season warming. Hyperspectral reflectance measurements coupled with machine learning regressions can be used to predict photosynthetic biochemical acclimation to high temperature.
The rising atmospheric CO2 concentration (CO2) can increase crop productivity, but there are likely to be intraspecific variations in the response. To meet future world food demand, screening for ...genotypes with high CO2 responsiveness will be a useful option, but there is no criterion for high CO2 responsiveness. We hypothesized that the Finlay–Wilkinson regression coefficient (RC) (for the relationship between a genotype's yield versus the mean yield of all genotypes in a specific environment) could serve as a pre‐screening criterion for identifying genotypes that respond strongly to elevated CO2. We collected datasets on the yield of 6 rice and 10 soybean genotypes along environmental gradients and compared their responsiveness to elevated CO2 based on the regression coefficients (i.e. the increases of yield per 100 µmol mol−1 CO2) identified in previous reports. We found significant positive correlations between the RCs and the responsiveness of yield to elevated CO2 in both rice and soybean. This result raises the possibility that the coefficient of the Finlay–Wilkinson relationship could be used as a pre‐screening criterion for CO2 responsiveness.
•The effects of increased temperature on soybean yield and dry matter production were investigated.•The yield and aboveground dry matter were reduced by increased temperature.•Reduced pod number, ...reduced seed number and, to some extent, reduced seed size led to reduced harvest index.•Reduction in seed yield was caused by those of aboveground dry matter.
The global surface temperature is projected to rise and will affect crop performances. This study investigated the effects of increased temperature on yield and dry matter production in a controlled environment that mimicked field conditions using a temperature gradient chamber (TGC). Experiments were conducted from 2009 to 2012 using the soybean cultivar Enrei, which was grown in soil culture beds. Plants were grown in two TGCs as replicates for temperature treatment. Three temperature treatments, near ambient temperature (Ta), ambient temperature+1°C (Ta+1), and ambient temperature+3°C, in 2009 and 2010, and ambient temperature+2°C, in 2011 and 2012 (Ta+2/Ta+3), were established by dividing the rows along which the temperature gradient was created. The aboveground dry matter was significantly reduced by increased temperature from 11% in 2012 to 27% in 2009. Decrease of dry matter accumulation was obvious particularly from flowering to early seed filling and it was associated with decline of leaf photosynthetic rate, stomatal conductance and the carbon isotope discrimination. Reduced pod number, reduced seed number, and, to some extent, smaller seeds led to a decreased harvest index (HI). These phenomena might be associated with the delayed pod set and lower seed growth rate under warmer treatment. Seed yield was the most responsive parameter in 2009 and 2010, and in 2011 and 2012, it was still reduced under continuously wet conditions. Combined data showed that total dry matter, seed yield, and HI were consistently reduced by increased temperature. It is suggested that the concomitant increase of vapor pressure deficit with increased temperature exacerbated the temperature effects. In addition, reduced ambient CO2 and low light intensity as the artifacts of the facility might have accounted for the greater effect of high temperature.
• Background and Aims Rice (Oryza sativa) plants lose significant amounts of volatile NH₃ from their leaves, but it has not been shown that this is a consequence of photorespiration. Involvement of ...photorespiration in NH₃ emission and the role of glutamine synthetase (GS) on NH₃ recycling were investigated using two rice cultivars with different GS activities. • Methods NH₃ emission (AER), and gross photosynthesis (PG), transpiration (Tr) and stomatal conductance (gs) were measured on leaves of 'Akenohoshi', a cultivar with high GS activity, and 'Kasalath', a cultivar with low GS activity, under different light intensities (200, 500 and 1000 μmol m⁻² s⁻¹), leaf temperatures (27·5, 32·5 and 37·5 °C) and atmospheric O₂ concentrations (O₂: 2, 21 and 40 %, corresponding to 20, 210 and 400 mmol mol⁻¹). • Key Results An increase in O₂ increased AER in the two cultivars, accompanied by a decrease in PG due to enhanced photorespiration, but did not greatly influence Tr and gs. There were significant positive correlations between AER and photorespiration in both cultivars. Increasing light intensity increased AER, PG, Tr and gs in both cultivars, whereas increasing leaf temperature increased AER and Tr but slightly decreased PG and gs. 'Kasalath' (low GS activity) showed higher AER than 'Akenohoshi' (high GS activity) at high light intensity, leaf temperature and O₂. • Conclusions Our results demonstrate that photorespiration is strongly involved in NH 3 emission by rice leaves and suggest that differences in AER between cultivars result from their different GS activities, which would result in different capacities for reassimilation of photorespiratory NH₃. The results also suggest that NH₃ emission in rice leaves is not directly controlled by transpiration and stomatal conductance.
Abstract
Photosynthesis is a key target to improve crop production in many species including soybean Glycine max (L.) Merr.. A challenge is that phenotyping photosynthetic traits by traditional ...approaches is slow and destructive. There is proof-of-concept for leaf hyperspectral reflectance as a rapid method to model photosynthetic traits. However, the crucial step of demonstrating that hyperspectral approaches can be used to advance understanding of the genetic architecture of photosynthetic traits is untested. To address this challenge, we used full-range (500–2,400 nm) leaf reflectance spectroscopy to build partial least squares regression models to estimate leaf traits, including the rate-limiting processes of photosynthesis, maximum Rubisco carboxylation rate, and maximum electron transport. In total, 11 models were produced from a diverse population of soybean sampled over multiple field seasons to estimate photosynthetic parameters, chlorophyll content, leaf carbon and leaf nitrogen percentage, and specific leaf area (with R2 from 0.56 to 0.96 and root mean square error approximately <10% of the range of calibration data). We explore the utility of these models by applying them to the soybean nested association mapping population, which showed variability in photosynthetic and leaf traits. Genetic mapping provided insights into the underlying genetic architecture of photosynthetic traits and potential improvement in soybean. Notably, the maximum Rubisco carboxylation rate mapped to a region of chromosome 19 containing genes encoding multiple small subunits of Rubisco. We also mapped the maximum electron transport rate to a region of chromosome 10 containing a fructose 1,6-bisphosphatase gene, encoding an important enzyme in the regeneration of ribulose 1,5-bisphosphate and the sucrose biosynthetic pathway. The estimated rate-limiting steps of photosynthesis were low or negatively correlated with yield suggesting that these traits are not influenced by the same genetic mechanisms and are not limiting yield in the soybean NAM population. Leaf carbon percentage, leaf nitrogen percentage, and specific leaf area showed strong correlations with yield and may be of interest in breeding programs as a proxy for yield. This work is among the first to use hyperspectral reflectance to model and map the genetic architecture of the rate-limiting steps of photosynthesis.
The conversion between the two different systems, ISSS and FAO/USDA, of particle size distribution and soil texture classification is useful to characterize soil physical properties and usage of each ...published. The objective of this study is to test some functions that have been published for conversion from ISSS to FAO/USDA system for Japanese paddy soils and to select the best method. We tested the topsoils of 267 Japanese paddy fields using the log-linear method, log-normal method, multiple regression method, Skaggs et al.'s method, and Minasny and McBratney's method. The least AIC was obtained using multiple regression method, and the equation derived was given as follows:
si
FAO/USDA
= 1.305si
ISSS
+ 0.396fs
ISSS
−0.100cs
ISSS
− 12.323
where si, fs, and cs are the percentage of silt, fine sand, and coarse sand respectively; ISSS and FAO/USDA is the fractionation system; and its RMSE was 3.1%. For the case that only the total sand content (s) is available instead of fine sand and coarse sand, the following equation was obtained:
si
FAO/USDA
= 1.533si
ISSS
+ 0.314s
ISSS
− 20.903 (RMSE = 3.7%)
Among the non-empirical methods, the best estimation method was Skaggs et al.'s method, and its RMSE was 3.3%. The soil texture classification by FAO/USDA system using estimated particle size fractions by the above equation can be classified to correct categories. The accuracy ratio of the classification was 93-97%.
Yields decrease when soybean is sown later than recommended in the cool climate of the Tohoku region of Japan. However, the factors responsible for this decrease are not fully understood. We ...investigated the effects of late sowing on growth, phenological development, yield, yield components, and radiation interception of three soybean cultivars in two consecutive years and analyzed the relationships of those variables with temperature and soil volumetric moisture content (SMC). Averaged across years and cultivars, yields decreased significantly when plants were sown approximately three weeks late. Yield reductions were partially due to reductions in node number per plant, dry matter production, and capture of cumulative irradiance, resulting from slowed canopy development during vegetative and early reproductive stages. The number of seeds per pod was one of the major determinants of the variation in yield. Owing to the delay in sowing date, the reduction in seeds per pod was likely due to low temperatures during the 20 days after seed filling began. Occasional lower SMC during reproductive stages did not affect yield, yield components, and growth parameters. However, these results were obtained from the two years’ experiments. Therefore, further investigations of the relationship of yield with temperature and SMC under different years and sites are needed.
The present study investigated the effects of elevated carbon dioxide concentration (CO
2
) and air temperature on the germination of seed bulbils and the seedling vigour of two Chinese yam lines. ...Plants were grown under two CO
2
levels, ambient and elevated (ambient + 200 μmol mol
−1
), and two mean air temperature regimes, 22.2 °C (ambient + 1.4 °C) and 25.6 °C (ambient + 5.2 °C). Elevated CO
2
did not affect bulbil germination under both air temperature regimes. During the early growth stage, the dry weight (DW) of leaves, vines, shoots, roots, belowground parts (roots + tubers) and whole plants were higher under elevated CO
2
than ambient CO
2
for both lines under the low- and high-temperature regimes. The values of vigour indexes (index I = germination % × seedling length and index II = germination % × seedling DW) were also higher under elevated CO
2
than ambient CO
2
for both lines. These results indicated that Chinese yam seedlings respond positively to elevated CO
2
during the early growth stage. The above:belowground DW ratios were lower under elevated CO
2
than ambient CO
2
in seedlings with very small new tubers for both yam lines, indicating that elevated CO
2
strongly affected the root growth in the early growth stage. The DWs of post-treatment seed bulbils were higher in the elevated CO
2
under both air temperature regimes. The results showed that Chinese yam used a smaller amount of the reserves in seed bulbils under elevated CO
2
than under ambient CO
2
.
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