Predicting biochemical acclimation of leaf photosynthesis in soybean under in-field canopy warming using hyperspectral reflectance

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

High-throughput characterization, correlation, and mapping of leaf photosynthetic and functional traits in the soybean (Glycine max) nested association mapping population

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 \u3c10% 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

Genotypic differences in soybean yield responses to increasing temperature in a cool climate are related to maturity group

To adapt soybean production to climate change, a thorough understanding of its response to high temperature is required. Modeling studies have predicted that high temperature would shorten the growth period and hence lower seed yield of less day length-sensitive (early-maturing) soybean cultivars, whereas the magnitude of yield reduction by high temperature would be smaller in cultivars with higher day length sensitivity (late-maturing), suggesting that late-maturing cultivars would benefit from a future high-temperature environment. Current mean growing season temperature ranges from 19.4 to 22.6 degrees C in the northern, cool regions of Japan, which is near or below the reported optimum temperature (22-24 degrees C) for seed yield. We tested the hypothesis that adaptation by growing late-maturing cultivars will be successful in maintaining seed yield under a cool climate when temperature is increased during 21st century. We used three Japanese soybean cultivars, early-maturing Yukihomare and late-maturing cultivars Ryuhou and Enrei. Plants were grown over 3 years from June to September (a conventional season) under three temperature regimes, T1 (ambient), T2 (1.8-3.6 degrees C above ambient), T3 (4.8-5.7 degrees C above ambient), in a sunlit temperature gradient chamber. The leaf area at the full expansion stage, pod and seed numbers, and seed yield increased at elevated temperature in the late-maturing cultivars but not in the early-maturing one. The photosynthetic rate and effective quantum yield of photosystem II at the flowering stage increased at elevated temperature in all three cultivars. The period from sowing to the beginning of flowering (R1) decreased in all three cultivars at elevated temperature, whereas the period from R1 to the beginning of pod addition and the flowering period were prolonged in the late-maturing cultivars, but not in the early-maturing one. The differential response in post-flowering development in different maturity groups is probably related to the differences in the day length requirements of these cultivars. Our data clearly demonstrate that yield enhancement by increasing temperature in the late-maturing cultivars resulted from both the improvement in sources (leaf area and leaf photosynthesis) and the increase in sink size (number of flowers, pods and seeds) due to the longer flowering period. We conclude that the yield of the late-maturing cultivars sown during the conventional season in the cool regions of Japan will increase during the 21st century. (C) 2014 Elsevier B.V. All rights reserved

Soybean (Glycine max (L.) Merr.) Yield Reduction due to Late Sowing as a Function of Radiation Interception and Use in a Cool Region of Northern Japan

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

Correlation of Chlorophyll Meter Readings with Gas exchange and Chlorophyll Fluorescence in Flag Leaves of Rice (Oryza sativa L.) Plants

The objective of this study was to establish the correlation of the chlorophyll meter (SPAD) readings with the contents of chlorophyll (Chl) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), the gross photosynthetic rate (Pg), and the maximum quantum yield of photosystem II (PSII) (Fv/Fm) in flag leaves of rice (Oryza sativa L.) in ripening stage. The SPAD readings significantly correlated with the Chl content, the Rubisco content, Pg and Fv/Fm (R2 = 0.848, 0.648, 0.671 and 0.712, respectively), which suggests that the SPAD meter has the potential to estimate the photosynthetic capacity of the flag leaves. However, both Pg and Fv/Fm had a stronger relationship with the Rubisco content than the SPAD readings, indicating that the PSII photochemical and CO2 assimilation capacities are strongly influenced by the Rubisco content. Therefore, accurate calibration would be indispensable to obtain the physiological information from the SPAD readings of flag leaves

Comparison of Susceptibility to Photoinhibition and Energy Partitioning of Absorbed Light in Photosystem II in Flag Leaves of Two Rice (Oryza sativa L.) Cultivars that Differ in Their Responses to Nitrogen-Deficiency

Abstract: The energy partitioning in photosystem II (PSII) and the susceptibility to photoinhibition in PSII were investigated in flag leaves of two rice cultivars, Shirobeniya (a traditionaljaponica) and Akenohoshi (an improved japonica-indica intermediate) grown under standard-nitrogen (N) (SN) and low-N (LN) conditions. N-deficiency resulted in significant decreases in total dry weight, net photosynthetic rate (Pn), the energy flux via carboxylation (Jc), and content of ribulose-1,5-bisphosphate carboxylase /oxygenase (Rubisco) in flag leaves in the two cultivars, and these parameters of Shirobeniya were lower than those in Akenohoshi under the LN condition. In the two cultivars, the energy flux via alternative electron flow was significantly increased by N-deficiency, which was accompanied by enhanced activity of superoxide dismutase (SOD). Although under the LN condition no cultivar differences were found in Ja and SOD, ascorbate peroxidase activity in Shirobeniya was lower than that in Akenohoshi. N-deficiency resulted in more significant increases in the susceptibility to photoinhibition (the degree of decrease in maximum quantum yield of PSII), hydrogen peroxide (H2O2) content and malondialdehyde content after exposure to high irradiance in Shirobeniya than those in Akenohoshi. These results indicated that the increased susceptibility to photoinhibition in the LN plants of Shirobeniya was mainly due to oxidative damages to chloroplasts, resulting from lower carboxylation and H2O2-scavenging capacities. Therefore, both carboxylation and H2O2-scavenging capacities could be important factors in determining the cultivar difference in the productivity of rice under LN conditions

Ammonia Emission from Leaves of Different Rice (Oryza sativa L.) Cultivars

NH3 emission from leaves of three rice (Oryza sativa L.) cultivars, Akenohoshi, Shirobeniya and Kasalath, was examined using a simple open chamber system.　In the three cultivars, NH3 emission rate (AER) and NH4+ content of leaves decreased with decreasing NH4+ concentration in the root medium, but these values differed significantly with the cultivar. In the daytime, AER, NH4+ content and glutamine synthetase (GS) activity in leaves changed similarly with maximum values around midday. Akenohoshi showed significantly lower AER and NH4+ content but higher GS activity than Kasalath. The difference in AER among the rice cultivars may be related to the activity of GS involved in photorespiratory NH3 recycling. Akenohoshi can be a breeding material useful for improving N recycling