Relationships between δ13C, δ18O and grain yield in bread wheat genotypes under favourable irrigated and rain-fed conditions

In previous investigations, carbon isotope composition (δ13C) has been used in C3 cereals to screen for genotypes with high transpiration efficiency and oxygen isotope composition (δ18O) has been shown to correlate with transpiration rate. We examined associations of δ13C of the grain and flag leaf and δ18O of the flag leaf with respect to grain yield in wheat cultivars in UK field conditions. Field experiments were carried out at University of Nottingham in 2009–10 and 2010–11 testing 17 wheat cultivars under fully irrigated and rain-fed conditions. Averaging across years grain yield was reduced by 1.69 t ha−1 (16.5%) in the rain-fed treatment (P < 0.001). There was a negative linear relationship between grain yield and grain δ13C amongst cultivars, under both irrigated (R2 = 0.47, P < 0.01) and rain-fed (R2 = 0.70, P < 0.001) conditions. Grain δ13C was negatively correlated with flag-leaf stomatal conductance (r = −0.94, P < 0.01) in a subset of six of the cultivars, indicating that higher transpiration efficiency was associated with lower stomatal conductance. The associations between grain yield and flag-leaf δ13C and flag-leaf δ18O amongst cultivars under irrigated and rain-fed conditions were not statistically significant. There was a positive linear relationship between flag-leaf δ18O and grain δ13C amongst cultivars under irrigated conditions (R2 = 0.38, P < 0.01), indicating a trade-off between transpiration and transpiration efficiency (TE). Genetic variation in grain yield under rain-fed conditions was also associated with delayed onset of flag-leaf senescence (R2 = 0.35, P < 0.05). The 17 wheat cultivars ranged in year of release (YoR) from 1964 to 2009 and grain yield increased linearly under irrigated conditions by 60.4 kg ha−1 yr−1 (0.72% yr−1) and under rain-fed conditions by 47.5 kg ha−1 yr−1 (0.66% yr−1) over the 45 year period and grain δ13C composition decreased by 0.0255 and 0.0304‰ yr−1, respectively, indicating genetic gains in wheat yield potential in the UK seem likely to have been achieved through a lower TE, higher water uptake and lesser limitation of stomatal conductance

Enhancing crop yields through improvements in the efficiency of photosynthesis and respiration

Published online January 2023The rate with which crop yields per hectare increase each year is plateauing at the same time that human population growth and other factors increase food demand. Increasing yield potential (Yp) of crops is vital to address these challenges. In this review, we explore a component of Yp that has yet to be optimised – that being improvements in the efficiency with which light energy is converted into biomass (ϵc) via modifications to CO2 fixed per unit quantum of light (α), efficiency of respiratory ATP production (ϵprod) and efficiency of ATP use (ϵuse). For α, targets include changes in photoprotective machinery, ribulose bisphosphate carboxylase/oxygenase kinetics and photorespiratory pathways. There is also potential for ϵprod to be increased via targeted changes to the expression of the alternative oxidase and mitochondrial uncoupling pathways. Similarly, there are possibilities to improve ϵuse via changes to the ATP costs of phloem loading, nutrient uptake, futile cycles and/or protein/membrane turnover. Recently developed high-throughput measurements of respiration can serve as a proxy for the cumulative energy cost of these processes. There are thus exciting opportunities to use our growing knowledge of factors influencing the efficiency of photosynthesis and respiration to create a step-change in yield potential of globally important crops.Andres Garcia, Oorbessy Gaju, Andrew F. Bowerman, Sally A. Buck, John R. Evans, Robert T. Furbank, Matthew Gilliham, A. Harvey Millar, Barry J. Pogson, Matthew P. Reynolds, Yong-Ling Ruan, Nicolas L. Taylor, Stephen D. Tyerman, and Owen K. Atki

Comparing The Quality Of Two Composts Produced From Municipal Solid Waste and Bagasse/Broiler Litter

In Mauritius, composting is viewed more as a means of waste disposal than a safe and environmental-friendly  process, the product of which can be used for agricultural purposes. The aim of this paper is to compare the  quality of two types of composts; one derived from Municipal Solid Waste (MSW) and the other from Bagasse and Chicken Waste (BCW) and assesses their response on Phaseolus vulgaris. The physical and chemical characteristics of the composts were analysed and the maturity of compost was also determined. The two composts were applied at 20 tons/ha and 40 tons/ha. Better plant response was obtained when MSW was applied at 40 tons/ha. When decreasing the level of MSW to 20tons/ha, no significant change was obtained in terms of number of flowers, number of pods, weight of pods, length and width of pods. It has been found that most of the quality parameters investigated fall within the range of standards established by United States Environment Protection Agency and that both MSW and BCW are good quality composts.Keywords: composting, municipal solid wastes, quality, bagass

Microcosm experiments of oil degradation by microbial mats. II. The changes in microbial species

11 pages, 2 tables, 4 figures.The influence of microbial mats on the degradation of two crude oils (Casablanca and Maya) and the effect of oil pollution on the mat structure were assessed using model ecosystems, prepared under laboratory conditions subject to tidal movements, from pristine Ebro Delta microbial-mat ecosystems. Both selected oils are examples of those currently used for commercial purposes. Casablanca crude oil is aliphatic with a low viscosity; Maya represents a sulphur-rich heavy crude oil that is predominantly aromatic. In the unpolluted microcosms, Microcoleus chthonoplastes-, Phormidium- and Oscillatoria-like were the dominant filamentous cyanobacterial morphotypes, whilst Synechoccocus-, Synechocystis- and Gloeocapsa-like were the most abundant unicellular cyanobacteria. After oil contamination, no significant changes of chlorophyll a and protein concentrations were observed, though cyanobacterial diversity shifts were monitored. Among filamentous cyanobacteria, M. chthonoplastes-like morphotype was the most resistant for both oils, unlike the other cyanobacteria, which tolerated Casablanca but not Maya. Unicellular cyanobacteria seemed to be resistant to pollution with both essayed oils, with the exception of the morphotype resembling Gloeocapsa, which was sensitive to both oils. The crude-oil addition also had a significant effect on certain components of the heterotrophic microbial community. Casablanca oil induced an increase in anaerobic heterotrophic bacteria, whereas the opposite effect was observed in those heterotrophs when polluted with Maya oil. The overall results, microbiological and crude-oil transformation analysis, indicate that the indigenous community has a considerable potential to degrade oil components by means of the metabolic cooperation of phototrophic and heterotrophic populationWe would like to thank the Salines de la Trinitat and Parc Natural del Delta de l’Ebre (Generalitat de Catalunya) for permission to access the sampling site, and REPSOL-YPF for providing samples of Casablanca and Maya crude oils. We also thank members of the Servei de Microscòpia at the Autonomous University of Barcelona (UAB) for support with CLSM. We are grateful to Lidia Hernandez and Carol Egea for technical assistance with the microcosms and sample processing. This research was funded by the European Union MATBIOPOL project EVK3-CT-1999-00010.Peer reviewe

Phenotyping wheat photosynthesis using ‘Leaf Hyperspectral Reflectance’

Wheat is an important cereal crop contributing to global food security. Growing human population requires continuous increase in production. While increases in wheat yield gained by modifying harvest index have been fully exploited by plant breeders, improving photosynthesis has the potential to increase wheat yield. Due to a lack of efficient phenotyping methods for photosynthetic traits, it has been hard to explore photosynthetic variation and its genetic regulation. This has prevented the use of photosynthetic traits for crop improvement in wheat. We used ‘leaf hyperspectral reflectance’, a high-throughput phenotyping method, to predict multiple leaf photosynthetic traits in two wheat populations (Seri/Babax, and PSTails) grown at the International Maize and Wheat Improvement Centre (CIMMYT, Mexico). Leaf reflectance spectra were measured on wheat plants at four different growth stages (tillering, booting, anthesis+7 days and grain-filling) from which nitrogen content per unit leaf area (Narea), leaf dry mass per unit leaf area, Rubisco capacity per unit area or nitrogen (Vcmax25, Vcmax25/Narea, respectively) and electron transport rate (J) were calculated. We observed significant variation for different photosynthetic traits among the genotypes of Seri/Babax and PSTails when measured at different growth stages, but rankings between genotypes were not consistent across different growth stages. The average predicted values for Vcmax25, J, and Vcmax25/Narea differed among different growth stages. For Seri/Babax and PSTails, predicted values for Vcmax25/Narea were highest at the tillering stage and lowest at the anthesis+7 stage. Further experiments are being conducted in both Australia and Mexico

Identification of traits to improve the nitrogen-use efficiency of wheat genotypes

Nitrogen (N) fertilizer represents a significant cost for the grower and may also have environmental impacts through nitrate leaching and N2O (a greenhouse gas) emissions associated with denitrification. The objectives of this study were to analyze the genetic variability in N-use efficiency (grain dry matter (DM) yield per unit N available from soil and fertilizer; NUE) in winter wheat and identify traits for improved NUE for application in breeding. Fourteen UK and French cultivars and two French advanced breeding lines were tested in a 2 year/four site network comprising different locations in France and in the UK. Detailed growth analysis was conducted at anthesis and harvest in experiments including DM and N partitioning. Senescence of either the flag leaf or the whole leaf canopy was assessed from a visual score every 3-4 days from anthesis to complete canopy senescence. The senescence score was fitted against thermal time using a five parameters monomolecular-logistic equation allowing the estimation of the timing of the onset and the rate of post-anthesis senescence. In each experiment, grain yield was reduced under low N (LN), with an average reduction of 2.2 t ha(-1) (29%). Significant N x genotype level interaction was observed for NUE. Crop N uptake at harvest on average was reduced from 227 kg N ha(-1) under high N (HN) to 109 kg N ha(-1) under LN conditions while N-utilization efficiency (grain DM yield per unit crop N uptake at harvest; NUtE) increased from 34.0 to 52.1 kg DM kg(-1) N. Overall genetic variability in NUE under LN related mainly to differences in NUtE rather than N-uptake efficiency (crop N uptake at harvest per unit N available from soil and fertilizer; NUpE). However, at one site there was also a positive correlation between NUpE and NUE at LN in both years. Moreover, across the 2 year/four site network, the N x genotype effect for NUpE partly explained the N x genotype effect for grain yield and NUE. Averaging across the 16 genotypes, the timing of onset of senescence explained 86% of the variation in NUtE amongst site-season-N treatment combinations. The linear regression of onset of senescence on NutE amongst genoytpes was not significant under HN, but at three of the four sites was significant under LN explaining 32-70% of the phenotypic variation amongst genotypes in NutE. Onset of senescence amongst genotypes was negatively correlated with the efficiency with which above-ground N at anthesis was remobilized to the grain under LN. It is concluded that delaying the onset of post-anthesis senescence may be an important trait for increasing grain yield of wheat grown under low N supply. (C) 2011 Elsevier B.V. All rights reserved