Field-grown Winter Wheat Research Articles

Solar-induced chlorophyll fluorescence imperfectly tracks the temperature response of photosynthesis in winter wheat.

Solar-induced fluorescence (SIF) is a promising proxy for photosynthesis, but it is unclear whether it performs well in tracking the gross primary productivity (GPP) under different environmental conditions. In this study, we investigated the dynamics of the two parameters from October 2020 to June 2021 in field-grown winter wheat (Triticum aestivum) and found that the ability of SIF to track GPP was weakened at low temperatures. Accounting for the coupling of light and temperature at a seasonal scale, we found that SIF yield showed a lower temperature sensitivity and had a lower but broader optimal temperature range compared with light-use efficiency (LUE), although both SIF yield and LUE decreased in low-temperature conditions. The discrepancy between the temperature responses of SIF yield and GPP caused an increase in the ratio of SIF/GPP in winter, which indicated the variation in the relationship between them during this period. The results of our study highlight the impact of low temperature on the relationship between SIF and GPP and show the necessity of reconsidering the dynamics of energy distribution inside plants under changing environments.

Selection and screening of fungal endophytes against wheat pathogens

Tissues of field grown winter wheat ‘AC Morley’ and ‘25R34′ and spring wheat ‘Sumai’ and ‘Scotia’ were collected from Ariss, Ontario in June 2016. These cultivars are considered to be moderately resistant to Fusarium head blight. More than 90 endophytic fungal isolates with 54 distinct morphotypes were obtained from these tissues. These fungal isolates were screened using dual culture plates for antagonism against three wheat pathogens: Fusarium graminearum, Waitea circinata, and Microdochium majus. Out of 54 isolates, 33 were found to cause obvious inhibition of pathogen growth or demarcation lines with at least one of the three wheat pathogens. These antagonistic strains were then tested for pathogenicity on wheat leaves in growth room tests, and 16 showed no phytopathogenicity. Among these non-pathogenic strains, three were selected and identified by internal transcribed spacer-polymerase chain reaction (ITS-PCR) as Valsa friesii, Simplicillium lamellicola and Cladorrhinum flexuosum. These three were then tested for their ability to inhibit disease in growth room tests. Hyphal plugs of these fungi inhibited the pathogenicity of wheat pathogens F. graminearum, and W. circinata on leaves of wheat seedlings, and reduced lesion lengths by 36–87% and 31%-86%, respectively. The wheat endophytes, S. lamellicola and C. flexuosum, are promising biocontrol agents against F. graminearum and W. circinata.

Dynamic changes in leaf wax n-alkanes and δ13C during leaf development in winter wheat under varied irrigation experiments

Leaf wax n-alkanes serve as biomarkers that record environmental information with their carbon isotopic composition (δ13Calk) recording water availability. Agricultural and paleoclimate applications would benefit from a greater understanding of how water shortages are recorded in δ13Calk across the growing season, and controlled experiments can contribute to understanding as they constrain cause and effect, although they represent highly simplified versions of natural ecosystems. In this study, we use field-grown winter wheat (Triticum aestivum L.) under three water treatments (full irrigation, deficit irrigation and dry/rain-fed) to investigate the changes of flag (top) leaf traits including leaf mass per area, wax n-alkanes and carbon composition of bulk leaf and n-alkanes (δ13Calk) during leaf development. We find that leaf wax n-alkane synthesis ceases when the leaf reaches its maximum area (fully expanded) under dry conditions. However, fully expanded leaves can still increase their n-alkane concentrations by 42% and 70% under deficit and full irrigation, respectively. Total leaf wax n-alkane concentrations and δ13Calk show no difference at leaf flush between rain-fed (dry) and deficit irrigation treatments, but δ13Calk under full irrigation is more depleted as expected, with more pronounced offsets between the experiments developing during the growing season. δ13Calk decreases logarithmically during leaf development perhaps indicating a shift from stored carbohydrate to fresh photosynthate and shoot growth related responses. Our results indicate that the water information at leaf flush is not ‘locked-in’ to the δ13Calk signal carried by the leaf wax n-alkanes. Instead, the first flush likely reflects the signal of stored carbohydrate more so than ambient environmental conditions. Total leaf wax n-alkane concentrations and δ13Calk at the mature stage carry a more complete record of differences in water use efficiency experienced during the growing season.

Using HJ-CCD image and PLS algorithm to estimate the yield of field-grown winter wheat

Remote sensing has been used as an important means of estimating crop production, especially for the estimation of crop yield in the middle and late growth period. In order to further improve the accuracy of estimating winter wheat yield through remote sensing, this study analyzed the quantitative relationship between satellite remote sensing variables obtained from HJ-CCD images and the winter wheat yield, and used the partial least square (PLS) algorithm to construct and validate the multivariate remote sensing models of estimating the yield. The research showed a close relationship between yield and most remote sensing variables. Significant multiple correlations were also recorded between most remote sensing variables. The optimal principal components numbers of PLS models used to estimate yield were 4. Green normalized difference vegetation index (GNDVI), optimized soil-adjusted vegetation index (OSAVI), normalized difference vegetation index (NDVI) and plant senescence reflectance index (PSRI) were sensitive variables for yield remote sensing estimation. Through model development and model validation evaluation, the yield estimation model’s coefficients of determination (R2) were 0.81 and 0.74 respectively. The root mean square error (RMSE) were 693.9 kg ha−1 and 786.5 kg ha−1. It showed that the PLS algorithm model estimates the yield better than the linear regression (LR) and principal components analysis (PCA) algorithms. The estimation accuracy was improved by more than 20% than the LR algorithm, and was 13% higher than the PCA algorithm. The results could provide an effective way to improve the estimation accuracy of winter wheat yield by remote sensing, and was conducive to large-area application and promotion.

Predicting grain protein content of field-grown winter wheat with satellite images and partial least square algorithm.

Remote sensing has been used as an important means of modern crop production monitoring, especially for wheat quality prediction in the middle and late growth period. In order to further improve the accuracy of estimating grain protein content (GPC) through remote sensing, this study analyzed the quantitative relationship between 14 remote sensing variables obtained from images of environment and disaster monitoring and forecasting small satellite constellation system equipped with wide-band CCD sensors (abbreviated as HJ-CCD) and field-grown winter wheat GPC. The 14 remote sensing variables were normalized difference vegetation index (NDVI), soil-adjusted vegetation index (SAVI), optimized soil-adjusted vegetation index (OSAVI), nitrogen reflectance index (NRI), green normalized difference vegetation index (GNDVI), structure intensive pigment index (SIPI), plant senescence reflectance index (PSRI), enhanced vegetation index (EVI), difference vegetation index (DVI), ratio vegetation index (RVI), Rblue (reflectance at blue band), Rgreen (reflectance at green band), Rred (reflectance at red band) and Rnir (reflectance at near infrared band). The partial least square (PLS) algorithm was used to construct and validate the multivariate remote sensing model of predicting wheat GPC. The research showed a close relationship between wheat GPC and 12 remote sensing variables other than Rblue and Rgreen of the spectral reflectance bands. Among them, except PSRI and Rblue, Rgreen and Rred, other remote sensing vegetation indexes had significant multiple correlations. The optimal principal components of PLS model used to predict wheat GPC were: NDVI, SIPI, PSRI and EVI. All these were sensitive variables to predict wheat GPC. Through modeling set and verification set evaluation, GPC prediction models' coefficients of determination (R2) were 0.84 and 0.8, respectively. The root mean square errors (RMSE) were 0.43% and 0.54%, respectively. It indicated that the PLS algorithm model predicted wheat GPC better than models for linear regression (LR) and principal components analysis (PCA) algorithms. The PLS algorithm model’s prediction accuracies were above 90%. The improvement was by more than 20% than the model for LR algorithm and more than 15% higher than the model for PCA algorithm. The results could provide an effective way to improve the accuracy of remotely predicting winter wheat GPC through satellite images, and was conducive to large-area application and promotion.

Determining and modelling the effective period of fungicides against septoria leaf blotch in winter wheat

The aim of this work was to develop a model to predict the effective period of fungicides for control of Zymoseptoria tritici (septoria leaf blotch) in winter wheat. Efficacy and duration of fungicidal effects of three fungicides, namely Bravo 500 (chlorothalonil), Epoxion (epoxiconazole), Imbrex (fluxapyroxad) and a mixture of Epoxion + Imbrex, were examined under field and laboratory conditions. In order to design a simulation model, a method for calculating the effective period of fungicides was developed. Key feature of this method is the comparison of disease progress curves on treated and untreated plants, based on data recorded in field trials. The effective period was considered to end when, after a prior fungicide application, rates of disease progress on treated and untreated plants became equal again. The effective periods of fungicides were calculated by subtracting latency periods of Z. tritici from the time point of recovery of maximum disease progress and lay between 16 and 22 days, depending on the fungicide. These findings were confirmed by fungicide residue analyses at the calculated time of expired fungicide efficacy where 3–44% of the initially applied doses of active substance were detectable. Based on calculations from field trials, a model to predict the fungicide effective periods was developed for field-grown winter wheat. Air temperature, precipitation and, depending on the fungicide, relative humidity were identified to be significant determinants of fungicide efficacy and effective periods. The validation confirmed the reliable prediction of the effective period of fungicides and a corresponding model named OPTIFUNG was developed. OPTIFUNG will be integrated in the wheat disease decision support model SEPTRI in order to optimize the timing and frequency of fungicide applications against septoria leaf blotch by including fungicide effective periods. As the method is based on general epidemiological principles, it may be useful for and is adaptable to yet any other leaf diseases in cereals which require sequential sprays with fungicides.

Root growth in field-grown winter wheat: Some effects of soil conditions, season and genotype.

This work compared root length distributions of different winter wheat genotypes with soil physical measurements, in attempting to explain the relationship between root length density and soil depth. Field experiments were set up to compare the growth of various wheat lines, including near isogenic lines (Rht-B1a Tall NIL and Rht-B1c Dwarf NIL) and wheat lines grown commercially (cv. Battalion, Hystar Hybrid, Istabraq, and Robigus). Experiments occurred in two successive years under rain fed conditions. Soil water content, temperature and penetrometer resistance profiles were measured, and soil cores taken to estimate vertical profiles of pore distribution, and root number with the core-break method and by root washing. Root length distributions differed substantially between years. Wetter soil in 2014/2015 was associated with shallower roots. Although there was no genotypic effect in 2014/2015, in 2013/2014 the dwarf wheat had the most roots at depth. In the shallower layers, some wheat lines, especially Battalion, seemed better at penetrating non-structured soil. The increase in penetrometer resistance with depth was a putative explanation for the rapid decrease in root length density with depth. Differences between the two years in root profiles were greater than those due to genotype, suggesting that comparisons of different genotypic effects need to take account of different soil conditions and seasonal differences. We also demonstrate that high yields are not necessarily linked to resource acquisition, which did not seem to be limiting in the low yielding dwarf NIL.

Mineral composition of field grown winter wheat inoculated with phosphorus solubilizing bacteria at different plant growth stages

ABSTRACTA two year field experiment was conducted in field conditions using wheat (Triticum aestivum ssp. vulgare L. cv. Bezostaja) as the test plant for the evaluation of phosphate solubilizing (+PS) microorganisms. Bacterial strains significantly (P < 0.05) increased plant biomass (by 13 to 36%) without plant P enrichment. Only Bacillus sp. #189 significantly (P < 0.05) raised plant P-content, biomass and rhizosphere soil Olsen P at Zadoks Scale 62 simultaneously. Inoculations variably increased plant potassium (K-), magnesium (Mg-), zinc (Zn-), and managenese (Mn-) contents at harvest (Zadoks 92) but not earlier (Zadoks 31 and 61). The enrichment of the inoculated plants with nutrients other than P indicates the presence of alternative plant growth promoting mechanisms. This study showed that promising phosphate solubilizing microorganisms could increase not only the P content of the plants, but also the soil available P in rhizosphere transiently.

Protein carbonylation during natural leaf senescence in winter wheat, as probed by fluorescein-5-thiosemicarbazide.

Leaf senescence is characterised by a massive degradation of proteins in order to recycle nitrogen to other parts of the plant, such as younger leaves or developing grain/seed. Protein degradation during leaf senescence is a highly regulated process and it is suggested that proteins to be degraded are marked by an oxidative modification (carbonylation) that makes them more susceptible to proteolysis. However, there is as yet no evidence of an increase in protein carbonylation level during natural leaf senescence. The aim of our study was thus to monitor protein carbonylation level during the process of natural senescence in the flag leaf of field-grown winter wheat plants. For this purpose, we adapted a fluorescence-based method using fluorescein-5-thiosemicarbazide (FTC) as a probe for detecting protein carbonyl derivatives. As used for the first time on plant material, this method allowed the detection of both quantitative and qualitative modifications in protein carbonyl levels during the last stages of wheat flag leaf development. The method described herein represents a convenient, sensitive and reproducible alternative to the commonly used 2,4-dinitrophenylhydrazine (DNPH)-based method. In addition, our analysis revealed changes in protein carbonylation level during leaf development that were associated with qualitative changes in protein abundance and carbonylation profiles. In the senescing flag leaf, protein carbonylation increased concomitantly with a stimulation of endoproteolytic activity and a decrease in protein content, which supports the suggested relationship between protein oxidation and proteolysis during natural leaf senescence.

Integrating irrigation management for improved grain yield of winter wheat and rhizosphere AM fungal diversity in a semi-arid cropping system

Irrigation of farmland is a popular agricultural practice in semi-arid areas in China. However, little is known about the impacts of different irrigation strategies on grain yield and soil microbial communities, particularly economically-important arbuscular mycorrhizal (AM) fungi. The aim of this study was to optimize irrigation strategies to integrate maximized grain yield, AM fungal diversity and water productivity (defined here as grain yield per unit water supplied). Six irrigation strategies consisting of different amounts of water supplied and time of supply were imposed for field-grown winter wheat (Triticum aestivum) in a typical cropping system in northern China. Results showed that all irrigation strategies significantly increased grain yield compared with the non-irrigation practice (P < 0.01). Irrigation strategy (treatment WJF180) with a total of 180-mm water supplied at Wintering, Jointing, and Grain filling stages (60 mm each) achieved maximal grain yield and water productivity than other treatments. Irrigation strategies also significantly influenced mycorrhizal colonization on roots, fungal species and spore abundance in rhizosphere soil. A total of 17 AM fungal species belonging to Glomus, Acaulopora, Scutellospora and Entrophospora were detected in the soil. The relative abundance of Glomus was the highest and Entrophospora the lowest among the four fungal genera. WJF180-treated plots had the largest species richness and spore abundance in various sampling times with plant growth. Fungal diversity differed greatly among different plant phenological stages. There were significant interactions between irrigation treatments and plant growth stages on both grain yield and AM fungi (species diversity and spore abundance). Irrigation strategies in terms of water amount and watering time integrated with biological, environmental and crop management could have potential for improved grain yield and mycorrhizal diversity leading to maximized farmers' economic productivity and water-use efficiency.

Photosystem II thermostability in situ: Environmentally induced acclimation and genotype-specific reactions in Triticum aestivum L

Photosystem II (PSII) thermostability and acclimation effects on PSII photochemical efficiency were analyzed in thirty field grown winter wheat (Triticum aestivum L.) genotypes using prompt chlorophyll a fluorescence kinetics before and after dark heat treatment. A gradual increase in temperature caused the appearance of K-bands at 300 μs on the chlorophyll fluorescence induction curve, indicating the impairment of the PSII donor side (even by heat treatment at 38 °C). An increase in basal fluorescence, commonly used as a criterion of PSII thermostability, was observed beyond a temperature threshold of 44 °C. Moreover, an acclimation shift (increase of critical temperature) was observed at the 3.5 °C identified for K-band appearance, but only by 1.1 °C for a steep increase in F(0). The single temperature approach with regular weekly observations completed within two months using dark heat treatment at 40 °C demonstrated that the acclimation effect is not gradual, but occurs immediately and is associated with an increase of daily temperature maxima over 30 °C. The acclimated heat treated samples had less effect on the donor side of PSII, the higher fraction of active Q(A)(-) reducing reaction centers and causing a much lower decrease of connectivity among PSII units compared to non-acclimated samples. In the non-treated plants the reduction of antennae size, increase of PSII connectivity and changes in the acceptor side occurred as a result of heat acclimation. The enhancement of PSII thermostability persisted over several weeks regardless of weather conditions. The genotype comparison identified three groups that differed either in initial PSII thermostability or in acclimation capacity; these groupings were clearly associated with the origin of the genotypes.

Calcium Silicate Suppresses Powdery Mildew and Increases Yield of Field Grown Wheat

During three consecutive years of field trials conducted in northwestern New Jersey on a Quakertown silt loam soil (fine–loamy, mixed, active, mesic Typic Hapludult), a calcium silicate, steel slag by‐product (CSS), was added as an effective liming agent to long winter wheat (Triticum aestivum L.) and evaluated for its suppressive effects on powdery mildew disease (Erysiphe graminis DC. f. sp. tritici Em. Marchal Blumeria graminis (DC.) E.O. Speer = E. graminis DC. Oidium monilioides (Nees) Link [anamorph]). Limestone was used as the control in a completely random design, consistent for treatment during all trial years. Plots were split for one fungicide, propiconazole (1‐[[2(2,4‐Dichlorophenyl)‐4‐propyl‐1,3‐dioxolan‐2‐yl]methyl]1‐H‐1,2,4‐triazole), application per year. The field was allowed to become naturally inoculated. In 2006 disease symptoms did not appear until late in the season. Although no significant grain yield response was exhibited in 2006, powdery mildew lesions were reduced by 29% on the flag leaves of wheat plants in the CSS treated plots. In 2007, powdery mildew was not diagnosed, but non‐pathogenic Alternaria spp. leaf blotch was observed late season. Leaf blotch lesions were reduced 25% on flag leaves in the CSS‐treated plots. During 2008, powdery mildew lesions on flag leaves were 44% less and yields were 10% greater in plots treated with CSS. Our results suggest that the use of CSS as an effective neutralizer of soil acidity may have the added benefit of suppressing powdery mildew in field grown winter wheat.

Ozone exposure of field-grown winter wheat affects soil mesofauna in the rhizosphere

A 2-year open-top chamber experiment with field-grown winter wheat ( Triticum aestivum L. cv. Astron) was conducted to examine the effects of ozone on plant growth and selected groups of soil mesofauna in the rhizosphere. From May through June in each year, plants were exposed to two levels of O 3: non-filtered (NF) ambient air or NF+ 40 ppb O 3 (NF+). During O 3 exposure, soil sampling was performed at two dates according to different plant growth stages. O 3 exposure reduced above- and below-ground plant biomass in the first year, but had little effect in the second year. The individual density of enchytraeids, collembolans and soil mites decreased significantly in the rhizosphere of plants exposed to NF+ in both years. Differences were highest around anthesis, i.e. when plants are physiologically most active. The results suggest that elevated O 3 concentrations may influence the dynamic of decomposition processes and the turnover of nutrients.

The relationship between grain weight and alpha-amylase in winter wheat: varietal comparison from UK field experiments

The relationship between Hagberg falling number and grain size was investigated in field-grown winter wheat varieties. Data was obtained for all varieties included in the UK Recommended List from 1997 to 2007. Overall, a negative association was found between thousand grain weight and Hagberg falling number. The negative association was detected between varieties in all years and within varieties in the majority of cases. Detailed Recommended List data from 2001 was used to examine variation in the relationship across 19 trial sites. Again, a negative association overall with both within and between variety associations was detected. However, there were also many cases where the association was not found. The association appears to be driven by both genetic and environmental factors; however, the association is not consistent enough to indicate a direct mechanistic link across all varieties.

Benzoxazinoid concentrations show correlation with Fusarium Head Blight resistance in Danish wheat varieties

Fusarium Head Blight (FHB) is a destructive disease that affects the grain yield and quality of cereals. The relationship between the natural defense chemicals benzoxazinoids and the FHB resistance of field grown winter wheat varieties was investigated. FHB resistance was assessed by the inoculation of wheat ears with mixtures of Fusarium avenaceum, Fusarium culmorum, Fusarium graminearum, and Microdochium nivale. The benzoxazinoids detected in the highest concentration were 2,4-dihydroxy-7-methoxy-(2 H)-1,4-benzoxazin-3(4 H)-one (3.7–9.4 μmol/kg DW) and 2-hydroxy-7-methoxy-(2 H)-1,4-benzoxazin-3(4 H)-one (HMBOA, 2.0–11 μmol/kg DW). The cultivars most susceptible to FHB were cvs. Hanseat, Asketis, and Ritmo, while cvs. Petrus, Terra, and Hattrick showed high resistance. 2- O-β- d-Glucopyranosyloxy-4,7-dimethoxy-(2 H)-1,4-benzoxazin-3(4 H)-one (HDMBOA-glc) and 2- O-β- d-glucopyranosyloxy-7-methoxy-(2 H)-1,4-benzoxazin-3(4 H)-one (HMBOA-glc) were detected. HMBOA-glc was found in higher concentrations than 2- O-β- d-glucopyranosyloxy-2,4-dihydroxy-7-methoxy-(2 H)-1,4-benzoxazin-3(4 H)-one (DIMBOA-glc). Principal component analyses demonstrated correlation between the susceptibility to FHB and the concentrations of DIMBOA-glc, HMBOA-glc, HMBOA, 2- O-β- d-glucopyranosyloxy-4-hydroxy-(2 H)-1,4-benzoxazin-3(4 H)-one (DIBOA-glc), 2- O-β- d-glucopyranosyloxy-1,4-benzoxazin-3(4 H)-one, and 2- O-β- d-glucopyranosyloxy-4-dihydroxy-(2 H)-7,8-dimethoxy-1,4-benzoxazin-3(4 H)-one (DIM 2BOA-glc).

Predictability of wheat growth and yield in light-limited conditions

In seeking better predictions of grain yield under light-limited conditions, shading was applied to field-grown winter wheat cv. Slejpner during each of five consecutive phases (canopy expansion, ear expansion, pre-flowering, grain expansion and grain filling). Absolute measures were taken of solar radiation and its effects on growth in three seasons, at a site where water and nutrient supplies were not limiting. Replicate mobile shades automatically occluded 0·80 of incident light when mean total solar radiation exceeded 250 J/m2 per s. Mean effects over seasons of shading on incident total solar radiation were −296, −139, −78, −157 and −357 MJ/m2 for the five phases respectively, and corresponding effects on shoot dry weight were −236, −184, −58, −122 and −105 g/m2. Estimated efficiency of radiation use after flowering was 1·2 g/MJ unshaded, tending to increase with shading. Shading in all phases reduced grain dry matter yield: mean effects over seasons were −106, −64, −61, −93 and −281 g/m2 for the five consecutive shading periods. Shading from GS31–39 increased mean maximum area of the two top leaves from 2700 to 3100 mm2 per leaf but, with fewer stems, canopy size remained unaffected. This and the next shading, from GS39–55, reduced specific leaf weight from 42 g/m2 by 4 and 3 g/m2 respectively, but effects on shoot dry weight were largely due to stem and ear. By flowering, stem weights, and especially their reserves of water-soluble carbohydrates, had partially recovered. Effects on yield of shading from GS31–39 were explained by a reduction in grains/m2 of 3070 from 26109. Shading from GS39–55 reduced grains/m2 by 4211 due to fewer grains per ear, whilst mean weight per grain increased in compensation. Shading from GS55–61 decreased grains/ear by 2·5. Shading from GS61–71 decreased ear growth and reduced stem weight, and at harvest resulted in 4·3 less grains/ear. Effects of the final shading from GS71–87 were fully explained by a reduction in mean dry weight/grain of 10·3 mg. Except for shading from GS71–87, source- and sink-based explanations of grain yield both proved feasible, within the precision of the measurements. Constraints to accurate comparison of source- and sink-based approaches are identified, and the implications for yield forecasting are discussed.

Association of dehydrins with wheat mitochondria during low-temperature adaptation

In mitochondria from the crowns of field-grown winter wheat plants or their seedlings hardened in the laboratory, thermostable proteins immunologically related to dehydrins were detected. It was found that two dehydrins with mol wts of 63 and 52 kD bound with the outer mitochondrial membrane during autumnal hardening or during adaptation to low temperature in the laboratory. Dehydrins of similar mol wts were detected among proteins in the total membrane fraction from low-temperature-adapted wheat plants. In addition, dehydrins with mol wts of 209 and 196 kD were present in this fraction as well. Dehydrins of similar mol wts were bound with mitochondria from seedlings adapted to low temperature and those from the crowns of plants after autumnal hardening. In spring, the amount of dehydrins associated with mitochondria from the crowns declined to the level characteristic of early autumn. Dehydrin association with mitochondria is evidently an important defense mechanism of frost-resistant plants.

Predicting leaf appearance in field-grown winter wheat: evaluating linear and non-linear models*1

Predicting leaf appearance in field-grown winter wheat: evaluating linear and non-linear models*1

Predicting leaf appearance in field-grown winter wheat: evaluating linear and non-linear models

Leaf appearance is often simulated using the phyllochron concept that assumes a linear relationship between leaf appearance rate (LAR) and temperature. A 2-year field experiment was conducted in winter wheat ( Triticum aestivum L.) to evaluate a non-linear model and two versions of the phyllochron approach to predict LAR, and to compare the differences in predictions of leaf appearance using daily, hourly, and maximum and minimum air temperatures. In the non-linear model, daily LAR (DLAR) was simulated based on the product of temperature and photoperiod response functions. The temperature function was a beta type distribution, while the photoperiod response was an exponential function. The non-linear model accurately predicted leaf appearance, and generally had a lower root mean square error (RMSE) than the two models based on the phyllochron over the two growing seasons. The mean square error was divided into systematic and unsystematic errors. For the first season, all models had a greater systematic than unsystematic error. For the second growing season, the phyllochron models had as large or larger systematic error than the non-linear model using the different temperatures. No significant improvement in the prediction of the Haun stage using hourly air temperature was found as compared to daily mean air temperature. In general, using the maximum and minimum temperatures provided the poorest predictions of LAR and resulted in the largest RMSE because these two temperatures do not represent the mean daily temperature.

Influence of soil water status and atmospheric vapor pressure deficit on leaf gas exchange in field-grown winter wheat

Soil water status and atmospheric vapor pressure deficit (VPD) are important environmental parameters that influence plant gas exchange. The objective of this study was to investigate the effect of soil water potential ( Ψ s) on the responses of gas exchange to VPD in four field-grown winter wheat ( Triticum aestivum L.) cultivars. The gas exchange parameters: net CO 2 assimilation rate ( A n), stomatal conductance ( g s), transpiration rate ( E), and intercellular CO 2 concentration ( c i) were measured under different VPD and Ψ s conditions during the period from heading to the middle of grain filling. The soil water potential had a significant effect on the responses of gas exchange parameters to VPD. At high Ψ s (−0.09 MPa), A n did not respond to increased VPD. However, A n was sensitive to increased VPD at low Ψ s, and the most pronounced decrease in A n as VPD increased was observed under severe water stress ( Ψ s=−0.7 MPa). Stomatal conductance decreased with increased VPD even at high Ψ s (−0.09 MPa). Transpiration rate increased as VPD increased at high Ψ s, but decreased as VPD increased under low Ψ s. The response of g s to VPD cannot be explained as feedback mechanism, i.e. the decrease in g s is not due to increase in E at high VPD. The response of g s to VPD in this study was consistent with a feedforward mechanism. Among the four cultivars, Karl 92 had the lowest A n, g s, and E, while the other three cultivars (Arapahoe, Cheyenne, and Scout 66) had higher A n, g s, and E than Karl 92 under low Ψ s and high VPD conditions.