Drought Tolerance and Water‐Use Efficiency of Biogas Crops: A Comparison of Cup Plant,Maize and Lucerne‐Grass

The cup plant (Silphium perfoliatum L.) is discussed as an alternative energy crop for biogas production in Germany due to its ecological benefits over continuously grown maize. Moreover, a certain drought tolerance is assumed because of its intensive root growth and the dew water collection by the leaf cups, formed by fused leaf pairs. Therefore, the aim of this study was to estimate evapotranspiration (ET ), water‐use efficiency (WUE ) and the relevance of the leaf cups for the cup plant's water balance in a 2‐year field experiment. Parallel investigations were conducted for the two reference crops maize (high WUE ) and lucerne‐grass (deep and intensive rooting) under rainfed and irrigated conditions. Root system performance was assessed by measuring water depletion at various soil depths. Transpiration‐use efficiency (TUE ) was estimated using a model approach. Averaged over the 2 years, drought‐related above‐ground dry matter reduction was higher for the cup plant (33 %) than for the maize (18 %) and lucerne‐grass (14 %). The WUE of the cup plant (33 kg ha^?1 mm^?1) was significantly lower than for maize (50 kg ha^?1 mm^?1). The cup plant had a lower water uptake capacity than lucerne‐grass. Cup plant dry matter yields as high as those of maize will only be attainable at sites that are well supplied with water, be it through a large soil water reserve, groundwater connection, high rainfall or supplemental irrigation.     

The Physiology and Stability of Leaf Carbon Isotope Discrimination as a Measure of Water‐Use Efficiency in Barley on the Canadian Prairies

Temporal and seasonal water deficit is one of the major factors limiting crop yield on the Canadian prairie. Selection for low carbon isotope discrimination (Δ¹³C) or high water‐use efficiency (WUE) can lead to improved yield in some environments. To understand better the physiology and WUE of barley under drought conditions on the Canadian prairie, 12 barley (Hordeum vulgare L.) genotypes with contrasting levels of leaf Δ¹³C were investigated for performance stability across locations and years in Alberta, Canada. Four of those genotypes (‘CDC Cowboy’, ‘Niobe’, ‘170011’ and ‘Kasota’) were also grown in the greenhouse under well‐watered and water‐deficit conditions to examine genotypic variations in leaf Δ¹³C, WUE, gas exchange parameters and specific leaf area (SLA). The water‐deficit treatment was imposed at the jointing stage for 10 days followed by re‐watering to pre‐deficit level. Genotypic ranking in leaf Δ¹³C was highly consistent, with ‘170011’, ‘CDC Cowboy’ and ‘W89001002003’ being the lowest and ‘Kasota’‘160049’ and ‘H93174006’ being the highest leaf Δ¹³C. Under field and greenhouse (well‐watered) conditions, leaf Δ¹³C was significantly correlated with stomatal conductance (g_s). Water deficit significantly increased WUE, with ‘CDC Cowboy’– a low leaf Δ¹³C genotype with significantly higher WUE and lower percentage decline in assimilation rate (A) and g_s than the other three genotypes (‘Niobe’, ‘170011’ and ‘Kasota’). We conclude that leaf Δ¹³C is a stable trait in the genotypes evaluated. Low leaf Δ¹³C of ‘CDC Cowboy’ was achieved by maintaining a high A and a low g_s, with comparable biomass and grain yield to genotypes showing a high g_s under field conditions; hence, selection for a low leaf Δ¹³C genotype such as ‘CDC Cowboy’ maybe important for maintaining productivity and yield stability under water‐limited conditions on the Canadian prairie.     

Genotypic Variation of Gas Exchange Parameters and Leaf Stable Carbon and Nitrogen Isotopes in Ten Quinoa Cultivars Grown under Drought

Genotypic variations in leaf gas exchange and grain yield were analysed in 10 highland‐adapted quinoa cultivars grown in the field under drought conditions. Trials took place in an arid mountain region of the Northwest of Argentina (Encalilla, Amaicha del Valle, 22°31′S, 65°59′W). Significant changes in leaf gas exchange and grain yield among cultivars were observed. Our data demonstrate that leaf stomatal conductance to water vapour (g_s) is a major determinant of net CO₂ assimilation (A_n) because quinoa cultivars with inherently higher g_s were capable of keeping higher photosynthesis rate. Aboveground dry mass and grain yield significantly varied among cultivars. Significant variations also occurred in chlorophyll, N and P content, photosynthetic nitrogen‐use efficiency (PNUE), specific leaf area (SLA), intrinsic water‐use efficiency (_iWUE) and carboxylation capacity (A_n/C_i). Many cultivars gave promissory grain yields with values higher than 2000 kg ha^?1, reaching for Sayaña cultivar 3855 kg ha^?1. Overall, these data indicate that cultivars, which showed higher photosynthesis and conductances, were also generally more productive. Carbon isotope discrimination (Δ) was positively correlated with the grain yield and negatively with _iWUE, but δ¹⁵N did not show significant correlations. This study provides a reliable measure of specific responses of quinoa cultivars to drought and it may be valuable in breeding programmes.     

Leaf,canopy and agronomic water‐use efficiency of field‐grown sugar beet in response to potassium fertilization

Potassium (K) fertilization is important to maintain adequate concentrations of plant available K in agricultural soils to achieve best yields and improve crop stress tolerance and water‐use efficiency (WUE). Water‐use efficiency (WUE) can be expressed on various spatiotemporal scales, and it is known that responses of WUE to external stress are not uniform across scales. Multiscale evaluations of the impact of varying K fertilization on the WUE of C₃ crops under field conditions are missing so far. In the present field study, we evaluated effects of K fertilization on WUE of sugar beet (Beta vulgaris L.) on short‐termed leaf‐ (WUE_Leaf) and canopy‐scales (WUE_Canopy) and as the agronomic ratio of white sugar yield (WSY) to in‐season water use (i.e. WUE_WSY). In K‐fertilized plots, WUE_WSY was enhanced by 15.9%. This effect is attributed to increased beet yield and WSY, as no differences in total in‐season water use between fertilized and unfertilized plots were observed. Potassium (K) fertilization significantly enhanced the leaf area index, resulting in a more efficient depletion of soil moisture by roots in K‐fertilized plots. As a consequence, WUE_Leaf was increased due to stomatal adjustment. Potassium (K) improved WUE_Canopy only by tendency. It is concluded that K fertilization improves the WUE of field‐grown sugar beet across scales, but processes that regulate WUE are highly scale dependent.     

Electron Transport Through Photosystem II Is Not Limited By A Wide Range of Water Deficit Conditions In Field‐Grown Gossypium hirsutum

Despite exhaustive literature describing drought stress effects on photosynthesis in Gossypium hirsutum, the sensitivity of photosynthetic electron flow to water deficit is heavily debated. To address this, G. hirsutum plants were grown at a field site near Camilla, GA under contrasting irrigation regimes, and pre‐dawn water potential (Ψ_PD), stomatal conductance (g_s), net photosynthesis (P_N), actual quantum yield of photosystem II (Φ_PSII) and electron transport rate (ETR) were measured at multiple times during the 2012 growing season. Ψ_PD values ranged from ?0.3 to ?1.1 MPa. Stomatal conductance exhibited a strong (r² = 0.697), sigmoidal response to Ψ_PD, where g_s was ≤0.1 mol m^?2 s^?1 at Ψ_PD values ≤ ?0.86 MPa. Neither Φ_PSII (r² = 0.015) nor ETR (r² = 0.010) was affected by Ψ_PD, despite exceptionally low Ψ_PD values (?1.1 MPa) causing a 71.7 % decline in P_N relative to values predicted for well‐watered G. hirsutum leaves at Ψ_PD = ?0.3 MPa. Further, P_N was strongly influenced by g_s, whereas ETR and Φ_PSII were not. We conclude that photosynthetic electron flow through photosystem II is insensitive to water deficit in field‐grown G. hirsutum.     

Responses to N Deficiency in Stay Green and Non‐Stay Green Argentinean Hybrids of Maize

Breeding has developed better yielding maize hybrids for low N environments, which also have delayed leaf senescence (‘stay green’ trait, SG). Here, we studied whether the SG trait can further improve yield of modern hybrids under N‐limiting conditions. In two field experiments, four maize hybrids with different senescence behaviour were grown under three N fertilization levels, from 0 to 200 kg N ha^?1 (N0, N100 and N200). After silking, hybrids differed for senescence depending on the canopy layer (P < 0.05): the SG AX878 only delayed senescence at the mid and upper canopy layers while the SG NK880 delayed senescence of all layers. Across N doses, higher yields were achieved by both SG hybrids, AX878 and NK880 (P < 0.05) but yield was not only determined by senescence behaviour. Kernel weight (KW) response to N availability was larger for SGs than for their non‐‘stay green’ counterparts. Delayed senescence in SG hybrids was not related to higher post‐silking N uptake but to higher (P < 0.05) %N in leaves and lower (P < 0.05) %N in kernels at harvest (below the critical 1.1 % under N deficiency). Across N levels, KW positively related to N content per kernel, with a steeper slope (P < 0.05) for the SG hybrids. Taken together, our results suggest that a condition where N limits kernel growth, in a scenario of saturating C availability, may be common to stay green genotypes of maize.     

Radiation‐Use Efficiency,Biomass Production,and Grain Yield in Two Maize Hybrids Differing in Drought Tolerance

Drought‐tolerant (DT) maize (Zea mays L.) hybrids have potential to increase yield under drought conditions. However, little information is known about the physiological determinations of yield in DT hybrids. Our objective was to assess radiation‐use efficiency (RUE), biomass production, and yield in two hybrids differing in drought tolerance. Field experiments were conducted in 2013 and 2014 with two hybrids, P1151HR (DT hybrid) and 33D49 (conventional hybrid) under well‐watered (I₁₀₀) and drought (I₅₀) conditions. I₁₀₀ and I₅₀ refer to 100 % and 50 % evapotranspiration requirement, respectively. On average, P1151HR yielded 11–27 % greater than 33D49 at I₁₀₀ and about 40 % greater at I₅₀, At I₁₀₀, greater yield in P1151HR was due to greater biomass at physiological maturity (BM_pm) resulting from greater post‐silking biomass accumulation (BM_post). At I₅₀, both hybrids had similar BM_pm but P1151HR showed a higher harvest index and greater BM_post. RUE differed significantly (P < 0.05) between the hybrids at I₁₀₀, but not at I₅₀. At I₁₀₀, the RUE values for P1151HR and 33D49 were 4.87 and 4.28 g MJ^?1 in 2013, and 3.71 and 3.48 g MJ^?1 in 2014. At I₅₀, the mean RUE was 3.89 g MJ^?1 in 2013 and 3.16 g MJ^?1 in 2014. Results indicate that BM_post is important for maintaining high yield in DT maize.     

Infrared Thermal Imaging as a Rapid Tool for Identifying Water‐Stress Tolerant Maize Genotypes of Different Phenology

The main task of this research was to evaluate canopy temperature and Crop Water Stress Index (CWSI) by assessing genotype variability of maize performance for different water regimes. To that end, three hundred tropical and subtropical maize hybrids with different phenology in terms of date of anthesis were evaluated. The influence of phenology on the change in canopy temperatures and CWSI was not equal during the three dates of measurement. At the end of vegetative growth (82 days after sowing, DAS) and at the blister stage (DAS 97), a high significant difference in temperatures and CWSI (P < 0.001) were obtained between the early‐ and late‐maturity genotypes. During anthesis (DAS 89), phenology had a significant effect (P < 0.01) only for the well‐watered genotypes, while under water‐stress conditions, no differences were found between early and late genotypes in terms of canopy temperature and CWSI. High significant differences (P < 0.001) in stomatal conductance (g_s) between early and late genotypes for different treatments were observed. A relationship (R² = 0.62) between g_s and canopy temperature was obtained. Under a water‐stress canopy, temperature was measured at anthesis, which was negatively correlated with grain yield of the early (r = ?0.55)‐ and late (r = ?0.46)‐maturity genotypes in the water‐stressed condition.     

Effect of Phosphorus Nutrition on Growth and Physiology of Cotton Under Ambient and Elevated Carbon Dioxide

Phosphorous deficiency in soil limits crop growth and productivity in the majority of arable lands worldwide and may moderate the growth enhancement effect of rising atmospheric carbon dioxide (CO₂) concentration. To evaluate the interactive effect of these two factors on cotton (Gossypium hirsutum) growth and physiology, plants were grown in controlled environment growth chambers with three levels of phosphate (Pi) supply (0.20, 0.05 and 0.01 mm ) under ambient and elevated (400 and 800 μmol mol^?1, respectively) CO₂. Phosphate stress caused stunted growth and resulted in early leaf senescence with severely decreased leaf area and photosynthesis. Phosphate stress led to over 77 % reduction in total biomass across CO₂ levels. There was a below‐ground (roots) shift in biomass partitioning under Pi deficiency. While tissue phosphorus (P) decreased, tissue nitrogen (N) content tended to increase under Pi deficiency. The CO₂ × Pi interactions were significant on leaf area, photosynthesis and biomass accumulation. The stimulatory effect of elevated CO₂ on growth and photosynthesis was reduced or highly depressed suggesting an increased sensitivity of cotton to Pi deficiency under elevated CO₂. Although, tissue P and stomatal conductance were lower at elevated CO₂, these did not appear to be the main causes of cotton unresponsiveness to elevated CO₂ under severe Pi‐stress. The alteration in the uptake and utilization of N was suggested due to a consistent reduction (18–21 %) in the cotton plant tissue N content under elevated CO₂.     

Effect of Salinity on Growth Parameters,Soil Water Potential and Ion Composition in Cucumis melo cv. Huanghemi in North‐Western China

A field trial conducted on the melon cultivar Huanghemi irrigated with saline water was carried out in Minqin County in the 2‐year period, 2007 and 2008. In three irrigation treatments, different saline water concentrations were applied, that is 0.8 g l^?1 (Control C), 2 g l^?1 (Treatment S₁) and 5 g l^?1 (Treatment S₂), reproducing the natural groundwater concentration in the county. The electrical conductivity of the saline water was as follows: 1.00, 2.66 and 7.03 dS m^?1, respectively. The aims of the study were (i) to monitor water consumption and water potential, (ii) assess, during the whole crop cycle, some growth parameters and their relations for estimating the morpho‐functional plant response irrigated with saline water and (iii) determine the ion concentration in different plant tissues to evaluate which mechanism the plant activates in the presence of high salt concentrations. Under salinity stress, the plants sustained the concentration of Ca, Mg and K, but at a level not sufficient to limit the Na adsorption. Therefore, the melon yield decreased and it was determined by a displacement of the ratio K/Na and by a lower (total potential MPa). Consequently with increasing salinity, a significant reduction was observed in: water consumption (ET c, mm), leaf area duration (LAD, m² d), on shoot dry weight aboveground (W , g plant^?1), on specific leaf area (SLA, cm² g^?1) and on leaf area ratio (LAR, cm² g^?1). In treatment S₂, in addition to these changes which mainly affected the plant morphology with effects on the biomass produced, a moderate reduction was also observed in net assimilation rate (NAR, g m^?2 d^?1), water use efficiency (WUE), a significant reduction in the energy conversion efficiency (ECE, %) and, in short, in a reduction in the relative growth rate (RGR, g g^?1 d^?1).     

Leaf Carbon Isotope Discrimination as an Accurate Indicator of Water‐Use Efficiency in Sunflower Genotypes Subjected to Five Stable Soil Water Contents

Leaf carbon isotope discrimination (CID) has been suggested as an indirect tool for breeding for water‐use efficiency (WUE) in various crops. This work focused on assessing phenotypic correlations between WUE and leaf CID and analysing genotypic variability in four sunflower genotypes grown in a greenhouse in pots with five different stable levels of soil water content (SWC). We measured WUE at whole plant and leaf (intrinsic) level. At whole plant level, WUE was derived from the ratio of total dry aerial biomass (BM) to cumulative water transpired (CWT). At leaf level, intrinsic WUE was calculated as the ratio of light‐saturated CO₂ assimilation to stomatal conductance (A/g_s) in younger expanded leaves. Significant differences among the four genotypes and the five SWCs were observed for whole plant and leaf WUE and CID. Strong negative correlations were observed between whole plant WUE and CID as well as between intrinsic WUE and CID with decreasing water availability. No relationships appeared between BM production and WUE or CID. Our results can help agronomists and breeders to evaluate sunflower lines with high WUE for adaptation to drought conditions and for reducing water consumption and crop water needs. Leaf CID appears to be a pertinent and valuable trait to select sunflower genotypes with high WUE.     

Heritability of spotted wilt resistance in a Florida‐EP™ “113”‐derived peanut (Arachis hypogaea) population

Spotted wilt, caused by tomato spotted wilt virus (TSWV), is a major disease of peanut (Arachis hypogaea ) in the south‐eastern United States. Cultivar resistance is the most important factor in disease control. However, spotted wilt resistance in current cultivars still carries risk in the absence of other practices when disease is severe. In contrast, a newly developed cultivar, Florida‐EP? “113,” has demonstrated excellent resistance even when spotted wilt is severe. Information on heritability of this resistance can help breeders better utilize it in breeding. F₂‐derived populations from the cross Florida‐EP? “113”/Georgia Valencia were developed and tested in field experiments in Florida from 2012 to 2014. Disease symptoms were evaluated visually, and the frequency of TSWV infection was measured by ImmunoStrip^®. Heritability estimated from ImmunoStrip^® was higher (0.66) compared to visual ratings (0.48). Genetic correlations among evaluation methods (r _A = 0.92–0.99) and environments (r _B = 0.86–0.99) were high. These results indicate that resistance in Florida‐EP? “113” is highly heritable and that selection in a high disease risk environment is feasible without significant erosion of genetic gain.     

Effects of Increasing Salinity Stress and Decreasing Water Availability on Ecophysiological Traits of Quinoa (Chenopodium quinoa Willd.) Grown in a Mediterranean‐Type Agroecosystem

Quinoa is a native Andean crop for domestic consumption and market sale, widely investigated due to its nutritional composition and gluten‐free seeds. Leaf water potential (Ψ_leaf) and its components and stomatal conductance (g_s) of quinoa, cultivar Titicaca, were investigated in Southern Italy, in field trials (2009 and 2010). This alternative crop was subjected to irrigation treatments, with the restitution of 100 %, 50 % and 25 % of the water necessary to replenish field capacity, with well water (100 W, 50 W, 25 W) and saline water (100 WS, 50 WS, 25 WS) with an electrical conductivity (EC_w) of 22 dS m^?1. As water and salt stress developed and Ψ_leaf decreased, the leaf osmotic potential (Ψ_π) declined (below ?2.05 MPa) to maintain turgor. Stomatal conductance decreased with the reduction in Ψ_leaf (with a steep drop at Ψ_leaf between ?0.8 and 1.2 MPa) and Ψ_π (with a steep drop at Ψ_π between ?1.2 and ?1.4 MPa). Salt and drought stress, in both years, did not affect markedly the relationship between water potential components, RWC and g_s. Leaf water potentials and g_s were inversely related to water limitation and soil salinity experimentally imposed, showing exponential (Ψ_leaf and turgor pressure, Ψ_p, vs. g_s) or linear (Ψ_leaf and Ψ_p vs. SWC) functions. At the end of the experiment, salt‐irrigated plants showed a severe drop in Ψ_leaf (below ?2 MPa), resulting in stomatal closure through interactive effects of soil water availability and salt excess to control the loss of turgor in leaves. The effects of salinity and drought resulted in strict dependencies between RWC and water potential components, showing that regulating cellular water deficit and volume is a powerful mechanism for conserving cellular hydration under stress, resulting in osmotic adjustment at turgor loss. The extent of osmotic adjustment associated with drought was not reflected in Ψ_π at full turgor. As soil was drying, the association between Ψ_leaf and SWC reflected the ability of quinoa to explore soil volume to continue extracting available water from the soil. However, leaf ABA content did not vary under concomitant salinity and drought stress conditions in 2009, while differing between 100 W and 100 WS in 2010. Quinoa showed good resistance to water and salt stress through stomatal responses and osmotic adjustments that played a role in the maintenance of a leaf turgor favourable to plant growth and preserved crop yield in cropping systems similar to those of Southern Italy.     

Leaf Gas Exchange Characteristics of Jatropha as Affected by Nitrogen Supply,Leaf Age and Atmospheric Vapour Pressure Deficit

Facing a steadily increasing world energy demand, jatropha, among other energy crops, has been reported to potentially contribute to biofuel production. A basic characterisation of plant responses to abiotic environmental factors is important for assessing the model‐assisted potential of this plant in view of the many agro‐ecological zones in which jatropha is presently cultivated. Two pot experiments and two field studies were used to record gas exchange parameters in response to light, nitrogen supply, atmospheric vapour pressure deficit (VPD), leaf age and time of measurements. Variation of N supply from 0 to 16 mm resulted in lower rates of photosynthesis (A) and stomatal conductance (g_s) of treatment 0 mm N compared with other N levels, whereas the light compensation point (I_C), quantum yield (QY) and dark respiration rates (R_d) were similar in all treatments. In the field, diurnal effects were evident with higher light‐saturated photosynthetic rate (A_max) and QY and lower I_C and R_d in the morning than in the afternoon. Considering leaf age effects, fully expanded leaves had a lower A_max compared with expanding leaves and this variation in leaf gas exchange was not related to changes in the chlorophyll index value (SPAD) which steadily increased with leaf age. QY of field and greenhouse plants varied from 0.023 to 0.037 and was substantially lower than in C3 plants. A was positively correlated with g_s in a hyperbolic function. A varied from 0.64 to 21.13 μmol m^?2 s^?1 and g_s varied from 12 to 469 mmol m^?2 s^?1. With increasing VPD, g_s decreased, but this response differed between the field experiments and the two pot experiments which contrasted each other distinctively. Applying the inverse logistic function of Webb (Ecological Modeling, 56 (1991), 81), the maximal stomatal conductance of jatropha was in the range of 382 mmol m^?2 s^?1 and g_s is predicted to be close to zero at 5 kPa. These data altogether indicate that light absorption characteristics of single leaves and carbohydrate status parameters should be investigated further to explain the low QY and the pronounced diurnal variation.     

Salt‐Induced Regulation of Some Key Antioxidant Enzymes and Physio‐Biochemical Phenomena in Five Diverse Cultivars of Turnip (Brassica rapa L.)

A greenhouse experiment was carried out to examine the differential morpho‐physiological responses of five cultivars of turnip (Brassica rapa L.) to salt stress. Five diverse cultivars of turnip (shaljum desi surakh, shaljum purple top, shaljum golden bal, neela shaljum, and peela shaljum) were subjected for 6 weeks to varying levels of NaCl, i.e. 0, 80 and 160 mm in Hoagland’s nutrient solution in sand culture. Imposition of varying levels of salt substantially decreased shoot and root fresh and dry weights, chlorophyll contents, leaf osmotic potential, relative water contents, different gas exchange attributes, total phenolics, malondialdehyde, activities of superoxide dismutase, peroxidase catalase, and leaf and root K⁺ levels while enhanced the proline contents, membrane permeability, level of H₂O₂, leaf and root Na⁺ and Cl^? and leaf Ca²⁺ in all turnip cultivars under study. Of all cultivars, peela shaljum and neela shaljum were consistently higher in their growth than the other turnip cultivars at all salt concentrations of the growth medium. Photosynthetic capacity (A) and stomatal conductance (g_s) were higher in high biomass‐producing cultivars, i.e. peela shaljum and neela shaljum, which provide to be potential selection criteria of salt tolerance in turnip. However, the regulation of antioxidant system was cultivar‐specific under saline conditions.     

Correlation between Fusarium head blight severity and DON content in triticale as revealed by phenotypic and molecular data

Fusarium head blight (FHB) in triticale (× Triticosecale Wittmack) results in yield losses and mycotoxin contamination, for example, by deoxynivalenol (DON). This study aimed to analyse the correlation between FHB severity and DON content in a DH population of 146 entries across environments. Additionally, Fusarium damaged kernel (FDK) rating, heading stage and plant height were recorded. Highly significant (P < 0.001) genotypic variances were found throughout, but also significant (P < 0.001) genotype–environment interaction variances occurred. Correlation between FHB severity and heading stage or plant height was low (r = 0.144 and r = ?0.153, P < 0.10). A prediction of DON content from FHB severity or FDK rating is not possible caused by low correlations (r = 0.315 and 0.572, respectively, P < 0.001). A common quantitative trait locus (QTL) for all FHB‐related traits was found on wheat chromosome 2A being of minor importance for FHB severity, but of high importance for DON content and FDK rating. Another QTL on rye chromosome 5R was more important for FHB severity. In conclusion, DON content has to be measured in triticale after selection for FHB severity to gain for healthy and mycotoxin‐reduced feed.     

Silicon Alleviates PEG‐Induced Water‐Deficit Stress in Upland Rice Seedlings by Enhancing Osmotic Adjustment

This study investigates the effect of added silicon (Si, as sodium silicate) on water status–related parameters, osmolytes accumulation and gas exchange in the leaves of hydroponically grown upland rice seedlings under polyethylene glycol (PEG‐6000)‐induced water stress, the aims being to explore whether Si has been involved in osmotic adjustment (OA) in upland rice plants. Fifty‐five‐day‐old seedlings were subjected to 8.5 % (m/v) PEG‐6000 treatment without or with 2.5 mm Si for 7 days. The results showed that addition of Si to culture solution could partially improve total, free, and bound water contents in both leaves and roots, which were all decreased under water stress. Application of Si increased water potential (Ψ_w) and osmotic potential (Ψ_π) in both roots and leaves while maintained higher turgor pressure (Ψ_p), in comparison with the plants without Si application. Added Si also stimulated the active accumulation of some osmolytes in both leaves and roots of stressed plants, which suggested enhanced OA ability. Analysis of gas exchange in leaves showed that net photosynthetic rate, transpiration, and water‐use efficiency (WUE) were decreased under water stress, whereas application of Si enhanced the photosynthesis and improved the WUE. This study suggests that PEG‐induced water stress in rice could be partially alleviated by addition of Si. This alleviative effect was partially attributable to enhanced OA ability by means of active accumulation of osmolytes.     

玉米水分利用效率、碳稳定同位素判别值和叶面积之间的关系

通过盆栽试验,研究了水分胁迫对玉米各生育期叶面积(LA)、比叶面积(SLA)、水分利用效率(WUE)和碳稳定同位素判别值(Δ¹³C)的影响以及不同水分条件下WUE、茎叶Δ¹³C和SLA之间的关系。试验设4个水分处理, 分别为田间持水量的75%~100%(W1)、50%~75%(W2)、30%~50%(W3)和0~30%(W4)。W2和W3处理对生物量干重的影响在玉米拔节期明显,而W4处理导致各生育期生物量干重的极大降低。在W2和W3处理下,玉米各生育期的WUE随着水分胁迫程度的增加而增加;而W4处理下,WUE在孕穗期后则显著降低。SLA在孕穗期达到最大。玉米各生育期叶片Δ¹³C在W1、W2和W3处理中呈随水分胁迫的增加而降低的趋势,而W4处理下的叶片Δ¹³C则高于W2和W3处理。玉米叶片光合同化物质往茎秆转移时没有发生碳同位素的分馏作用。在玉米的各生育期,叶片Δ¹³C、茎秆Δ¹³C和玉米WUE呈一致性的负相关;各生育期的SLA与Δ¹³C呈正相关关系,而与WUE呈显著的负相关。     

Kernel δ18O reflects changes in apical dominance and plant transpiration in tropical maize

Modification of source–sink ratios in tropical maize through detasseling is an ancestral agronomical practice used for increasing yields under stressful conditions. However, the mechanisms behind such effect are not well understood given the difficulties to determine physiological processes such as photosynthesis and whole‐plant transpiration in the field. We have tested the potential ability of kernel δ ¹⁸O to assess differences in grain yield (GY ) through changes in plant transpiration caused by the modification of water availability and source–sink modification treatments, (including removal of the tassel and different numbers of leaves) in three tropical maize hybrids differing in drought tolerance. Drought‐tolerant genotypes displayed higher yields and lower kernel δ ¹⁸O values than the drought‐susceptible genotype under both well‐watered (WW ) and water‐stressed (WS ) conditions. Detasseling caused a positive increase in GY under well‐watered (up to 8%) and water‐deficit conditions (up to 36%). Reduction in leaf area (source) through defoliation treatments caused a large impact on GY showing a trade‐off between maintaining a photosynthetic versus transpiring leaf area. Thus, while a reasonable reduction in leaf area significantly improved plant water availability (as shown by lower kernel δ ¹⁸O values) and consequently GY under water deficit (up to 40%), it caused a maximum reduction of 25% in GY under well‐watered conditions. Variations in GY were significantly (p  <  .05) correlated with changes in δ ¹⁸O under both well‐watered (r  =  ?.67) and WS conditions (r  =  .75 and .82). Our results also reinforce the utility of δ ¹⁸O measured in mature kernels as a powerful ecophysiological tool for assessing genotypic differences in apical dominance, transpiration and yield under both WW and WS conditions in tropical maize.     

A Simple Drought‐Sensitive Model for Leaf : Stem Partitioning of Wheat

We investigated the leaf : stem partitioning of winter wheat (Triticum aestivum L. varieties ‘Dekan’ and ‘Batis’) with and without drought influence. Irrigated and drought‐stressed winter wheat, grown in a rainout shelter in 2009/10 and 2013/14, were sampled during shoot elongation phase at the experimental Farm Hohenschulen located in Northern Germany. The data set contains leaf (DM_L) and stem dry masses (DM_S), as well as measured water contents for several soil layers. A reduced relative dry matter allocation to leaves was observed under drought stress. Our results clearly show that, if simulated leaf : stem partitioning is not sensitive to drought, this will cause a positive bias in simulated leaf and a negative bias in simulated stem dry matter under water‐limited conditions. This is in accordance with previous studies which revealed that crop simulators often overestimate the impact of drought on light‐use efficiency, whereas the consequences on leaf area development are underestimated. However, the drought stress‐induced shift in leaf : stem partitioning is yet not considered by most common wheat crop simulators. Our aim was to fill the gap in simulation of drought stress implications on leaf area development. A simple allometric model for leaf : stem partitioning () was parameterized. Starting from the allometric leaf : stem relationship observed under optimum water supply, a correction term was introduced, which allows to adapt the partitioning to drought stress conditions. The lg‐transformed root‐weighted soil water potential in the rooting zone (lgψ_root, lg(hPa)), calculated as a function of measured water contents and simulated root distribution, was used as a drought stress indicator. The linear correction term assumes an increase of the stem fraction, proportional to the difference between lgψ_root and a drought stress threshold (pF_crit, lg(hPa)). The analysis revealed that the shift in allometric partitioning towards stem fraction starts with lgψ_root greater than 1.92 [lg(hPa)]. The slope of the relative increase of dry matter allocated to the stem fraction was determined with 0.26 [lg(hPa)^?1]. Both parameters of the correction term were found to be highly significant. Implications for crop modelling are discussed.