Growth,Root Characteristics,and Leaf Nutrients Accumulation of Four Faba Bean (Vicia faba L.) Cultivars Differing in Their Broomrape Tolerance and the Soil Properties in Relation to Salinity

The effects of salinity on four faba bean (Vicia faba L) cultivars [Giza 429, Giza 843, Misr 1 (Orobanche-tolerant), and Giza 3 (Orobanche-susceptible)] and soil properties were investigated in a pot experiment with addition of 0, 50, and 100 mM sodium chloride (NaCl) for 9 weeks. Salinity significantly decreased calcium (Ca²⁺), magnesium (Mg²⁺), potassium (K⁺), bicarbonate (HCO₃ ^?), and sulfate (SO₄ ^2?) while significantly increasing sodium (Na⁺), chloride (Cl^?), pH, and electrical conductivity (EC; dS m^?1). Root length density (cm cm^?3), root mass density (mg cm^?3), total dry weight, and salt-tolerance indexes were significantly reduced as a result of application of salinity. The results presented support evidence on the positive relationship between Orobance tolerance and salt tolerance in the three cultivars (Giza 429, Giza 843, and Misr 1). This adaptation was mainly due to a high degree of accumulation of inorganic nitrogen (N), phosphorus (P), K⁺, Ca²⁺, and Mg²⁺ and lesser quantities of Na⁺ and Cl^?, as well as greater K⁺/Na⁺ and Ca²⁺/Na⁺ ratios.     

Nitrogen yield and nitrogen fixation of winter faba beans

Introducing autumn-sown legumes into Central European farming systems could be beneficial for addressing two challenges for European agriculture, i.e., the substantial deficit of protein sources for livestock and expected changes in agroclimatic conditions. Therefore, a two-year field experiment was conucted under Pannonian climate conditions in eastern Austria to assess nitrogen (N) yield and N fixation of several winter faba bean varieties from different European countries as compared to a spring faba bean. Winter wheat was used as a reference crop for estimating atmospheric N fixation. Winter faba beans were susceptible to frost damage especially in the harder of the two winters. Winter faba bean varieties could not achieve a higher grain yield and a higher grain N yield than the spring faba bean but had a higher grain N concentration (except for one variety). Grain yield and grain N yield of faba beans were severely impaired by drought in one year (with a mean of varieties of 8.3 g N m^?2, winter wheat: 6.4 g N m^?2); in the other year, grain N yield of faba beans considerably surpassed that of winter wheat (with a mean of varieties of 21.5 g N m^?2, winter wheat: 8.8 g N m^?2). After harvest, faba beans left higher nitrate residues in the soil, especially in the subsoil, and higher amounts of N in above-ground residues compared to winter wheat. Faba beans showed high N fixation under optimum conditions (with a mean of varieties of 21.9 g N m^?2) whereas drought considerably impaired N fixation (with a mean of varieties of 6.3 g N m^?2; with no differences between autumn- and spring-sown faba beans). In conclusion, growing winter faba bean varieties in eastern Austria did not result in higher grain yield, grain N yield, and N fixation compared to growing a spring faba bean.     

Jasmonic acid alleviates negative impacts of cadmium stress by modifying osmolytes and antioxidants in faba bean (Vicia faba L.)

We examined the role of jasmonic acid (JA) in faba bean under cadmium (Cd) stress, which reduces the growth, biomass yield, leaf relative water content (LRWC) and pigment systems. Hydrogen peroxide (H₂O₂) and lipid peroxidation (malondialdehyde [MDA]) levels increased by 2.78 and 2.24-fold, respectively, in plants under Cd stress, resulting in enhanced electrolyte leakage. Following foliar application to Cd-treated plants, JA restored growth, biomass yield, LRWC and pigment systems to appreciable levels and reduced levels of H₂O₂, MDA and electrolyte leakage. Proline and glycine betaine concentrations increased by 5.73 and 2.61-fold, respectively, in faba bean under Cd stress, with even higher concentrations observed following JA application to Cd-stressed plants. Superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase levels rose by 87.47%, 130.54%, 132.55% and 37.79%, respectively, with Cd toxicity, with further enhancement of antioxidant activities observed following foliar application of JA. Accumulation of Cd in roots, shoots and leaves was also minimized by external supplementation of JA. In conclusion, JA mitigates the negative impacts of Cd stress in faba bean plants by inhibiting the accumulation of Cd, H₂O₂ and MDA, and by enhancing osmolyte and antioxidant activities that reduce oxidative stress.     

The role of potassium fertilizer in nodulation and nitrogen fixation of faba bean (Vicia faba L.) plants under drought stress

Three-week-old nodulated faba bean plants were subjected to different levels of drought stress (onehalf, one-quarter, or one-eighth field capacity) for 5 weeks. Half the stressed plants were treated with KCl at 10 mg kg^-1 soil or 150 mg kg^-1 soil at the beginning of the drought stress. Nodulation and nitrogenase activity were significantly decreased by increasing drought stress. Leghaemoglobin and protein contents of nodule cytosol were also severely inhibited by drought sttess. This decline was attributed to the induction of protease activity. However, carbohydrate contents of the nodule cytosol increased significantly. This accumulation was attributed to a sharp decline in invertase activity and low use of sugar by the bacteroids We conclude that harmful effects of water deficits can be alleviated by increasing K⁺ supplementation.     

Do faba bean (Vicia faba L.) accessions from environments with contrasting seasonal moisture availabilities differ in stomatal characteristics and related traits?

Drought is a major constraint to faba bean (Vicia faba L.) production, and there are many mechanisms by which leaves can regulate water loss. Our primary objective was to test if the origin of the faba bean accessions, from drought-prone and non-drought-prone environments, was associated with differences in measurable aspects of stomatal morphology and physiology related to water use. Two sets, each consisting of 201 faba bean accessions, were chosen from environments with contrasting seasonal moisture profiles following the focused identification of germplasm strategy (FIGS), and then screened under well watered conditions. From these, two subsets of 10 accessions each were chosen to test for differences in response to drought. Parameters related to stomatal function and water status were measured. The dry-adapted set had bigger stomata, higher leaf relative water content (LRWC) and cooler leaves under well watered conditions. Stomatal density and stomatal area per unit area of leaflet were negatively correlated with gas exchange parameters and positively correlated with intrinsic water use efficiency. Drought caused stomatal densities to increase in the dry set while stomatal length decreased in both sets. The moisture deficit was sufficient to decrease gas exchange in both sets to similar levels, but the dry-adapted set maintained warmer leaves and a higher LRWC that showed no significant correlations with leaf morphology or gas exchange, demonstrating more effective stomatal regulation. The results also support that collection site data from the environment where genetic resources are collected can be used as indicators of adaptive traits in an herbaceous annual species.     

Accumulation of Reserve Compounds in Common Bean Seeds under Drought Stress

To investigate the seed protein and major mineral nutrient (Fe, Zn, P, and N) contents and their accumulation procedure in the seeds of common bean (Phaseolus vulgaris L.), a biennial experiment was conducted under two contrasting moisture regimes (normal irrigation and water deficit). Seed reserves of eight genotypes (WA4502-1, WA4531-17, Akhtar, D81083, AND1007, KS21486, MCD4011, and COS16) were investigated at four stages of seed filling period (SFP). Split-plot experiments were performed as randomized complete block design with four replications. The results showed significant differences in the evaluated characteristics in both factors, the genotypes and the moisture regimes. Fe content of the seeds was affected the most by drought stress and reduced in all stages, while seed nitrogen and protein contents were affected the least under stress condition. The percentages of reductions due to water deficit were higher in stage 1 for Fe, stage 2 for Zn, and stage 4 for P and N. In the stage 3, minerals had the least changes. Nitrogen content of the seeds at mid-stages of SFP increased slightly under drought stress. Drought stress also caused 39–69% reductions in the grain yield of the genotypes. Under drought stress condition, the concentrations of Fe and N in the white bean seeds were less than that of the red and the Chitti genotypes. However, the seed P contents of the white bean seeds were higher than that of the other genotypes.     

Response of nitrogen fixation,nodule activities,and growth to potassium supply in water‐stressed broad bean

Three‐week‐old nodulated faba bean plants were subjected to two levels of water stress (0.5 and 0.25 field capacity; soil water content of 20 and 10%) for five weeks. Half of the stressed plants was treated with potassium chloride (KC1) at 10 (K₁) and 150 mg (K₂)/kg soil at the beginning of water deficit. Nodulation was examined and some nodule activities were assayed. Nodulation, nitrogenase activity, total nitrogen (N), and dry matter yield were significantly decreased by increasing stress but were significantly higher with the two levels of potassium (K) supply. Leghaemoglobin and protein contents of cytosol as well as nodule protease and invertase were severely depressed by drought stress. Soluble carbohydrate contents of nodules, however, was significantly increased. Protein and leghaemoglobin contents and enzyme activities were greater with K fertilization but less soluble carbohydrate was accumulated. The results indicate that K supply, particularly at the 150 mg/kg soil level, increased faba bean resistance to water stress.     

Nodulation and root growth increase in lower soil layers of water‐limited faba bean intercropped with wheat

Below‐ground niche complementarity in legume–cereal intercrops may improve resource use efficiency and root adaptability to environmental constraints. However, the effect of water limitation on legume rooting and nodulation patterns in intercropping is poorly understood. To advance our knowledge of mechanisms involved in water‐limitation response, faba bean (Vicia faba L.) and wheat (Triticum aestivum L.) were grown as mono‐ and intercrops in soil‐filled plexiglass rhizoboxes under water sufficiency (80% of water‐holding capacity) and water limitation (30% of water‐holding capacity). We examined whether intercropping facilitates below‐ground niche complementarity under water limitation via interspecific root stratification coupled with modified nodulation patterns. While no significant treatment effects were measured in intercropped wheat growth parameters, water limitation induced a decrease in shoot and root biomass of monocropped wheat. Likewise, shoot biomass and height, and root length of monocropped faba bean significantly decreased under water limitation. Conversely, water limitation stimulated root biomass of intercropped faba bean in the lower soil layer (15–30 cm soil depth). Similarly, total nodule number of faba bean roots as well as nodule number in the lower soil layer increased under intercropping regardless of water availability. Under water limitation, intercropping also led to a significant increased nodule biomass (48%) in the lower soil layer as compared to monocropping. The enhanced nodulation in the lower soil layer and the associated increase in root and shoot growth provides evidence for a shift in niche occupancy when intercropped with wheat, which improves water‐limited faba bean performance.     

新开垦土壤上构建玉米/蚕豆-根瘤菌高效固氮模式

为了在新开垦土壤上构建高效种植模式,本文采用温室盆栽和大田试验相结合的方法,选用4种根瘤菌接种方式(保水剂拌种、清水拌种、三叶期灌根和种子丸衣化)接种4种不同蚕豆根瘤菌(NM353、CCBAU、G254和QH258),分析接菌后新开垦土壤上玉米/蚕豆间作体系的生产潜力、地上部氮素吸收和结瘤特性以及生物固氮等方面的优势,拟为该体系筛选出高效的根瘤菌及其接种技术。结果表明:接种NM353后,玉米/蚕豆间作体系中蚕豆籽粒产量比单作平均增加152.84%,而玉米保持相对稳产;以保水剂拌种的方式接种NM353的间作蚕豆地上部氮素积累量最高,蚕豆结瘤数、瘤重、固氮比例和固氮量均高于本试验中其他3种方式接种的根瘤菌。在盛花期和盛花鼓粒期,接种NM353蚕豆的固氮比例比接种CCBAU的分别高19.1%和11.1%,在各个生育时期两者固氮量之间差异均达显著水平;接种NM353与接种其他菌种间固氮量和固氮比例差异更显著。因此,在新开垦土壤上,用保水剂拌种的方式对间作蚕豆接种NM353根瘤菌,构建玉米/蚕豆-根瘤菌高效固氮体系,为新开垦土壤合理开发利用的可持续发展模式。     

Limited winter survival and compensation mechanisms of yield components constrain winter faba bean production in Central Europe

A substantial deficit of protein sources for livestock and expected changes in agro-climatic conditions are two challenges for European agriculture. Both can be addressed by introducing more autumn-sown legumes into Central European farming systems. Therefore, a three-year field experiment was conducted under Pannonian climate conditions in eastern Austria in which several winter faba bean varieties from different European countries were compared to a spring faba bean variety. Winter faba bean was susceptible to frost damage. Best overwintering was observed with the German variety Hiverna and the French variety Diva. Regarding overwintering, the first winter allowed for a clear differentiation between varieties, in the second winter, severe frost caused loss of almost all winter faba bean plants and in the third winter, which was mild, most varieties showed good overwintering. Grain yield of winter faba bean was mainly determined by variations of plants m^?2 (i.e. by overwintering) whereas compensatory mechanisms between yield components had a minor influence on yield formation. No grain yield advantage could be observed for winter faba bean varieties compared to the spring faba bean variety even in the year with good overwintering. Regarding yield components, winter faba bean had generally more shoots plant^?1 and a higher thousand kernel weight but spring faba bean tended to have more pods shoot^?1 and grains shoot^?1 whereas pods plant^?1, grains plant^?1 and grains pod^?1 generally did not differ. In conclusion, limited winter hardiness together with the minor influence of compensatory mechanisms between yield components on yield formation are serious constraints for increasing the cultivation of winter faba bean in Central Europe.     

Drought stress tolerance and photoprotection in two varieties of olive tree

Abstract

The olive tree (Olea europaea L.) is adapted to tolerate severe drought and high irradiance levels. Relative electron transport rate (J), photosynthetic efficiency (in terms of F _v /F _m and Φ_PSII), photochemical (qP) and non-photochemical quenching (NPQ) were determined in 2-year old olive plants (cultivars ‘Coratina’ and ‘Biancolilla’) grown under two different light levels (exposed plants, EP, and shaded plants, SP) during a 21-day controlled water deficit. After reaching pre-dawn leaf water potentials of about -6.5 MPa, plants were rewatered for 23 days. During the experimental period, measurements of gas exchange and chlorophyll fluorescence were carried out to study the photosynthetic performance of olive plants. The effect of drought stress and high irradiance levels caused a reduction of gas exchange, J, Φ_PSII and F _v/F _m and this decrease was more marked in EP. Under drought stress, EP showed a higher degree of photoinhibition, a higher NPQ and a lower qP if compared to SP. Coratina was more sensitive to high light and drought stress and had a slower recovery during rewatering. The results confirm that photoprotection is an important factor that affects photosynthetic productivity in olive, and that the degree of this process varies between the cultivars. This information could give a more complete picture of the response of olive trees grown under stressful conditions of semi-arid environments, and could be important for the selection of drought-tolerant cultivars with a high productivity.     

Wheat response to N2 fixed by faba bean (Vicia faba L.) as affected by sulfur fertilization and rhizobial inoculation in semi‐arid Northern Ethiopia

Nitrogen fixation in faba bean (Vicia faba cv. Mesay) as affected by sulfur (S) fertilization (30 kg S ha^–1) and inoculation under the semi‐arid conditions of Ethiopia was studied using the ¹⁵N‐isotope dilution method. The effect of faba bean–fixed nitrogen (N) on yield of the subsequent wheat crop (Triticum aestivum L.) was also assessed. Sulfur fertilization and inoculation significantly (p < 0.05) affected nodulation at late flowering stage for both 2004 and 2005 cropping seasons. The nodule number and nodule fresh weighs were increased by 53% and 95%, relative to the control. Similarly, both treatments (S fertilization and inoculants) significantly improved biomass and grain yield of faba bean on average by 2.2 and 1.2 Mg ha^–1. This corresponds to 37% and 50% increases, respectively, relative to the control. Total N and S uptake of grains was significantly higher by 59.6 and 3.3 kg ha^–1, which are 76% and 66% increases, respectively. Sulfur and inoculation enhanced the percentage of N derived from the atmosphere in the whole plant of faba bean from 51% to 73%. This corresponds to N₂ fixation varying from 49 to 147 kg N ha^–1. The percentage of N derived from fertilizer (%Ndff) and soil (%Ndfs) of faba bean varied from 4.3% to 2.8 %, and from 45.1% to 24.0%, corresponding to the average values of 5.1 and 47.9 kg N ha^–1. Similarly, the %Ndff and %Ndfs of the reference crop, barley, varied from 8.5 % to 10.8% and from 91.5% to 89.2%, with average N yields of 9.2 and 84.3 kg N ha^–1. Soil N balance after faba bean ranged from 13 to 52 kg N ha^–1. Beneficial effects of faba bean on yield of a wheat crop grown after faba bean were highly significant, increasing the average grain and N yields of this crop by 1.11 Mg ha^–1 and 30 kg ha^–1, relative to the yield of wheat grown after the reference crop, barley. Thus, it can be concluded that faba bean can be grown as an alternative crop to fallow, benefiting farmers economically and increasing the soil fertility.     

Effects of intercropping and Rhizobium inoculation on yield and rhizosphere bacterial community of faba bean (Vicia faba L.)

The effects of intercropping with maize and Rhizobium inoculation on the yield of faba bean and rhizosphere bacterial diversity were analyzed by terminal restriction fragment length polymorphism, amplified 16S rDNA restriction analysis (ARDRA), and 16S rDNA sequencing. The results showed that intercropping but not Rhizobium inoculation significantly increased the faba bean yield. Probably the relatively high level of native rhizobia in soil annulled the effect of rhizobia inoculation. ARDRA results showed that intercropping did not affect bacterial diversity whereas Rhizobium inoculation decreased bacterial diversity. The canonical correspondence analysis showed that the composition of bacterial community was changed apparently by intercropping, and there was a positive correlation (P = 0.724) between faba bean yields and intercropping and an apparent correlation (P = 0.648) between intercropping and total N. The available content of K and P had a lower effect on the bacterial community composition than did the total N content, Rhizobium inoculation, and microbial biomass C. Rhizobium inoculation negatively correlated with microbial biomass C (P = −0.827). These results revealed a complex interaction among the intercropped crops, inoculation with rhizobia, and indigenous bacteria and implied that the increase of faba bean production in intercropping might be related to the modification of rhizosphere bacterial community.     

Nodulation and N2 fixation of faba bean (Vicia faba L.) after soil amendment with crop residues

The effect of prior soil amendment with different N sources at 50 mg N (kg soil)^—1 on nodulation and N₂ fixation of faba bean (Vicia faba L. cv. Troy) using wheat (Triticum aestivum L. cv. Star) as reference crop was assessed in a pot experiment. Four treatments viz legume manure (LEGM) as clover shoots, cereal manure (CEREM) as barley straw, N fertilizer (FERT‐N) as Ca(NO₃)₂, and no‐manure control (NOMAN) were investigated consecutively at 45, 70, and 90 days after sowing (DAS). Faba bean nodulated profusely, with an increase on average from 629 nodules per pot at 45 DAS to nearly 2.3‐ and 3.3‐fold at 70 and 90 DAS, respectively. Low nodule numbers and nodule dry matter occurred under FERT‐N and CEREM, whereas high values were found for NOMAN and LEGM. Soil amendment affected percent N₂ fixation in relation to N source and plant age. Highest percent N₂ fixation (≥ 90 %) was found under the lowest N‐supplying amendments, no‐manure, and cereal manure, respectively. FERT‐N depressed N₂ fixation particularly at 45 DAS when N₂ fixation was reduced to as low as 23 %. The rise in N₂ fixation thereafter suggests that faba bean adjusted after depletion of mineral N in the soil. N₂ fixation was also decreased after cereal straw application, even though N concentration in faba bean plants was high. The results indicate that plant residues, both with high and low N concentration, applied to soil to raise its fertility may interfere with N₂ fixation of faba bean.     

Complementary resource use in intercropped faba bean and cabbage by increased root growth and nitrogen use in organic production

Intercropping can improve yield and nitrogen use efficiency in organic vegetable production by pairing crops with complementary resource use. An intercrop field experiment was conducted to determine yield, root growth and nitrogen (N) dynamics using faba bean (Vicia faba L.) grown as a vegetable and pointed cabbage (Brassica oleracea var. capitata cv. conica). Both crops were grown in monocropping (MC) and intercropping systems (IC). Minirhizotrons were used to measure root growth. Yield of pointed cabbage per metre row was 28% higher under the IC system than under MC, whereas faba bean yield as fresh seeds did not differ. The land equivalent ratio was 1.06, showing that improved yield under IC resulted from efficient land resource use. Even though MC cabbage had the highest aboveground biomass, total N accumulation was higher under IC and MC faba bean systems. Both root frequency and intensity were greater under IC faba bean rows compared with MC faba bean because of the presence of cabbage roots in faba bean rows. Monocropped cabbage had the highest root intensity and the lowest amount of soil mineral N in the 0–1.5 m depth after harvest. Monocropped cabbage was efficient in assimilating N, whereas MC faba bean was efficient in exporting N as harvestable yield. The nitrogen use efficiency using the IC system (75%) was higher than growing faba bean (44%) and cabbage (65%) alone. Thus, faba bean as an intercrop in organic cabbage production systems improves land and N use efficiency by complementary root growth.     

小麦||蚕豆间作提高间作产量的优势及其氮肥响应

为探明小麦||蚕豆间作体系种间互补和竞争与产量优势的关系及其氮肥响应,为豆科禾本科间作最佳氮素管理提供指导,本研究通过为期2年（2015—2017年）的田间定位试验,在不施氮（N0）、低氮（N1,90 kg·hm^-2）、常规施氮（N2,180 kg·hm^-2）和高氮（N3,270 kg·hm^-2）4个施氮水平下,研究小麦||蚕豆间作的产量优势及其相关种间关系。结果表明,与单作相比,两年的间作小麦产量平均显著增加23.50%,单、间作蚕豆的产量均维持在4 000 kg·hm^-2左右,土地当量比均表现为N0 > N1 > N2 > N3 > 1的趋势,系统生产力平均达5 023 kg·hm^-2。与单作相比,间作小麦和蚕豆的花后干物质累积比例、干物质转移率和贡献率均不同程度增加,增幅随着施氮量增加而降低。不同施氮水平下,小麦的种间相对关系指数均表现出明显的互利效应,相对种间竞争强度在低氮水平为种内竞争,常规氮和高氮水平为种间竞争;蚕豆的种间相对关系指数则表现出竞争效应,相对种间竞争强度表现为种内竞争。较蚕豆而言,小麦的相对种间竞争力表现出不同程度的竞争优势,在种间竞争力为0.629 2时可获得最大的间作体系混合干物质量16 093 kg·hm^-2。综上,小麦||蚕豆间作降低了低氮水平下的种间竞争强度,扩大了小麦的互利效应和竞争优势,增加了间作作物的花后干物质累积比例以及干物质贡献率,表现出明显的间作产量优势。     

苯甲酸胁迫下间作对蚕豆自毒效应的缓解机制

苯甲酸是引起蚕豆连作障碍的主要自毒物质之一。本文采用水培试验,研究了不同浓度苯甲酸[C0(0 mg?L-1)、C1(50 mg?L-1)、C2(100 mg?L-1)和C3(200 mg?L-1)]处理对与小麦间作的蚕豆幼苗生长和枯萎病发生的影响,从生理抗性角度探讨小麦与蚕豆间作对缓解苯甲酸自毒效应的机制,为合理利用间作缓解连作障碍,实现农业可持续发展提供科学依据。结果表明:与C0处理相比,不同浓度苯甲酸处理均显著抑制了蚕豆幼苗的生长,并且随处理浓度升高,抑制效应增强;同时显著提高了蚕豆枯萎病发病率和病情指数;蚕豆根系和叶片的MDA含量显著提高,但抗氧化酶(POD和CAT)活性和病程相关蛋白(β-1,3-葡聚糖酶和几丁质酶)活性均随苯甲酸处理浓度升高而降低。表明不同浓度苯甲酸处理均显著抑制了蚕豆的生长,降低蚕豆的生理抗性而促进枯萎病发生。与单作蚕豆相比,蚕豆与小麦间作显著提高了苯甲酸胁迫下蚕豆的地上部干重(17.0%~47.1%),降低了发病率(11.1%~25.0%)和病情指数(20.0%~42.1%);蚕豆根系和叶片中POD活性分别提高12.9%~16.9%和9.3%~24.9%,CAT活性分别提高10.3%~54.0%和6.6%~20.5%,蚕豆根系的β-1,3-葡聚糖酶和几丁质酶活性分别提高4.7%~13.1%和6.7%~15.8%,MDA含量分别降低19.5%~25.4%和20.5%~29.9%。C2处理下间作提高抗氧化酶和病程相关蛋白活性的效果最好,抗病效果最佳。表明小麦与蚕豆间作通过提高蚕豆的生理抗性而减轻苯甲酸引起的枯萎病危害,促进蚕豆生长,是缓解苯甲酸自毒效应的有效措施。     

Growth and Nutrient Use in Four Grasses Under Drought Stress as Mediated by Silicon Fertilizers

Field water stress is a common problem in crop production, especially in arid and semi-arid zones and it is widely hypothesized that silicon (Si) could reduce water stress in plants. We set up a greenhouse study to evaluate some silicon sources—potassium silicate (K₂SiO₃), calcium silicate (CaSiO₃) and silica gel for growth and nutrient uptake by four grass species under adequate and deficit irrigation. The four species studied were Rhodes grass (Chloris gayana), Timothy grass (Phleum pratense), Sudan grass (Sorghum sudanense) and Tall fescue (Festuca arundinacea). For all species, the biomass yield response to applied silicon under deficit irrigation was significantly better than under adequate irrigation. The yield response of Rhodes grass across silicon sources was 205% under deficit irrigation compared with only 59% under adequate irrigation; for Sudan grass it was 49% compared with 26% and for Timothy, it was 48% compared with a mere 1%. The higher responses under deficit irrigation suggest that the plants relied more on silicon to endure drought stress. Biomass yield of individual plants also differed according to soil water levels with Timothy grass being the most sensitive to water stress as it exhibited the highest yield response (209%) to adequate irrigation. This was followed by tall fescue (122%) and Rhodes grass (97%). Sudan grass was the least affected by deficit irrigation, possibly on account of improved root mass and its natural drought tolerance. Strong associations were noted between the uptake of silicon and those of nitrogen (N) and phosphorus (P) irrespective of soil water condition, but the uptake of potassium (K) was more strongly correlated with that of Si under deficit than adequate irrigation. Improvements in plant growth following Si application could therefore be linked to enhanced uptake of major essential nutrients.     

Effects of drought stress on the seedling growth,development, and metabolic activity in different cultivars of canola

ABSTRACT

The comparative effects of drought stress on seed performance, growth parameters, free proline content, lipid peroxidation, and several antioxidative enzymes activities were studied in both cultivars of Brassica napus L. Drought stress increased mean germination rate and mean of day germination in both cultivars, and its effect was more pronounced in RGS003. The length and dry weight of root increased significantly in both cultivars under drought. RGS003 was more tolerant and obtained more biomass under drought than that of Sarigol. Proline content and pyrroline-5-carboxylate synthetase expression increased in Sarigol under drought. Measurement of malondialdehyde content in seedlings showed that lipid peroxidation was lower in RGS003 than in Sarigol. Antioxidant enzyme activities showed different trends in the two cultivars under drought stress but were higher in RGS003 than in Sarigol. These results suggest that RGS003 is better protected against drought-induced oxidative damage. Lipoxygenase activity only induced under water deficit condition in RGS003. Changes of respiratory enzymes activities of RGS003 subjected to drought stress showed a pattern different with Sarigol. Drought stress induced aconitase activity in RGS003, but it reduced fumarase and succinate dehydrogenase activity in Sarigol. This study showed that RGS003 exhibits a better protection mechanism against oxidative damage and RGS003 is more drought-tolerant than Sarigol possibly by maintaining and/or increasing growth parameters, antioxidant enzyme activities, and respiratory enzymes activities.     

Quality,yield and nitrogen fixation of faba bean seeds as affected by sulphur fertilization

Abstract

Faba bean (Vicia faba L.) is an important source of plant protein for humans and animals; however, nutritional value of seeds is notoriously deficient in sulphur (S)-containing amino acids. In this article, the effect of S fertilization on faba bean's capability of N₂ fixation, grain yield and chemical characteristics in terms of protein fractions, fatty acids and minerals composition is reported. A randomized, complete block design with three replicates was used, and three S applications (0, 30 and 60 kg ha^?1, respectively) for faba bean were performed. The S fertilization was split into two applications: 50% before sowing and 50% in the beginning of March as K₂SO₄. At the same time, both the legume and oat crops were fertilized uniformly with 10 kg N ha^?1 as ¹⁵N NH₄ ¹⁵NO₃ (10% ¹⁵N atomic excess) in solution form. In a Mediterranean climate under optimal spring rainfall situations, faba bean produced high yield of grain and protein. Sulphur application resulted in an increase in overall plant yield and N₂ fixation. In addition, S fertilization enhanced the protein quality, increasing its degradable fraction. Fertilizing faba bean with 30 kg ha^?1 of S resulted in a more appropriate dose in order to obtain a quantitative and qualitative crop improvement. From our findings, it can be concluded that S fertilization to faba bean should be recommended to soils with suboptimal S levels to obtain maximum seed and protein yields.