Nitrogen accumulation in plant tissues and roots and N mineralization under oilseeds, pulses, and spring wheat

To understand how pulse and oilseed crops might use nitrogen (N) more efficiently under varying levels of water and N availability in soil, we conducted a 2-year field study to monitor N accumulation in aboveground (AG-N) and root material at five growth stages, for canola (Brassica napus L.), mustard (Brassica juncea L.), chickpea (Cicer arietinum L.), dry pea (Pisum sativum L.) and lentil (Lens culinaris Medicum) alongside spring wheat (Triticum aestivum L.). Crops were grown in lysimeters (15 cm diameter × 100 cm deep) installed in the field in southern Saskatchewan, Canada. AG-N in all crops was greater under high-water than under low-water conditions. In oilseeds and wheat, AG-N increased until flowering then tended to level off, while in pulses it increased gradually to maturity. At maturity, dry pea and wheat had the greatest AG-N and mustard the least. Enhanced water availability increased seed N but did not affect straw N; consequently, N harvest index was greater under high-water than under low-water conditions. Root N increased until late-flowering or late-pod (dough stage in wheat) then decreased to maturity. Mustard had the lowest root N, chickpea the second lowest, and canola, wheat, dry pea, and lentil the highest. Improved water availability increased root N for oilseeds and wheat but did not affect root N in pulses. At maturity, average root N of oilseeds, pulses, and wheat was 14, 17, and 20 kg ha^-1, respectively. At the seedling stage pulse crops had about 27% of total plant N in their roots, a much greater proportion than for the non-legumes. However, by maturity all crops had about 14% of plant N in their roots. Soil NO₃-N increased gradually between seedling and maturity in non-legumes but in pulses there was a sharp spike at early flowering. Estimated apparent net N mineralized was similar for wheat and pulse crops which were greater than for canola and mustard. Soil N amounts and temporal change patterns varied substantially among crops evaluated, and these differences need to be considered in the development of diverse cropping systems where cereals, legumes, and oilseeds are included in rotation systems.     

Quantifying relationships between rooting traits and water uptake under drought in Mediterranean barley and durum wheat

In Mediterranean regions drought is the major factor limiting spring barley and durum wheat grain yields. This study aimed to compare spring barley and durum wheat root and shoot responses to drought and quantify relationships between root traits and water uptake under terminal drought.One spring barley（Hordeum vulgare L. cv. Rum） and two durum wheat Mediterranean cultivars（Triticum turgidum L. var durum cvs Hourani and Karim） were examined in soil‐column experiments under well watered and drought conditions. Root system architecture traits, water uptake, and plant growth were measured. Barley aerial biomass and grain yields were higher than for durum wheat cultivars in well watered conditions. Drought decreased grain yield more for barley（47%） than durum wheat（30%, Hourani）. Root‐to‐shoot dry matter ratio increased for durum wheat under drought but not for barley, and root weight increased for wheat in response todrought but decreased for barley. The critical root length density（RLD） and root volume density（RVD） for 90% available water capture for wheat were similar to（cv. Hourani） or lower than（cv. Karim） for barley depending on wheat cultivar. For both species, RVD accounted for a slightly higher proportion of phenotypic variation in water uptake under drought than RLD.     

Crop water availability in early agriculture: evidence from carbon isotope discrimination of seeds from a tenth millennium BP site on the Euphrates

The analysis of carbon isotope discrimination (Δ) in crop plant remains from archaeological sites may help to assess water availability for early agriculture. This study presents the analysis of Δ in seeds of naked wheat (Triticum aestivum/durum), lentil (Lens orientalis/culinaris), and flax (Linum sp.) found at the archaeological site of Tell Halula in the valley of the Middle Euphrates (Syria). This Neolithic site is the oldest in this region of the Fertile Crescent where the cultivation of domesticated plants has been reported, with seed remains ranging from 9550 to 8465 BP. Most of the seeds analysed showed Δ values greater than 16 ‰, reaching 20 ‰ for some samples of flax. For wheat, Δ values were much higher than those reported in present-day (1996) durum wheat crops cultivated under rainfed conditions in north-west Syria under environments with somewhat higher rainfall than Tell Halula. Similarly, grains of present-day (1997) barley cultivated in the archaeological site also showed lower values than those found in archaeological kernels. An empirical relationship between Δ of mature kernels and total precipitation (plus irrigation where applicable) from heading to maturity (r² = 0.82, n = 11) was established for durum wheat, currently cultivated in different environments of the Mediterranean basin. The resulting relationship was applied to the data on Δ of wheat fossil kernels from Tell Halula to estimate the accumulated water inputs during the time (about 6 weeks) the kernels were produced. Calculated water inputs for wheat during early agriculture were (over 110 mm) at least 5 times higher than current-day rainfall accumulated in Tell Halula during the same phenological period. These results strongly suggest that early agriculture wheat was cultivated at Tell Halula under much wetter conditions than are currently to be found in the area. The presence of flax and its very high Δ values also support this conclusion. Whether such humid conditions during cultivation were due to moister conditions prevailing at this time, by planting in alluvial areas or by irrigation works is discussed.     

The efficiency of a durum wheat-winter pea intercrop to improve yield and wheat grain protein concentration depends on N availability during early growth

Grain protein concentration of durum wheat is often too low, particularly in low-N-input systems. The aim of our study was to test whether a durum wheat-winter pea intercrop can improve relative yield and durum wheat grain protein concentration in low-N-input systems. A 2-year field experiment was carried out in SW France with different fertilizer-N levels to compare wheat (Triticum turgidum L., cv. Nefer) and pea (winter pea, Pisum sativum L., cv. Lucy) grown as sole crops or intercrops in a row-substitutive design. Without N fertilization or when N was applied late (N available until pea flowering less than about 120 kg N ha^?1), intercrops were up to 19% more efficient than sole crops for yield and up to 32% for accumulated N, but were less efficient with large fertilizer N applications. Wheat grain protein concentration was significantly higher in intercrops than in sole crops (14% on average) because more N was remobilized into wheat grain due to: i) fewer ears per square metre in intercrops and ii) a similar amount of available soil N as in sole crops due to the high pea N₂ fixation rate in intercrops (88% compared to 58% in sole crops).     

Determining the fluxes of Tl+ and K+ at the root surface of wheat and canola using Tl(I) and K ion-selective microelectrodes

The objectives of this study were to develop and evaluate a Tl⁺ ion-selective microelectrode (ISME) and to determine the basis for observed differences in Tl accumulation by durum wheat (Triticum turgidum L. var ‘Kyle’) and spring canola (Brassica napus L. cv ‘Hyola 401’). Seedlings were grown hydroponically and fluxes of K⁺ and Tl⁺ were measured at the root surface in solutions containing 5 μM Tl⁺ or 3 mM K⁺. After testing two different Tl(I) ionophores, a functional Tl⁺ ISME was developed from calix[4]arene tetra-n-propyl ether which had a detection limit of 2.5 µM and a slope of 56.6 mV/dec. Measurements of Tl⁺ flux indicate that Tl⁺ efflux occurred within 300–500 µm of the root tip, and influx farther from the root tip. Compared with canola, wheat had a slightly larger region of efflux and a smaller region of maximal influx, resulting in flux per root branch that was 2.3 to 4 times greater in canola than in wheat. The magnitude and pattern of K⁺ fluxes by the two species were more similar. Our results indicate that observed differences in Tl accumulation by wheat and canola are due both to differences in the magnitude of Tl flux per root branch of these species, and to differences in root morphology resulting in more root tips in canola than in wheat roots.     

Insect invasions of agroecosystems in the western Canadian prairies: case histories,patterns, and implications for ecosystem function

Agroecosystems in the western Canadian provinces of Alberta, Saskatchewan, and Manitoba have been invaded by several alien herbivorous insects from several orders and families. These species have caused very substantial reductions in yield and quality of the dominant crops grown in this region, including cereals (primarily wheat, Triticum aestivum L., barley, Hordeum vulgare L., and oats Avena sativa L.), oilseeds (primarily canola, Brassica napus L. and Brassica rapa L., and mustard, Sinapis alba L. and Brassica juncea (L.) Czern.), and pulses (primarily field pea, Pisum sativum L., lentil, Lens culinaris Medik., and chickpea, Cicer arietinum L.). In this study, we used literature searches to identify the major species of insect pests of field crops in western Canada and determine those species indigenous to the region versus species that have invaded from other continents. We summarize invasion patterns of the alien species, and some estimated economic costs of the invasions. We document the invasion and dispersal patterns of the cereal leaf beetle, Oulema melanopus L. (Coleoptera: Chrysomelidae), for the first time in all three provinces. We also report the co-occurrence of its exotic parasitoid, Tetrastichus julis (Walker) (Hymenoptera: Eulophidae), and implications for classical biological control. We present results of field studies describing the dispersal patterns of a second recent invader, the pea leaf weevil, Sitona lineatus L. (Coleoptera: Curculionidae). The implications of invasions in this region are discussed in terms of economic and ecological effects, and challenges posed for pest mitigation.     

Effect of 2,4-Dichlorophenoxyacetic Acid and NaCl on the Establishment of Callus and Plant Regeneration in Durum and Bread Wheat

Optimal callus induction and plant regeneration were obtained in bread and durum wheat by manipulating the NaCl concentration in the induction medium. Immature embryos from a high regeneration line of spring wheat (Triticum aestivum L.), 'MPB-Bobwhite 26', and an elite durum wheat (Triticum turgidum var. durum L.), 'Mexicali', were cultured in E3 induction medium consisting of Murashige and Skoog (MS) medium, 2.5 mg l^–1 2,4-dichlorophenoxyacetic acid (2,4-D), 2% sucrose and 0.9% Bacto agar. The treated embryos were transferred to E3 liquid medium supplemented with various levels of 2,4-D and NaCl. Incubation on medium containing 2.5 mg l^–1 2,4-D for 45 days produced callus and plant regeneration in 'MPB-Bobwhite 26', but lower callus yield and plant regeneration in 'Mexicali', indicating that 2,4-D alone was not sufficient for callus induction and plant regeneration in this durum variety. Callus yield and regeneration frequencies were higher in 'Mexicali' embryos that were incubated in media containing 2 mg l^–1 2,4-D and 2 mg l^–1 NaCl. The presence of NaCl in the medium beyond the initiation phase was detrimental to plant regeneration. The use of NaCl in the callus formation could form the basis for improved transformation of durum wheat varieties.     

The effect of transpiration on thallium uptake and mobility in durum wheat and spring canola

Aims

The objective of this study was to investigate the role of transpiration on accumulation and distribution of thallium (Tl) in young durum wheat (Triticum turgidum L. var ‘Kyle’) and spring canola (Brassica napus L. cv ‘Hyola 401’) plants.

Methods

Seedlings were grown hydroponically and exposed to Tl(I) under different high relative humidity (RH) conditions which resulted in different rates of transpiration among treatments. Plants were harvested prior to exposure, after a dark period of 9 (wheat) or 10?h (canola), and after 24?h of exposure. Harvested plant material was digested and analyzed for Tl by GFAAS.

Results

Our results indicated that accumulation and distribution of Tl by plants was dependent on plant species, Tl(I) dose, duration of exposure and RH, but that the effect of RH was influenced by plant species and Tl dose. Plants exposed to Tl(I) under different RH conditions did not accumulate more Tl overall. In wheat, shoots with higher transpiration rates contained a higher Tl concentration. In canola, the rate of transpiration did not consistently affect the concentration of Tl in shoots.

Conclusions

Overall, our results suggest that accumulation and translocation of Tl by plants is influenced by environmental factors that affect transpiration, in addition to soil characteristics.     

Plant growth-promoting activities of fluorescent pseudomonads,isolated from the Iranian soils

Fluorescent pseudomonads are among the most influencing plant growth-promoting rhizobacteria in plants rhizosphere. In this research work the plant growth-promoting activities of 40 different strains of Pseudomonas fluorescens and Pseudomonas putida, previously isolated from the rhizosphere of wheat (Triticum aestivum L.) and canola (Brassica napus L.) and maintained in the microbial collection of Soil and Water Research Institute, Tehran, Iran, were evaluated. The ability of bacteria to produce auxin and siderophores and utilizing P sources with little solubility was determined. Four strains of Wp1 (P. putida), Cfp10 (Pseudomonas sp.), Wp150 (P. putida), and Wp159 (P. putida) were able to grow in the DF medium with ACC. Thirty percent of bacterial isolates from canola rhizosphere and 33% of bacterial isolates from wheat rhizosphere were able to produce HCN. The results indicate that most of the bacteria, tested in the experiment, have plant growth-promoting activities. This is the first time that such PGPR species are isolated from the Iranian soils. With respect to their great biological capacities they can be used for wheat and canola inoculation in different parts of the world, which is of very important agricultural implications.     

Free proline accumulation in drought-stressed plants

Summary Free-proline accumulation was measured in leaves of intact wheat (Triticum vulgare L. cv. Kalyan Sona), plantago (Plantago ovata Forsk-Isabgool), papavar (Papaver somnifera L. Opium poppy) and mustard (Brassica juncea L. var. Varuna) grown in the field with low to high field water content and thus they were subjected to water stress. Leaf water deficit in percentage was used to determine the degree of stress at the time of proline anlysis.Free proline content was higher in mustard leaves as compared to wheat, plantago and papavar leaves. Water stress enhances the proline content but at same water deficit level the content differ in the leaves of the plants studied.     

Photosynthetic characteristics and enzymatic antioxidant capacity of leaves from wheat cultivars exposed to drought

Two durum (Triticum durum L.), Barakatli-95 and Garagylchyg-2; and two bread (Triticum aestivum L.) wheat cultivars, Azamatli-95 and Giymatli-2/17 with different sensitivities to drought were grown in the field on a wide area under normal irrigation and severe water deficit. Drought caused a more pronounced inhibition in photosynthetic parameters in the more sensitive cvs Garagylchyg-2 and Giymatli-2/17 compared with the tolerant cvs Barakatli-95 and Azamatli-95. Upon dehydration, a decline in total chlorophyll and relative water content was evident in all cultivars, especially in later periods of ontogenesis. Potential quantum yield of PS II (F(v)/F(m) ratio) in cv Azamatli-95 was maximal during stalk emergency stage at the beginning of drought. This parameter increased in cv Garagylchyg-2, while in tolerant cultivar Barakatli-95 significant changes were not observed. Contrary to other wheat genotypes in Giymatli-2/17 drought caused a decrease in PS II quantum yield. Drought-tolerant cultivars showed a significant increase in CAT activity as compared to control plants. In durum wheat cultivars maximal activity of CAT was observed at the milk ripeness and in bread wheat cultivars at the end of flowering. APX activity also increased in drought-treated leaves: in tolerant wheat genotypes maximal activity occurred at the end of flowering, in sensitive ones at the end of ear formation. GR activity increased in the tolerant cultivars under drought stress at all stages of ontogenesis. SOD activity significantly decreased in sensitive cultivars and remained at the control level or increased in resistant ones. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.     

Is there an associational resistance of winter pea–durum wheat intercrops towards Acyrthosiphon pisum Harris?

Acyrthosiphon pisum Harris (Aphididae: Hemiptera), the pea aphid, is an important pest in organic farming systems. In this work, the objective was to gather empirical field data on the associational resistance of durum wheat–winter pea intercrops towards the pea aphid, compared with pure stands of winter pea. Our results showed that intercropping winter pea with durum wheat significantly decreased A. pisum abundance in all the situations. Moreover, it was systematically observed that pea grew bigger in pure than in intercropped stands but after considering pea dry mass as a covariate, it appeared that the durum wheat–winter pea intercrop was still significantly less attacked by pea aphids than the sole crop. Intercrop sowing designs had an incidence on infestation levels: substitutive diversification systems of different types are more effective in decreasing the level of aphid infestation than does the additive system. In addition, substitutive row intercrop is significantly less infested than substitutive mixture. These results suggest that a mechanism related to the resource concentration hypothesis may explain the associational resistance of the IC of durum wheat–winter pea towards A. pisum.     

Effects of water deficit on photosynthetic rate and osmotic adjustment in tetraploid wheats

Osmotic adjustment, accumulation of soluble saccharides, and photosynthetic gas exchange were studied in five durum wheat (Triticum turgidum L. var. durum) and one wild emmer wheat (Triticum turgidum L. var. dicoccoïdes) cultivars of contrasting drought tolerance and yield stability. Soil water contents (SWC) were 100, 31, 20, and 12 % of maximum capillary capacity. Under mild water stress (SWC 31 to 20 %), osmotic adjustment capacity and high accumulation of saccharides were found in cv. Cham1, a high yielding and drought tolerant cultivar, and in var. dicoccoïdes, while lowest values were noted in the durum wheat landraces Oued-Zenati and Jennah-Khotifa. Under more severe water stress (SWC 12 %), the cv. Cham1 maintained higher net photosynthetic rate (PN) than other genotypes. The observed changes in the ratio intercellular/ambient CO2 concentration (ci/ca) indicated that under mild and severe water stress, the decrease in PN was mainly due to stomatal and non-stomatal factors, respectively.     

The parameters of grain filling and yield components in common wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) and durum wheat (<Emphasis Type="Italic">Triticum turgidum</Emphasis> L. var. <Emphasis Type="Italic">durum</Emphasis>)

Final grain dry weight, a component of yield in wheat, is dependent on the duration and the rate of grain filling. The purpose of the study was to compare the grain filling patterns between common wheat, (Triticum aestivum L.), and durum wheat, (Triticum turgidum L. var. durum), and investigate relationships among grain filling parameters, yield components and the yield itself. The most important variables in differentiating among grain filling curves were final grain dry weight (W) for common wheat genotypes and grain filling rate (R) for durum wheat genotypes; however, in all cases the sets of variables important in differentiating among grain filling curves were extended to either two or all three parameters. Furthermore, in one out of three environmental conditions and for both groups of genotypes, the most important parameter in the set was grain filling duration (T). It indicates significant impact of environmental conditions on dry matter accumulation and the mutual effect of grain filling duration and its rate on the final grain dry weight. The medium early anthesis date could be associated with further grain weight and yield improvements in wheat. Grain filling of earlier genotypes occurs in more temperate environments, which provides enough time for gradual grain fill and avoids the extremes of temperature and the stress of dry conditions.     

Diamondback moth oviposition: effects of host plant and herbivory

The oviposition behaviour of Plutella xylostella L. (Lepidoptera: Plutellidae) on Chinese cabbage (Brassica rapa L. Pekinensis, cv. Wombok), canola (Brassica napus L. cv. Thunder TT), and cabbage (Brassica oleracea L. Capitata, cv. sugarloaf) (Brassicaceae) was studied in the laboratory. In no‐choice experiments moths laid most eggs on the stems and lower three leaves of cabbage plants, the lower three leaves of canola plants, but on the upper three leaves of Chinese cabbage plants. The effects of conspecific herbivore damage to foliage could be replicated by mechanical damage. When foliage was damaged, injured cabbage and canola plants were preferred for oviposition over intact conspecifics, whereas injured Chinese cabbage plants were less preferred than intact conspecifics. However, when root tissue was damaged, intact cabbage and canola plants were preferred over injured conspecifics, whereas moths did not discriminate between root‐damaged and intact Chinese cabbage plants. Injury to upper leaves significantly affected the intra‐plant distribution of eggs. In cabbage and canola plants, injury to leaf 6 significantly increased the number of eggs laid on this leaf, resulting in a significant decrease in the number of eggs laid on the lower foliage/stem of plants, whereas in Chinese cabbage plants it significantly decreased the number of eggs laid on leaf 6. Following oviposition on intact plants, neonate larvae established the vast majority of feeding sites on leaves 5–8 in all three host plants, indicating that larvae moved a considerable distance from preferred oviposition sites in cabbage and canola plants. The growth rate of neonates fed on leaf‐6 tissue was significantly greater than that of those fed on leaf‐1 tissue; >90% of larvae completed development when fed exclusively on leaf‐6 tissue but no larvae completed development when fed exclusively on leaf‐1 tissue. The study demonstrates the complex and unpredictable interactions between P. xylostella and its host plants and provides a basis from which we can begin to understand observed distributions of the pest in Brassica crops.     

Phytotoxic, clastogenic and bioaccumulation effects of the environmental endocrine disruptor bisphenol A in various crops grown hydroponically

The effects of the endocrine disruptor bisphenol A (BPA) at concentrations of 10 and 50 mg l⁻¹ were evaluated on the germination and morphology, micronuclei (MN) content in root tip cells and BPA bioaccumulation of hydroponic seedlings of broad bean (Vicia faba L.), tomato (Lycopersicon esculentum Mill.), durum wheat (Triticum durum Desf.) and lettuce (Lactuca sativa L.) after 6 and 21 days of growth. In general, BPA at any dose used did not inhibit germination and early growth (6 days) of seedlings of the species examined, with the exception of primary root length of tomato which decreased at the higher BPA dose. In contrast, an evident phytotoxicity was induced by BPA in all species after 21 days of growth with evident morphological anomalies and significant reductions of the lengths and fresh and dry weights of shoots and roots of seedlings. With respect to the nutrient medium without seedlings, BPA concentration decreased markedly during the growth period in the presence of broad bean and tomato seedlings, and limitedly in the presence of durum wheat and, especially, lettuce. Further, the presence of BPA measured in roots and shoots of broad bean and tomato after 21-day growth indicated that bioaccumulation of BPA had occurred. The number of MN in broad bean and durum wheat root tip cells increased markedly by treatment with BPA at both concentrations, thus suggesting a potential clastogenic activity of BPA in these species.     

Influence of paddy and corn in different rotations on wheat yield,nutrient removal and soil properties

Summary In a 3 year field study, the effect of two rotations, paddy (Oryza sativa L.), wheat (Triticum aestivum L.), mung (Phaseolus aureus L.) and corn (Zea mays L.), wheat (Triticum aestivum L.), mung (Phaseolus aureus L.) on wheat yield and chemical, physical and biological properties of soil was evaluated. Grain yield of the wheat sown after paddy during 1972–73, 1973–74 and 1974–75 was lesser by 0,300 and 390 kg/ha respectively than that of the wheat following corn. The reduction in the yield of wheat was attributed to relatively higher NPK removal by paddy, greater immobilization of N applied to wheat and deterioration of soil physical conditions in the paddy field. Total NPK removal by paddy average 131 kg/ha more than that by corn. Sharp increase in bacterial population of soil during early growth of wheat that followed paddy and the concurrent less available N in soil and low N content in wheat plants suggested that the N applied to wheat was immobilised to organic form. The increase in soil bulk density and particle dispersion ratio and decrease in water storage in deeper soil layers in the paddy field probably restricted the root proliferation and growth of wheat.     

Pressure-volume curves and drought resistance in two wheat genotypes

The water relations of two durum wheat cultivars ( Triticum durum Desf.) were studied throughout the growing season. Irrigated and unirrigated plants were compared from booting to milk stage; a period where water stress occurred naturally in the field. Modulus of elasticity (ε), turgid weight/dry weight ratio (TW/DW), relative water content at zero turgor (RWC_o) and osmotic potential at full turgor (ε) declined throughout the season while average turgor (ψ_p) increased. Water stress induced a further decrease in ψ_π¹⁰⁰ and the TW/DW ratio. The elastic modulus varied greatly. During the first stages of growth, cv. Appulo (the more resistant cultivar) showed lower ε values than cv. Valforte. At the milk stage, ε was lower for the unirrigated than the irrigated plants. Correlation coefficients between the TW/DW ratio and the osmotic potential were significant for both cultivars. In cv. Valforte, TW/DW was also correlated with the average turgor and the bulk modulus of elasticity. Structural changes that affect the TW/DW ratio seem to be important factors influencing water relations and drought tolerance in durum wheat.     

Damage potential of grasshoppers (Orthoptera: Acrididae) on early growth stages of small-grains and canola under subarctic conditions

We characterized the type and extent of grasshopper injury to above- and below-ground plant parts for four crops [barley (Hordeum vulgare L.), oats (Avena sativa L.), wheat (Triticum aestivum L.), and canola (Brassica campestris L.)] commonly grown, or with potential to grow, in central Alaska. Cages were placed on 48 pots containing plants in second to third leaf stages and stocked with 0, 2, 4, and 6 first-instar Melanoplus sanguinipes F. pot(-1). Plants were harvested 22 d after planting. Stem growth of barley and oats was not affected except at the highest grasshopper treatment. In canola, stem biomass was reduced at the medium and high grasshopper treatments, when most of the leaves had been consumed. The highest grasshopper treatment reduced leaf area in barley and oats by approximately 55%, and caused a significant reduction in dry weight of leaves, stems, and roots (41-72%). Wheat and canola plants were smaller than barley and oats across all treatments and, at the highest grasshopper density, above-ground portions of wheat and canola were completely destroyed. Length and surface area of roots of barley and oats were reduced by 20-28% again at the highest grasshopper density, whereas the reduction for wheat and canola ranged from 50 to 90%. There was little or no difference among all grasshopper densities for C-N ratio in leaf and stem tissues of all crops. The results suggest that wheat and canola are more susceptible than barley and oats and that densities > or = 2 pot(-1) (approximately > or = 50 m(-2)) of even very small grasshoppers could cause significant damage in small-grain and oilseed crop production.     

The Temperature Gradient Air–Soil as a Factor in the Optimization of Net Photosynthesis in Whole Plants

The effect of soil temperature on the net photosynthetic rate was studied by the method of multifactor analysis at early growth stages of narrow-leaved lupine (Lupinus angustifolius L.), white cabbage (Brassica capitata Lisg.), spring wheat (Triticum aestivum L.), cucumber (Cucumis sativus L.), tomato (Lycopersicon esculentum Mill.), and cotton (Gossypium hirsutum L.) plant species and cultivars contrasting in their heat demand. The optimum level of the net photosynthetic rate was observed in a wide range of soil and air temperatures, from cold- to heat-hardening temperatures, irrespective of the sign of the temperature gradient, whereas the magnitude and sign of the temperature gradient favorable for the highest potential net photosynthetic rate were species- and cultivar-specific and were not related to the cold tolerance of a species or cultivar.