The influence of NO3 - and NH4 + nutrition on the carbon and nitrogen partitioning characteristics of wheat (Triticum aestivum L.) and maize (Zea mays L.) plants

The carbon and nitrogen partitioning characteristics of wheat (Triticum aestivum L.) and maize (Zea mays L.) grown hydroponically at a constant pH on either 4 mM or 12 mM NO₃ ^- or NH₄ ⁺ nutrition were investigated using either ¹⁴C or ¹⁵N techniques. Greater allocation of ¹⁴C to amino-N fractions occurred at the expense of allocation of ¹⁴C to carbohydrate fractions in NH₄ ⁺-compared to NO₃ ^--fed plants. The [¹⁴C]carbohydrate:[¹⁴C]amino-N ratios were 1.5-fold and 2.0-fold greater in shoots and roots respectively of 12 mM NO₃ ^--compared to 12 mM NH₄ ⁺-fed wheat. In both 4 mM and 12 mM N-fed maize the [¹⁴C]carbohydrate:[¹⁴C]amino-N ratios were approximately 1.7-fold and 2.0-fold greater in shoots and roots respectively of NO₃ ^--compared to NH₄ ⁺-fed plants. Similar results were observed in roots of wheat and maize grown in split-root culture with one root-half in NO₃ ^--and the other in NH₄ ⁺-containing nutrient media. Thus the allocation of carbon to the amino-N fractions occurred at the expense of carbohydrate fractions, particularly within the root. Allocation of ¹⁴N and ¹⁵N within separate sets of plants confirmed that NH₄ ^--fed plants accumulated more amino-N compounds than NO₃ ^--fed plants. Wheat roots supplied with ¹⁵NH₄ ⁺ for 8 h were found to accumulate ¹⁵NH₄ ⁺ (8.5 g ¹⁵N g^-1 h^-1) whereas in maize roots very little ¹⁵NH₄ ⁺ accumulated (1.5 g ¹⁵N g^-1 h^-1)It is proposed that the observed accumulation of ¹⁵NH₄ ⁺ in wheat roots in these experiments is the result of limited availability of carbon within the roots of the wheat plants for the detoxification of NH₄ ⁺, in contrast to the situation in maize. Higher photosynthetic capacity and lower shoot: root ratios of the C₄ maize plants ensure greater carbon availability to the root than in the C₃ wheat plants. These differences in carbon and nitrogen partitioning between NO₃ ^--and NH₄ ⁺-fed wheat and maize could be responsible for different responses of wheat and maize root growth to NO₃ ^- and NH₄ ⁺ nutrition.     

Soil nitrogen heterogeneity in a Dehesa ecosystem

The C mineralization and N transformations during the decomposition of sunflower stalks (Helianthus annuus L.) and wheat straw (Triticum aestivum L.) with and without addition of (NH₄)₂SO₄ (27.53 atom% ¹⁵N) were studied in a Vertisol. Soil samples were incubated under aerobic conditions for 224 days at 22 °C. The plant residues were added at a rate of 5.2 g kg^-1 soil. Nitrogen was applied at a rate of 50.7 mg N kg^-1 soil. Carbon dioxide emission and inorganic N content in soil were periodically determined. Gross N immobilization and remineralization were calculated on the basis of the isotopic dilution technique. At the end of the incubation period a ¹⁵N balance was established. Respectively, 68 and 45% of the applied residue-C mineralized from the sunflower stalks and wheat straw after 224 days. Both crop residues caused losses of up to 25% of added ¹⁵N after 224 days of incubation. These ¹⁵N losses were about three times larger than in the control soil, and were probably due to denitrification. The net immobilization of soil derived N following residue incorporation was largest in the case of wheat straw, depleting all soil inorganic N. In the wheat straw treatment with added (NH₄)₂SO₄ soil inorganic N remained available, resulting in an enhanced initial C mineralization and N immobilization compared to the treatment without added N. In the case of the sunflower stalks, the high inorganic N content of the stalks suppressed the effects of N addition on C mineralization and N immobilization/mineralization. Gross N immobilization amounted to 31.9 and 28.2 mg N g^-1 added C after 14 days for wheat straw and sunflower stalks, respectively. At the end of the incubation, about 35% of the newly immobilized N was remineralized in both plant residue treatments. Gross N immobilization plotted against decomposed C suggests that fairly uniform C-N relationships exist during the decomposition of divers C substrates. The results demonstrate that low fertilizer N use efficiencies may be expected in a wheat-sunflower cropping system with incorporation of crop residues, as the fertilizer N applied becomes largely immobilized in the soil organic fraction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Transformation of14C labelled plant components in soil in relation to immobilization and remineralization of15N fertilizer

Summary Uniformly¹⁴C labelled glucose, cellulose and wheat straw and specifically¹⁴C labelled lignin component in corn stalks were aerobically incubated for 12 weeks in a chernozem soil alongwith¹⁵N labelled ammonium sulphate. Glucose was most readily decomposed, followed in order by cellulose, wheat straw and corn stalk lignins labelled at methoxyl-, side chain 2-and ring-C. More than 50% of¹⁴C applied as glucose, cellulose and wheat straw evolved as CO₂ during the first week. Lignin however, decomposed relatively slowly. A higher proportion of¹⁴C was transformed into microbial biomass whereas lignins contributed a little to this fraction.After 12 weeks of incubation nearly 60% of the lignin¹⁴C was found in humic compounds of which more than 70% was resistant to hydrolysis with 6N HCl. Maximum incorporation of¹⁵N in humic compounds was observed in cellulose amended soil. However, in this case more than 80% of the¹⁵N was in hydrolysable forms.Immobilization-remineralization of applied¹⁵N was most rapid in glucose treated soil and a complete immobilization followed by remineralization was observed after 3 days. The process was much slow in soil treated with cellulose, wheat straw or corn stalks. More than 70% of the newly immobilized N was in hydrolysable forms mainly reepresenting the microbial component.Serial hydrolysis of soil at different incubation intervals showed a greater proportion of 6N HCl hydrolysable¹⁴C and¹⁵N in fractions representing microbial material.¹⁴C from lignin carbons was relatively more uniformly distributed in different fractions as compared to glucose, cellulose and wheat straw where a major portion of¹⁴C was in easily hydrolysable fractions.     

Thermodynamic analysis of the physical state of water during freezing in plant tissue, based on the temperature dependence of proton spin-spin relaxation

Multi-proton spin-echo images were collected from cold-acclimated winter wheat crowns (Triticum aestivum L.) cv. Cappelle Desprez at 400 MHz between 4 and ?4 °C. Water proton relaxation by the spin-spin (T2) mechanism from individual voxels in image slices was found to be mono-exponential. The temperature dependence of these relaxation rates was found to obey Arrhenius or absolute rate theory expressions relating temperature, activation energies and relaxation rates, Images whose contrast is proportional to the Arrhenius activation energy (E_a), Gibb's free energy of activation (ΔG^?), and the entropy of activation (ΔS^?) for water relaxation on a voxel basis were constructed by post-image processing. These new images exhibit contrast based on activation energies rather than rules of proton relaxation. The temperature dependence of water proton T₂ relaxation rates permits prediction of changes in the physical state of water in this tissue over modest temperature ranges. A simple model is proposed to predict the freezing temperature kof various tissue in wheat crowns. The average E_a and ΔH^? for water proton T₂ relaxation over the above temperature range in winter wheat tissue were ?6.4 ± 14.8 and ?8.6 ± 14.8kj mol^?1, respectively. This barrier is considerably lower than the E_a for proton translation in ice at 0°C, which is reported to be between 46.0 and 56.5 kj mol^?1     

Solid-state fermentation,lignin degradation and resulting digestibility of wheat straw fermented by selected white-rot fungi

Summary Lignin biodegradation, carbon loss and in vitro dry matter digestibility (IVDMD) have been investigated during the solid state fermentation of wheat straw by eight previously selected strains of white-rot fungi. A mathematical model of the degradation kinetics is presented. [The time period required to reach maximum rates of ¹⁴CO₂ and unlabeled CO₂ release from (¹⁴C)-lignin-labelled wheat straw and from whole wheat straw, respectively, was generally short (6–10 days).] High rates of ¹⁴C-lignin degradation were achieved by Pycnoporus cinnabarinus (2.9% ¹⁴CO₂ evolved/day), an unidentified strain Nancon (3.0%/day), Sporotrichum pulverulentum Nov. (3.4%/day), Bjerkandera adusta (2.4%/day), and Dichomitus squalens (2.3%). However, only the latter two strains degraded whole wheat straw slowly and Bjerkandera adusta was not able to degrade more than 23% of the ¹⁴C-lignin. Cyathus stercoreus and Dichomitus squalens facilitated the highest improvement in IVDMD (68% against 38% for the sound straw) after 20 and 15 days of cultivation respectively, with low dry matter losses (15–20%). A study of the fate of ¹⁴C-lignin during fermentation using these two fungal strains showed that maximal levels of (¹⁴C)-water-soluble compounds are reached before peak levels of ¹⁴CO₂ evolution suggesting that these compounds are intermediates in lignin degradation. A possible relationship between water-soluble lignins and IVDMD improvement is discussed.     

Induction of Plant Pyridoxine (Pyridoxamine) 5′-Phosphate Oxidase Activity by Light

Botrytis cinerea, which was isolated from the surface of stored sunflower seed, produced a novel biologically active natural product when cultured on shredded wheat medium. The metabolite, trivially named cinereain, was a ruby red crystalline product with the molecular formula C₁₈H₂₁N₃O₃ and melting point 201~203°C. The structure was unequivocally established by single crystal X-ray diffraction; UV, IR, NMR (¹H and ¹³C) and mass spectrometry supported the crystallographic data. Cinereain significantly inhibited the growth of etiolated wheat. coleoptiles (p < 0.01) at 10^-3 and 10^-4 m in bioassays. No effects were noted on treated intact greenhousegrown bean and tobacco plants, but there was mild necrosis and chlorosis in corn.     

Effect of Ophiobolus graminis infection on the assimilation and distribution of 14C in wheat

The uptake of ¹⁴C and movement of ¹⁴C-labelled assimilates in wheat plants inoculated with Ophiobolus graminis was examined following exposure of the second youngest leaf to ¹⁴CO₂. Autoradiographs of plants with infected seminal roots showed that assimilates were not translocated past the sites of root infection but accumulated in the undamaged portions of infected root systems, in particular the developing crown roots. There was no evidence that assimilates accumulated in the vicinity of O. graminis lesions. The net assimilation of ¹⁴CO₂ by wheat plants over a 5 h feeding period was not significantly affected by O. graminis infection. However, infection reduced the amount of ¹⁴C lost through respiration. Infection delayed the transfer of labelled assimilates from the fed leaf to the remainder of the plant but increased the proportion translocated to the roots. The latter effect was not apparent when infected plants were continuously irrigated during, and for 20 h following, the feeding period.     

Soil–atmosphere exchange of CH4, CO,N2O and NOx and the effects of land‐use change in the semiarid Mallee system in Southeastern Australia

The semiarid and arid zones cover a quarter of the global land area and support one‐fifth of the world's human population. A significant fraction of the global soil–atmosphere exchange for climatically active gases occurs in semiarid and arid zones yet little is known about these exchanges. A study was made of the soil–atmosphere exchange of CH₄, CO, N₂O and NO_x in the semiarid Mallee system, in north‐western Victoria, Australia, at two sites: one pristine mallee and the other cleared for approximately 65 years for farming (currently wheat). The mean (± standard error) rates of CH₄ exchange were uptakes of ?3.0 ± 0.5 ng(C) m^?2 s^?1 for the Mallee and ?6.0 ± 0.3 ng(C) m^?2 s^?1 for the Wheat. Converting mallee forest to wheat crop increases CH₄ uptake significantly. CH₄ emissions were observed in the Mallee in summer and were hypothesized to arise from termite activity. We find no evidence that in situ growing wheat plants emit CH₄, contrary to a recent report. The average CO emissions of 10.1 ± 1.8 ng(C) m^?2 s^?1 in the Mallee and 12.6 ± 2.0 ng(C) m^?2 s^?1 in the Wheat. The average N₂O emissions were 0.5 ± 0.1 ng(N) m^?2 s^?1 from the pristine Mallee and 1.4 ± 0.3 ng(N) m^?2 s^?1 from the Wheat. The experimental results show that the processes controlling these exchanges are different to those in temperate systems and are poorly understood.     

Screening of white-rot fungi on (14C)lignin-labelled and (14C)whole-labelled wheat straw

Summary 74 Basidiomycetes have been tested for ligninolytic capability on (¹⁴C)lignin-labelled wheat straw. Fifteen strains were selected and rested more accurately for ligninolytic activity and the capacity to degrade wheat straw. The asymptote, inflexion point and degradation rate were determined using a model approach. The fungi exhibited very different responses with respect to lignin biodegradation: high asymptote for Pleurotus ostreatus (77%), low inflexion points for Sporotrichum pulverulentum Nov. (6.1 days) and Pycnoporus spp. (2.7 to 4.7 days) with high and slow degradation rates, respectively (0.91% and 0.45% of ¹⁴CO₂ release/day). Degradation values for (¹⁴C)whole-labelled wheat straw exhibited less variation. Finally, the strains Pleurotus ostreatus, Dichomitus squalens and Bjerkandera adusta showed the highest selectivity of lignin removal.     

Carbon and nitrogen partitioning during the post‐anthesis period is conditioned by N fertilisation and sink strength in three cereals

Further knowledge of the processes conditioning nitrogen use efficiency (NUE) is of great relevance to crop productivity. The aim of this paper was characterise C and N partitioning during grain filling and their implications for NUE. Cereals such as bread wheat (Triticum aestivum L. cv Califa sur), triticale (× Triticosecale Wittmack cv. Imperioso) and tritordeum (× Tritordeum Asch. & Graebn line HT 621) were grown under low (LN, 5 mm NH₄NO₃) and high (HN, 15 mm NH₄NO₃) N conditions. We conducted simultaneous double labelling (¹²CO₂ and ¹⁵NH₄¹⁵NO₃) in order to characterise C and N partitioning during grain filling. Although triticale plants showed the largest total and ear dry matter values in HN conditions, the large investment in shoot and root biomass negatively affected ear NUE. Tritordeum was the only genotype that increased NUE in both N treatments (NUE_total), whereas in wheat, no significant effect was detected. N labelling revealed that N fertilisation during post‐anthesis was more relevant for wheat and tritordeum grain filling than for triticale. The study also revealed that the investments of C and N in flag leaves and shoots, together with the ‘waste’ of photoassimilates in respiration, conditioned the NUE of plants, and especially under LN. These results suggest that C and N use by these plants needs to be improved in order to increase ear C and N sinks, especially under LN. It is also remarkable that even though tritordeum shows the largest increase in NUE, the low yield of this cereal limits its agronomic value.     

Heterotrophic carbon gain by the root hemiparasites, Rhinanthus minor and Euphrasia rostkoviana (Orobanchaceae)

Hemiparasitic plants gain virtually all mineral nutrients and water from their host plant whilst organic carbon is provided, at least in part, by their own photosynthetic activity, although their rates of assimilation are substantially lower than that found in non-parasitic plants. Hence, hemiparasites must gain at least some of their organic carbon heterotrophically from the host plant. Despite this, heterotrophic carbon gain by root hemiparasites has been investigated only for a few genera. We investigated heterotrophic carbon gain by two root hemiparasites, Rhinanthus minor L. and Euphrasia rostkoviana Hayne (Orobanchaceae), using natural abundance stable isotope (δ¹³C) profiles of both parasites attached to C₃ (wheat) and C₄ (maize) hosts coupled to a linear two-source isotope-mixing model to estimate the percentage of carbon in the parasite that was derived from the host. Both R. minor and E. rostkoviana attached to maize hosts were significantly more enriched in ¹³C than those attached to wheat hosts with R. minor becoming more enriched in ¹³C than E. rostkoviana. The natural abundance ¹³C profiles of both parasites were not significantly different from their wheat hosts, but were less enriched in ¹³C than maize hosts. Using a linear two-source isotope-mixing model, we estimated that R. minor and E. rostkoviana adult plants derive c. 50 and 25% of their carbon from their hosts, respectively. In light of these results, we hypothesise that repeatedly observed negative effect of competition for light on hemiparasites acts predominantly in early ontogenetic stages when parasites grow unattached or the abstraction of host nutrients is less effective.     

Carbon balance assessment of a Belgian winter wheat crop (Triticum aestivum L.)

The carbon balance of a winter wheat crop in Lonzée, Belgium, was assessed from measurements carried out at different spatial and temporal scales between November 2004 and August 2005. From eddy covariance measurements, the net ecosystem exchange was found to be ?0.63 kg C m^?2 and resulted from the difference between gross primary productivity (GPP) (?1.58 kg C m^?2) and total ecosystem respiration (TER) (0.95 kg C m^?2). The impact of the u_* threshold value on these fluxes was assessed and found to be very small. GPP assessment was partially validated by comparison with an estimation scaled up from leaf scale assimilation measurements. Soil respiration (SR), extrapolated from chamber measurements, was 0.52 kg C m^?2. Net primary productivity, assessed from crop sampling, was ?0.83 kg C m^?2. By combining these fluxes, the autotrophic and heterotrophic components of respiration were deduced. Autotrophic respiration dominated both TER and SR. The evolution of these fluxes was analysed in relation to wheat development.     

Purification and characterization of a cellulase-free xylanase of a moderate thermophile Bacillus licheniformis A99

Two cellulase-free xylanases were secreted by a thermophile, Bacillus licheniformis A99. Of the two, the predominant one was purified to homogeneity. The enzyme was optimally active at 60 °C, pH 6–7.5, and had a molecular weight of about 45 KDa and isoelectric point of 7.0 ± 0.2. The K _m (for birchwood xylan) and V _max were 3.33 mg/ml and 1.111 mmols mg^–1 protein min^–1 respectively. The half-life of the enzyme was 5 h at 60 °C. All cations except Hg²⁺ and Ag⁺ as well as EDTA were well tolerated and did not adversely affect xylanase activity. However, SDS inhibited the enzyme activity. The release of reducing sugars from unbleached commercial pulp sample on treatment with the enzyme indicated its potential in prebleaching of paper pulp. The enzyme caused saccharification of lignocellulosics such as wheat bran, wheat straw and sawdust. This is the first report on purification and characterization of cellulase-free xylanase from a moderate thermophile Bacillus licheniformis.     

Organic nitrogen content and nitrate and nitrite reductase activities in tritordeum and wheat grown under nitrate or ammonium

Tritordeum is a fertile amphiploid derived from durum wheat (Triticum turgidum L. conv. durum) × a wild barley (Hordeum chilense Roem. et Schultz.). The organic nitrogen content of tritordeum grain (34 mg g^-1 DW) was significantly higher than that of its wheat parent (25 mg g^-1 DW). Leaf and root nitrogen content became higher in tritordeum than in wheat after four weeks of growth, independently of the nitrogen source (either NO₃ ^- or NH₄ ⁺). Under NO₃ ^- nutrition, tritordeum generally exhibited higher levels of nitrate reductase (NR) activity than wheat. Nitrite reductase (NiR) levels were however lower in tritordeum than in its wheat parent. In NH₄ ⁺-grown plants, both NR and NiR activities progressively decreased in the two species, becoming imperceptible after 3 to 5 weeks of growth. Results indicate that, in addition to a higher rate of NO₃ ^- reduction, other physiological factors must be responsible for the greater accumulation of organic nitrogen in tritordeum grain.     

Modelling the effect of soil moisture on germination and emergence of wheat and sugar beet with the minimum number of parameters

Soil moisture and temperature, sowing depth and penetration resistance affect the time and percentage of seedling emergence, which are crucial for the simulation of drought‐limited crop production. The aim of this research was to measure the effect of soil water potential on germination and emergence, shoot and root elongation rates (SER and RER) of two different seed/crop types. Sugar beet and durum wheat seeds were sown into two soils (clay and loam), submitted to five matric potentials (?0.01, ?0.1, ?0.2, ?0.4 and ?0.8 MPa) and incubated at constant temperature (25°C) and humidity. Cumulative count analysis was used to estimate parameters of the distribution of germination or emergence times for each box of beet or wheat seeds and to derive estimates for base potentials (ψ_b), hydrothermal times (H) and numbers of viable units. In a second experiment, NaCl solution was used to mimic the soil matric potentials to estimate potential RER and SER. Germination of sugar beet was slightly more sensitive to matric potential than durum wheat (ψ_b of ?1.13 and ?1.23 MPa, respectively). H_(g) was longer for sugar beet than for durum wheat (67 vs 47 MPa °Cd). For emergence ψ_b was similar for both seed types and soils but hydrothermal times (H_(e)) were 40 MPa °Cd higher for sugar beet than for wheat. Emergence was about 20 MPa °Cd earlier in loam than in clay. SER measured in soils were similar for both crops and for durum wheat it agreed with those determined in NaCl solution. RER and SER fell with decreasing osmotic potential to approximately 20% of their maximum values (1.03 mm h^?1 and 0.57 mm h^?1, respectively). Seedling viability decreased with decreasing matric potential and more in clay than in loam soil and more for sugar beet than durum wheat. Seed and soil aggregate size are discussed with respect to the effects of water diffusion and soil–seed contact on germination and emergence modelling.     

Photosynthetic Acclimation to Elevated CO2 in Relation to Leaf Saccharide Constituents in Wheat and Sunflower

Wheat (T. durum cvs. HD 4502 and B 449, T. aestivum cvs. Kalyansona and Kundan) and sunflower (Helianthus annuus L. cv. Morden) were grown under atmospheric (360±10 cm³ m^–3, AC) and elevated CO₂ (650±50 cm³ m^–3, EC) concentration in open top chambers for entire period of growth and development till maturity. Leaf net photosynthetic rate (P _N) of EC-grown plants of wheat measured at EC was significantly decreased in comparison with AC-plants of wheat measured at EC. Sunflower, however, showed no significant depression in P _N in EC-plants. There was a decrease in ribulose-1,5-bisphosphate carboxylase (RuBPC) activity, its activation state and amount in EC-plants of wheat, whereas no significant decrease was observed in sunflower. The above different acclimation to EC in wheat and sunflower was related with saccharide constituents accumulated in the leaves. Under EC, sunflower accumulated in the leaves more starch, whereas wheat accumulated more sugars.     

Carbon and nitrogen allocation and partitioning in traditional and modern wheat genotypes under pre‐industrial and future CO2 conditions

The results of a simultaneous ¹³C and ¹⁵N labelling experiment with two different durum wheat cultivars, Blanqueta (a traditional wheat) and Sula (modern), are presented. Plants were grown from the seedling stage in three fully controllable plant growth chambers for one growing season and at three different CO₂ levels (i.e. 260, 400 and 700 ppm). Short‐term isotopic labelling (ca. 3 days) was performed at the anthesis stage using ¹³CO₂ supplied with the chamber air and ¹⁵NH₄‐¹⁵NO₃ applied with the nutrient solution, thereby making it possible to track the allocation and partitioning of ¹³C and ¹⁵N in the different plant organs. We found that photosynthesis was up‐regulated at pre‐industrial CO₂ levels, whereas down‐regulation occurred under future CO₂ conditions. ¹³C labelling revealed that at pre‐industrial CO₂ carbon investment by plants was higher in shoots, whereas at future CO₂ levels more C was invested in roots. Furthermore, the modern genotype invested more C in spikes than did the traditional genotype, which in turn invested more in non‐reproductive shoot tissue. ¹⁵N labelling revealed that the modern genotype was better adapted to assimilating N at higher CO₂ levels, whereas the traditional genotype was able to assimilate N more efficiently at lower CO₂ levels.     

Effects of buffer capacity on growth,photosynthesis, and solute accumulation of a glycophyte (wheat) and a halophyte (<Emphasis Type="Italic">Chloris virgata</Emphasis>)

Two species with different resistances to alkaline pH, the glycophylic Triticum aestivum (wheat) and the halophilic Chloris virgata, were chosen as test organisms. The salt-alkaline (SA) mixed stress conditions with different buffer capacities (BC) but with the same salt molarities and pH were established by mixing neutral (NaCl, Na₂SO₄), and alkaline salts (NaHCO₃ and Na₂CO₃) in various proportions. Growth, photosynthetic characteristics, and solute accumulation of the seedlings were monitored to test the validity of BC as a decisive index of alkali-stress (AS) intensity in SA mixed stress. At the same salinities and pHs, the relative growth rate, the content of photosynthetic pigments, and net photosynthetic rates of wheat and C. virgata decreased, while Na⁺ content and Na⁺/K⁺ ratios in shoots increased with increasing BC. Hence BC was a true measure of AS intensity at mixed SA stress and the alkali-resistance mechanism of plants was easy to interpret. BC of soil solution is an important parameter for estimating the alkalization degree of salt-alkalized soil.     

Diurnal Changes in Photosynthesis,Sugars, and Nitrogen of Wheat and Mungbean Grown Under Elevated CO2 Concentration

The diurnal changes in leaf net photosynthetic rate (P _N) and sugar and nitrogen contents in wheat [Triticum aestivum (L.) cv. HD 2285] and mungbean [Vigna radiata (L.) Wilczek cv. PS 16] were analysed under ambient, AC [350±25 µmol mol^–1] and elevated, EC [600±50 µmol mol^–1] CO₂ concentrations. In both mungbean and wheat P _N of AC- and EC-grown plants compared at the same CO₂ concentration showed that P _N was higher under EC. However, increased P _N in EC-plants declined in the afternoon and approached P _N of AC-plants. Depression in P _N, however, was less in mungbean compared with the large depression in wheat. Greater down regulation of P _N in wheat was associated with the accumulation of large amount of sugars and low nitrogen content in wheat leaves. Mungbean leaves accumulated mostly starch under EC and the difference in N content in AC- and EC-plants was relatively less than in wheat.     

Production of mosquitocidal <Emphasis Type="Italic">Bacillus sphaericus</Emphasis> by solid state fermentation using agricultural wastes

In this study, Bacillus sphaericus NRC 69 was grown in culture media, in which 12 agricultural wastes were tested as the main carbon, nitrogen and energy sources under solid state fermentation. Of the 12 tested agricultural by-products, wheat bran was the most efficient substrate for the production of B. sphaericus mosquitocidal toxins against larvae of Culex pipiens (LC₅₀ 1.2 ppm). Mixtures of tested agricultural wastes separately with wheat bran enhanced the produced toxicity several folds and decreased LC₅₀ between 3.7- and 50-fold in comparison with that of agricultural wastes without mixing. The toxicity of B. sphaericus grown in wheat bran/rice hull at 8/2 (g/g) and wheat bran/barley straw at 1/4 (g/g) showed the same toxicity as that in wheat bran medium (LC₅₀ decreased 17- and 16-fold, in comparison with that in rice hull or barely straw media, respectively). In wheat bran medium, the maximum toxicity of the tested organism obtained at 50% moisture content, inoculum size 84 × 10⁶ CFU/g wheat bran and incubation for 6 days at 30°C. Addition of cheese whey permeate at 10% to wheat bran medium enhanced the toxicity of B. sphaericus NRC 69 about 46%.