Soil‐microbial response to sugarcane filter cake and biogenic waste compost

An incubation experiment was carried out to examine the N‐immobilizing effect of sugarcane filter cake (C : N = 12.4) and to prove whether mixing it with compost (C : N = 10.5) has any synergistic effects on C and N mineralization after incorporation into the soil. Approximately 19% of the compost‐C added and 37% of the filter cake–C were evolved as CO₂, assuming that the amendments had no effects on the decomposition of soil organic C. However, only 28% of the added filter cake was lost according to the total‐C and δ¹³C values. Filter cake and compost contained initially significant concentrations of inorganic N, which was nearly completely immobilized between day 7 and 14 of the incubation in most cases. After day 14, N remineralization occurred at an average rate of 0.73 µg N (g soil)^–1 d^–1 in most amendment treatments, paralleling the N mineralization rate of the nonamended control without significant difference. No significant net N mineralization from the amendment N occurred in any of the amendment treatments in comparison to the control. The addition of compost and filter cake resulted in a linear increase in microbial biomass C with increasing amounts of C added. This increase was not affected by differences in substrate quality, especially the three times larger content of K₂SO₄‐extractable organic C in the sugarcane filter cake. In most amendment treatments, microbial biomass C and biomass N increased until the end of the incubation. No synergistic effects could be observed in the mixture treatments of compost and sugarcane filter cake.     

Genetic analysis of post-weaning growth traits of Thalli sheep under tropical conditions

Present investigation was carried out to study the influence of genetic and non-genetic factors affecting post-weaning performance traits in Thalli sheep. Data on post-weaning growth of Thalli sheep maintained at Livestock Experiment Station, Rakh Ghulaman, District Bhakkar-Punjab, Pakistan during 1977–2003 were subjected to genetic analysis. The average values for weight at 180 and 270 days of age, yearling weight and post-weaning average daily gain were 22.37?±?4.21, 25.96?±?4.90 and 28.93?±?5.20 kg and 28?±?0.01 g/day, respectively. Weight at 180, 270 and 365 days of age and post-weaning average daily gain were significantly affected by year of birth, sex, type of birth and weaning weight (covariable) whereas season of birth was a significant source of variation for 180 and 270 days of age. The heritability estimates for 180 and 270 days, yearling weight and post-weaning average daily gain were 0.07?±?0.02, 0.08?±?0.02, 0.07?±?0.02 and 0.07?±?0.02, respectively.     

Chitinolytic <Emphasis Type="Italic">Streptomyces griseorubens</Emphasis> E44G enhances the biocontrol efficacy against <Emphasis Type="Italic">Fusarium</Emphasis> wilt disease of tomato

Streptomyces griseorubens E44G is a chitinolytic bacterium isolated from cultivated soil in Saudi Arabia (a hot, arid climatic region). In vitro, antifungal potential of S. griseorubens E44G was assessed against the phytopathogenic fungus, Fusarium oxysporum f. sp. lycopersici (the causative agent of the Fusarium wilt disease of tomato). An inhibition zone of 24 mm was recorded. The chitinolytic activity of S. griseorubens E44G was proved when the colloidal chitin agar plate method was used. A thermostable chitinase enzyme of 45 kDa molecular weight was purified using gel filtration chromatography. The optimum activity was obtained at 60 °C and pH 5.5. The purified enzyme has shown a very pronounced activity against the phytopathogenic fungus, F. oxysporum. The molecular characterization of the chitinase gene indicated that it consists of 1218 bp encoding 407 amino acids. The phylogentic analysis based on the nucleotide DNA sequence and the deduced amino acids sequence showed high similarity percentages with other chitinases isolated from different Streptomyces species. In the field evaluation, application of both S. griseorubens E44G treatments significantly increased all tested growth and yield parameters and decreased the disease severity compared with the infected-untreated tomato plants suggesting potential as a biocontrol agent.     

2-Keto-4-methylthiobutyric acid-dependent biosynthesis of ethylene in soil

2-Keto-4-methylthiobutyric acid (KMBA) has been identified as an intermediate in methionine-derived ethylene (C₂H₄) biosynthesis by microbial cultures. This study was designed to assess the effectiveness of KMBA as an C₂H₄ precursor in soil. Gas chromatographic analysis indicated that amendment with KMBA (up to 10 mM) stimulated the biosynthesis of C₂H₄ in two Pakistani soils. Results also revealed that substrate- (KMBA)-dependent C₂H₄ production was inhibited when the soils were amended either with glucose (as a C source), NH₄NO₃ (N source) or antibiotics. The KMBA-derived C₂H₄ biosynthesis in both soils was maximum when the soil suspension was amended with 10 mM substrate and incubated at pH 7.5 for a period of 120 h at 35°C with shaking. Comparison of soils revealed that C₂H₄ production was relatively greater in a silty clay loam S₁ (containing 1.15% organic C) soil compared to a loamy S₂ (containing 0.54% organic C) soil. KMBA was found to be an equally effective substrate of C₂H₄ when compared with another intermediate, 1-aminocyclopropane-1-carboxylic acid (ACC), whereas, f-ketglutaric acid failed to serve as an C₂H₄ substrate in soil. As far as we know, this is the first study reporting KMBA-dependent C₂H₄ production in soil.     

Substrate-dependent biosynthesis of ethylene by rhizosphere soil fungi and its influence on etiolated pea seedlings

Several fungi were isolated from rhizosphere soils of various crops through enrichment on l-methionine (l-MET) as a sole C and N source. These fungi were examined for their C₂H₄ production potential in vitro. GC-FID analysis indicated that 78%, 83%, 89% and 72% of fungi isolated from rhizosphere soil of wheat, maize, potato and tomato, respectively, produced C₂H₄ from substrate l-MET. Eight of the most efficient C₂H₄-producing fungal isolates (two from each crop) were further tested for their ability to produce C₂H₄ from 2-keto-4-methylthiobutyric acid (KMBA) and α-ketoglutaric acid (α-KGA). Interestingly, all eight fungi produced C₂H₄ from KMBA, but none used α-KGA as C₂H₄ precursor. This result implies that the MET→KMBA→C₂H₄ pathway was most likely operating in these fungi. The most efficient C₂H₄ producer fungus (isolated from maize rhizosphere soil) was identified as Aspergillus terreus; this isolate was further studied to determine the optimal conditions for C₂H₄ production from l-MET. It was observed that a substrate (l-MET) concentration of 10 mmol l⁻¹, a glucose (C-source) concentration of 6.0 g L⁻¹, no nitrogen, a pH of 6.0, an incubation temperature of 30 °C and an incubation time of 72 h were optimal conditions for l-MET-derived C₂H₄ biosynthesis by Aspergillus terreus. In addition, C₂H₄ released from precursor (l-MET) by Aspergillus terreus significantly affected the seedling length and stem diameter of etiolated pea seedlings in both sterilized and non-sterilized soils compared to a control. C₂H₄-producing microflora may be ubiquitous in soil, and the availability of a substrate like l-MET could enhance C₂H₄ synthesis in the rhizosphere of a plant, in turn evoking a physiological response. As far as we know, this study represents the first comprehensive screening of rhizosphere fungi for their ability to produce C₂H₄ from l-MET and KMBA.     

Sources of Heavy Metals and Their Long-term Effects on Microbial C, N and P Relationships in Soil

The effects of heavy metals (Zn, Pb, and Cu) on microbial biomass C, N, and P were assessed in soils contaminated over a wide range by sewage sludge, exhaust dust deposition of a lead factory and river sediments of mining residues. Microbial biomass C, N, and P did not show any clear heavy metal effect related to soil dry weight. Also the ratios of microbial biomass C/N and biomass C/P remained unaffected by heavy metals. The ratios of microbial biomass C/soil organic C, biomass N/total N, and biomass P/total P were all negatively affected by increasing concentrations of Zn, Pb, and Cu as detected by a source-specific analysis of covariance using the different heavy metal fractions as covariate. Negative effects of Zn on the ratios microbial biomass C/soil organic C and biomass N/total N increased with increasing metal solubility in the order: (X-ray fluorescence analysis) XFA-detectable <HNO₃ <EDTA ?NH₄NO₃-extractable Zn. The Zn effects on the microbial biomass N/total N were always smaller than those on the microbial biomass C/soil organic C ratio. The same was true for all effects of the Pb and Cu fractions on these two ratios. For this reason, the deposition of highly soluble Zn and Pb by exhaust dust has the most negative effects, although sediments contained the maximum total burden of Zn and Pb. All fractions of Zn, Pb, and Cu had similar negative effects on the microbial biomass P/total P ratio, although the NH₄NO₃-extractable fraction again showed the most pronounced effects.     

Grassland plants affect dissolved organic carbon and nitrogen dynamics in soil

Dissolved organic carbon (DOC) and nitrogen (DON) are central in many nutrient cycles within soil and they play an important role in many pedogenic processes. Plants provide a primary input of DOC and DON into soil via root turnover and exudation. Under controlled conditions we investigated the influence of 11 grass species alongside an unplanted control on the amount and nature of DOC and DON in soil. Our results showed that while the presence of plants significantly increases the size of a number of dissolved nutrient pools in comparison to the unplanted soil (e.g. DOC, total phenolics in solution) it has little affect on other pools (e.g. free amino acids). Grass species, however, had little effect on the composition of the DOC, DON or inorganic N pools. While the concentration of free amino acids was the same in the planted and unplanted soil, the flux through this pool was significantly faster in the presence of plants. The presence of plants also affected the biodegradability of the DOC pool. We conclude that while the presence of plants significantly affects the quantity and cycling of DOC and DON in soil, comparatively, individual grass species exerts less influence.     

Response of Sunflower to Sulfur Rate and Time of Application under Two Tillage Systems in a Silty Clay Soil of Dera Ismail Khan Pakistan

ABSTRACT

Sulfur (S) availability is a characteristic of conservation tillage. We studied the effects of S on sunflower yield and fatty acid profile under conventional and conservation tillage in silty clay soil of D.I. Khan, Pakistan. Conventional tillage consisted of disk plowing followed by tiller and rotavator, while conservation tillage comprises tiller and disc harrowing. Treatments comprise six sulfur levels (S₁ = 0, S₂ = 20 kg S ha^?1 at sowing, S₃ = 10 kg S ha^?1 at sowing +10 kg S ha^?1 25 days after sowing (DAS), S₄ = 40 kg S ha^?1 at sowing, S₅ = 20 kg S ha^?1 at sowing + 20 kg S ha^?1 25 DAS, and S₆ = 20 kg S ha^?1 at sowing + 10 kg S ha^?1 25 DAS + 10 kg S ha^?1 50 DAS) replicated thrice. After 2 years of experimentation, soil samples were collected (from 0 to 0.30 m depth) for organic matter (OM), total soil N (TSN), and available sulfur analysis. Conservation tillage significantly increased OM, TSN, and S contents in 0–0.30 m soil compared to conventional tillage. Likewise, sunflower plants showed higher achene yield, better fatty acid profile, and net economic returns in conservation tillage than in conventional tillage. Application of 20 kg S ha^?1 at sowing and 10 kg S ha^?1 at each 25 and 50 DAS recorded significantly higher achene yield, higher oil, and linoleic acid contents; however, oleic and oleic/linoleic ratio did not increase with higher S rates. Conservation tillage was effective in increasing OM, TSN, and available S besides increasing yield and economics in silty clay soil.     

Seasonal morphology and immunoreactivity of cytokeratin and atrial natriuretic peptide in dromedary camel poll glands

Poll glands are characteristic feature of dromedary camels; although they yield a yellowish offensive secretion, especially during rutting (breeding) season, their function is not yet exactly specified. The present study shows the seasonal morphology and immunoreactivity of cytokeratin (CK) and atrial natriuretic peptide (ANP) in the camel poll gland; the result could clearly specify the role of the gland in camel reproduction. Poll glands are compound tubulo-alveolar in structure. During rutting season, the secretory units showed wide lumina and simple squamous epithelium surrounded by myoepithelial cells; the lumina became narrower and the epithelium changed to simple cuboidal during non-rutting season. Many glandular lobules showed abundant interlobular connective tissue with fewer and smaller secretory units during non-rutting season compared to rutting season. Positive CK and ANP immunoreactivity was detected in the cytoplasm of epithelial cells of secretory units and ducts together with the myoepithelial cells and blood vessels. Although CK immunoreactivity was more intense during rutting season in comparison to non-rutting season, there was no seasonal variation in ANP immunoreactivity. During both seasons, while the glandular capsule, connective tissue septa, interstitium showed negative CK immunoreactions, they reacted moderately to ANP. In conclusion, the poll gland undergoes annual structural and functional changes which are suggested to correlate with the male seasonal sexual behaviour. Further, the biological role of CK and ANP proteins together with their immunohistochemical expression in the camel poll gland suggests a stimulatory effect in the glandular secretory cells, and hence, they might modify camel sexual activity.