Nor Aini Ab Shukor

pH dominates variation in tropical soil archaeal diversity and community structure

Little is known of the factors influencing soil archaeal community diversity and composition in the tropics. We sampled soils across a range of forest and nonforest environments in the equatorial tropics of Malaysia, covering a wide range of pH values. DNA was PCR-amplified for the V1-V3 region of the 16S rRNA gene, and 454-pyrosequenced. Soil pH was the best predictor of diversity and community composition of Archaea, being a stronger predictor than land use. Archaeal OTU richness was highest in the most acidic soils. Overall archaeal abundance in tropical soils (determined by qPCR) also decreased at higher pH. This contrasts with the opposite trend previously found in temperate soils. Thaumarcheota group 1.1b was more abundant in alkaline soils, whereas group 1.1c was only detected in acidic soils. These results parallel those found in previous studies in cooler climates, emphasizing niche conservatism among broad archaeal groups. Among the most abundant operational taxonomic units (OTUs), there was clear evidence of niche partitioning by pH. No individual OTU occurred across the entire range of pH values. Overall, the results of this study show that pH plays a major role in structuring tropical soil archaeal communities.

Demographic history and interspecific hybridization of four Shorea species (Dipterocarpaceae) from Peninsular Malaysia inferred from nucleotide polymorphism in nuclear gene regions

Shorea acuminata Dyer, Shorea curtisii Dyer ex King, Shorea leprosula Miq., and Shorea parvifolia Dyer are dominant tree species in the tropical rainforest of Peninsular Malaysia, which experienced several climatic changes during Pleistocene. To investigate the current population structure and demographic history of these species, we analyzed levels and patterns of nucleotide polymorphism of the nuclear gene region PgiC. We also used sequence data of the GapC gene region obtained in our previous study. Negative Tajimas D values observed in both investigated gene regions for S. curti- sii, S. leprosula, and S. parvifolia implied that all three species have experienced population expansion events. Little to moderate levels of population differentiation in S. acuminata and S. curtisii suggested recent divergence of the investigated populations after postglacial colonization of the Peninsular Malaysia. In addition, some haplotypes were similar or identi- cal to haplotypes of the other species. The existence of such haplotypes could be partially explained by interspecific hy- bridization. Indeed, we found some putative hybrid individuals. Interspecific hybridization among closely related species might have contributed to the polymorphism of the investigated species.

Overexpression of Arabidopsis thaliana gibberellic acid 20 oxidase (AtGA20ox) gene enhance the vegetative growth and fiber quality in kenaf (Hibiscus cannabinus L.) plants.

Kenaf (Hibiscus cannabinus L.; Family: Malvaceae), is multipurpose crop, one of the potential alternatives of natural fiber for biocomposite materials. Longer fiber and higher cellulose contents are required for good quality biocomposite materials. However, average length of kenaf fiber (2.6 mm in bast and 1.28 mm in whole plant) is below the critical length (4 mm) for biocomposite production. Present study describes whether fiber length and cellulose content of kenaf plants could be enhanced by increasing GA biosynthesis in plants by overexpressing Arabidopsis thaliana Gibberellic Acid 20 oxidase (AtGA20ox) gene. AtGA20ox gene with intron was overexpressed in kenaf plants under the control of double CaMV 35S promoter, followed by in planta transformation into V36 and G4 varieties of kenaf. The lines with higher levels of bioactive GA (0.3–1.52 ng g−1 fresh weight) were further characterized for their morphological and biochemical traits including vegetative and reproductive growth, fiber dimension and chemical composition. Positive impact of increased gibberellins on biochemical composition, fiber dimension and their derivative values were demonstrated in some lines of transgenic kenaf including increased cellulose content (91%), fiber length and quality but it still requires further study to confirm the critical level of this particular bioactive GA in transgenic plants.

Isozyme Variation Between Two Closely Related Species Crang On Crangon (L.) and Crangonallmanni Kinahan (Decapoda, Caridea)

Crangon crangon (L.) and C. allmanni Kinahan were screened at 11 enzyme loci for electrophoretically detectable variation. The mean observed heterozygosity was 0.1346 + 0.06295 in C. crangon and 0.0567 + 0.0352 in C. allmanni. The possible causes of these rather low levels of genetic variation are considered in relation to the physical factors and feeding behaviour. The results also suggest that C. crangon and C. allmanni are two separate species that differ genetically although morphologically similar.

Recovery of Acacia auriculiformis from fire damage

An assessment of damage and recovery of Acacia auriculiformis in a provenance trial at the Universiti Pertanian Malaysia was undertaken following an accidental surface fire. The results showed significant differences (P < 0.05) between provenances in their ability to recover vegetatively after being affected by different levels of foliage scorch, with the 1hr. S. Balamuk (16103) provenance being the best. The ability to resprout is possibly a result of the insulating properties of the bark, which protects the dormant buds present underneath it. The results provide a basis of selection of suitable provenances for future breeding for fire resistance and for fire management and silvicultural treatments of this species.

Comparative water relation of three varieties of Hibiscus cannabinus L. (Kenaf)

Kenaf ( Hibiscus cannabinus L.) is an industrial fiber crop that is being grown increasingly in tropical and subtropical areas. Choosing the proper variety with the most growth rate and biomass content is a critical point for successful commercial cultivation of kenaf. Since growth and biomass production of plants are strictly related to their physiology attribute, it is therefore, necessary to provide knowledge on the physiologic characteristics of kenaf varieties. This study was designated to elucidate water relation characteristics of three kenaf varieties; Guatemala 4 (G4), kohn-kaen 60 (KK60) and V36. 20 plants of each varieties were cultivated in completely randomized design under controled conditions. Throughout a period of 120 days, parameters of gas exchange characteristics were measured within four regular intervals of 30 days. The results of this study showed that varieties significantly differ in water use efficiency so that the greatest value belonged to variety KK60. It was concluded that KK60 could be considered as preferable choice of kenaf variety for cultivation.

Effects of Albizia saman (Jacq. Mull) leaf mulch on vegetative growth of maize (Zea mays L.) and soil chemical properties through biomass transfer

The study presents the effects of Albizia saman (Jacq. Mull) leaves in a biomass transfer as a source of organic fertilizer on the soil chemical properties and vegetative growth of maize (Zea mays) compared with NPK (15-15-15) in greenhouse condition. Albizia saman leaves and NPK (15-15-15) were applied at the rate of 2.5, 5.0 and 7.5 t/ha or 60, 90 and 120 kg/ha respectively, separately or in combination. The findings revealed that application of 2.5 t/ha A. saman leaves produced the maximum values for mean leaf number, leaf area and stem height (7.77, 212.24 cm2 and 49.67 cm, respectively) among the leaf much treatments but were not significantly different from those obtained by applying 90 kg/ha NPK fertilizer (7.86, 225.55 cm2 and 48.78 cm, respectively). However, the maximum number of leaf (8.4), leaf area (240.5 cm2), plant height (54.64 cm) and biomass (16.17 g) were obtained from the combination of 2.5 t/ha leaves with 90 kg/ha NPK. There was significant improvement in the soil chemical status with the application of 2.5 or 5.0 t/ha A. saman leaves whereas the application of 5.0 t/ha A. saman leaves experienced the highest value for organic carbon (3.56%), total nitrogen (0.23%) and potassium (0.16 mg/kg) and 2.5 t/ha leaves gave the highest value for available phosphorus (22.30 mg/kg). It can, therefore, be inferred that the application of 2.5 t/ha A. saman leaves as source of organic fertilizer will give a better growth of maize and the combination of this quantity with 90 kg/ha of NPK would give better results in crop yield and maintenance of soil fertility.