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The present study describes the occurrence of a unique archaeal ammonia monooxygenase alpha subunit (amoA) gene in nitrifying acid-sulfate soil microcosms at pH 3.5. The soil was collected from an abandoned paddy field in Thailand. Microcosms were incubated in the dark at 30°C for 372 days with the following three treatments: addition of ammonium sulfate solution once a month (I) or once a week (II), and addition of only sterilized water (III). A quantitative PCR analysis revealed an increase in abundance of the archaeal amoA gene in microcosm soils in which nitrate concentrations increased after incubation. A phylogenetic analysis indicated a predominance of the novel gene, and a predominance of a betaproteobacterial amoA gene affiliated with the genus Nitrosospira. A 16S rRNA gene-based PCR assay revealed that crenarchaeotic Group I.1d was predominant among the Crenarchaeota in microcosms. These results suggest the presence of ammonia-oxidizing archaea corresponding to the unique amoA lineage in nitrifying acid-sulfate soil microcosms at pH 3.5.

To estimate the aboveground biomass of tropical secondary forests dominated by pioneer species, allometric equations to relate diameter at breast height with the dry mass of the aboveground organs of several pioneer species were developed. The aboveground biomass of secondary forests was estimated using four methods based on the allometric equations. Biomass estimated with an allometric equation for all species combined was equivalent to that estimated with species-specific allometric equations. However, the estimated biomass based on a general-purpose allometric equation was substantially higher than that using other allometric equations. The allometric equation for all species combined is suitable for estimating the biomass of a secondary forest from the view points of accuracy and labor.

Adaptability to light conditions was examined for seedlings of three species of Dipterocarpaceae, Shorea leprosula, S. ovalis and Dryobalanops lanceolata, possessing different ecological and silvicultural properties. S. leprosula and S. ovalis showed significant morphological adaptations to weak light conditions by changing leaf weight ratio, root weight ratio and leaf areal weight, as compared with D. lanceolata which is the most shade tolerant among the three species. When the shade-adapted leaves of each species were released from shading, they showed depression in photosynthetic activity, though the extent of depression differed with species. Only S. leprosula showed a recovery in photosynthetic rate 18 days after the release from shading. This result indicates that S. leprosula was more adaptable to increase in light intensity than the other two species. S. leprosula could be regarded as one of the adaptable species for reforestation in degraded open land.

A gene for chlorophyll a/b-binding protein (cab) of pine (Pinus thumbergii) was isolated and sequenced. The gene (cab-6) contains an intron at a position equivalent to the type II cab genes of angiosperms. Transcript mapping analyses show that the amount of the mRNA in the dark is about half of that in the light. The cab-6 gene is expressed in dark-grown seedlings at a very high level, differing from angiosperm cab genes which are induced by light. The cab-6 gene typifies the coniferous plant cab genes in light-independent gene expression.

The physiological characteristics of the dominant tree species in the tropical rain forest mainly belonging to dipterocarps as well as the environmental conditions especially for the light in the forest were studied to establish the silvicultural system for the forest regeneration in the tropical South Asia. The flowering patterns of the dipterocarp trees are usually irregular and unpredictable, which make difficult to collect sufficient seeds for raising the seedlings. The field survey revealed the diverged features of the so-called gregarious or simultaneous flowering of various species of this group. Appropriate conditions and methods for the storage of the seeds were established according to the detailed analyses of the morphological and physiological characteristics of the seeds such as the low temperature tolerance and the moisture contents. The intensity and spectra of the light in the forest primarily determine the growth and the morphological development of the seedlings under the canopy. Based on the measurements of the diffused light at the sites in the tropical forest in the varying sunlight, the parameters such as “the steady state of the diffuse light” and “the turning point” were defined, which were useful to evaluate the light conditions in the forest. To improve the survival of the transplanted seedlings, a planting method of “the bare-root seedlings”, the seedlings easy to be handled by removal of all leaves, soil and pots, was developed. Its marked efficiency was proved with various dipterocarps and other tropical trees by the field trial in the practical scale. Tolerance of the various species to the extreme environmental conditions such as fires, acid soils and drought were examined by the experiments and the field survey, which revealed marked adaptability of Shorea roxburghii as a potential species for regeneration of the tropical forests. (Contributed by Satohiko SASAKI, M.J.A.)

The ammonia-producing bacteria B55T, CA73, SA69 and SA72 were isolated from the waterweeds Ludwigia adscendens (B55T) and Eleocharis dulcis (CA73, SA69 and SA72) grown in highly acidic swamps (pH 2–4) in actual acid sulfate soil areas of Vietnam. The isolates were Gram-positive, irregular rod-shaped, non-spore-forming bacteria. On the basis of 16S rRNA gene sequence similarity, strain B55T was shown to belong to the genus Curtobacterium of the class Actinobacteria. Chemotaxonomic data (MK-9 as major isoprenoid quinone, d-ornithine as cell-wall diamino acid, acetyl as the acyl type of peptidoglycan) supported the affiliation of all four strains to this genus. Although their 16S rRNA gene sequence similarity was 99 % to species with validly published names within the genus, they formed a group that was distinct in the phylogenetic tree, and DNA–DNA relatedness values to these established species were less than 10 %. The results of physiological and biochemical tests and major fatty acids (cyclohexyl-C17 : 0, anteiso-C17 : 0 and cyclohexyl-C19 : 0) allowed phenotypic differentiation of these strains from the species of Curtobacterium with validly published names. Therefore, strains B55T, CA73, SA69 and SA72 represent a novel species, for which the name Curtobacterium ammoniigenes sp. nov. is proposed. The type strain is B55T (=NBRC 101786T=VTCC D6-11T=JCM 14609T).