Satohiko Sasaki

Effects of saline and osmotic stress on proline and sugar accumulation in Populus euphratica in vitro

The use of in vitro shoot cultures to evaluate osmotic and salt tolerance and the effects of salt and mannitol in the medium on proline and sugar accumulation were investigated in two poplar species, P. euphratica and P. alba cv. Pyramidalis × P. tomentosa. Shoot length, leaf number, whole plant dry weight, and the accumulation of proline and total soluble sugars in leaves were quantified after 2 weeks. All P.euphratica plantlets survived at all levels of mannitol and NaCl, while the mortality of P. alba cv. Pyramidalis × P. tomentosa increased both at the mannitol and the NaCl treatments. A significant increase in proline accumulation was observed in both young and mature P. euphratica leaves at 200 mM mannitol and above, and at 150 mM NaCl and above. The total soluble sugar content increased in young P. euphratica leaves at 250 mM NaCl; however, it decreased in the mature leaves. Similar increases of the total soluble sugar content were not seen in P. alba cv. Pyramidalis × P. tomentosa plants in response to either mannitol or NaCl treatment. Our results suggest that accumulated proline and sugars promote osmotic and salt tolerance. The effects of accumulated proline and total soluble sugars on leaves are discussed in relation to growth and osmotic adjustment.

Impacts of secondary seed dispersal and herbivory on seedling survival in Aesculus turbinata

. Aesculus turbinata is a tree species with large seeds (6.2 g mean dry weight). We studied the demography of its seeds and seedlings in a temperate deciduous forest in northern Japan to elucidate the ecological significance of large seeds with special reference to herbivory and secondary dispersal. Both seed and seedling stages suffered greatly from herbivores. Seedling herbivory was important judged from experiments with shoot clipping and hypogeal cotyledon removal. However, some seedlings survived through re-sprouting after herbivory. Survival rate and percentage resprouting seedlings were lower than those with remaining cotyledons, though seedling size was not affected. This suggests that stored resources in hypogeal cotyledons are working as a kind of ‘risk hedge’ against severe aboveground shoot clipping experienced by A. turbinata. The spatial distribution of seedlings was expanded via seed scatter-hoarding by rodents. Seedling survival rate was higher within canopy gaps than under closed canopy, indicating that canopy gaps are safe sites for establishment, and was negatively correlated with seedling density. Therefore, secondary seed dispersal in this species seems to be effective in ‘finding’ safe sites and in ‘escaping’ density-dependent mortality. The large seeds and seedlings of A. turbinata are attractive to herbivores, but the high resistance of seedlings to herbivory due to large reserves and the effective secondary dispersal appear to mitigate these disadvantages.

Aluminum distribution and reactive oxygen species accumulation in root tips of two Melaleuca trees differing in aluminum resistance

To elucidate the mechanism of the high aluminum (Al) resistance of a Myrtaceae tree, Melaleuca cajuputi Powell, we investigated the responses of root tips to Al and compared them with those of an Al-sensitive species, M. bracteata F. Muell. Roots of seedlings of both species were treated with a calcium solution (pH 4.0) containing 0 or 1 mM AlCl3. After 3 h of Al treatment, inhibition of root elongation and deposition of callose and lignin in root tips, typical signs of Al injury, were induced in M. bracteata but not in M. cajuputi, yet Al accumulation in root tips was similar in both species. These results indicate that internal Al tolerance mechanisms, not Al exclusion mechanisms, are responsible for the Al resistance of M. cajuputi. After 3 h of Al treatment, amount of Al tightly bound to root tips, Al remaining after washing with a desorbing solution, was less in M. cajuputi than in M. bracteata. In M. bracteata, 6 h of Al treatment triggered the accumulation of hydrogen peroxide (H2O2) in root tips despite the upregulation of antioxidant mechanisms, activity of peroxidase and concentration of reduced glutathione. In M. cajuputi, 6 h of Al treatment did not affect the concentration of H2O2, but decreased activity of peroxidase, and increased concentration of reduced glutathione in root tips. These results suggest that the less Al tightly bound to root tips is involved in the suppressing the H2O2 accumulation and the internal Al tolerance in M. cajuputi, and that the H2O2 accumulation or changes in cellular environment that bring about H2O2 accumulation despite the upregulation of antioxidant mechanisms results in Al-induced inhibition of root elongation in M. bracteata.

Growth Response of Melaleuca cajuputi to Flooding in a Tropical Peat Swamp

We investigated the growth response ofMelaleuca cajuputi Powell to flooding at 3 sites in a tropical swamp in southern Thailand. The relative growth rate (RGR) in height tended to be higher where the water level was higher. The maximumRGR in height was achieved during the flood period at the 2 sites where water levels were higher than at the other site. The height growth ofM. cajuputi was not reduced by flooding, but enhanced. No decline in growth due to post-anoxic injury was observed after flooding.Melaleuca cajuputi may have mechanisms to tolerate rhizospheric oxygen deficiency and to avoid post-anoxic injury.

Characteristics of newly isolated ammonia-oxidizing bacteria from acid sulfate soil and the rhizoplane of leucaena grown in that soil

Abstract We isolated four new ammonia-oxidizing bacterial strains from leucaena (Leucaena leucocephala) grown in fields of an acid sulfate soil (ASS) in Thailand; 17SS from the surface soil and 17RS from the rhizoplane of a non-limed plot; 9SS from the surface soil and 9RS from the rhizoplane in a limed plot. The cells of all strains had the typical lobate shape of the genus Nitrosospira (“Nitrosolobus”). The percentage similarity of the 16S rRNA genes of these strains to that of Nitrosospira (“Nitrosolobus”) multiformis ATCC25196T (ATCC25196T) was 99.52% (strains 17SS, 17RS and 9SS) and 99.66% (strain 9RS). These newly isolated bacteria were all identified as Nitrosospira sp. Each strain, especially 17SS isolated from ASS, had higher urease activity than that of ATCC25196T. The o-acetylserine(thiol)lyase activity of 17SS was the highest of all the isolates. At pH 6.0, every isolate and ATCC25196T were able to utilize urea as the sole nitrogen source, in particular, strain 17SS grew best. The isolates from ASS showed higher urea utility than the isolates from the rhizoplane. Strain 17SS tolerated copper at levels up to 6.3 mmol L−1, but ATCC25196 T was inhibited at that concentration.

Physiological characteristics of tropical rain forest tree species: a basis for the development of silvicultural technology.

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.

Planting Techniques and Growth of Dipterocarps in an Abandoned Secondary Forest in East Kalimantan, Indonesia

A large forest fire occurred in East Kalimantan, Indonesia, from 1982 to 1983, and about 3.1 million ha of forest were lost. Degradation of the damaged forest was further accelerated by shifting cultivation and illegal felling. Various efforts have been made to find an effective and realistic remedy for the degradation (Adjjers et al. 1995; Palmiotto 1993; Nussbaum et al.l995; Ang and Maruyama 1995). One solution is to reforest the degraded forest, which has become an urgent matter in this area. Therefore, silvicultural techniques for reforestation and sustainable forest utilization must be developed. The 3,000 ha Sebulu Experimental Forest, located in Sebulu, East Kalimantan, was granted by the Indonesian Ministry of Forestry in 1991, with the aim of developing reforestation techniques and establishing a sustainable management system for the forest. We planted approximately 500,000 seedlings, mainly dipterocarps, on 300 ha of this forest from 1991 to 1997, in order to study and develop the most efficient and cost-effective planting technique. However, in February and March of 1998, the last big forest fire burned 80% of the plantation. In this report the results of various planting methods are described with consideration given to cost savings.

Forestry education and research in Japan

Recent trends in the world scientific circles including their influence to the environment and society were analyzed. In Japan, significant changes in forestry education and research occurred to adapt with these developments. For instance, the concept of “forestry” was changed to “forest science”, utilization of domestic wood becomes a trend, biomass and bioprocess are being promoted, effective absorption sources for carbon dioxide as remedy for global warming are being identified, and forest therapy is recognized. In addition, organization of national forestry universities and departments changed into a broader context and field science was broadly accepted. These changes in forestry education and research in Japan seeks to improve society and forest to suit the world progress.

Studies on an Evaluation Method of the Plant Activity

「樹幹表面温度と気温との較差により求められる活力度値」を従来の活力度と区分するため「活性度」とし, 新しい活力指標としての可能性を検討した。樹木の幹の表面温度は気温と較差が生じ, その程度は樹液流量と対応していることをケヤキの切断幹中を異なる流速で水を人工的に流す実験により確認した。さらに, 植栽現場において, 樹幹表面温度と樹木への外部からの熱源である気温との較差, 科学技術庁による4ランク評価法で定義される活力度, 成育活動結果としての直径成長量について検討を行なったところ, 幹気温較差 (樹幹表面温度-気温) は, 活力度や直径成長量との関連が認められた。