Soil nutrient concentrations and tree dynamics were examined in two Bornean tropical forests on contrasting geological substrates, one on volcanic and the other on sedimentary rocks. Concentrations of P extracted by the Hadley fractionation method and inorganic N of topsoils were much greater in the volcanic site than in the sedimentary site. Dipterocarps showed greater relative growth rates in the volcanic site than in the sedimentary site at the smallest size class (10cm ≤ diameter at breast height<20cm), but not at larger size classes. Dipterocarps in the two sites demonstrated the same values of crown position index (a surrogate of light conditions), implying that the greater tree growth in the volcanic site was associated with the greater soil nutrient availability, but not with light availability. On the other hand, relative growth rates of non-dipterocarps did not differ between the sites at all size classes despite the considerable differences in the soil nutrient concentrations, suggesting that factors other than N and P availabilities limit the growth of these trees. Contrary to growth rate, annual mortality rate was greater in the volcanic site at all size classes for all phylogenetic groups. Our results suggest that the volcanic site is characterized as high soil nutrient availability and a greater tree turnover, and that tree size is an important factor that differentiates tree growth between the two tropical forests with contrasting nutrient availabilities.
Medicinal plants are still used for healthcare and as medicaments especially in developing countries and some rural areas. The potential and high expectation of medicinal plants for local healthcare and livelihood and as biodiversity management is prevalent globally. This study assesses the extent to which medicinal plants bring benefits in biodiversity management and improve livelihood and healthcare in indigenous villages near a small city, a second tier city in the central Peruvian Amazon, taking into consideration the course of urbanization. A total of 81 people living in two villages were interviewed. The results show that unlike areas surrounding large cities in the Amazon, areas around the second tier city do not have the conditions to commercialize medicinal plants to support livelihood. Therefore, the local utilization of medicinal plants does not deteriorate the forest resources, thus medicinal plants would not be expected to be a driver for biodiversity management. Although medicinal plants still support healthcare of the locals, the reliance on modern medicine is aparent. The distance to the urbanized city and modern facilities influences the use of medicinal plants. While close proximity facilitates the use of modern medicine, it is found that mal-accessibility to modern medicine does not increase the variety of medicinal plant use.
Oil-degrading filamentous fungi (ODF) were enumerated and isolated from two islands, Iriomote, Japan, and Con Dao, Vietnam. Iriomote has a subtropical and Con Dao a tropical climate. The counts of total fungi and ODF in sediment samples from supratidal and intertidal zones on Iriomote were statistically higher than on Con Dao. Water samples from seawater, however, gave a reverse result. In total, 23 ODF including 11 isolates in 5 genera from Iriomote and 12 isolates in 4 genera from Con Dao were isolated. On Iriomote, the isolates which showed the highest potential of oil degradation were 2 Penicillium isolates and one Trichoderma, however they did not grow at 37°C nor survived at 37°C. One Candida isolate has higher potential of oil-degradation, and grew and survived at temperature 42°C. On the contrary, on Con Dao, 2 Aspergillus, one Penicillium and one Trichodermaisolates had potential of oil-degradation, and grew and survived at temperature 42°C. This result suggests that comparing with subtropical Iriomote, the tropical Con Dao maintains more oil-degrading fungi which have higher-temperature resistance.
Many studies have reported the presence of soil respiration hot spots, which are areas of extremely high soil respiration, but little is known about their causes. Because previous studies implied that they were caused by macrofauna, we conducted a field survey in a Malaysian lowland rainforest to examine whether increased soil respiration was induced by the activities of macrofauna such as termites, ants and earthworms. Soil respiration was measured in a grid system of 10m intervals in a 1ha plot. We measured soil respiration again three or four days after the first measurement to examine the spatiotemporal change in hot spots. After the second measurement, we excavated soil to a depth of 20cm at the five points showing the highest soil respiration rates (hot spots) and their neighboring points as controls and visually searched for macrofauna. The average soil respiration for two measurements did not differ significantly (8.21 and 7.93μmol CO2 m－2 s－1, respectively). Four hot spots were revealed in each of the two measurements, but only one appeared in both measurements. Several ants (100‐500 individuals, Lophomyrmex sp.) were observed in soil under soil respiration chamber areas at one hot spot and one control point, respectively. This suggests that the hot spots in the study site were not located near active nests or intensively active areas of macrofauna, and it is possible that the hot spots may represent the points of mass CO2flux transport events.
Since microbial biomass is a key factor controlling nutrient dynamics in the soil through mineralization of soil organic nutrients or microbial turnover, investigating the seasonal changes of microbial activities and biomass is essential for better understanding the nutrient dynamics in tree plantation. We investigated the seasonal changes in soil respiration, microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) in five tropical tree plantation stands. Although CO2 emissions and MBN contents were high in hot-rainy season and low in cool-dry season, MBC contents in cool-dry season kept in the same level as rainy season. We assumed that the different response of MBC and MBN to cool-dry condition was because of the changes in microbial fauna or individual adaptation for drought. The influence of the microbial dynamics observed in the present study on soil nutrient dynamics needs to be studied in the future.
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