Genetic differentiation and distribution routes of the bronze featherback Notopterus notopterus (Osteoglossiformes: Notopteridae) in Indochina

Mitochondrial DNA analysis was used to investigate genetic variation in the bronze featherback fish Notopterus notopterus in Indochina. Five hundred and five fish samples collected from 11 localities were separated into three genetically differentiated intraspecific groups. Chao Phraya River samples formed a distinct group. Mekong River samples were clearly separated into two different groups, namely, middle and lower Mekong groups. The lower Mekong group was closely related to Malay Peninsula group, even though the two groups are separated by a tract of ocean. F‐values (0.82–0.95) also confirmed genetic differentiation of the middle and lower Mekong groups. Although the two Mekong groups inhabit the same river basin, molecular clock calculations indicate they separated approximately 1.2 Mya, suggesting (1) evolutionary divergence before invasion of the Mekong River; (2) differences in migration routes to the river; and/or (3) differences in the timings of invasion. The complexities of historical events cannot be ignored in determinations of factors responsible for the exceptional biodiversity in the Mekong basin. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 575–582.     

Soil organic carbon stocks in Laos: spatial variations and controlling factors

Surface soils, which contain the largest pool of terrestrial organic carbon (C), may be able to sequester atmospheric C and thus mitigate climate change. However, this remains controversial, largely due to insufficient data and knowledge gaps in respect of organic C contents and stocks in soils and the main factors of their control. Up to now and despite numerous evaluations of soil organic carbon (SOC) stocks worldwide, the sloping lands of southeast Asia, one of the most biogeochemically active regions of the world, remain uninvestigated. Our main objective was to quantify SOC stocks and to evaluate the impact of various environmental factors. We, therefore, selected Laos with 230 566 km² of mostly forested steep slopes, and where cultivation is still mainly traditional, i.e. a system of shifting cultivation without fertilization or mechanical tillage. Analytical data from 3471 soil profiles demonstrated that the top 1 m of soil depth holds an estimated 4.64 billion tons of SOC, 65% of which is in the first 0.3 m. SOC stocks to 0.3 m exhibit a high coefficient of variation (CV=62%) with values from 1.8 to 771 Mg C ha^?1 and a mean at 129 Mg C ha^?1. Furthermore, these stocks are significantly (at P<0.05 level) affected by land use as shown by principal components analysis and t‐tests with the largest amount being found under forest, less under shifting cultivation and the smallest under continuous cultivation. Moreover, SOC stocks correlated regionally to total annual rainfalls and latitude, and locally at the hill‐slope level to the distance to the stream network and the slope angle. It is hypothesized that this correlation is through actions on mineral weathering, soil clay content, soil fertility and SOC redistributions in landscapes. These relationships between SOC stocks and environmental factors may be of further use in (1) predicting the impact of global changes on future SOC stocks; and (2) identifying optimal strategies for land use planning so as to minimize soil C emissions to the atmosphere while maximizing carbon sequestration in soils.