One new genus and one new species are described from Halong Bay, Vietnam: Asymmelaimus vietnamicus gen. n., sp. n. and Dorylaimopsis halongensis sp. n. Asymmelaimus vietnamicus gen. n., sp. n. is characterized by an asymmetrical head with the anterior part of the buccal cavity leaning to the dorsal side and a narrow posterior part with weakly cuticularized walls and one dorsal and two ventrosublateral small teeth situated at the base of the anterior part, and a cuticular ornamentation consisting of one or two longitudinal rows of dots. Dorylaimopsis halongensis sp. it. is characterized by the head set off from the body by constriction, massive spicules with a 'velum' and a long tail (11.3 to 13.6 anal body diameters).
Agricultural by-products such as rice husks are very popular in Vietnam, which are often burned in the fields, causing an increase in dust smoke and greenhouse gas (GHG) emissions.To study the effects of different irrigation methods, quality of irrigation water and additive biochar from rice husk (BFRH) on leaching nitrate from paddy fields into shallow groundwater and methane (CH 4 ) emissions, we investigated a two-season experiment (2021-2023) under two irrigation methods: water-saving irrigation and flood irrigation with 120 kg N/ha.The results illustrated that seasonal CH 4 emissions and leaching nitrate were affected by irrigation practices and significantly correlated with the quality of irrigation and the amount of BFRH added.To compare of control, the flood irrigation water increased the leaching of GHG and NO 3 -into shallow groundwater from 27.3-32.4% and 16.4-31.25%,respectively.Meanwhile, the saving water irrigation reduced CH 4 and leaching of NO 3 -into shallow groundwater from 13.3-17.8%and 15.63-18.9%,respectively.Applying biochar with controlling fertilizer reduces CH 4 and NO 3 -content in surface field water, contributing to the decreased leaching of NO 3 -into groundwater.Reducing 20% fertilizer rate of N (96 kg N/ha) with application biochar of 5% without a change in yield reduces NO 3 -content into shallow groundwater from 13.7-14.3%.We conclude that water-saving irrigation combined with biochar from rice husk incorporation simultaneously mitigates CH 4 emissions, improves yield, and reduces leaching nitrate into groundwater, making it a suitable environment-friendly nitrogen management practice for sustainable farming in northern Vietnam.
Our perception of diversity, including both alpha- and beta-diversity components, depends on spatial scale. Studies of spatial variation of the latter are just starting, with a paucity of research on beta-diversity patterns at smaller scales. Understanding these patterns and the processes shaping the distribution of diversity is critical to describe this diversity, but it is paramount in conservation too. Here, we investigate the diversity and structure of a tropical community of herbivorous beetles at a reduced local scale of some 10 km2, evaluating the effect of a small, gradual ecological change on this structure. We sampled leaf beetles in the Núi Chúa National Park (S Vietnam), studying changes in alpha- and beta-diversity across an elevation gradient up to 500 m, encompassing the ecotone between critically endangered lowland dry deciduous forest and mixed evergreen forest at higher elevations. Leaf beetle diversity was assessed using several molecular tree-based species delimitation approaches (with mtDNA cox1 data), species richness using rarefaction and incidence-based diversity indexes, and beta-diversity was investigated decomposing the contribution of species turnover and nestedness. We documented 155 species in the area explored and species-richness estimates 1.5–2.0x higher. Species diversity was similar in both forest types and changes in alpha-diversity along the elevation gradient showed an expected local increase of diversity in the ecotone. Beta-diversity was high among forest paths (average Sørensen's dissimilarity = 0.694) and, tentatively fixing at 300 m the boundary between otherwise continuous biomes, demonstrated similarly high beta-diversity (Sørensen's dissimilarity = 0.581), with samples clustering according to biome/elevation. Highly relevant considering the local scale of the study, beta-diversity had a high contribution of species replacement among locales (54.8%) and between biomes (79.6%), suggesting environmental heterogeneity as the dominant force shaping diversity at such small scale, directly and indirectly on the plant communities. Protection actions in the Park, especially these addressed at the imperative conservation of dry forest, must ponder the small scale at which processes shape species diversity and community structure for inconspicuous, yet extraordinarily diverse organisms such as the leaf beetles.
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