Jihua Wu

Freshwater fish biodiversity in the Yangtze River basin of China: patterns, threats and conservation

We synthesized information on freshwater fish biodiversity in the Yangtze River basin. We documented 361 species and subspecies that had been recorded and described from the basin. Of these, 177 species are endemic. The basin is usually divided into three parts, i.e. the upper reaches, the middle reaches and the lower reaches. This study indicated that the ‘three reaches’ approach was not supported by fish distribution patterns. Hydrological alterations are perhaps the largest threat to fish biodiversity in the basin. Fishes in the upper reaches will be seriously affected by the construction of the Three Gorges Dam and other dams, and action should be taken for priority conservation. The most immediate restoration need is reconnection of the Yangtze River with its lakes. The cluster of lakes in the Central Yangtze should be protected to maintain habitats for spawning, feeding and migration of migratory fishes. Our study indicates a need to identify areas of high fish biodiversity and to select nature reserves to mitigate the loss of fish biodiversity in the Yangtze River basin.

Soil faunal response to land use: effect of estuarine tideland reclamation on nematode communities

Effects of reclaiming estuarine tideland on soil fauna biodiversity were studied in the Yangtze river estuary of China, focusing on nematodes. The responses of the nematode community to the disturbance caused by reclamation can be summarized as: (1) there was no distinct decline in the density of nematodes, but the community structure changed greatly; (2) the proportions of plant feeders and omnivorous nematodes increased after reclamation, whereas the proportions of bacterial feeders and predators decreased; (3) more apparent patchiness of nematode distribution was found in the reclaimed terrestrial environment than in intertidal marshes. Generally, agrocenoses have been characterized by low proportions of predator-omnivores. Our study indicated that omnivorous dorylaimids can be markedly abundant in agroecosystems, depending on the annual crop rotation and tillage practices. The predominant trophic group in cultivated land shifted between omnivorous nematodes and plant feeders, implying that the food chain path changed with agricultural processes. The maturity index (MI) provides little information in the present study, probably because the MI value embraced information of many disturbances including vegetation succession and changes in soil features. The faunal profile, representing both enrichment and structural conditions, is believed to be effective and more informative for analyzing the nematode successional trends.

Elevational gradients of diversity for lizards and snakes in the Hengduan Mountains, China

Comparing elevational gradients across a wide spectrum of climatic zones offers an ideal system for testing hypotheses explaining the altitudinal gradients of biodiversity. We document elevational patterns of lizard and snake species richness, and explore how land area and climatic factors may affect species distributions of lizards and snakes. Our synthesis found 42 lizard species and 94 snake species known from the Hengduan Mountains. The lizards are distributed between 500 and 3500 m, and the snakes are distributed between 500 and 4320 m. The relationship between species richness and elevation for lizards and snakes is unimodal. Land area explains a significant amount of the variation in lizard and snake species richness. The cluster analysis reveals pronounced distinct assemblages for lizards and snakes to better reflect the vertical profiles of climate in the mountains. Climatic variables are strongly associated with lizard and snake richness along the elevational gradient. The data strongly implicate water availability as a key constraint on lizard species richness, and annual potential evapotranspiration is the best predictor of snake species richness along the elevational gradient in the Hengduan Mountains.

Communities of ammonia oxidizers at different stages of Spartina alterniflora invasion in salt marshes of Yangtze River estuary

Spartina alterniflora, an aggressive invasive plant species at the estuarine wetlands of China’s coasts, has become a major threat to the natural ecosystems. To understand its potential influence on nitrification processes, the community structures and abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) were investigated using 454-pyrosequencing and quantitative real-time PCR (qPCR) in S. alterniflora invading salt marsh sediments at the Yangtze River estuary in Chongming island, Shanghai, China. Copy numbers of archaeal and bacterial ammonia monooxygenase subunit A (amoA) genes did not show accordant shifts with S. alterniflora invasion in the two sampling sites. However, the copy numbers of archaeal amoA gene were higher in summer than in spring. Phylogenetic analysis indicated that more than 90% of the archaeal and 92% of the bacterial amoA gene sequences were closely related to marine group I.1a and the clusters 13 and 15 in Nitrosospira lineage, respectively. The effect of different seasons (spring and summer) was important for the abundance variation of AOA, while different stages of S. alterniflora invasion did not show significant effect for both AOA and AOB. Variation of AOA community was significantly related to total carbon (TC) and sulfate concentration (P < 0.05), whereas the AOB community was significantly related to sulfate concentration, total nitrogen (TN), TC and pH (P < 0.05). In conclusion, the abundance and diversity of ammonia oxidizing microbial communities were not strongly affected by S. alterniflora invasion.

Trophic Dynamics of Filter Feeding Bivalves in the Yangtze Estuarine Intertidal Marsh: Stable Isotope and Fatty Acid Analyses

Benthic bivalves are important links between primary production and consumers, and are essential intermediates in the flow of energy through estuarine systems. However, information on the diet of filter feeding bivalves in estuarine ecosystems is uncertain, as estuarine waters contain particulate matter from a range of sources and as bivalves are opportunistic feeders. We surveyed bivalves at different distances from the creek mouth at the Yangtze estuarine marsh in winter and summer, and analyzed trophic dynamics using stable isotope (SI) and fatty acid (FA) techniques. Different bivalve species had different spatial distributions in the estuary. Glauconome chinensis mainly occurred in marshes near the creek mouth, while Sinonovacula constricta preferred the creek. Differences were found in the diets of different species. S. constricta consumed more diatoms and bacteria than G. chinensis, while G. chinensis assimilated more macrophyte material. FA markers showed that plants contributed the most (38.86 ± 4.25%) to particular organic matter (POM) in summer, while diatoms contributed the most (12.68 ± 1.17%) during winter. Diatoms made the largest contribution to the diet of S. constricta in both summer (24.73 ± 0.44%) and winter (25.51 ± 0.59%), and plants contributed no more than 4%. This inconsistency indicates seasonal changes in food availability and the active feeding habits of the bivalve. Similar FA profiles for S. constricta indicated that the bivalve had a similar diet composition at different sites, while different δ13C results suggested the diet was derived from different carbon sources (C4 plant Spartina alterniflora and C3 plant Phragmites australis and Scirpus mariqueter) at different sites. Species-specific and temporal and/or spatial variability in bivalve feeding may affect their ecological functions in intertidal marshes, which should be considered in the study of food webs and material flows in estuarine ecosystems.

Latitudinal variation in nematode diversity and ecological roles along the Chinese coast

Abstract Aim To test changes in the phylogenetic relatedness, niche breadth, and life‐history strategies of nematodes along a latitudinal gradient. Location Sixteen wetland locations along the Pacific coast of China, from 20°N to 40°N. Methods Linear regression was used to relate nematode phylogenetic relatedness (average taxonomic distinctness (AvTD) and average phylogenetic diversity [AvPD]), life‐history group (based on “c‐p” colonizer–persister group classification), and dietary specificity (based on guild classification of feeding selectivity) to latitude. Results Wetland nematode taxonomic diversity (richness and Shannon diversity indices) decreased with increasing latitude along the Chinese coast. Phylogenetic diversity indices (AvTD and AvPD) significantly increased with increasing latitude. This indicates that at lower latitudes, species within the nematode community were more closely related. With increasing latitude, the nematode relative richness and abundance decreased for selective deposit feeders but increased for nonselective deposit feeders. The proportion of general opportunists decreased with increasing latitude, but persisters showed the opposite trend. The annual temperature range and the pH of sediments were more important than vegetation type in structuring nematode communities. Main conclusion Nematode niche breadth was narrower at lower latitudes with respect to dietary specificity. Higher latitudes with a more variable climate favor r over K life‐history strategists. Nematode communities at lower latitudes contained more closely related species.

Invasive cordgrass facilitates epifaunal communities in a Chinese marsh

Structural aspects of the environment frequently influence the taxonomic and functional diversity of associated ecological communities. Spartina alterniflora and Phragmites australis both are structure-forming species in salt marshes but reciprocal invaders. Epifaunal communities on invasive Phragmites on the east coast of North America are reduced relative to native Spartina. But, the impacts of invasive Spartina on epiphytic communities in Phragmites dominated marshes in the Western Pacific are unknown. We examined epifauna on live and dead stems of invasive S. alterniflora and native P. australis in the Yangtze River estuary in China. Epiphytic invertebrate abundance on S. alterniflora was ~5× greater than on P. australis, suggesting that S. alterniflora supports more abundant epiphytic communities than P. australis, irrespective of region. For both live and dead stems, most epifaunal groups, including Namatoda, Copepoda, Halacarida and Oligochaeta, were more abundant on S. alterniflora than P. australis. Enhanced epifaunal abundance could benefit the nursery function of marshes by increasing secondary production. Dead S. alterniflora were the best habitat for nematodes, especially bacterivores and fungivores. This suggests that differences in litter quality may be important in these nematode communities and that more active biological processes may occur on Spartina influencing nutrient cycling rates.

Four new and four known species of Tylencholaimoidea (Dorylaimida: Nematoda) from China

Four new and four known species of soil nematodes belonging to the superfamily Tylencholaimoidea Filipjev, 1934 are reported from China. Tylencholaimus orientalis sp. nov. is characterized by having a 0.45–0.61‐mm body; a 5–6‐µm odontostyle; a monoprodelphic genital system with a short post‐uterine sac; and a conoid to hemispheroid tail. Tylencholaimus sinensis sp. nov. is characterized by having a 0.76–0.82‐mm body; a 7–7.5‐µm odontostyle; an amphidelphic genital system; a conoid to hemispheroid tail; and males with 32‐µm spicules and three ventromedians. Proleptonchus sinensis sp. nov. is characterized by having a 1.4–1.7‐mm body; wide amphids; 8–9‐µm odontostyle; a monoprodelphic genital system, the posterior branch with well‐developed uterus and oviduct rudiments; slender and slightly arcuate spicules; and a short conoid tail with thick cuticle at terminus. Dorylaimoides alpinus sp. nov. is characterized by having a 1.4–1.5‐mm body; a lip region offset by a depression; a 12–13‐µm odontostyle; an arcuate odontophore; an amphidelphic genital system with transverse vulva; and a tail that gradually tapers to a blunt terminus.

The variability and causes of organic carbon retention ability of different agricultural straw types returned to soil

ABSTRACT Retaining the organic carbon (C) content of agricultural straw when returned to soil is restricted by rapid decomposition. In order to clarify the difference in returned straw decomposition and the causes, and to develop a straw returning mode with high-efficiency of organic C accumulation, the decomposition processes of corn, soybean, rice and wheat straws were systematically studied in fields. When returned in situ (the original planting area), the C in soybean straw was decomposed most quickly with a decomposition constant of 0.00542 d–1, but wheat straw showed a longer retention in soil with 0.00303 d–1. However, for ex situ return of all straw in one area away from in situ return, soybean straw was decomposed most slowly (0.00452 d–1) and wheat straw more quickly (0.00652 d–1). The sequence of C decomposition rate in 270 d was soybean > corn > rice > wheat (in situ) and corn > wheat > rice > soybean (ex situ). Both surrounding soil and straw nature were important factors influencing the decomposition rate. The farmland with rice and wheat rotation retained more C from returned straws due to its high moisture and low nitrogen (N) content, while the soybean field was a contrast. Soybean straw had a low decomposition rate after ex situ return due to its low N content and high C/N ratio. The farmland of wheat–rice rotation combined with soybean straw ex situ return may develop into a field of higher C retention ability.

Status of soil nematode communities during natural regeneration of a subtropical forest in southwestern China

Forest recovery has been extensively evaluated using plant communities but fewer studies have been conducted on soil fauna. This study reports the status of soil nematode communities during natural re-establishment after deforestation in a subtropical forest in southwestern China. Soil nematode communities of two secondary succession stages, shrub-grassland and secondary forest, were compared with those of virgin forest. Shrub-grassland had higher herbivore relative abundance but lower fungivore and bacterivore relative abundance than forests. Between secondary and virgin forest, the latter had higher abundance of bacterivores. Shrub-grassland had lower nematode diversity, generic richness, maturity index and trophic diversity index than virgin forest, whereas there were no differences in these indices between secondary forest and virgin forest. The small differences in nematode community structures between secondary forest and virgin forest suggest that soil nematode communities recovered to a level close to that of the undisturbed forest after up to 50 years of natural succession.