Nematodes As An Indicator Of Their Habitats At Shapotou In The Tengger Desert, China

The characteristics of nematode communities and their composition were investigated under various crusts, in artificial vegetation belt with or without irrigation, along an age sequence after sand dunes stabilized, under assisted re-vegetation plant of Caragana korshinskii Kom., Hedysarum scoparium Fisch. and Artemisia ordosica Krasch. at Shapotou in the Tengger Desert. In contrast to native vegetation sites at Hongwei, evolution characteristics of the nematode communities were also investigated. Additionally, spatial distribution of nematode trophic groups was also studied in stabilized sand dunes at early and late stage. The objective is to evaluate whether nematodes could be as an indicator of their inhabitats during ecological reclaimation after sand dunes stabilized at Shapotou.Our results showed that soil nematodes distributed mainly at the upper soil layer in sand dunes at Shapotou, and bacterivores and fungivores were dominant in our system, indicating that the principal food source for nematodes was microbial. Especially, bacterivores were predominant in most observed sites, it suggested decomposition processes in our system were often bacterial based energy channel, occasionally fungal based channel in algal crusts and moss crusts in autumn, althougy they were dependent ultimately on the plants. In addition, plant feeders i.e. Rotylenchus could get dominant after rainfall.The abundance of nematodes (N), the proportion of predators, maturity index (MI), the number of nematode taxa identified (S) and Shannon index (H') were affected significantly by crust type. Bare soil, physical soil crusts, algal crusts and moss crusts also were comprised of differing community composition as indicated by principal response curves (PRC) analysis. These results indicate that nematode communities develop parallel to crust development during the assisted re-vegetation of migrating sand dunes.N, the proportion of fungivores, omnivores and predator, MI, H', evenness and structure index were affected significantly by the age of stabilized sand dunes, and were correlated with soil physical and chemical properties on different degrees. There were differences on N, the proportion of fungivores, H' and evenness between the shifting dunes and the stabilized dunes, but not within the different succession stages of the stabilized dunes. The result of redundancy analysis (RDA) using data on nematode community composition showed that shifting sand dunes were clearly separated from stabilized sand dunes, and younger sand dunes stabilized for 16 years and 26 years were also separated from older dunes stabilized for 43 years and 51 years to a lesser degree. Those results indicated that changes on nematode communities could predict the initial sand dune stabilization due to the planting of artificial vegetation, and clearly differentiate sand dune succession accompanied by the vegetation succession and the variation of soil properties.In bare soil between vegetation and soil under the vegetation in Shapotou, N, the relative abundance of plant feeders, S, species richness (SR) and cp groups responded to vegetation. The relative abundance of omnivores, S, H', dominance, SR, cp3-5 were significantly affected by irrigation supplements. Principal component analysis (PCA) revealed that a vegetation gradient from bare soil between vegetation to soil under vegetation along the first axis, while an irrigation gradient along the second axis. Similarly, classification analysis based on all cased involved indicated that two-main group of nematodes was distinguished by their habitats under vegetation from bare soil. Those results suggested that vegetation input might play a more important role on nematode community composition than irrigation supplements for stabilization of shifting sand dunes.The abundance of nematode and trophic groups aggregated stronger in depth of 0-10 cm than that in depth of 10-20 cm in sand dune stabilized for 26 years and 51 years. Nematode communities were more spatial heterogenous in late than in early successional sand dunes since stabilization except plant feeders. The spatial heterogenous distribution patterns can be explained by the intrinsic nematode population process and mediated by vegetation patterns.Assisted re-vegetation plant species and function groups affect nematode communities. The abundance of fungivores and predators, relative abundance of fungivores, nematode channel ratio and diversity index diffentiated significantly between shallow rooted shrub of Artemisia ordosica and deep rooted shrub of Caragana korshinskii and Hedysarum scoparium at 0-10 cm soil depth. The plant species induced trophic diversity different significantly at upper soil layer, and the abundance of nematode genera, plant feeders, omnivores, S and SR at lower soil layer. Assisted re-vegetation plant function groups may play a more important role than plant species.Nematode communities along dune age at 0-10 cm soil depth in Shapotou region developed towards the level of a reference site of Hongwei native vegetation region. However, nematode communities at 10-20 cm soil depth differentiated significantly between those two region. Those could be due to crust coverage, plant vegetation and the reclamation status of soil physical and chemical characteristics.MI was only higher significantly under moss crusts than beneath algal crusts in April, it was affected by age for sand dune stabilization, irrigation and plant input. MI may be a poor indicator of changes in nematode communities under various inhabitat in our system. Whereas structure index increased significantly with dune age and it could act as robust indicators of stabilized sand dune succession. Multivariate methods of PRC, RDA, PCA and classtification analysis could be discriminatory for subtle differences, and these methods are sensitive to respond changes in nematode inhabitat conditions in Shapotou.