Effect of short-term enclosure on soil nematode communities in an alpine meadow in Northern Tibet

Alpine meadow is extensively distributed throughout Northern Tibet,and is the typical ecosystem of the Tibetan plateau. Collectively,alpine meadow represents the largest and most important ecosystem in Northern Tibet. The aim of the present study was to examine the restoration of degraded grassland and the rational use of grassland resources,and to provide a theoretical basis for local animal husbandry development in the alpine meadow of northern Tibet. We conducted an experiment using alpine meadow sample plots of both enclosed and grazed land in Naqu County in the Naqu region of the Tibet Autonomous Region,China( 31[degrees]38'38.87"N,92[degrees]00'51.44"E). To better understand the effect of grazing on alpine meadow habitats,and how degraded land may recover following enclosure,we surveyed the variation in soil nematode communities at soil depths from 0-25 cm. From May to November 2013,we carried out a survey in all sample plots to investigate variation in soil nematode communities in different soil layers ranging from 0 to 25 cm,in order to understand the effect of grazing on alpine meadows and the role of enclosure for the recovery of degraded alpine meadows in northern Tibet.We collected soil nematodes using the shallow basin method,and measured the following soil chemical properties: soil pH,organic matter content,and concentrations of total nitrogen,phosphorus,and potassium. We compared the composition,distribution,and diversity of nematode communities between grazed and enclosed plots using indices of individual density,diversity,and trophic composition. We also analyzed the relationships between nematode communities and soil chemical properties. Overall,nematode communities differed between grazed and enclosed sample plots. Short-term( 3a) enclosure increased the biodiversity and total abundance of soil nematodes. Nematode groups increased in abundance in grazing plots from Plant parasites Bacterivores Fungivores Omnivores-predators,while group abundances in enclosed sample plots decreased from Fungivores Plant parasites Bacterivores Omnivores-predators. Various trophic groups showed no significant differences between the two sample areas. Enclosures reduced the proportion of plant predatory nematodes,and stabilized the nematode composition of the alpine meadow ecosystem. The Shannon-Wiener( H') and Margalef indices( SR) were higher in enclosed plots than grazed plots,whereas the dominance index( [lambda]) was lower for grazed than for enclosed p