Short-term grazing exclusion improved topsoil conditions and plant characteristics in degraded alpine grasslands

Grazing exclusion by fencing is one of the most effective practices to recover the degraded alpine grasslands in Tibetan Plateau. In the present study, the effects of 8-year (GE8) and 4-year (GE4) grazing exclusion were studied in comparison with free grazing (FG) in the plant-soil ecosystems of alpine grasslands. Within fencing, improved plant characteristics such as aboveground biomass (AGB), belowground biomass (BGB) and plant total cover developed without grazing and trampling were observed. Also, there were significant improvements of soil organic carbon (SOC), ammonia nitrogen (NH 4(+)-N) and dissolved organic carbon (DOC) concentrations usually in the topsoil (0-30 cm) but a stable C:N ratio with the number of years of grazing exclusion. Fencing enhanced soil main enzyme (invertase, phosphatase, urease and beta-glucosidase) activities by providing sufficient substrates for microbial activities. Unexpectedly, GE4 had higher soil invertase, phosphatase, urease and beta-glucosidase activities than GE8, which had less plant diversity, richness and higher total cover causing a lowering of soil temperature. Additionally, the results supported the allometric allocation hypothesis for the ABG versus BGB in the grasslands of Tibetan Plateau. Our results indicated that SOC and BGB can be used as indicators of the restoration process of degraded alpine grassland. Cautions should be taken for a long-term fencing in degraded alpine grasslands because of the loss of plant richness, diversity and soil enzyme activities. The present results also suggested that a suitable grazing regime combined with fencing should be focused in the future study of the alpine grasslands. Research results obtained in the present study should, therefore, be helpful to offer a better guidance towards the management practices of the degraded alpine grasslands.