Short-term effect of targeted placements of sheep excrement on grassland in inner mongolia on soil and plant parameters

Grazing animal excrement plays an important role in nutrient cycling and redistribution in grazing ecosystems, due to grazing in large areas and return in small areas. To elucidate the changes to the soil and pasture caused by sheep urine, fresh dung, and compost patches, a short- term field experiment using artificially placed pats was set up in the autumn of 2003 in the Inner Mongolian steppe. Urine application significantly increased soil pH during the first 32 days in soil layers at depths of both 0 - 5 cm and 5 - 15 cm. Rapid hydrolysis of urea gave large amounts of urine- nitrogen ( N) as ammonium ( NH4+) in soil extracts and was followed by apparent nitrification from day 2. Higher inorganic N content in the urine- treated soil was found throughout the experiment compared with the control. No significant effects of sheep excrement on soil microbial carbon ( C) and soil microbial N was found, but microbial activities significantly increased compared with the control after application of sheep excrement. Forty- six percent of dung- N and 27% of compost- N were transferred into vegetation after the experiment. The results from this study suggest that large amounts of nutrients have been lost from the returned excrement patches in the degraded grassland of Inner Mongolia, especially from sheep urine- N.

Long-term grazing alters species composition and biomass of a shrub meadow on the Qinghai-Tibet Plateau

Livestock grazing has long been the most widespread land use on the Qinghai-Tibet Plateau, one of the world's highest ecosystems. However, there has been increasing concern during recent decades because of the rapid increase in livestock numbers. To assess the possible influences of grazing on the vast grassland, a long-term grazing experiment in a shrub meadow on the northern Qinghai-Tibet Plateau was carried out. The experiment included five treatments with different stocking rates and one non-grazing (N) treatment. After 17 years of grazing, treatment differences were clear. The species composition differed markedly between grazing intensities, with a decrease in palatable grass species and an increase in unpalatable forbs at higher grazing intensities. The species richness and species diversity, however, were not significantly different between treatments. Vegetation height decreased significantly at higher grazing intensities. Total above,ground biomass declined considerably and the biomass of forbs increased significantly under the higher grazing intensities. The amount of litter was significantly lower under the higher grazing intensities. The results suggest that long-term grazing alters the species composition, vegetation height and biomass production of the alpine grassland ecosystem without significantly changing species richness.

Experimental warming causes large and rapid species loss, dampened by simulated grazing, on the Tibetan Plateau

We investigated the independent and combined effects of experimental warming and grazing on plant species diversity on the north-eastern Tibetan Plateau, a region highly vulnerable to ongoing climate and land use changes. Experimental warming caused a 26-36% decrease in species richness, a response that was generally dampened by experimental grazing. Higher species losses occurred at the drier sites where N was less available. Moreover, we observed an indirect effect of climate change on species richness as mediated by plant-plant interactions. Heat stress and warming-induced litter accumulation are potential explanations for the species' responses to experimental warming. This is the first reported experimental evidence that climate warming could cause dramatic declines in plant species diversity in high elevation ecosystems over short time frames and supports model predictions of species losses with anthropogenic climate change.

Grazing intensity alters soil respiration in an alpine meadow on the Tibetan plateau

Grazing intensity may alter the soil respiration rate in grassland ecosystems. The objectives of our study were to (1) determine the influence of grazing intensity on temporal variations in soil respiration of an alpine meadow on the northeastern Tibetan Plateau; and (2) characterise, the temperature response of soil respiration under different grazing intensities. Diurnal and seasonal soil respiration rates were measured for two alpine meadow sites with different grazing intensities. The light grazing (LG) meadow site had a grazing intensity of 2.55 sheep ha(-1), while the grazing intensity of the heavy grazing (HG) meadow site, 5.35 sheep ha(-1), was approximately twice that of the LG site. Soil respiration measurements - showed that CO2 efflux was almost twice as great at the LG site as at the HG site during the growing season, but the diurnal and seasonal patterns of soil respiration rate were similar for the two sites. Both exhibited the highest annual soil respiration rate in mid-August and the lowest in January. Soil respiration rate was highly dependent on soil temperature. The Q(10) value for annual soil respiration was lower for the HG site (2.75) than for the LG site (3.22). Estimates of net ecosystem CO2 exchange from monthly measurements of biomass and soil respiration revealed that during the period from May 1998 to April 1999, the LG site released 2040 g CO2 m(-2) y(-1) to the atmosphere, which was about one third more than the 1530g CO2 m(-2) y(-1) released at the HG site. The results suggest that (1) grazing intensity alters not only soil respiration rate, but also the temperature dependence of soil CO2 efflux; and (2) soil temperature is the major environmental factor controlling the temporal variation of soil respiration rate in the alpine meadow ecosystem. (C) 2003 Elsevier Ltd. All fights reserved.