Abstract. Chinese grasslands are extensive natural ecosystems that comprise 40 % of the total land area of the country and are sensitive to N deposition. A field experiment with six N rates (0, 30, 60, 120, 240, and 480 kg N ha −1 yr −1 ) was conducted at Duolun, Inner Mongolia, during 2005 and 2010 to identify some effects of N addition on a temperate steppe ecosystem. The dominant plant species in the plots were divided into two categories, grasses and forbs, on the basis of species life forms. Enhanced N deposition, even as little as 30 kg N ha −1 yr −1 above ambient N deposition (16 kg N ha −1 yr −1 ), led to a decline in species richness. The cover of grasses increased with N addition rate but their species richness showed a weak change across N treatments. Both species richness and cover of forbs declined strongly with increasing N deposition as shown by linear regression analysis (p < 0.05). Increasing N deposition elevated aboveground production of grasses but lowered aboveground biomass of forbs. Plant N concentration, plant δ 15 N and soil mineral N increased with N addition, showing positive relationships between plant δ 15 N and N concentration, soil mineral N and/or applied N rate. The cessation of N application in the 480 kg N ha −1 yr −1 treatment in 2009 and 2010 led to a slight recovery of the forb species richness relative to total cover and aboveground biomass, coinciding with reduced plant N concentration and soil mineral N. The results show N deposition-induced changes in soil N transformations and plant N assimilation that are closely related to changes in species composition and biomass accumulation in this temperate steppe ecosystem.

No abstract

An experiment was conducted to characterise N use efficiency and quantify urea fluxes in yaks offered four levels of dietary N (1.43%, 1.97%, 2.45% and 2.90% of diet DM) in a 4 · 4 Latin square design. The incremental increase in N intake linearly increased N retention (P = 0.003) and the excretion of urinary N (P < 0.001), but no difference (P > 0.05) in faecal N excretion was observed in growing yaks fed any of the four diets. Microbial N production had quadratic (P < 0.001) responses to dietary N, characterised by the highest microbial N production occurring in the 1.97% N diet (P < 0.05). As the N content of the diet increased, the urinary excretion of urea increased from 13% to 27% of urea entry rate (quadratic, P < 0.001), whereas gastrointestinal entry urea returned to ornithine cycling decreased from 46% to 40% (linear, P < 0.001), and the gastrointestinal entry urea used for anabolism increased from 50% to 56% (linear, P < 0.001). Gastrointestinal entry urea incorporated into bacterial N decreased linearly (P < 0.001) with incremental increase in N intake, and the greatest concentration (23.5%) of bacterial N originating from plasma urea N was in yaks fed the 1.43% N diet. As much as 87% of the urea synthesised in the liver was returned to the gastrointestinal tract when the yaks were fed a diet with 1.43% N (1.1 times the maintenance N level). Moreover, constantly greater urea production than the intake of digestible N, and the gastrointestinal-urea clearance than the kidney-urea clearance were observed, respectively, in the growing yaks, regardless of the level of N intake. These results suggest that yaks might be more efficient at utilising N under harsh environment than are cattle.

No abstract

The objective of this study was to evaluate the characteristics of lipid oxidation in the meat of free-range broilers feeding on grasshoppers in alpine rangeland on the Tibetan Plateau. Eighty 28-d-old Qinjiaoma male broilers were introduced into a rangeland where there was a dense population of grasshoppers (PB). Control birds were reared under intensive conditions and given a maize-soybean diet. At 91 d of age, 24 birds from each treatment were slaughtered. Fresh breast and thigh meats were packaged and refrigerated for determination. The results indicate that rearing conditions, which included a diet rich in grasshoppers for PB broilers, significantly (P < 0.05) affected α-tocopherol content, total iron, heme iron, and nonheme iron content in the muscle of both the breast and leg. Rearing system and diet also had an important effect on antioxidant activity and lipid oxidation during refrigerated storage. This influence changed with storage time between different tissues. The activities of glutathione peroxidase and superoxide dismutase in the muscle of chicken breasts or legs from PB broilers were significantly (P < 0.05) higher than those from the controls, but no significant (P > 0.05) differences were found for the activities of catalase between the PB broilers and the controls. In conclusion, the meat in free-range broilers feeding on grasshoppers has more antioxidative potential and longer storage life.