In order to explore the effects of grazing frequency on functional traits and to test whether Stipa gandis has compensatory photosynthesis during the frequent grazing period, we investigated morphological traits, biomass allocation, photosynthetic traits, and chlorophyll fluorescence parameters of the species in Inner Mongolia, China. The grazing frequency treatments included fencing (T 0), grazing in May and July (T 1 , i.e., two months per year) and grazing from May to September (T 2 , i.e., continuous five months per year). Results indicate that T 1 and T 2 treatments did not affect individual biomass, but T 2 treatment negatively affected individual size, i.e., plant height, stem length, and leaf length. Physiological traits of S. grandis were significantly affected by grazing, year, and their interaction. In July 2014 (i.e., dry environment and low relative humidity), the photosynthetic rate, transpiration rate and water use efficiency were highest under T 2 treatment, which was caused by the increase in stomatal conductance. However, in July 2015 (i.e., wet environment and high relative humidity), the photosynthetic rate and water use efficiency were higher under T 1 and T 2 treatments, which were caused by the increase in actual quantum efficiency and stomatal conductance. Our results implied that under frequent grazing treatment, S. grandis had small height and efficient compensatory photosynthesis, which promoted its resistance to severe grazing.

The main purpose of this study was to explore the dynamic changes of greenhouse gas (GHG) from grasslands under different degradation levels during the growing seasons of Inner Mongolia, China. Grassland degradation is associated with the dynamics of GHG fluxes, e.g., CO 2 , CH 4 and N 2 O fluxes. As one of the global ecological environmental problems, grassland degradation has changed the vegetation productivity as well as the accumulation and decomposition rates of soil organic matter and thus will influence the carbon and nitrogen cycles of ecosystems, which will affect the GHG fluxes between grassland ecosystems and the atmosphere. Therefore, it is necessary to explore how the exchanges of CO 2 , CH 4 and N 2 O fluxes between soil and atmosphere are influenced by the grassland degradation. We measured the fluxes of CO 2 , CH 4 and N 2 O in lightly degraded, moderately degraded and severely degraded grasslands in Inner Mongolia of China during the growing seasons from July to September in 2013 and 2014. The typical semi-arid grassland of Inner Mongolia plays a role as the source of atmospheric CO 2 and N 2 O and the sink for CH 4. Compared with CO 2 fluxes, N 2 O and CH 4 fluxes were relatively low. The exchange of CO 2 , N 2 O and CH 4 fluxes between the grassland soil and the atmosphere may exclusively depend on the net exchange rate of CO 2 in semi-arid grasslands. The greenhouse gases showed a clear seasonal pattern, with the CO 2 fluxes of-33.63-386.36 mg/(m•h), CH 4 uptake fluxes of 0.113-0.023 mg/(m•h) and N 2 O fluxes of-1.68-19.90 µg/(m•h). Grassland degradation significantly influenced CH 4 uptake but had no significant influence on CO 2 and N 2 O emissions. Soil moisture and temperature were positively correlated with CO 2 emissions but had no significant effect on N 2 O fluxes. Soil moisture may be the primary driving factor for CH 4 uptake. The research results can be in help to better understand the impact of grassland degradation on the ecological environment.

With increasingly intensifying degradation of natural grasslands and rapidly increasing demand of high quality forages, natural grasslands in China have been converted into planted grasslands at an unprecedented rate and the magnitude of the conversion in Inner Mongolia is among the national highest where the areal extent of planted grasslands ranks the second in China. Such land-use changes (i.e., converting natural grasslands into planted grasslands) can significantly affect carbon stocks and carbon emissions in grassland ecosystems. In this study, we analyzed the effects of converting natural grasslands into planted grasslands (including Medicago sativa, Elymus cylindricus, and M. sativa+E. cylindricus) on ecosystem respiration (F eco) in Inner Mongolia of China. Diurnal F eco and its components (i.e., total soil respiration (F ts), soil heterotrophic respiration (F sh) and vegetation autotrophic respiration (F va)) were measured in 2012 (27 July to 5 August) and 2013 (18 July to 25 July) in the natural and planted grasslands. Meteorological data, aboveground vegetation data and soil data were simultaneously collected to analyze the relationships between respiration fluxes and environmental factors in those grasslands. In 2012, the daily mean F eco in the M. sativa grassland was higher than that in the natural grassland, and the daily mean F va was higher in all planted grasslands (i.e., M. sativa, E. cylindricus, and M. sativa+E. cylindricus) than in the natural grassland. In contrast, the daily mean F ts and F sh were lower in all planted grasslands than in the natural grassland. In 2013, the daily mean F eco , F ts and F va in all planted grasslands were higher than those in the natural grassland, and the daily mean F sh in the M. sativa+E. cylindricus grassland was higher than that in the natural grassland. The two-year experimental results suggested that the conversion of natural grasslands into planted grasslands can generally increase the F eco and the increase in F eco is more pronounced when the plantation becomes more mature. The results also indicated that F sh contributed more to F eco in the natural grassland whereas F va contributed more to F eco in the planted grasslands. The regression analyses show that climate factors (air temperature and relative humidity) and soil properties (soil organic matter, soil temperature, and soil moisture) strongly affected respiration fluxes in all grasslands. However, our observation period was admittedly too short. To fully understand the effects of such land-use changes (i.e., converting natural grasslands into planted grasslands) on respiration fluxes, longer-term observations are badly needed.