Sheep Wool δ¹³C Reveals No Effect of Grazing on the C₃/C₄ Ratio of Vegetation in the Inner Mongolia–Mongolia Border Region Grasslands

<div><p>We tested whether the abundance of C₄ vegetation in grasslands of the Mongolian plateau is influenced by grazing conditions. The analysis exploited the politically originated contrast that exists between Mongolia (low stocking rate, transhumant system) and the district of Inner Mongolia, China (high stocking rate, sedentary system). We estimated the proportion of C₄ carbon (P_C4) in grazed vegetation from the relative carbon isotope ratio (δ¹³C) of sheep wool sampled from 298 annual shearings originating from 1996 to 2007. Annual stocking rates varying over time and between the districts of both countries were taken from regional statistics. The P_C4 pattern within the 0.7 million km² sampling area was geostatistically analyzed and related to stocking rates and temperature gradients. For similar climatic conditions, P_C4 was the same in both countries. Further, a unique relationship was found between P_C4 and July temperature on both sides of the border, which explained 71% of the pattern. Stocking rate and grazing system had no significant influences on present-day C₃/C₄ abundance ratio. This finding suggests that recent changes in the C₃/C₄ ratio of these grasslands are mainly a consequence of regional warming, not overgrazing.</p> </div

Carbon isotope ratio does not depend on stocking rate.

<p>Relative carbon isotope ratio (δ¹³C) in relation to stocking rate (log-scaled to increase readability) in different districts and years in Mongolia (blue crosses, all years; n = 152) and in Inner Mongolia prior to 2001 (green stars; n = 22) and after 2001 (red circles; n = 124).</p

Sampling sites, stocking rates, proportion of C₄ plants, and isotherms across Inner Mongolia and Mongolia.

<p>Top panel: Distribution of sampling sites and stocking rates across Inner Mongolia and Mongolia. Stocking rates were averaged for the years 1996 to 2007 and expressed as sheep units per km² and yr for the individual districts. Bottom panel: Regional relative proportion of C₄ plants to aboveground biomass (P_C4) estimated by ordinary block (5×5 km²) kriging, derived from wool originating from 1996–2007; mean SD_k for the blocks is 8.9%; the white lines denote the 21, 22 and 23°C isotherms of the July temperature, averaged for the years 1996–2007; towns are UB = Ulaanbaatar, SH = Sainshand, E = Erenhot and Zamny-Uud, XH = Xilinhot, D = Duolun and HU = Haliut.</p

Chen_et_al_FE_2015

Includes responses of extractable_Ca2+, extractable_Mg2+, extractable_Na+, and extractable_Al3+ to acid addition treatment

Comparison of 100 km-wide zones along the common border of Inner Mongolia and Mongolia regarding the number of samples (N), the stocking rate for the years of wool growth (expressed as sheep units SU), the proportion of C4 (P_C4), the mean annual precipitation (MAP), the mean July temperature for the years of wool growth (T_Jul), and the respective 95% confidence intervals of the means (CI_95%).

¶<p>Different capital letters within a line denote significant differences (<i>P</i><0.05) between means of Inner Mongolia and Mongolia.</p

Data_Li_et al_FE

Treatments are described in the main text

Species richness

Species richness was the average of number of species at each sampling area in each 5m × 5m plot. The N addition rates are 0.00, 1.75, 5.25, 10.50, 17.50, and 28.00 g N m-2 yr-1, respectively

Species abundance

Species abundance was the number of individuals for each species in each 5m × 5m plot. The N addition rates are 0.00, 1.75, 5.25, 10.50, 17.50, and 28.00 g N m-2 yr-1, respectively

F values and <i>P</i> values for variance analysis by a nested mixed model with N treatments as fixed factors and replicate and plant hierarchical level as random factors.

<p>F values and <i>P</i> values for variance analysis by a nested mixed model with N treatments as fixed factors and replicate and plant hierarchical level as random factors.</p

Effects of nutrient addition on biomass reproductive allocations (RAs) of <i>A. cristatum</i> at the spike (A1), tiller (A2) and individual (A3) levels and final RA (A) at the whole plant level.

<p>RA for each treatment is the average of 45 replicates (error bars indicate s.e.). Bars followed by the same letters are not significantly different according to LSMEANS at <i>P</i> = 0.05.</p