Study materials
In this study, four abundant species in the Inner Mongolia Steppe were used. S. grandis and S. krylovii were used as the target species and as neighbor for each other. Both S. grandis andS. krylovii , two perennial tussock grasses, are the two of the most widely distributed grasses and dominate the landscape of the vast semi-arid area of the Inner Mongolia steppe, China. S. grandiswith a canopy height over 100cm is a superior competitor for light and has lower tolerance to unfertile condition than S. krylovii , thusS. grandis occupies relatively moist and fertile typical grassland while S. krylovii occupies dry and infertile habitats (Chen et al. , 2013). The growth potential of S. kryloviishould be comparable to that of S. grandis because the communities under seriously disturbance such as grazing, S. krylovii would co-dominate the communities with S. grandis or even dominate the communities by replacing the dominance of S. grandis (Lu and Wu 1996).
Leymus chinensis and Agropyron cristatum were used as neighbor species in this study. L. chinensis can be a dominant species in the meadow grasslands, and usually co-dominates the typical communities with S. grandis or S. krylovii in the Inner Mongolia steppe, which indicated that the growth potential of L. chinensis may be one of the highest in the Inner Mongolia Steppe and the tolerance to low nutrition of L. chinensis should be comparable to that of S. krylovii (Zhu, 2004). A. cristatum is a companion species in non-degraded S. grandiscommunity and a subdominant species in moderate-grazed S. grandisor S. krylovii communities, suggesting that the growth potential and the tolerance to low nutrition of A. cristatum are between those of S. grandis and S. krylovii (Xu et al. 2015).
In a S. grandis - S. krylovii community in the middle of Inner Mongolia Steppe (44°15’N, 116°23’E, 1132 m altitude), the seeds of the four species were obtained and 5 ~20 cm soil was collected and homogenized for the microcosm experiment. The soil was a Calcic luvisol (FAO-UNESCO), with the pH of 7.35. The soil organic matter, availability of N and P were 15.6 mg/g, 0.17 mg/kg, 4.72 mg/kg, respectively.