Background and AimsGrazing exclusion is a powerful measure to restore the ecological environment in desert steppe. Studying the changing trend of functional traits and trade-off strategy about dominant species what is of great significance to understand the effect of grazing exclusion on species succession. Methods We studied that the change of leaf and root functional traits of three dominant species (Lespedeza potaninii, Agropyron mongolicum and Stipa breviflora) under different term of grazing exclusion. ResultsWe found that the leaf area and leaf nitrogen content, leaf dry matter content, total root length, specific root length and specific root surface of Lespedeza potaninii in grazing were higher than grazing exclusion. The highest specific leaf area, specific root length of Agropyron mongolicum and Stipa breviflora were observed in short-term grazing exclusion. Leaf tissue density and root tissue density significantly decreased in short-term grazing exclusion. Economic spectrum exist, Lespedeza potaninii have more conservation strategy in short-term grazing exclusion compared with grazing. Agropyron mongolicum and Stipa breviflora have more acquisition strategy in grazing exclusion. Average diameters have great effected on above-ground biomass.ConclusionThe result showed that grazing exclusion change leaf and root functional traits of three dominant species, different species have different trade-off strategy.

Alfalfa ( Medicago sativa L.) establishment is an effective strategy of managing desertification in arid regions; however, the course of artificial alfalfa grassland degradation remains poorly understood. Therefore, we investigated the dynamics of vegetation characteristics, soil edaphic factors, and rhizosphere microbial community structure in the course of artificial alfalfa grassland degradation. A space–for–time substitution approach was used to select nine alfalfa stands with different ages (1–50 years old) in the loess hilly region of northwest China. According to the plant diversity of vegetation and important value of alfalfa, the course of grassland degradation could be divided into three stages, artificial grassland (1–10 years), transitional grassland (10–30 years), and natural grassland (>30 years). With an increase in stand age, alfalfa productivity first increased, up to a maximum in the 7-year-old stand, and then decreased. Alfalfa was replaced as the dominant species by Stipa bungeana in the 50-year-old stand. Soil bulk density, total organic carbon, and major nutrient contents were the highest in the artificial grassland. Soil enzyme activity and the relative abundances of potentially beneficial microorganisms (e.g., Mortierella and Glomus) peaked in the transitional grassland. Soil water content and total porosity reached the maximum levels in the natural grassland. The species diversity indices of bacterial and fungal communities first increased and then decreased over time. Both microbial abundance and species diversity in the 0–20-cm soil layer were higher than in the 20–40-cm soil layer. Soil pH and catalase activity predominantly influenced vegetation characteristics, while total and available phosphorus contents were the major edaphic factors shaping rhizosphere microbial community structure. The results indicated that alfalfa establishment altered soil structure considerably, and improved soil fertility in the artificial grassland over the short term. Consequently, soil enzyme activity, microbial diversity, and potentially beneficial microorganisms in the rhizosphere increased during the transitional stage. Following considerable shifts in the soil environmental conditions, alfalfa was no longer the only dominant species and was eventually replaced by S. bungeana, leading to the establishment of a stable natural grassland system.