Abstract: Precipitation is one of the most important water sources in semi-arid desert steppe. The changes of rainfall in growing season directly affect plant growth, interspecific relationship, and thus the structure and function of plant community. In this study, a three-year rainfall manipulation experiment (-40%, -20%, 0 (CK), +20%, +40% rainfall in growing season) was carried out in the desert steppe in the west of the Loess Plateau, to explore the effects of precipitation change on density, height, coverage, functional type composition, the importance value of dominant species, and species diversity of plant communities from the perspective of monthly scale. It was found that: (1) compared with the increasing rainfall treatments, there were significant effects of extreme reducing rainfall (-40%) on the density, height and coverage of plant communities (P<0.05), with such effects being significantly stronger in the middle and late growing season (July, August and September) than in the early growing season (May and June). The rainfall in July and August was the key factor driving plant growth in the semiarid area. (2) Extreme rainfall reduction altered plant community structure by increasing the importance value of Stipa brevifloraand decreasing that of Ajania fruticulosa. Extreme rainfall reduction increased the dominance of Gramineae species. (3) The threeyear extreme rainfall reduction decreased plant species richness and diversity, which was not conducive to the stability of plant community. However, the continuous extreme rainfall increasing treatment (+40%) resulted in higher species richness than other treatments, and had significant difference with the precipitation reduction treatments (P<0.05). Under the scenario of changes in precipitation regime, more real-time management of desert steppe in different periods during the growing season is of great significance for vegetation protection and stability maintenance in ecologically sensitive areas.

Key words: growth characteristics, plant functional type, species diversity, resource utilization strategy, semi-arid area.