Research On The Phenological Period And Community Characteristics Of Typical Grassland Species Under Simulated Rainfall Changes In Loess Hilly Region

Under the background of global climate change,the precipitation pattern of the Loess Plateau will show the trend of increasing seasonal fluctuation and extreme precipitation events.Changes in precipitation patterns are bound to cause important changes in grassland community characteristics and phenological periods.At present,there are few studies on the characteristics and phenophase of grassland communities in loess hilly areas with water restriction caused by precipitation changes.Based on this,this study used canopy method to simulate the changes of different precipitation,setting 7 treatments:(DP60:-60%,DP40:-40%,DP20:-20%,CK: 0%,IP20: 20%,IP40: + 40% and IP60: + 60%),and observed the main phenological periods(green,breeding and yellow)and community characteristics changes of grassland communities under different precipitation treatments in April-October2019.The main results are as follows:(1)The greening,reproduction,and yellowing periods of the naturally restored community Lespedeza daurica L.were significantly advanced under the rainfall reduction treatment,while the reproduction and yellowing periods were delayed under the rainfall increase treatment;the reproduction and yellowing periods of dogwood were significantly delayed under the different precipitation treatment changes,causing an increase in growing season length;the greening period of Artemisia capillaris L.was advanced and the reproduction and yellowing periods were delayed under the rainfall increase treatment,causing an increase in growing season The growing season length of Artemisia capillaris L.increased under the rainfall treatment,while no consistent pattern of response was observed for early gram to different precipitation changes.The change of the phenological period of these dominant species under different precipitation changes may have an important impact on the growth of naturally restored vegetation in this area.(2)The response of each species in the artificially restored community to different precipitation treatments was weaker than that of the natural restored community.Only the re-greening period of white sheepgrass populations was significantly delayed under different rainfall treatments,resulting in a shorter growing season;however,the reproductive period,withering period and growing season length of other species did not change significantly under different rainfall treatments,indicating that the artificially restored community was less affected by extreme precipitation changes and had certain resistance to precipitation changes.(3)The species composition and abundance of the two communities differed significantly under different rainfall treatments.Compared with the control,both the rainfall increase and the rainfall treatment increased the species species variety in the communities;the effects of different rainfall treatments on the species composition were mainly reflected in the species importance values,with the rainfall reduction treatment significantly increasing the importance values of the dominant perennial species in the communities,while the rainfall increase treatment increased the importance values of the species in 2012;the species importance values of Lespedeza daurica L.in both natural and artificially restored communities were significantly higher under the rainfall reduction treatment than the rainfall increase treatment,indicating that the drought conditions favored Lespedeza daurica L.In both natural and artificially restored communities,the species importance values of Lespedeza daurica L.were significantly higher under reduced rainfall than under increased rainfall,indicating that the drought conditions were favorable to the growth of Lespedeza daurica L.(4)The vegetation coverage of natural restoration and artificial restoration communities have roughly the same response to precipitation changes.They were more sensitive to precipitation changes from May to August,but were not sensitive to changes at the end of the growing season;similar to the coverage response patterrns,the above-ground biomass was significantly higher under the rainfall increase treatment than the rainfall reduction treatment,and both IP20 and DP20 were able to significantly increase vegetation cover and above-ground biomass for both communities.The species diversity did not change significantly under different precipitation changes,indicating that the species composition and diversity of the communities were resistant and stable in response to the changes in precipitation.(5)The response thresholds of phenology and community structure of natural and artificial restored communities under different rainfall treatments were significantly different.The annual rainfall at DP60(202 mm)was the rainfall for the transformation of grassland community phenology,while the annual rainfall at IP20(606 mm)was the rainfall for the transformation of grassland community structure.Takentogether,future vegetation restoration measures in the loess hills in the context of changing precipitation patterns may require a comprehensive weighing of the pros and cons of vegetation phenology and community structure changes under changing precipitation on the ecosystem service functions of the area.