Study On The Yellowing Period Changes Of Stipa Krylovii And Its Relationship With Meteorological Conditions In Inner Mongolia

Plant phenology is the periodic change of plants affected by the environment,and is a sensitive index for climate change research.In particular,the turning green period and the withering period of plants together determine the length of the plant growth period,which affects the formation of plant biomass or crop yield.This study takes the yellowing period of Stipa krylovii as the research object,based on the long-term location observation data of Stipa krylovii phenology from the Xilinhot National Climate Observatory of China Meteorological Administration,and the in-situ control of the phenology responses of Stipa krylovii steppe to water and heat Test data,analyze and study the phenological changes of Stipa krylovii during the yellowing period and its relationship with meteorological conditions.the main conclusions are as follows:(1)From 1985 to 2018,the climate characteristics of the Stipa krylovii.steppe are characterized by increased temperature,reduced sunshine hours,and large inter-annual fluctuations in precipitation,with no obvious overall trend.(2)From 1985 to 2018,the interannual changes in the phenology of Stipa krylovii.during the yellowing period were drastic,but there was no significant trend to advance or postpone it.(3)The analysis of the relationship between the phenology of Stipa krylovii.and the meteorological factors on the daily,pentad,monthly,and seasonal scales shows that the beginning and the peak of yellowing period are significantly negative with the monthly average temperature of the month in which it occurs and the previous month.Correlation,among them,the yellowing period has a high correlation with the daily average temperature during the previous 55 days and during the 120-180 days,especially the temperature.Path analysis shows that under different time scales,meteorological factors have different ways of acting on the peak of yellowing period.On the monthly scale,only the monthly average surface temperature has a significant direct effect on the peak of yellowing period.Other meteorological factors indirectly affect the monthly average surface temperature.Affect the dry season;at the climatic scale,the average surface temperature,the average air relative humidity,and the average 2-minute wind speed all have a direct effect on the dry season.Cumulative precipitation indirectly affects the dry season by affecting the relative humidity of the air.(4)Under the warming background,precipitation was the main influencing factor of the yellowing period.The increase in precipitation(the decrease in precipitation)postponed(advanced)the occurrence time of both the beginning and the peak of the yellowing period,the duration of the yellowing period was prolonged,the effect of the decrease in precipitation on prolonging the duration of the yellowing period was more significant.(5)Under the background of warming,the changes of precipitation markedly affected the physiological and ecological characteristics of the yellowing period,and the effect was the most significant at the beginning of the yellowing period.The net photosynthetic rate(P_n),stomatal conductance(G_s),transpiration rate(T_r),and the maximum ribulose 1,5-bisphosphate(Ru BP)carboxylation rate(V_{c max}),Ru BP regeneration capacity(J_max)were obviously positively correlated with precipitation.The pathway analysis results showed that the photosynthetically physiological mechanism of yellowing period of Stipa krylovii would be different for diverse changes in precipitation and temperature.Under the current environmental conditions,J_max is the main influencing factor of the yellowing period,V_{c max} is the main limiting factor;under the warm and dry climate conditions and warm and wet climate conditions in the future,V_{c max} becomes the main influencing factor of the yellowing period,but the J_maxbecomes the main limiting factor in the warm and dry climate conditions,and there is no limiting factor in the warm and wet climate conditions.These indicated that the withered and yellow phenological change of Stipa krylovii relies on the photosynthetical capacity limitation resulted from meteorological conditions.(6)The main influencing factor of Stipa krylovii's yellowing period is temperature at present,but it will become precipitation in future climate scenarios,indicating that future climate scenarios will change the phenological change pattern of Stipa krylovii.