Effects Of Simulated Rainfall Pattern On The Phenotypic Plasticity Of Two Pioneer Grasses At Different Sowing Times

The changes in plant phenotypic plasticity reflect the adaptation of plants to the environment and the changes in rainfall patterns and differences in sowing time affect plant growth and reproduction.Setaria viridis and Chloris virgata are two common annual grassland pioneer plants,and their phenotypic characteristics are more sensitive to environmental changes.This study under 4 different sowing dates(5.30,6.24,7.19 and 8.13 in 2019 and 5.10,6.10,7.10 and 8.10 in 2020),three different rainfall(+30%,monthly average rainfall in the growing season,-50%),two different rainfall intervals(5d and 15d)and were set.The growth,biomass,and physiology related of the two species were measured,and the effects of changes in rainfall pattern and sowing time on the life history characteristics of the two species were explored.The main results are as follows:1.Overall,the growth and production characteristics of the two species showed an increasing trend with increasing rainfall,and a decreasing trend with decreasing rainfall: the crown diameter of S.viridis when the rainfall interval is 5d in the first sowing period in 2019,and the plant height and crown diameter of S.viridis when the rain interval is 5d in the third sowing period in 2020 are the smallest under the rain reduction treatment,when the rainfall interval was 5 days in the second sowing period in 2019,the crown diameter of C.virgata under the increased rainfall treatment significantly greater than 15 days.When the rain interval is 5d in the second sowing period in 2019,the stems,leaves,inflorescences and total biomass of C.virgata,as well as the inflorescences,seeds and total biomass of C.virgata when the rainfall interval is 5d in the fourth sowing period in 2020 all showed increasing trend with the increase of rainfall amount increased.When the rainfall interval is 5 days in the second sowing period in 2020,the root and leaf biomass of C.virgata under the rainfall enhancement treatment and the root and total biomass under the control rainfall treatment are significantly greater than 15 days.2.The response of the biomass allocation of the two species to changes in rainfall patterns is complex,showing different trends in different years and sowing dates: in 2019,when the rain interval of the first sowing period is 15 days,the distribution of leaves of the C.virgata,and the root distribution of the C.virgata when the interval of rains is 5d in the second sowing period decreases with the increase of rainfall.In 2019,when the rainfall interval of the second sowing period was 5 days,the stem allocation of S.viridis and the reproductive allocation of C.virgata when the rainfall interval was 15 days increased with the increase of rainfall.In 2019,when the rainfall interval of the first sowing period is 5d,the root distribution of S.viridis under the increased rainfall treatment is less than 15 d,and when the rainfall interval is 5d,the leaf distribution of C.virgata under the increased rainfall treatment is greater than 15 d.3.The growth,biomass and biomass allocation of the two species showed similar changes in response to different germination times.In the two-year experiment,the growth indicators(plant height,cluster diameter,root length,number of seeds)and biomass(roots,stems,leaves,inflorescence,seeds,and total biomass)of the two species showed a gradual decline with the delay of sowing time and there are significant differences between sowing dates.The allocation of roots,stems and leaves of the two species all tended to decrease gradually with the delay of sowing time,while the distribution of reproduction showed a trend of increasing gradually with the delay of sowing time.4.The physiological characteristics of the two species are more sensitive to drought treatment,but their response modes are different.The photosynthesis rate,transpiration rate and water use efficiency of the two species decreased with the decrease of rainfall,and increased with the extension of the interval between rainfall.Under the reduced rainfall treatment,the photosynthetic rate and transpiration rate of the two species in the first sowing period in 2019,and the photosynthetic rate and water use efficiency of the two species when the rainfall interval of the second sowing period in 2020 is 5 days are significantly lower than those of the control.In each sowing period,there are results that photosynthetic rate,transpiration rate or water use efficiency when the rainfall interval is 5 days are significantly less than 15 days.