Effects Of Simulated Precipitation Pattern Alterations And Delayed Germination On Phenotypic Plasticity Of Two Annual Plant Species

Phenotypic plasticity of plants is an important way for plants to adapt to changing environmental conditions.Precipitation pattern change is an important element of global change and has profound impacts on plants.Both Chenopodium album and Amaranthus retroflexus are widely distributed annual plants.In the temperate arid and semi-arid regions,their seeds are able to germinating within all growing season,which leads to a series of plant populations with huge phenotypic differences.This study conducted a two-year(2017,2018)control experiment in rainout shelters to simulate different precipitation amount(+30%,average annual precipitation,-30%,-50%)and different precipitation intervals(5d,15d)during the growing season.The growth,biomass,biomass allocation and photosynthetic characteristics of the two species under different sowing times(May 31,June 20,July 10 and July 30)were compared,which aimed at exploring plasticity changes to precipitation pattern changes.Results were as follows:1.Precipitation pattern alterations had different effects on the different germination times of the two species.For example,at the 5d interval of the 1st germination in 2018,the soil total nitrogen concentrates of C.album increased significantly with the increase of precipitation amount,and the difference between the 5d and 15 d intervals was significant,but there was no significant difference in the total nitrogen content of A.retroflexus.At the 15 d interval of the 4th germination,the soil total nitrogen concentrates of A.retroflexus increased with the increase of precipitation amount.2.Germination time and precipitation pattern had different effects on the growth characteristics of the two species.Height,crown diameter,1st branch number and 2nd branch number of C.album were 4.9 times,10.0 times,2.8 times,10.8 times of the 4th germination in 2017,and 7.4 times,23.8 times,3.1 times,18.2 times in 2018.As for A.retroflexus,they were 7.9 times,7.5 times,2.4 times,10.4 times in 2017,and 7.9 times,6.9 times,2.7 times,and 7.5 times in 2018.Changes of precipitation pattern had different effects at different germination times.For instance,there was no significant effect on height of C.album of 3rd germination in 2017,but 30% reduced precipitation significantly decreased the number of A.retroflexus.On the contrary,increasing precipitation amount significantly promoted height of C.album with 15 d interval,but had no significant effect on A.retroflexus at 4th germination.3.Germination time and precipitation pattern had different effects on biomass accumulation of two plants.Roots,stems,leaves,inflorescences and total biomass of C.album at 1st germination were 76.9 times,184.1 times,61.8 times,104.3 times,109.7 times of 4th germination in 2017,and 117.6 times,457.0 times,92.3 times,182.1 times,196.6 times in 2018.As for A.retroflexus,they were 22.9 times,107.9 times,62.9 times,110.8 times,95.5 times in 2017,and 68.5 times,162.9 times,58.6 times,96.0 times,94.4 times in 2018.Respond of biomass accumulation of two plants to precipitation pattern change was inconsistent.Such as the 1st germination in 2017,precipitation pattern changes had no significant effect on biomass of both two species,but at the interval of 15 d on the 4th germination,the leaves,inflorescences and total biomass increased significantly with the increase of precipitation of C.album,but A.retroflexus appeared the same trend at 5d interval.4.Under the conditions of delayed germination and precipitation pattern change,the biomass allocation of the two species had both similarity and difference.Delayed germination increased the root and leaf biomass allocation,and reduced the biomass allocation of the stem of two species.In addition,reproductive allocation of C.album increased first and then decreased with delayed germination,but A.retroflexus showed relatively stable.Precipitation pattern changes had different effects on the biomass allocation of the two species.For example,under the 5d interval of the first germination in 2018,reproductive allocation of C.album decreased with the increase of precipitation,and there was no significant difference between the 5d and 15 d intervals.However,reproductive allocation of A.retroflexus in the 15 d interval 30% reduced precipitation amount was significantly higher than others,5d and 15 d intervals were significantly different.5.Precipitation pattern changes had significant impacts on photosynthetic physiological characteristics of A.retroflexus.Photosynthetic rate(Pn),transpiration rate(Tr)and leaf water use efficiency(WUE)of A.retroflexus were both significantly affected by precipitation amount,intervals and their interaction in 2017 and 2018.Among them,Pn increased significantly with the increase of precipitation amount at the interval of 15 d.Additionally,Pn increased significantly with the prolonged of precipitation interval under the average annual precipitation and 30% added precipitation.Tr and WUE showed the same trends as Pn.