Responses Of Module Growth Of Chloris Virgata Clones To Shortened Growing Period Under Experimental Conditions In Songnen Plain

Chloris virgata is an annual tufted grass with a wide ecological adaptability,which is one of the most common weed in north china.It grows fast and has large plasticity during growth period.Seeds of C.virgata can germinate through complete life history from spring to summer.As a strong saline-alkali plant,C.virgata distributes in northeast salinization meadow widely.It can form a single dominant species or main associated species community in extreme alkali spot habitats where topsoil has been lost.It plays an important ecological role during the restoration of alkali spot vegetation.Therefore,experimental study on the growth of C.virgata in different sowing time has important theoretical and practical significance.By plot experiment and sample measurement at different sowing time in two years,we analyzed growth,production,biomass allocation and variation of C.virgata modules at different sowing time,which can provide scientific accumulation for ecological theory and research method of clonal plant.The main findings are as follows:(1)Growth,production and biomass allocation of C.virgata clones and modules were different at different sowing time.In a certain time interval of nine days,the largest tuft size was on May 25(the first sowing)and the minimum was on July 31(the last sowing).With the sowing time delayed,tuft size decreased gradually.The number of vegetative tillers,biomass of inflorescence,vegetative tillers,reproductive tillers and total tillers had the same trend with tuft size increase.With the sowing time delay,the number of vegetative tillers and total tillers firstly increased and then reduced,and reached the minimum value on June 4.The minimum value of reproductive allocation was 26.71%±3.46% on May 25,2014.The largest value of reproductive allocation was 49.07%±4.41% on July 24,2014.The minimum value of reproductive allocation was 30.35%±4.01% on June 4,2015.The largest value of reproductive allocation was 52.19%±9.93% on July 31,2015.The minimum value of heading rate was 67.07%±6.39% on June 14,2014.The largest value of heading rate was 99.44%±2.12% on July 31,2014.The minimum value of heading rate was 74.57%±8.68% on June 24,2015.The largest value of heading rate was 100% on July 24 and July 31,2015.With the sowing time delay,the overall trend of reproductive allocation and heading rate increased gradually.Quantitative characteristics of C.virgata clones and modules in 2015 were higher than that of 2014,but there was no significant difference between two years.(2)At different sowing time,reproductive tillers of C.virgata had only one 5th height class on July 31 and had 5 height classes from May 25 to July 3 in 2014;reproductive tillers of C.virgata had 4th or 5th height classe at last two sowing time,and had 5 classes from May 25 to June 24 in 2015.At the first sowing time,the largest number of reproductive tillers of C.virgata populations was 2nd height class in two years,were 319.18±26.47 ramets/m2 and 376.95±4.97 tillers/m2 respectively.With the sowing time delayed,the height class of reproductive tillers decreased gradually,but the largest number of height class increased gradually.The change of biomass of every height class was same to its change of number.Statistical analysis showed that: with the extending of growth time,the number of reproductive tillers of 1st,2nd and 3rd height class increased gradually,with linear function,power function and exponential function,reached significant or extremely significant levels(P < 0.05 or P < 0.01).The number of reproductive tillers in 4th height class increased in the form of conic.The number of reproductive tillers in 5th height class decreased gradually in the form of linear function,power function and exponential function and reached very significant levels.With the extending of growth time,the variation of biomass of reproductive tillers was same to number.With the extending of growth time,the growth rate of reproductive tillers was 1st class>2ed class>3rd class both in number and biomass.The number and biomass of reproductive tillers in 4th height class reached maximum about 80 days.(3)The change of each quantitative characteristics of C.virgata population had certain regularity.With the extending of growth time,tuft size,number of vegetative,biomass of inflorescence,vegetative tillers,reproductive tillers,total tillers increased remarkably and heading rate,reproductive allocation and reproductive growth rate decreased remarkably in the form of linear function,power function and exponential function,respectively.The number of reproductive tillers and total tillers increased after reduced in the form of conic and reached significant or very significant levels.The variation of each quantitative characteristics was same in two years.(4)The growth regularity of clone size of C.virgata is consistent with module at different sowing time.The number and biomass of vegetative tillers,reproductive tillers,total tillers all increase remarkably according to the growth of tufts in the form of linear function expect individual sowing time.The growth rate of fitting equation(b value)of the number of vegetative tillers at pre-sowing time were greater than the late sowing time and the number of reproductive tillers and total tillers at pre-sowing time were less than the late sowing time.With the sowing time delayed,the growth rate of biomass of vegetative tillers,reproductive tillers and total ramet reduced gradually.The variation of each quantitative characteristics was same in two years.