Intraspecific Differentiation Of Clonal Growth Characteristics Of Leymus Chinensis Rhizome And Its Relationship With Geographical And Climatic Factors Of Original Habitat

Leymus chinensis is one of the dominant species in the semi-arid steppe of northern China in Eastern Eurasian steppe.Due to the wide range of distribution and strong ecological adaptability,abundant intraspecific variation occurred during the long-term adaptation to heterogeneous environment.L.chinensis has a mixed propagation strategy,of which rapid rhizome clonal propagation is the key to expand its population size and living space to become the dominant species of grassland community.However,the intraspecific variation of clonal fecundity of L.chinensis rhizome and its influencing factors did not be systematically researched.And besides,most previous researches mainly field observations could not distinguish the relative contribution of genetic variation and phenotypic plasticity to intraspecific variation.Here,we developed a non-destructive research method and studied intraspecific trait variation of 66 L.chinensis accessions from different geographical origins excluding the influence of plasticity by cultivating them in a garden environment.The parental environmental effects of geographical and climatic factors of original habitat on the genetic differentiation of clonal fecundity of L.chinensis were analyzed to reveal the long-term adaptation mechanism of L.chinensis to large-scale geography and climate.The main findings were as follows:（1）L.chinensis traits had a significant intraspecific variation and showed relatively high genetic diversity.The traits related to extravaginal ramets showed the highest intraspecific variation,followed by the traits related to rhizome expansion and then by morphological traits.Among morphological traits,Leaf Length（LL）had the lowest variation,while Stem Length（SL）had the highest.Among the traits related to rhizome expansion,Maximum One-direction Extended Distance（MED）had the lowest variation,while Extended Area（EA）had the highest.Among the traits related to extravaginal ramets,Clonal Growth Rate（CGR）had the lowest variation,while Multiple of Parent Shoots through Rhizome Extension（MR）had the highest.The morphological traits showed a relatively higher genetic diversity than the traits related to rhizome expansion and extravaginal ramets,whereas the qualitative traits showed the lowest genetic diversity.The region where the accessions exhibited the highest genetic diversity was located in central Inner Mongolia.The L.chinensis accessions with higher performance mainly originated from the west of Heilongjiang province and central Inner Mongolia.（2）The intraspecific trait variation of L.chinensis was the evolutionary result of long-term adaptation to the climate and geography of original habitat.The climatic fadtors of original habitat had significantly stronger effects on intraspecific genetic differentiation of L.chinensis morphological traits which determine the yield of single plant than on clonal propagation of rhizome.The intraspecific variation of heading rate and tillering of parent shoots was relatively less but significantly affected by the climate and geography of the original habitat,in comparison,the effects on tillering of parent shoots were the least.The climatic factors integrated both temperature and precipitation were the most important factors which drive the genetic differentiation of L.chinensis traits,followed by mean temperature and low temperature factors.Most notably,the effects of low temperature and large daily temperature difference on clonal reproduction of L.chinensis rhizome could not be ignored for their significant inhibition.Latitude was the most important geographical factor affecting the intraspecific trait variation of L.chinensis.The increase of latitude significantly inhibited L.chinensis growth and reproduction of rhizome.With the increase of latitude and altitude,the decrease of longitude,the leaf size and plant height appeared downward,meanwhile clonal fecundity of rhizome presented a downtrend.（3）Climate and geography of the original habitat affected the clonal reproduction of rhizome by regulating the relationship between vegetative growth and clonal reproduction of rhizome.Stem length,plant height,leaf width and leaf size were important aboveground traits that significantly affected the clonal reproduction of L.chinensis rhizome.The longer the stem length,the higher the plant height,the wider and bigger the leaves were,the superior the clonal fecundity of L.chinensis rhizome was.The geography and climate of original habitat not only directly affected the clonal fecundity of rhizome,but also had indirect effects through regulating positive feedback between vegetative growth and clonal reproduction of rhizome.（4）Vegetative growth period after fruiting before dormancy was the most vital period for clonal propagation through rhizome,moreover,the clonal propagative performance of L.chinensis in this critical period was affected by the climatic and geographical factors of original habitat.At the end of autumn,after fruiting,L.chinensis exported a large number of extravaginal ramets and accelerated the rhizome expansion,which was the most important period for the plant to expand population size and occupy space.The clonal propagative performance of L.chinensis in this critical period was affected by the climatic and geographical factors of original habitat.It displayed as:L.chinensis originated from habitat characterized by low latitude,high temperature,relatively abundant precipitation and less temperature difference exported more extravaginal ramets,the clonal growth rate was higher and the rhizome expansion was faster in the late growing season.It could be seen that the output of a large number of winter ramets and the quick expansion of rhizome at the end of the growing season were the evolutionary result of L.chinensis to adapt to climate of original habitat.（5）Plant endogenous hormones participated in regulating clonal growth of L.chinensis rhizome.Eight kinds of plant endogenous hormones such as IAA-Asp were detected in different parts of the rhizome of L.chinensis,and there were significant differences in 5 kinds of plant endogenous hormones in 8 of the 18 comparison groups.The contents of 12-OH-JA-Ile,CH₃O-IAA and IAA-Asp in rhizome nodes were significantly higher than those in rhizome internodes and horizontal buds.The contents of SA in rhizome nodes decreased with the increase of clonal fecundity of rhizome.Rhizome node was the most important part for clonal growth of L.chinensis.The differentiation activity and selection of rhizome node under the regulation of plant hormones determine the survival and developmental strategy of L.chinensis population.