Research On Growth Characteristics , Stress Responses And Ecological Differentiation Of Medicago Ruthenica

Medicago ruthenica （Linn.） Trautv.is one of the most important and outstanding perennial forage legume in the world, and it plays an important role on livestock husbandry in China. It is a unique species of Medicago adapted to dry, stony locations with extremely low snowfall and very cold winters. It has more superior cold-tolerance and nutrition utilization efficiency than Alfalfa （Medicago sativa L.）, and was considered to be the most optimal forage legume cultivated in cold region. Nevertheless, the research on M. ruthenica is still less and lack systematicness, especially on the growing, development and harvest of seed, characteristics of root system, physioecological responses under salt-alkaline stress. M. rithenica distributes widely and contains many ecotypes which adapted to each original habitat, research on the ecotypic differentiation is of great significance for crossbreeding and hybridization.The results of morphological differentiation of two ecotypes, growing development under different density, seed optimal harvest time research indicated （1） The morphological differentiations of leaves, pods and seed in two ecotypes of M. ruthenica were evident. The differentias were adaptive, did not change with the environment alteration, results of local adaptation.（2） The effects of planting diversity on height, stem diameter, number of leaves, number of branches and biomass of every organ were diverse in different stage of M. ruthenica life history. On the beginning period of M. ruthenica growing season, 30 days after emergence, the effects of planting density on growth under all density treatments were unremarkable. In the final stage of growing season, planting density showed significantly effets on height, stem diameter, number of leaves, number of branches and biomass of every organ in both ecotypes of M. ruthenica. Height, stem diameter, number of leaves, number of branches and biomass of individual plant decreased with density increasing. （3） Planting density showed significant correlativity with stem diamter, number of leaves, leaves biomass and individual plant biomass in Woodland M. ruthenica; also showed significant correlativity with number of leaves and leaves biomass in Meadow M. ruthenica. Individual plant biomass markablely correlated with height, tem diameter, number of leaves, number of branches and biomass of every organ in both ecotypes. The optimal planting density for two ecotypes was 278 plants/m²,maximal hay yield for woodland and meadow M. ruthenica respectively were 2916.7 kg/hm² and 2794.5 kg/hm², maximal reproductive biomass were 333.33 kg/hm² and 622.23 kg/hm².（4） Seed of M. ruthenica which harvested on different period had diverse yield and quality due to irregular blossomming and pod maturation. The optimal harvest time was the period that can gain higher yield and higher quality of seeds. The optimal harvest time for meadow M. ruthenica was 57⁶0 days after initial anthesis, with seeds yield was 92.67⁹9.00 kg/hm²; for woodland M. ruthenica was 51⁶0 days after initial anthesis, with seeds yield was 93.33¹16.00 kg/hm². （5） The merits of woodland M. ruthenica such as more leaves, more branches, more individual plant biomass, shorter blooming period, fructification more synchronous, more infructescence, bigger thousand seeds weight, higher germination percentage, more seed yield and better root development ability were basis for breeding and hybridization work. It is a eminent material and had potential developmental prospect.Differences of taproot length, lateral root position and taproot biomass between three M. ruthenica were remarkable. Woodland M. ruthenica had better root development ability than Zhili and meadow, showed longer taproot, more lateral root and bigger root biomass. Vertical distribution pwttern of M. ruthenica root system was taproot diameter, biomass od taproot and lateral root decreased with soil depth increasing; taproot biomass mainly distributed in 0¹0cm section under root crown, lateral biomass mainly distributed in 0²0cm section under root crown. Taproot diameter, diameter and depth of root crown were acceptable indexes for breeding excellent M. ruthenica.The results of seed development and its relationship with hardseedness indicated that with the increasing of development days, water content and electrical conductivity of woodland M. ruthenica seeds decreased; fresh weight, germination percentage and thousand seeds weight raised at first reduced finally; dry weight and hard seed percentage rised gradually. The impermeability of palisade cells in spermoderm and seed hilum was one of the reason for seed hardness in woodland M. ruthenica.According to the physioecological responses of M. rithenica to mixed salt-alkaline stresses, we found that: （1） Salinity（concentration）, alkalinity（pH） and their interaction significantly influenced water content, relative growth rate, root activity and survival rate of M. ruthenica under mixed salt-alkali stresses. RGR and water content of shoots decreased with the increasing of salinity and alkalinity. Root activity was promoted by the combine of low salinity and low alkalinity, but decreased with salinity increasing under high alkalinity and salinity stresses. The influence of alkalinity on survival rate was bigger than salinity. （2） Salinity（concentration） and alkalinity（pH） significantly influenced the content of chloropyll a ,b and carotenoid in M. ruthenica under mixed salt-alkali stresses. The contents were all lower with salinity and alkalinity raising. Salinity（concentration）, alkalinity（pH） and their interaction significantly influenced photosynthetic rate, stomatal conductance and intercellular CO₂ concentration of M. ruthenica leaves. The photosynthesis indexes reduced with salt concentration and pH increasing.（3） Physioloucal responses of shoots and roots to mixed salt-alkali stresses in M. ruthenica were different. Oxalate accumulation showed very important effect on responses to mixed salt-alkali stresses in M. ruthenica. Salinity and buffer capacity reflected the mixed salt-alkali stresses better in shoots of M. ruthenica, but in roots, pH and buffer capacity reflected the mixed salt-alkali stresses better.