Ecological Research On Vegetative Production And Sexual Reproduction For Alfalfa Of Different Growth Forms

Alfalfa(Medicago sativa L.) is a high quality cultivation forage plant in the worldwide, there are differentiation of various stable growth forms in the cultivars in the process of long-term breeding and selection. Insight into the differences among different growth forms of alfalfa in biology and ecology characteristics such as growth, production, reproduction etc could provide scientific basis for breeding new alfalfa cultivars. Tap-rooted(Gongnong No.1), creeping-rooted(Gongnong No.3) and multiple-leaf(8920MF) cultivars, which are suitable planting area in Northeast China, belong to three growth forms. In this research, we surveyed and compared the characteristics of vegetative growth, sexual reproduction and production among different growth forms in same cultivation and management conditions during a three-year experimental periods. Our results and conclusions showed:(1) Number and biomass of vegetative shoots of three growth-form alfalfa increased exponentially, leaf number changed by quadratic polynomial, leaf biomass increased linearly in the first planting year. Number of vegetative shoots was significantly different among growth forms at flowering stage in the first and the second planting year. Biomass of vegetative shoots was significantly different among all three years and the highest biomass occurred in tap-rooted form plants. Leaf number among different growth forms was significantly different only in the first planting year. Leaf biomass had significantly differences in the first planting and the second year, and tap-rooted form had also the highest one.(2) Number of reproductive shoots of each growth form increased by logarithmic function in the first planting year. In the second year, number of both reproductive shoots and inflorescences was significantly different among three growth forms at flowering stage, and most reproductive shoots occurred in multiple-leaf growth form and most inflorescences did tap-rooted form. In the third planting year, number of reproductive shoots was no significantly different among any growth form at flowering stage, and pod number among growth forms had significant differences at maturation stage with a greatest number in tap-rooted form and a least number in multiple-leaf. Biomass percentages of reproductive shoots of both tap-rooted and creeping-rooted forms were significantly higher than that of multiple-leaf form at podding and maturation stages in all three years.(3) Number and biomass of shoots and leaves and aboveground biomass showed a power function increase and number and biomass of pod had a linear increase with increase of plant height in process of modular growth in different growth forms. Number and biomass of leaves, biomass of stems and aboveground biomass increased by the power function with increase of shoot number. With increase of leaf number, number of inflorescences and pods, biomass of pods and stems increased linearly, while biomass of leaves and aboveground parts showed a power increase.(4) Results of density treatments revealed that density effect on plant height was not significant, but shoots/m2 was significant and number of shoots gradually decreased with density decrease in three years. Effect of density on both inflorescences/m2 and florets/inflorescence was not significant, whereas seed yield was significant in three years. On the second experimental year, seed yield of tap-rooted and creeping-rooted forms with a row spacing of 30cm×30cm was highest, but a highest value of multiple-leaf form occurred in a row spacing of 40cm×40cm. As a whole, seed yield of tap-rooted and creeping-rooted forms were higher than that of multiple-leaf one. On the third experimental year, the highest seed yield of all growth forms occurred in a row spacing of 60cm×60cm, furthermore yield of tap-rooted alfalfa was significantly higher than that of creeping-rooted and multiple-leaf ones.(5) Results of fertilization treatments showed that effect of fertilization time on seed germination rate, pods/m2 and 1000-seed weight was significant in three years. Seed germination rate and 1000-seed weight increased 16.75% and 6.80%, respectively, in the first year and pods/m2 increased 28.84% in the second year in late-June treatments compared to late-May ones. Average seed yield, seed germination rate, pods/inflorescence, seeds/pod, and 1000-seeds weight in two years was higher of 29.50%, 13.98%, 24.31%, 12.28% and 7.09% at application rate of P2O5 240 kg/hm2 than these of P2O5 120 kg/hm2. P2O5 had a greatest effect on components of each cultivar compared to both N and K2 O.(6) Results of trace element treatments indicated that Mo had a greatest effect on seed germination rate, pods/m2 and 1000-seed weight. However, effect of Zn on seed yield and pods/inflorescence was most notable. Fertilization time of trace elements had an obvious effect on seeds/pod.(7) Under same culture conditions and managements and in three growth-form alfalfa, seasonal growing rules of quantity characteristics and production traits of modular in both vegetative growth and sexual reproduction were all uniform, and relationships between different modular were stable, but differences were obvious in the number and yield of modular. Number and yield of both vegetative growth and sexual reproduction in the tap-rooted form had obvious dominance.All above results and conclusions provide a theoretical basis for directional cultivating of new breeds, selection of production breeds, forage production and sexual reproduction in alfalfa. Also, they give technical supports for alfalfa seed production.