The Study Of Reproductive Ecology On Leymus Racemosus

L.racemosus (Lam.) Tzvel, gigantic, wild rye, is an endangered, but economically important, perennial rhizomatous grass. It is mainly occurring in the stabilized and semi-stabilized dunes in the northwest of the Junggar Basin of Xinjiang Uigar's Autonomous Region, China. It is not only a perfect candidate for sand stabilization and revegetation in the desert, but its genes can be used to improve cultivated wheat.Through the observation and investigation in the field and germination experiment in the laboratory, the flowering phenology, reproductive system, seed characteristics as well as seed bank in the soil were studied in the thesis. The reproductive strategies of it and its adapative mechanism to desert environment were also discussed. The main results are as follows:(1) Its flowering period, 10~15 days later than the local wheat's, was from the first ten days of June to the middle ten days of June in its natural condition. Generally, it's flowering period, no more than 10 days was very centralized, the inflorescence came into full bloom at the second day when the first floret in it opened, and the full bloom persisted approximately 3~4 days, then it turned into flowering termination.In the desert, drought air, heavy wind and other adverse factors were bad for anemogram, so the centralized opening of L.racemosus'florets could increased the pollen density in the atmosphere to make sure the stigma to receive enough pollen number.(2) Its pollen/ovule ratio was 3103, and it was self-incompatible. It owned unique characteristics of flower design and flower display: That florets in the same inflorescence opened in the way of stage and mass and its floret was dichogamous not only avoided self-pollination but geitonogamy; The hetero- velocity growth of filaments and anthers in one floret opening asynchronicly could relatively elongate"pollen longivity"; These characteristics that the lemma and palea of floret opened during blossom and closed after blossom afforded the function to protect the fertilized ovaries to guarrant the reproductive success in the extreme environment. Based on pollen fertility, pollen viability, the most pollen number laid on stigma, persistent time of viable pollen on the stigma, the delayed closure of the lemma and palea of floret and the elongation of the stigma receptivity when insufficient pollination occerred and other traits, it was easy to come to a conclusion that L.racemosus owned a series of adaptive mechanisms to the extreme desert environment to assure pollination success and the pollen shortage limiting burliness never happened.(3)The cold stratification could broadened the germination temperature range of L.racemosus, that was to say that the cold stratification decreased temperature need for germination, which indicated that L.racemosus'seed owned conditional dormancy. After a period of storage, the germination percent of the freshly harvested L.racemosus'seed gradually enhanced and the germination index gradually increased, which suggested that L.racemosus'seed needed some period of time to complete after–riping, namely it also owned no-deep physiological dormancy. Lemma and palea's existence could facilitate germiantion to some extent, but the effect wasn't significant. Disinfection treatment with sodium hydrochloride solution could restrict germination, and the restrictive function became more obvious with the concentration increasing. When the concentration was lower than 0.5%, disinfection treatment only prohibited germiantion but not decreased seed's viability. When the concentration was higher than 0.5%, disinfection treatment not only prohibited germiantion but also it decreased seed's viability. The range of its seed size was very wide, but there wasn't relationship between germiantion and seed size. The optimal thermoperiod for germination was 25℃/15℃(light/dark). The long time to onset of germination, low germintion percent, the dispersive germination process, short longivity in the soil and elongated seed not liable to come into the soil to form persistent seed bank and other negative factors were bad for the reproduction and renewal of L.racemosus'population in the nature.