准噶尔荒漠大翅霸王的生殖物候及结实格局

Reproductive phenology and fruit-set pattern of Zygophyllum macropterumin the Junggar Desert,Xinjiang

大翅霸王是多年生早春开花草本植物,是准噶尔荒漠地区的建群种之一。对野生大翅霸王的生殖物候、果实形态、结实格局和种子萌发特性进行了研究。结果表明:(1)大翅霸王的营养期生长期为20—30d,占整个生活周期的1/4,生殖生长期长约90—100d,其中花期约占1/2,果熟期短;(2)大翅霸王种群能产生3种形态的果实,可将植株分为5翅型、4/5翅型和3/4/5翅型植株,它们分别占种群植株数的3.45%、83.15%和13.40%。(3)依据个体大小的变化,3种类型果实在植株上的比例发生了显著变化。随植株个体的增大,三翅果所占比例逐渐增多,由0增加到2.65%;四翅果所占比例也增多,但在二级个体上有最大比例17.01%;五翅果实所占比例最高(>80%)且没有显著变化。(4)三翅果、四翅果和五翅果内种子形态无差异,萌发率均小于30%;划破种皮能不同程度的加速和促进种子的萌发。大翅霸王特有的生殖物候和果实的表型多样性是其对荒漠干旱地区恶劣多变环境长期适应的结果。

Zygophyllum macropterum is a perennial herb that flowers in early spring and produces three types of fruits, which differ in the number of wings. To better understand how Z. macropterum has adapted to its desert habitat, its reproductive phenology, fruit morphs, fruit-set patterns, and germination characteristics were studied in a population in the Junggar Desert, Xinjiang, China. Vegetative budding of Z. macropterum occurred in early March, and its annual growth cycle lasted 4 months. The vegetative phase was 20--30 days, which accounted for a quarter of its annual growth cycle. Flowering in the population initiated in mid-April and peaked at the end of April, and the total blooming period lasted 45 days. The total reproductive phase was 90--100 days, of which the flowering period accounted for about one third to one half. Young fruits gradually formed during the full-bloom stage, and the mature fruiting phase lasted only 14--18 days. In early June, fruits began to crack and fall off, and the fruiting season lasted 80 days. After the fruits fell in mid-July, most of the ground parts of the plants dried, and the underground parts became dormant. Small autumn shoot sprouted at the base of the stem, and the lamina was small, pachyntic, and dark in color. The fruit of Z. macropterum is a capsule with membranaceous wings. The fruits hang pairwise in leaf axils and can be divided into three types based on whether they have three （ Type 3 fruits）, four （ Type 4）, or five （ Type 5） wings. The three types differ in weight and in numbers of ovaries and seeds. Lighter fruits produce fewer seeds; hence, Type 3 and Type 4 capsules can easily disperse over a long distance by wind, whereas Type 5 fruits remain near the mother plant because of their weight. Depending on the types of fruit they produce, individual Z. macropterum plants are classified into Type 5 plants, Type 4/5 plants, and Type 3/4/5 plants, which occurred in the studied population at frequencies of 3.45%, 83.15%, and 13.40%, respectively. Additionally, depending on the number of growing stems, the plants can be considered class Ⅰ （ 〈 20 stems）, class Ⅱ （ 20--50 stems）, or class Ⅲ （ 〉 50 stems）. As the mother plants increased in size, the ratio of three-winged fruits increased from 0% to 2.65% ; Type 4 fruits have the largest proportion （ 17.01% ） on class II plants. Type 5 fruits consistently were present in high proportion （〉 80%）, with the largest proportion （92.9%） found in class I plants. Seeds from all fruit types had similar germination characteristics and no significant differences in morphology. The seeds were physiologically dormant because the germination rate was low （ 〈 30% ） across a temperature range. Germination occurred slowly, and seed coat scarification of all three types of seeds could promote germination at different degrees. In conclusion, the phenotypic diversity of the fruits and reproductive phenology of Z. macropterum may be the result of its adaptation to the extremely harsh desert environment. Studying the reproductive phenology and fruit-set patterns of plants can greatly enhance our understanding of the mechanisms of adaptation to habitats and the evolution of plant life-history strategies.