短命植物小疮菊异形瘦果特性及其对荒漠环境的适应

Characteristics of heteromorphic achenes of Garhadiolus papposus, an ephemeral Asteraceae species, with reference to their adaptations to desert environment

小疮菊(Garhadiolus papposus)是准噶尔荒漠中常见的具异形果实的菊科早春短命植物,其同一果序中由外到内分别产生外围果、过渡果和中央果3种不同形态和扩散方式的果实。在形态特征上,每果序中外围果5.24±0.05个,柱状弧形曲,深黄、黄至黄白色,果体长6.67±0.10mm,无冠毛,成熟时被宿存苞片所包被,果体背面下部与苞片合生,果皮厚约156.7μm,表面较光滑,瘦果及胚百粒重分别为118.10±1.30mg和46.70±0.50mg;过渡果5.39±0.14个,柱状弧形曲,灰白色,果体长7.60±0.11mm,具少量短冠毛,果皮厚约82.1μm,表面有两条纵向细棱,瘦果及胚百粒重分别为88.30±1.30mg和36.80±0.30mg;中央果5.77±0.13个,柱形近直立,深褐色,果体长9.74±0.14mm,具发育完全的冠毛,果皮厚约69.7μm,表面有多条纵向细棱,瘦果及胚百粒重分别为69.00±0.60mg和36.90±0.30mg。在扩散特点上,3种瘦果的扩散能力表现为中央果>过渡果>外围果,且散布能力与其形态特征密切相关。中央果成熟后容易从母株上脱落,发育完全的冠毛能借风力进行远距离扩散;外围果与宿存苞片紧密相连,成熟后不易脱落,散布距离很近;过渡果的散布特征介于两者之间。本文还讨论了小疮菊异形瘦果的形态特征与扩散特点对其在准噶尔荒漠中成功定居与生长发育以及物种延续和种群扩大、减少同胞果实间竞争等方面的影响。

Garhadiolus papposus is a common ephemeral Asteraceae species that germinates in early spring in the Junggar Desert. It produces three types of achenes in one infructescence that differ in morphology and dispersal behavior. To better understand how this species is adapted to its desert habitat, we studied morphological and dispersal characteristics of its achenes. The three types of achenes differed significantly in the number, shape, color, mass, length and density ofpappuses, and embryo size. Peripheral achenes, which were subtended by the inner involucral bracts （phyllaries）, were smooth, weighed 118.10 ± 1.30 mg per 100 achenes, were columnar and arcuate, yellow or yellow whitish, 6.67 ± 0.10 mm in length, and had a scarcely-developed pappus. Central achenes with numerous conspicuous thin longitudinal ribs weighed 69.00 ± 0.60 mg per 100 achenes, were columnar and arcuate or straight, brown, elongated （9.74 ± 0.14 mm length）, and had a well developed pappus. Intermediate achenes represented a range of morphologies between the ＂pure＂ central and peripheral types. In a given head, the central achenes were more numerous than intermediate and peripheral ones （5.77 ± 0.13 vs 5.39 ± 0.14 vs 5.24 ± 0.05）. In addition, central and intermediate achenes had thinner and anatomically different pericarps （half as much biomass） compared to peripheral achenes （69.7 μm vs 82.1 μm vs 156.7 μm）, and embryos in peripheral achenes were heavier than those in central and intermediate achenes （46.70 ± 0.50 mg vs 36.80 ± 0.30 mg vs 36.90 ± 0.30 mg per 100 embryos）. The three morphs differed in dispersal potential. In the laboratory, dispersal distance was longer for central than for intermediate achenes, and longer for intermediate than peripheral achenes. In the field, central ache- nes were dispersed relatively long distances by wind, whereas peripheral achenes, which are covered by lignified phyllaries, remained on the capitulum after maturation and were dispersed, close to the mother plants, only when the capitulum broke apart. Dispersal features of intermediate achenes are intermediate to those of central and peripheral achenes. We discuss how the morphological and dispersal characteristics of the three achenes types in G. papposus influenced the distribution of achenes to new areas, development of seedlings, population persistence and expansion, and competition among offspring. Heterocarpy may be partly responsible for the success of G. papposus in the Junggar desert.