关键词: 粘液繁殖体, 蒿属植物, 种子重量, 水浸, 浇水, 粘沙, 沙生适应性

Abstract: Myxospermy, a mechanism, where mucilage is produced upon being moistened, has been found in many species. Previous work indicates that myxospermy is frequently associated with species occurring in arid zones. There has been, however, little study on myxospermy with reference to a local flora. A screening on myxospermic diaspores of 124 species colonizing sandy habitats of western Horqin steppe, Inner Mongolia, was conducted to: (1) examine what species excrete mucilage, and (2) analyze the ecological significance of myxospermy. Myxospermy was judged by whether diaspores had the capacity to hold sand particles.Of the 124 species examined, 13 species, Artemisia frigida, A. gmelinii, A. halodendron, A. lavandulaefolia, A. sieversiana, A. scoparia, A. wudanica (Asteraceae), Eragrostis pilosa, E. poaeoides (Gramineae), Thymus mongolicus (Lamiaceae), Plantago depressa, P. maritime (Plantaginaceae) and Linum stelleroides (Linaceae) had myxospermic diaspores, accounting for 10.5% of the total species examined. In both treatments, i.e. soaking for 20 min and watering with 2 mm rainfall, Plantago depressa, P. maritime, Artemisia frigida, A. wudanica and Thymus mongolicus had a high proportion of myxospermic diaspores, but Artemisia gmelinii, A. scoparia and A. lavandulaefolia had a low one. In both treatments, big changes of diaspores in weight after sand-holding happened in the species such as Eragrostis pilosa, E. poaeoides, Plantago maritime, Artemisia wudanica and A. gmelinii. The mean amount of sand held by mucilaginous diaspores in both treatments was ordered as: Artemisia scoparia < A. lavandulaefolia, A. gmelinii < Eragrostis poaeoides < E. pilosaA. frigida < A. halodendron < A. sieversiana < Thymus mongolicus < Linum stelleroide < Plantago depressa < A. wudanica < Plantago maritime. For 13 species with myxospermy, diaspores were small, less than 1 mg. The mean amount of sand held by mucilaginous diaspores in both treatments was positively related to seed mass. Artemisia species were the main component of the species with myxospermy, all 7 species screened had myxospermic diaspores. However, there were differences in the mean amount of sand held by mucilaginous diaspores, weight increment of sand-holding achenes and percentage of mucilaginous diaspores between different Artemisia species. One of the adaptations of Artemisia species to shifting sand was their ability to secrete mucilage from achenes upon being moistened.Nevertheless, work on ecological significance of myxospermy of some species, and precise methods in examining mucilage of diaspores is needed before we can fully understand the relationships between myxospermic characteristics and field distribution.

Key words: mucilaginous diaspores, Artemisia, seed mass, soaking, watering, sand-holding capacity, adaptation to shifting sand