Abstract:

Previous studies have shown that seed mass is related to dispersal distance, seed longevity, establishment success and fecundity. Many ecologists have employed seed weight as a trait to classify plant functional types; however, few studies of this kind have been conducted in China. Horqin Sandyland, located in the semiarid agropastoral zone of northern China, has undergone severe desertification during the past decades. Formation of active dunes, degradation of natural vegetation, and loss of biodiversity are the primary issues of environmental concern. At present, no comparative studies on the regenerative strategies of the constituent plant species have been conducted, and basic information necessary for vegetation restoration activities is lacking. We conducted a comparative study on the seed weight of 69 species in Horqin Sandyland to better understand regeneration strategies of these species for purposes of improving vegetation management and restoration.Seeds were collected at the Wulanaodu region (119°39′-120°02′ E, 42°29′-43°06′ N, 480 m a.s.l.). The climate there is semiarid with a mean annual precipitation of ca. 340 mm and a mean annual temperature of 6.3 ℃. At present, 90% of the total land has been desertified and 70% of the meadow has become saline and sodic. Psammophile-dominated vegetation is well developed. Plant diaspores are usually referred to as seeds, even though many of them are in fact fruits. We analyzed data on seeds and indehiscent, single-seeded fruit. The air-dried weight of 100 diaspores was measured for each plant. Most grasses caryopses were measured with the persistent lemmas and awns with which they are normally dispersed. The achenes of Compositae were measured with pappus and seeds and those of Cynanchum sibiricum, Metaplexis japonica and Apocynum venetum were also measured with hairs. Fruits of Xanthium sibiricum, Lappula myosotis and Bassia dasyphylla were measured with thorn and hook.The results showed that species could be divided into four groups with regard to the weight of diaspores as fruits (<0.1 mg, 0.1-0.999 9 mg, 1-9.999 9 mg, 10-99.999 9 mg). The fruits of Artemisia scoparia (0.051　7 mg) and Typha minima (0.068　2 mg) were the lightest, and those of Xanthium sibiricum were the heaviest. Species could be divided into 3 groups with regard to the weight of diasporas: 0.1-0.999 9 mg; 1-9.999 9 mg; and 10-99.999 9 mg. Seeds of Portulaca oleracea (0.151　4 mg) were the lightest, while the seeds of Sophora flavescens (46.781　6 mg) were the heaviest. Small seeds and a persistent soil seed bank might be responsible for the extensive distribution of such species as Artemisia scoparia, Portulaca oleracea, Adenophora tetraphylla, Kochia sieversiana, Lysimachia barystachys, Chenopodium glaucum, Salsola ruthenica, Cuscuta chinensis, Artemisia sieversiana, Setaria viridis, and Arundinella hirta. The pioneering species that establish on sand dunes such as Agriphyllum squarrosum, Artemisia halodendron, A. wudanica, Setaria viridis and Bassia dasyphylla had medium or high diaspore weight, or had mechanisms to protect diaspores from being carried away by the wind.