Seed distribution of four co-occurring grasses around Artemisia halodendronshrubs in a sandy habitat

摘要

In a natural population of the perennial semi-shrub Artemisia halodendron in a shifting sandy habitat inthe Horqin Desert of eastern Inner Mongolia, six isolated adult A. halodendron individuals of similarcanopy size were chosen as target plants. The density of seeds in the top 5 cm soil depth around shrubswas measured using transects aligned to the four main wind directions and at different distances fromthe shrub base on both the windward and leeward sides. The effects of shrub presence on seed distri-bution of four co-occurring grasses were examined by linking seed distribution to seed traits. Of the fourspecies, Setaris viridis and Eragrostis pilosa had small but similar seed mass, while Chloris virgata andAristida adscensionis had large but similar seed mass. The species were grouped into two cohorts: small-seeded vs. large-seeded cohorts, and shrub presence effects on seed distribution of both cohorts wereexamined. We found marked difference in the seed distribution pattern among species, especiallybetween the small-seeded and large-seeded cohorts. The small-seeded cohort had significantly higherseed accumulation on the windward than the leeward sides in the most and least prevailing winddirections and much higher seed accumulation on the leeward than the windward sides in the secondand third most prevailing wind directions, while opposite patterns occurred in the large-seeded cohort.Four species also showed marked variation in the seed distribution pattern among transects andbetween windward and leeward sides of each transect. This study provided further evidence that shrubsembedded in a matrix of herbaceous plants is a key cause of spatial heterogeneity in seed availability ofherbaceous species. However, seed distribution responses to the presence of shrubs will vary withspecies as well as with wind direction, sampling position (windward vs. leeward sides of the shrub) anddistance from the shrub.