Seedbank characteristics of a Nebraska sandhills prairie

Abstract

Evaluating seedbank ecology is critical for understanding plant community development and successional patterns and for identifying factors regulating population dynamics. The relationships among seedbank composition, seedbank depth, seed dormancy, and vegetative expression were evaluated for a range site on a Valentine fine sand soil (mixed, mesic Typic Ustipsamments) in the Sandhills Prairie. Twenty soil samples were collected at each of 2 depths (0 to 5, 15 to 20 cm) in early June 1990 and 1991 from 12 macroplots (32 X 32 m) representing 3 range condition classes. A seed extraction and germination trial was conducted to determine the diversity, size, and germinability of the persistent seedbank. Seedling emergence was counted in a greenhouse, with and without a 14-day prechilling (3 to 5 degrees C) stratification treatment, to characterize seedbank dormancy. Fourteen grass species, 17 forb species, and Schweinitz flatsedge (Cyperus schweinitzii Torr.) were identified in the seed bank. Two additional genera (Carex and Euphorbia) also occurred in the seedbank. Only 10 species occurred in 8 or more macroplots in both years. Aboveground botanical composition was not correlated with (P > 0.10) seedbank species composition. More germinable seeds occurred in the 0 to 5 cm depth (P < 0.01) than the 15 to 20 cm depth. Also, the species diversity and seed number were greater in the shallower depth. Germination percentage was low for all types of vegetation. Lambsquarters (Chenopodium album L.) and annual eriogonum (Eriogonum annuum Nutt.) had the largest seedbanks, but germination was less than 6%. Sand dropseed [Sporobolus cryptandrus (Torr.) Gray] and sand lovegrass [Eragrostis trichodes (Nutt.) Wood] were the most abundant perennial grasses and accounted for about 60% of the germinated seeds. Prechilling increased seedling emergence of grasses (P < 0.01), forbs (P < 0.01), and grass-like species (P < 0.01). Perennial grasses emerged first, forbs later, and grasslike species exhibited a bimodal emergence pattern. Based on germination percentage and emergence data, sand dropseed has the potential to colonize openings in the Sandhills prairie, possibly to the exclusion of many annuals occurring in the seedbank.