Persistent soil seed banks in Phacelia secunda (Hydrophyllaceae):: experimental detection of variation along an altitudinal gradient in the Andes of central Chile (33°S)

1 It is unclear whether soil seed banks in alpine environments are a result of selection for extended seed dormancy, of ideal conditions for seed preservation in the soil, or a combination of both. 2 The nature of the soil seed bank was investigated in the perennial herb Phacelia secunda (Hydrophyllaceae) through reciprocal burial experiments using seeds obtained from populations growing at 1600, 2200, 2900 and 3400 m a.s.l. in the mediterranean Andes of central Chile. At the four elevations, six replicates of 50 seeds each, from each of the four elevational sources, were buried at 5 cm depth in mesh envelopes, placed in wire cages to protect against predation. Seeds were retrieved 1,2 and 3 years after burial, and numbers of ungerminated seeds, and of those that remained viable, were determined. 3 At all elevations of seed burial, increasing proportions of seeds remained ungerminated, and proportionately more of the ungerminated seeds remained viable, as elevation of source of seed increased. For seed from low elevation, more seeds remained viable in the soil at the higher burial sites. However, for the seeds from higher elevation sources, seeds remaining viable were similar in number at all sites for seed burial. Half-lives of seed buried at the source elevation, calculated from the log-logistic distribution, increased with elevation, and ranged from 188 days at 1600 m to 354 days at 3400 m. 4 The results suggest that the propensity to form a persistent seed bank in P. secunda increases with elevation. Seeds from the highest elevations had the longest persistence, and this was largely unaffected by soil preservation conditions. Seeds from lower elevations survived for less time, and this was modifiable by preservation conditions. These results suggest that both selective effects and soil conditions may be involved in soil seed bank expression in the alpine environment.