Effect of water supply on the germination of seven exotic and seven native species in Western Australia

摘要

The germination of seven common weeds and seven common species native to southwestern Australia was studied at three sites where they cooccur and in the laboratory. Under field conditions, final germination of the exotic species was much higher than that of the native species, and the number of days to reach 50% of final germination was lower. For some of the germination period, soil moisture was lower than expected after 48 h without rain, with one dry period lasting 10 days. Overall, germination rose with increasing wetness of the three sites, especially among the weeds. Most exotic species germinating under laboratory conditions needed less than 10 days to reach 50% of final germination which was further delayed by two days when seeds were removed from their moist substrate and allowed to dry out (air-drying) for 48 h before rewetting. Most native species took 10-35 days, with a mean delay of seven days after 48 h of air-drying. Total germination of the weeds was close to 100% and was little affected by periods of air-drying. Germination of the native species was more variable and greatly reduced by air-drying in two species. We conclude that water availability as it varies through time and space is significant in controlling germination even during the wet season. The quicker and greater responses of weed seeds to moisture may contribute towards the superior ability of weeds to colonise disturbed habitats. Differences in life form, seed size, flatness, presence of appendages, and ability to absorb or retain water only partially explain these results.