Seedlings of alpine species do not have better frost-tolerance than their lowland counterparts

In contrast to adult plants, little is known about the frost-tolerance of seedlings of alpine species, despite the fact that frost has been considered as one of the main factors limiting plant recruitment in high elevation. Here we report the results of a comparative study on seedling frost-tolerance of nine congeneric species pairs with lowland (0-900 m a.s.l.) and alpine (1800-2700 m a.s.l.) distribution. Similarly to adult alpine plants, we expected seedlings of alpine species to be more frost-tolerant than their lowland counterparts. Frost-tolerance was estimated under laboratory conditions by exposing seedlings to frost events from - 1 to - 9 degrees C, calculated as the temperature at which 50% of the seedlings were lethally damaged by frost (LT50). The LT(50)values varied between - 1.95 and - 6.11 degrees C suggesting that seedling of all tested species could potentially survive mild and/or short frosts, but might be lethally damaged by severe and/or continuous frost events. The LT(50)values for lowland and alpine species did not differ statistically and were on average - 3.96 +/- 0.18 degrees C and - 4.16 +/- 0.43 degrees C, respectively. These findings did not confirm our hypothesis that seedlings of alpine species have higher frost-tolerance than seedlings of lowland species. Four possible reasons could explain this pattern. They include (1) comparable levels of negative-stress in both lowland and alpine habitats, (2) opportunistic seed germination strategy in alpine plants, (3) peculiarities of our experimental set up and (4) potentially stronger effects of drought on alpine seedling survival than frost.