Kos, Martijn , Poschlod, Peter .
Determinants of inter-specific variation in germination response to rain in a semi-arid savanna: microhabitat versus life history.
IN (semi-)arid environments the risks of germination are mainly related to water availability. Two traits that determine the germination response to rain are germination speed and osmotic stress tolerance during germination. A fast response has potential fitness advantages but increases the chance of death due to insufficient rain. This risk may differ between microhabitats. Variation in these traits may therefore be related to different microhabitat associations. To test the hypothesis that variation between species in germination response to rain is caused by differences in microhabitat we determined in addition to the germination traits canopy association and soil texture preference for 28 plant species from the Southern Kalahari. However, variation between years in precipitation pattern at the start of the rainy season may favour risky early germination in some years and cautious late germination in others. This may lead to different germination strategies even within the same microhabitat. Other life history traits are expected to differ between high-risk and low-risk germination strategies. It has been demonstrated that decreasing germination fractions cause increased specialisation to favourable conditions and large seedlings are more tolerant to drought. To control for life history effects on germination traits we also measured germination fraction and seed mass. Data were analyzed using phylogenetically independent contrasts in multiple regression models. We only found an effect of microhabitat in annuals: germination speed was positively correlated with preference for fine-textured soils and negatively correlated with canopy association. Osmotic stress tolerance was not correlated with habitat variables at all, but there was a positive correlation with germination fraction for all species and perennials. Germination speed was also positively correlated with germination fraction for all species and perennials. This demonstrates that life history is a major determinant of the variation in germination responses to rain within (semi-)arid environments.
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1 - University of Regensburg, Institute of Botany, Regensburg, D-93040, Germany
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 31st, 2006
Time: 10:30 AM