Local adaptation of the clonal plant Ranunculus reptans to flooding along a small-scale gradient JOHN P. M. LENSSEN, MARK VAN KLEUNEN*t, MARKUS FISCHER *-r and HANS DE KROON Department of Ecology, University of Nijmegen, Toemooiveld 1,6525 ED Nijmegell, the Netherlands, and t Institute of Environmelltal Sciences, University of Zurich , Wintherthurerstrasse 190, CH-8057 Zurich, Switzerlalld Summary 1 Plant species are known to segregate along small-scale flooding gradients. We tested whether differences in flooding duration can also result in genetic differentiation in the clonal species Ranuneu/us replans, which naturally grows in both a lakeside microhabi tat and a landside microhabitat with shorter periods of flooding. 2 We compared traits related to fitness, and clonal life-history traits, of 432 plants rep- resenting nine genotypes from each microhabitat, grown without flooding or with short or long flooding duration. We also determined aerenchyma contents and carbohydrate use efficiencies during flooding in plants of these 18 genotypes. 3 In the flooding treatments, genotypes from the lakeside microhabitat produced sig- nificantly more rosettes and rooted rosettes than genotypes from the landside microhabi tat. This indicates small-scale local adaptation to flooding duration in R. replans. 4 Unexpectedly, genotypes from the landside microhabitat had a higher proportion of aerenchyma in their roots than those from the lakeside microhabitat. Carbohydrate use efficiency was high in all genotypes. These physiological traits cannot therefore explain the observed local adaptation. S Genotypes from the lakeside microhabitat produced shorter stolon internodes than genotypes from the landside microhabitat when flooded. Moreover, in the treatment with long flooding duration, there was selection for reduced stolon internode lengths, which might help to reduce respiratory losses. This suggests that local adaptation is a consequence of differences in plasticity of internode length. 6 Our results indicate an important role for flooding in plant microevolution by demon- strating that variation in flooding duration can induce intraspecific specialization even within populations. Physiological traits that determine differences in flooding tolerance between species do not, however, seem to have played a key role in this differentiation. Key-words: aerenchyma, carbohydrate storage, clonal plant, flooding, local adaptation, microevolution, phenotypic plasticity, Ranuneu/us Introduction Variation in duration of Hooding isan important factor maintaining species diversity in plant communities (Keddy 1984; Pollock et al. 1998; Silvertown et at. 1999) because species can be specialized for different Hooding regimes and many species can therefore coexist on a larger spatial scale (Keddy 1984; Silvertown et al. 1999 , Correspond ence: Jo hn P. M. Lenssen (tel. +31 243653 3 47 ; fax +31 24365 2409; e-mail John.Lenssen@sci.kun.nl). 'Present address: Institute of Biochemistry and Biology, University of Potsdam , Villa Liegnitz, Lennestr. 7a, D-1447 1 Potsdam, Germany. 200 I). Evidence for such a niche separation mechanism is provided by large differences between species in survival and growth responses to Hooding duration (Crawford 1992; He et al. 1999; Vervuren et al. 2003), which are associated with differences in physiological and morphological trait s. For example, species from habitats with long flooding periods may reduce respiratory losses when Hooded by red ucing their size (Sand-Jensen & Frost-Christensen 1999; Voesenek et al. 2004) and may also increase photosynthesis by improving internal aeration (Justin & Armstrong 1987; He et al. 1999) and increase carbohydrate use efficiency (Crawford 1992). Niche separation along Hooding gradients, and accom- panying differences in physiological traits, suggest that First publ. in: Journal of Ecology 92 (2004), 4, pp. 696-706 DOI: 10.1111/j.0022-0477.2004.00895.x Konstanzer Online-Publikations-System (KOPS) URN: http://nbn-resolving.de/urn:nbn:de:bsz:352-124758