ALLOCATION PLASTICITY AND MODULAR STRUCTURE IN CLONAL GRAMINOIDS IN RESPONSE TO WATERLOGGING

Three clonal rhizomatous graminoids (Carex gracilis, C. vesicaria and Calamagrostis canescens), co-dominants of Central European marshlands, were examined for their response to waterlogging. A three-year growth study was carried with treatments where the water level was (a) below , (b) at, and (c) above the soil surface to assess the changes in allo cation of plant biomass and modular structure. In waterlogged plants t otal biomass production was lower. The relatively greater shoot system s of waterlogged plants were characterized by the production of a grea ter number of tiller modules (of the order of 20%). Roots were the mos t supressed organs both in sedges and C canescens. Higher leaf area ra tios and specific leaf areas in stressed plants indicate the relative enlargement of photosynthetic structures where stems form a significan t component of the shoot (LWR < 0.5 as in Calamagrostis) in unstressed conditions; above-ground biomass in stressed plants decreased. But wh ere leaves form a major part of the shoot (LWR > 0.5 as in sedges) the n above-ground biomass and rhizomes in stressed plants increased and l eaf area index became higher. Variation of the mean module biomass in particular species was also associated with the LWR characteristics: m odules of Carex gracilis and C vesicaria were stable in biomass in all the treatments and reached 0.97 +/- 0.04 g and 0.44 +/- 0.03 g, respe ctively; in Calamagrostis the biomass of tillers varied. The number of modules increased in all species under waterlogging regardless of the architectural and reallocation differences between species. The incre ase in clonal modules is regarded as a general adaptive response to th e stress of waterlogging.