COMPARATIVE STUDIES OF PLANT GROWTH AND DISTRIBUTION IN RELATION TO WATERLOGGING

SummaryThe tolerance of Geum rivale L. and G. urbanum L. to soil waterlogging was investigated by growing plants in a compost under a variety of flooding regimes. Chemical analyses showed that high concentrations of available ammonium, iron and manganese but almost no nitrate could be extracted from this compost if conditions became sufficiently reducing, though a considerable period of flooding was required for such reducing conditions to develop. This slow rate of reduction may be due to the absence of an anaerobic microflora in the loam base of the compost.Waterlogging caused a reduction in root biomass and a change in the distribution of living roots of both species such that rooting was restricted to the surface zones of flooded soil. G. rivale possessed a rhizome‐like caudex, which is virtually absent in G. urbanum, and it is suggested that this may facilitate adventitious rooting which aids survival in waterlogged soil. The numbers of leaves, shoot apices and leaves per apex were reduced by flooding in G. urbanum but not in G. rivale. The responses of the two species to transient flooding, soil volume and soils with and without a previous flooding history are discussed in relation to their distribution.