INTRASPECIFIC VARIATION IN THE RESISTANCE TO FLOODING AND DROUGHT IN POPULATIONS OF PASPALUM-DILATATUM FROM DIFFERENT TOPOGRAPHIC POSITIONS

Many studies have analysed plant responses to flooding or drought sepa rately, without addressing the relations between plant resistance to e ach of these factors. In this paper, we compare the responses to droug ht and flooding under glasshouse conditions of three populations of Pa spalum dilatatum, a perennial C-4 grass dominant at different position s along a topographic gradient in the flooding pampa of Argentina. Our results showed that flooding effects on yield were negative on an upl and, null on an intermediate, and positive on a lowland population, wh ereas drought reduced yield equally across populations, showing that r esistance to flooding was not related to resistance to drought at a po pulation level. Drought decreased height and aerenchyma, and increased the proportion of roots, while flooding had opposite effects on these traits. The responses of the single clones that made up each populati on showed a positive relation between the resistances to both factors: along the ecocline formed by 58 clones, those more resistant to droug ht were also more resistant to flooding. In addition, the combined res istance of each clone to both factors was negatively related to yield at field capacity, (i.e. the most resistant clones were less productiv e) and unrelated to the proportion of roots and aerenchyma. This resul t agrees with predictions of Grime's plant strategy theory and differs from a few previous studies, which showed negative relations between the resistances to flooding and drought among genera and species.