A comparison of physiological, morphological and growth responses of 13 hybrid poplar clones to flooding

Summary Effects of a 30-day fl ooding period on some morphological and physiological changes and on relative growth rate (RGR) of 13 hybrid poplar clones, belonging to four different parentages i.e. T × N, T × D, D × N and N × E (with T = Popolus trichocarpa , N = P. nigra , D = P. deltoids and E = P. euramericana ) were studied under controlled conditions. Responses of the 13 clones to fl ooding differed, and they varied with duration of fl ooding period. Stomatal conductance was not reduced in any of the plants during the fi rst few days of fl ooding. However , in trees of some clones , stomata opened and then closed as fl ooding was prolonged. Net photosynthesis rates (Pn) of fl ooded trees of some clones decreased during fl ooding, but in some fl ooded clones it returned to the value of the control following a period of decrease. RGR was reduced by fl ooding in 10 clones and was correlated with reduction of Pn. Other responses to fl ooding included formation of adventitious roots and relative amount of carbon allocated to the aboveand below-ground tissues. Based on the dendrogram from the hierarchical cluster analysis, the 13 clones tested could be divided into two groups. Clones 58-280, DN-34, 311-93, DN-70, Simplot, R-419 and OP-367 were grouped into a cluster with high tolerance to fl ooding; clones 309-74, PC-1, DN-14273, 195-529, NE-353 and R-247 into a cluster with low tolerance to fl ooding.