SEISMIC STRESS RESPONSES OF SOYBEAN TO DIFFERENT PHOTOSYNTHETIC PHOTON FLUX

Physical agitation applied as periodic seismic stress (shaking) reduced stem clongation, leaf expansion, and biomass accumulation by vegetative soybeans. Level of photon flux (PPF) influenced the type and extent of plant response to mechanical stress. Plant parts responded differently as PPF varied between 135 and 592 μmol m-2 S-1. Stem length was significantly reduced by seismic stress at 135 μmol m-2 s-1 but this effect was insignificant at higher PPFs. Reduced stem length resulted from an inhibition of internode elongation. Stem diameter was unaffected by stress at the PPFs tested. In contrast to effects on stem elongation, leaf area was insensitive to stress treatments at 135 μmol m-2 S-1 but was progressively inhibited by stress as PPF increased. Statistically significant reductions in shoot f. wt and d. wt by seismic stress occurred only at 295 μmol m-2 S-1. Root biomass accumulation was not affected by seismic stress at any PPF used in this study. © 1990 Annals of Botany Company.