Germination and Early Growth of Prosopis strombulifera Seedlings in Different Saline Solutions

Salinity and temperature interact in their control of seed germination, with the greatest inhibition due to salinity usually found at the minimum or maximum temperature-tolerance limits. Few researchers have recently reported results on the effects of Na2SO4 on germination and plant growth. Besides, most salinity studies have been performed using monosaline solutions, thus limiting the possibility to extrapolate the results to field conditions. The aims of the present work were a) to evaluate the germination response of P. strombulifera seeds to monosaline iso-osmotic solutions of KCl, NaCl, Na2SO4, K2SO4, anionic bisaline iso-osmotic solutions of NaCl + Na2SO4 and KCl + K2SO4 and PEG at the maximum optimum germination T° for this species (35°C), to elucidate the possible variations in ionic interactions and osmotic effects in relation to previous results obtained at 30°C, b) to determine if cationic bisaline solutions (NaCl + KCl and Na2SO4 + K2SO4) alleviate ionic toxicity similarly to anionic bisaline solutions and c) to analyze the effect of all these treatments on radicles and hypocotyls growth. The temperature shift altered ionic interactions with no alleviation of SO42 toxicity by the salt mixtures as previously demonstrated. Present work provides new evidence that the diversity of results of different authors trying to explain temperature-salinity interactions may be due not only to the intrinsic characteristics of each species but also to the differential effects of temperature on the osmotic and ionic components of salinity, on one side, and the chemical nature of the ions involved on the other, which interactions may change from synergistic to antagonistic or vice versa. Salt treatments inhibited hypocotyls and root growth with a similar pattern, being the main differences in their growth induced by PEG treatment which indicates that osmotic effect is the key factor regulating growth in these organs.