Abstract: Employing monocotyledon Aneurolepidium chinense and dicotyledon Helianthus annuus,the two species with high alkali-saline resistance as test materials,and stressing them with neutral,alkalic,and mixed salts,this paper studied the characteristics of various stresses and their interrelations,with relative growth rate (RGR) as the main strain index.The results showed that under the same concentration,alkalic salt had a stronger effect than neutral salt,and the RGR of A.chinense and H.annuus was decreased with increasing salt concentration under the same kind of salt stress and pH conditions.When the pH was higher,the RGR decreased more obviously.In addition,the proline and citric acid contents in test plants were increased with increasing stress.The transformation of proline in A.chinense was greater than that in H.annuus,while that of citric acid was in adverse.In a word,alkalic salt stress was different from neutral salt stress in stressing plants and in plant responses.Alkalic salt stress and neutral salt stress were actually two distinct kinds of stresses.The former was better called "alkali-stress",while "salt-stress" only meant neutral salt stress.The key difference between them was their different pH value.It was reasonable to consider the buffer capacity as the strength value of alkali-stress,and the salinity as the strength value of salt-stress.An interactive effect between salt-stress and alkali-stress could be seen under mixed saline and alkali stress.

Key words: Alkali-stress, Salt-stress, Buffer capacity, pH, Aneurolepidium chinense, Helianthus annuus