Abstract:Using field investigations and laboratory experiments, we examined the factors influencing the distribution and composition of three plant communities of Song-Nen Plain. Our results showed that:1. The salt content in the soil was a key factor determining the distribution and composition of plant communities. The dominances of Chloris virgata, Puccinellia tenuiflora and Suaeda glauca in different communities changed along a soil salt content gradient, with Suaeda glauda being the most dominant species in the soils of highest pH, Chloris Virgata being in the soils of lowest pH, and Puccinellia tenuiflora falling in between. The distribution range of Chloris virgata was wider than either Puccinellia tenuiflora or Suaeda glauca.2. Under controlled conditions in the laboratory, the germination rate, growth performances(fresh weight, height), respiration intensity,ATP content and cell membrane permeability of the three species decreased as the concentrations of Na2CO3 in the growth media increased. The salt-tolerant strength followed the order of Suaeda glauca>Puccinellia tenuiflora>Chloris virgata. Because Suaeda glauca and Puccinellia tenuiflora needed certain concentrations of salt to grow, they could not grow well at the conditions of low salt content in the soil, and, therefore, their distribution range was limited. On the other hand, the growth of Chloris virgata was evidently inhibited under high salt conditions, but not inhibited when the salt content was low, and thus their distribution spanned a wide range.3. The proline content in the tissues of Puccinellia tenuiflora was positively correlated with the total salt(particularly Na+)content in the soil, indicating that Puccinellia tenuiflora can adapt to high-salt environments by changing their internal physiological reactions.