A thorough discussion and analysis on the history as well as the current states of the environment and vegetation in Maowusu Sandy grassland is presented. Using a combination of both qualitative and quantitative methods, the author proposed the general principles and models for the grassland development there based on the ecological background information. Particularly this includes: the water balance principle, sustained development principle for semi-fixed sand dunes, net-belt planting principle; grass and agroforestry model for low land, semi-artificial cultural model for soft hills and natural grazing model for hard hills.

The seasonal changes of N, P and K contents in the soil of an Aneurolepidium chinensis grassland were relatively high in the initial growth stage, relatively low in the peak growth stage from June to August and went up again at the end of the growth season.The N, P and K concentrations in the aboveground tissues were 3.6, 2.9 and 2.8 times, respectively, of those in the below ground. The seasonal changes of these three elements assumed a singlepeaked curve. They gradually increased at the initial growth stage, maximized in August, and then gradually declined. The concentrations of the three elements tended to increase during the growth season, and an apparent gradual accumulation of them in the growing roots was found.An analysis of the seasonal dynamics of N, P and K in the plant-soil system revealed that the proportions of them in different compartments tended to reach a constant with time. In the steady state, the N, P and K contents decreased 21.23, 5.14 and 2.99%, respectively, in comparison with the initial concentrations. In other states, the N, P and K concentrations tended to increase in all the compartments, especially in the litter and roots, which suggested that litter and dead roots are the major nutrient storage pools.

Kochia sieversiana is an alkali-tolerant annual herb belonging to Chenopodieceae. Based on data measured in tow growing seasons, the density-dependent rule of different quantitative characters and the mechanism of quantitative regulation on the natural population of K. sieversiana in the alkaline meadow in the Song-Nen Plain of China were analysed in this paper. The mergence equations of power function that were simulated by sampling two growing seasons were the best descriptive models describing the density-dependence of the population characters, including mean weight per plant, mean fruit weight per plant, fruit weight per unit area, fruit weight/above-ground biomass ratio in the ripening stage. The results of our comprehensive analysis showed that the carrying capacity of environment varied with habitat conditions, and that both the carrying capacities of environment and the effects of density-dependence were larger in the ripening stage than in the flowering stage in the two seasons. The effect of density-dependence was a process of chain reaction. The population regulation was lastly realized by reproductive strategies which increased or lessened energy allocation to the reproductive growth.

The patterns of accumulation and distribution of K+ and Na+ in the tissues of Aneurolepidium chinense(Kitag), Puccinellia tenuiflora (Scribn. et Merr.), Chloris virgata (SW.), Aelirepus litoralis var. sinensis and Suaeda glauca (Bunge) in a saline grassland of Song-Nen Plain were discussed. The results showed that S. glauca had the highest Na+ concentration (5,491.0μmol Na/g dw), followed by A. litoralis and P. tenuiflora which had 225.85 and 177.7μmol Na/g. dw, respectively. The lowest levels were found in A. chinense and C. virgata which contained 20.2 and ll.31μmol Na/g. dw, respectively. The Na+ content of these species was correlated with the levels of Na+ in the soil. The Na/K ratio was highest in S. glauca (25.74) and lowest in C. virgata(0.028).The sodium accumulation (y=μmol Na/g dw) in A. chinense and C. virgata could be best described by an equation y=Ym/[-1+e(a+b1x1+b2x2)], where x1 is the soil salt content and x2 is the soil PH. In S. glauca, P. tenuiflora and A. litoralis, the Na+ accumulation was described by the equation y = a + b1x1 +b2x2. The Na+ accumulation rate, which was defined as the % increase in the Na+ concentration in the tissues of grass for every 0.1% increase in the soil salt content, followed the order of C. virgata>A. chinense>P. tenuiflora, A. Litoralis var. sinensis and S. glauca. The younger tissues, having a more active metabolism, were found to be the major sinks of accumulated Na+ with increasing soil salinity. The Na+ accumulation rate in C. virgata was markedly increased in different plant tissues, while K+ content decreased with the increase in the Na+ accumulation rate. However, in S. glauca the rate of K+ accumulation increased with the increased in the rate of Na+ accumulation.

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.

The relationship between vegetation degeneration and soil salinization in an Aneurolepidium chinense grassland of Song-Nen Plain is discussed in this paper. Importance Value (Ⅳ). Relative Coverage (C′) and Relative Above-ground Biomass (W′) are used as indicators of vegetation degeneration. Electrical Conductivity (EC) and Exchangeable Sodium Percentage (ESP) are used as indices of soil salinization. The relationships among Ⅳ, C′, EC and ESP can be best described by Ⅳ=60.1 × 0.69EC, Ⅳ =64.03 ×0.97ESP, C′ =95.48 ×0.95ESP, and C′=96.2×0.56EC, respectively. This suggests that Ⅳ and C′are negatively correlated with EC and ESP of the soil. It is shown that W′is positively correlated with both soil organic matter (OM) and hydrolysable nitrogen (N) contents (rOM=0.6486** and rN=0.8809**). Both EC and ESP can be described as a function of OM. The regression equations are EC = 8.84 × 0.85OM and ESP= 38.93 ×0.96OM, respectively. The results indicate that the saline soils of Song-Nen Plain can be effectively ameliorated by increasing soil organic matter and nitrogen inputs.

A differential equation system model was proposed and implemented to simulate the dynamic interactions between the plants and soil variables such as water and main salt element concentrations on the alkalized grassland on songnen plain in Northeast China. The system variables in the model included above and underground biomass of major plant species, soil water content, soil organic content, and soluble and exchangeable cation concentrations of sodium and calcium in the soil. The processes considered in the model included soil cation and water movement, plant growth under different soil alkality, plant transpiration and soil evaporation, liter accumulation and decomposition, and soil organic matter accumulation and mineralization. The model emphasized the effects of underground biomass on soil moisture characteristics and soilhydraulic conductivity and successfully explained the coupling between the biomass and soil environment.

Grazing degradation trajectories of the main steppe rangelands in Inner Mongolia were studied by combining the experiments in the typical steppe area and the investigation in a large region. 1. The positive and negative,qualitative and quantitative grazing indicator species were distinguished; Species with preference to moderate grazing pressure were also recognized.2. Restoration of the degraded steppe rangeland demonstrated that the rhizomatic grass rehabilitated more quickly than tossuck grass; the restoration process was of monostable state; and the restoration dynamics corresponded generally to its spatial changes along a grazing gradient.3. The main steppe rangeland communities dominated by Stipa gobica, S. breviflora, S. krylovii, S. grandis, S. baicalensis and Aneurolepidium chinense will converge into Artemisia frigida community under sustaining grazing influence. A. frigida is the most effective quantitative indicator species of grazing pressure. It is also a fine forage species and an important species for resisting steppe degradation.4. The concept of steppe degradation was discussed. The difference and relations between steppe retrogression and rangeland degradation were analyzed. The grazing retrogression of steppes was divided into two successive stages, that is, rangeland utilization (improvement) and degradation. The quantitative critaria of rangeland degradation were established.5. A computerized monitoring and decision-making system of steppe rangelands was preliminarily discussed, including the three steps of monitoring, assessment and decision-making.

Ecological mapping is to analyse the spatial patterns and the relationships of vegetation and ecological factors with the aid of graph. The use of geographic information system (GIS) for ecological mapping makes vegetation ecology develop from qualitative analysis to quantitative and graphical analysis and image processing. This paper introduces the establishment of the ecological mapping system of the Ordos Grassland Station using EPPL7 GIS software, and the automatic production of the potentical desertification map, the ecological planning map for vegetation, the integrated ecological map and the desertification monitoring map of the Ordos Grassland Station.

This paper concerns mainly the midday depression of transpiration and water potential gradiant of the soil-plant system of some mesophytes and xerophytes in ordos Sandland of China. The conclusions are given below:1. A new concept of dividing the ecological types in light of plant water relations is provided based on the midday depression of transpiration, and three types of typical features of different plant species are given: a. non midday depression type; b. weak midday depression type; c. strong midday depression type.2. By analyzing the water potential gradiant of the soil-plant system, we hypothesized that population density is affected by the sensitivity of soil water availability change to the change of leaf stomatal resistance

Forty seven quadrats were surveyed in a saline meadow land of Hexi Corridor. The samples were analyzed using DCA ordination procedure to determine the distr bution patterns of the plant communities. Five quadrat groups were separated after DCA ordination. The vegetation distribution patterns were explained by soil environmental parameters including organic matter content, total salt content, pH and underground water depth. The results indicated that soil salt content and moisture were closely related to the under ground water depth in arid-saline area.