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The study showed that Artemisia scoparia contained 0.38% of volatile oil, in which, a total of 38 chemical components were identified, accounting for 87.53% of the substances detected,and 12 kinds of terpenoids compounds were the main components, accounting for 45.04% of the total. The oil had a high and rapid poison activity on Culex pipiens pallens larva and adult. The LC50 value for the larva was 12.5 mg x L(-1) within 2 days, and the mortality of the adult in 24 hours was 70% and 100% when the dosage was 1 and 10 microg x cm(-2).

The study showed that in the soil-plant ecosystem of the Songnen Plain Leymus chinensis grassland, the contents of total and available iron in soil were relatively low, while Leymus chinensis was abundant in iron. The concentrations of soil total and available iron decreased with soil depth. Soil available iron positively correlated with soil organic matter, while negatively correlated with soil pH. The dynamics of soil total iron showed a "V" curve during the growth season, with the lowest in July, and that of soil available iron was similar to soil total iron from May to August, and gradually decreased after August. The iron concentration in Leynus chinensis changed dramatically with the trend of root > rhizome > leaf > litter > stem. The iron concentrations in leaf and stem had a fluctuant decrease, while those in root, rhizome and litter were fluctuated in "V" curve. Soil A layer enriched in a little more available iron. The iron activation with an average of 0.64% increased from May to August, and decreased after August, with the lowest in October. The shift ratio from underground to aboveground part of Leymus chinensis dropped during May-July, went up in August, and then dropped again. The average shift ratio from aboveground part to litter was 105.0%, which negatively correlated with that from underground to aboveground part.

Based on the pollen combination, 14C dating, and depositional facies analysis of Momoge profile in Zhenlai County, Jilin Province, three pollen belts were divided. The results showed that Momoge Lake was formed by blocked paleo-river course depression 1500 years ago, which included three development stages, i.e., the period when river converted into lake, the early period of lake development, and the steady period. Its corresponding plant types were Artemisia-Chenopodium grassland, Artemisia-Chenopodium grassland accompanied by Betula, and meadow grassland, and its paleo-climate was dry-cold, warm-dry, and then cool-wet, and there was a warm-dry tendency in recent fifty years.

By soil column culture and field experiment, the comparison of roots distribution of spreading-leaf and upright-leaf maize cultivars in the Songnen Plain was studied. The results showed that there were differences in the roots distribution of different maize cultivars. The maximum of root dry weight appeared on the 15th day and 30th day after silking for spreading-leaf and upright-leaf maize cultivar, respectively. Compared to spreading-leaf maize cultivar, the root dry weight of upright-leaf maize cultivar was higher by 12.2%. The vertical distribution of different maize cultivar roots was different. The root dry weight rate below 20 cm depth of spreading-leaf maize cultivar was less than 19%, whereas that of upright-leaf maize cultivar was more than 23%. Compared with spreading-leaf maize cultivar, the root dry weight rate at 40-100 cm depth was higher by 43.3%. There were differences between the different maize cultivars in the horizontal roots distribution. The roots of upright-leaf maize cultivar distributed tightly in horizon. The percentage of root dry weight of upright-leaf maize cultivar in a horizontal area 0-10 cm from the plant center was higher than that of spreading-leaf maize cultivar by 9.6%. Upright-leaf maize cultivar had more roots in deeper soil depth and it distributed tightly in horizon. Therefore, it was suitable for compact-planting. It was easier to acquire high yield for upright-leaf maize cultivar because it had good roots distribution characteristics.

Stellera chamaejasme is a perennial herbaceous plant of Thymelaceae, as one of major poisonous plant species to animal, distributing in Northeast, Northwest, and Southeast of China. In some area on the degraded steppes, the plant grew with abnormal abundance and badly endangered the health of animals. The germination capacity of Stellera chamaejasme seed that collected from soil seed bank and immediately gathered from the plant was studied under different temperature, light condition and five pretreatments (rupture seed pericarp, remove seed pericarp, soaked in 98% H2SO4 for 5 min, soaked in 0.2% KNO3 for 24 h, and kept at 10 degrees C for a week). The seed germination percentage (GP) of the plant was lower in the mass and it was 13% under constant temperature 25 degrees C with dark condition. The suitable temperatures for germination of the seeds were constant 30 degrees C or alternative 10-30 degrees C. To rupture or to remove seed pericarp could significantly increase GP and it was 49% and 47%, respectively. GP under pretreatment of seed soaked in 98% H2SO4 for 5 min was 32%. The pretreatments of seed soaked in 0.2% KNO3 for 24 h and seed kept at 10 degrees C for a week had no significantly effects on increasing GP. The seed germination was not sensitive to light condition. The hardness of the seeds was mainly responsible for the seed dormancy and low germination rate. The GP of S. chamaejasme seeds in the soil seed bank was higher than that gathered in the immediate year. Based on the comprehensive analysis with the lower GP and the results of field observation, it was concluded that S. chamaejasme seeds did not germinate every year in nature, and chance of population regeneration was random or periodic.

Studies on the effects of grazing, cutting and decapitating on grass populations on the artificial grassland in the subtropical zone of China showed that moderate grazing and cutting could increase the adaptability of Dactylis glomerata and Lolium prenn due to decapitating. Decapitating could rescind the apical dominance and reproduction growth of grass, and hence, the ecological effects of grazing and cutting on grass could be realized by decapitating, and the population density, caloric value and energy accumulation of Dactylis glomerata and Lolium prenn increased obviously. Apical dominance of grasses could lower the population density, energy accumulation and intra-population competitive ability.

The calorific value of plants is dependent on their biological characteristics and energy-containing materials. The allocation of calorific value in different organs of Aneurolepidium chinese, Calamagrostic epigejos, Puccinellia tenuiflora and Chloris virgata was inflorescence > leaf > stem > dead standing. The seasonal dynamics of standing crop energy of aboveground part of four plant populations showed single-peak curve, and the energy production was Aneurolepidium chinense > Calamagrostic epigejos > Chloris virgata > Puccinellia tenuiflora. Energy increasing rate showed double-peak curve, with the first peak at heading stage and the second peak at maturing stage of seeds. Energy increasing rate was negative at the final stage of growth. The horizontal distribution of energy of aboveground part was that the allocation ratio of different organs at different growth stages was different. There existed a similar trend for vertical distribution of energy among four plant populations, i.e., was the vertical distribution of energy of aboveground part showed a tower shape, with the maximum value in 10-30 cm height. The vertical distribution of energy of underground part showed an inverted tower shape from soil surface to deeper layer, with the maximum value in 0-10 cm depth. The standing crop energy of underground part was about 3-4 times than that of aboveground part.

The seasonal dynamics of soil catalase activity of three different plants communities in Leymus chinensis grassland in northeast China were in a parabolas shape. The seasonal variation of Chloris virgata community was greater than those of Leymus chinensis community and Puccinellia tenuiflora community, and "seed effect" might be the main reason. The correlation between the activity of soil catalase in different soil layers and environmental factors were analyzed. The results showed that the activity of soil catalase was decreased gradually with depth of soil layer. The activity of soil catalase was closely correlated with rainfall and air temperature, and it was affected by soil temperature, soil moisture, and their interactions. The correlation between the activity and aboveground vegetation was very significant, and the growing condition of plant communities could be reflected by the activity of soil catalase.

This study dealt with the effects of maize stubble remaining in field on dynamics of soil microbial biomass C and soil enzyme activities. The results showed that maize stubble remaining in field could raise soil microbial biomass C and the activities of urease, phosphatase, cellulase, and invertase in soil remarkably. According to the dynamics of soil microbial biomass C and activities of the four enzymes, the five characters reached their maximum values about 60 days after sowing, and the crops were in bloom of growth. The results also showed that maize stubble remaining in field had positive effects on improving fertility and keeping high and steady yield of maize.