The field trial was established to investigate the effects of planting condition(soil water content,soil buried depth,rhizome length)and time on the survival rate and growth of Phragmites australis rhizomes.The results indicated that survival rate and growth of Phragmites australis were affected by soil water content and rhizome length significantly,but not by soil buried depth.The survival rate of Phragmites australis in moist condition was higher than those in natural and flooding conditions.Rhizomes length did not affect survival rate,height and shoot number,but influenced biomass and buds number,which were higher with 15 cm length than those with 30 cm length.Based on the suitable soil water content(moisture)and rhizome length(15 cm),the survival rate of Phragmites australis was the highest when they were planted in May(91%)comparing to June and July.The number of shoots and buds were the highest in June,which had more suitable temperature and light for Phragmites australis to grow.Therefore,the optimizing transplanting condition of Phragmites australis was that rhizomes of 15 cm with some buds were planted in May with moisture(soil water content).
To evaluate the diurnal and seasonal variations in soil respiration （Rs） and understand the controlling factors, we measured carbon dioxide （CO2） fluxes and their environmental variables using a LI-6400 soil CO2 flux system at a temperate Leymus chinensis meadow steppe in the western Songnen Plain of China in the growing season （May-October） in 2011 and 2012. The diurnal patterns of soil respiration could be expressed as single peak curves, reaching to the maximum at 11：00-15：00 and falling to the minimum at 21：00-23：00 （or before dawn）. The time-window between 7：00 and 9：00 could be used as the optimal measuring time to represent the daily mean soil CO2 efflux. In the growing season, the daily value of soil CO2 efflux was moderate in late spring （1.06-2.51μnol/（m2.s） in May）, increased sharply and presented a peak in summer （2.95-3.94 μmol/（m2.s） in July）, and then decreased in autumn （0.74-0.97 μmol/（m2.s） in October）. Soil temperature （Ts） exerted dominant control on the diurnal and seasonal variations of soil respiration. The temperature sensitivity of soil respiration （Q10） exhibited a large seasonal variation, ranging from 1.35 to 3.32, and decreased with an increasing soil temperature. Rs gradually increased with increasing soil water content （Ws） and tended to decrease when Ws exceeded the optimum water content （27%） of Rs. The Ts and Ws had a confounding effect on Rs, and the two-variable equations could account for 72% of the variation in soil respiration （p 〈 0.01）.
WANG MingLIU XingtuZHANG JitaoLI XiujunWANG GuodongLI XiaoyuLU Xinrui
To study the effect of different water compensation on growth and physiology of reed in degraded wetlands,three water treatments in the field were conducted to test the height and photosynthesis of reed,the ions and soluble sugar contents of different organs.In the controls(without extra water compensation for 10 years),the height of reed was only 50 cm,the net photosynthetic rate,stomatal conductance,the intercellular CO2 concentration and transpiration rate were very low.The contents of Na + and Clin rhizome were higher than those in other organs.Discontinuous water compensation(continuous for 8 years,then stopped for 2 years)increased the height(2.1-fold),the net photosynthetic rate(41.8%),stomatal conductance(1.8-fold),transpiration rate(1.3-fold)of reed(Phragmites australis),and decreased the content of Na + (62.3%)and Cl- (71.1%)of rhizome significantly.Continuous water compensation(continuous for 10 years)increased the height(3.2-fold),the net photosynthetic rate(104%),stomatal conductance(2.4-fold),transpiration rate(1.5-fold)of reed,and decreased Na + (82.5%)and Cl - (64.7%)contents in rhizome, then accumulated the K+ ,H2PO4-,SO42- and soluble sugar contents significantly in rhizome.Interrupting water compensation led to the decrease of height(25.3%),the net photosynthetic rate(30.7%),stomatal conductance(17.3%) and increase of Na + (1.16-fold)in rhizome when comparing to the continuous water compensation.These results showed that recovering the degraded reed wetlands needed continuous water compensation yearly to promote reed growth.The organs of reed had corresponding physiological response characteristic to the different water compensation condition.Under long-time dry and waterlogging condition,the rhizomes both helped reed to adapt located environment,by enriching the ions such as Na+ ,Cl- ,and K+ ,H2PO4-,SO42- ,respectively.
Aims Soil CO_(2) emission from steppes is affected by soil properties and vegetation in different successional stages.Primary and secondary succession of plants frequently occurred at the meadow steppe in Songnen Plain,Northeast China,which indicates the large uncer-tainty associated with CO_(2) emission in this environment.This study aims to investigate the temporal variations of soil respiration(Rs)and the effect of plant succession on cumulative soil CO_(2) emission during the growing season.Methods Using a LI-6400 soil CO_(2) flux system,Rs of five vegetation types which represented different stages of plant succession in meadow steppes of Songnen Plain,China,was investigated during the grow-ing seasons of 2011 and 2012.Important Findings Soil temperature(Ts)was the dominant controlling factor of Rs,which could explain~64%of the change in CO_(2) fluxes.The Q10 values of Rs were ranged from 2.0 to 6.7,showing a decreasing trend with the plant successional stages.The cumulative CO_(2) emis-sion increased with the degree of vegetation succession and it aver-aged to 316±6 g C m^(−2)(ranges:74.8±6.7 to 516.5±11.4 g C m^(−2))during the growing season.The magnitude of soil CO_(2) emission during the growing season was positively correlated with above-ground plant biomass,soil organic carbon content and mean soil water content,while negatively linked to mean Ts,pH,electrical conductivity and exchangeable sodium percentages.The results implied that soil CO_(2) emission increased with the development of plant communities toward more advanced stages.Our findings pro-vided valuable information for understanding the variations of CO_(2) emission in the process of vegetation succession.
Ming WangXingtu LiuJitao ZhangXiujun LiGuodong WangXiaoyu LiWeiwei Chen
