湿地水分变化对小叶章根系分解及氮素动态的影响

Effects of the changes in water content on root decomposition and nitrogen dynamics of Calamagrostis angustifolia in a natural wetland of Sanjiang Plain,northeastern China

2005年5月—2006年9月,利用三江平原典型碟形洼地的自然水分梯度作为水分变化研究的替代系统,结合分解袋法,模拟研究了湿地水分变化对典型草甸小叶章（TMC）和沼泽化草甸小叶章（MMC）根系分解及氮动态的影响。试验沿水分梯度设漂筏苔草群落（PF）、毛果苔草群落（MG）、乌拉苔草群落（WL）、沼泽化草甸小叶章群落（XII）、典型草甸小叶章群落（XI）和岛状林群落（DZL）6个分解小区。研究表明：水分条件对根系分解具有重要影响,当未来降水格局变化导致小叶章湿地形成积水环境后,TMC和MMC的根系失重率分别将降低29.12%~48.54%和21.81%~42.22%,分解速率将降低36.36%~55.17%和14.10%~32.91%,95%分解时间将增加2.95~6.34年和1.75~5.24年。TMC和MMC的根系氮含量及氮积累系数的变化较为一致,但不同小区间的变化模式差异较大。二者根系的氮素一直表现为释放,但不同小区间的释放模式差别较大。C/N对分解过程氮养分的调控作用更为重要。TMC和MMC根系的氮现存量分别为10.24和25.80 g/m2,氮年归还量分别大于3.90和4.96 g/（m2.a）。温度对根系相对分解速率具有促进作用,水分条件对其具有抑制作用。当分解环境的养分状况不发生较大变化时,相对分解速率取决于根系基质质量,当养分状况发生较大改变时,相对分解速率取决于环境养分供给状况。

From May 2005 to September 2006, the effects of the changes in water content on root decomposition and nitrogen （N） dynamics of the typical meadow Calamagrostis angustifolia （TMC） and the marsh meadow C. angustifolia （MMC） were studied using the litterbag technique in the dish-shape wetland of the Sanjiang Plain, northeastern China. In this study, a natural water gradient was applied to simulate the changes in the hydrological condition in six decomposition sub-zones vegetated with six plant communities： Carex pseudocuraica, Carex lasiocarpa , Carex meyeriana , marsh meadow C. angustifolia , typical meadow C. angustifolia and island forest. Results showed that hydrological condition had significant effects on the decomposition rate of plant roots. The formation of a hydrous environment in C. angustifolia wetland due to the changes in future precipitation pattern would lead to the decreases in the root weightless rates of TMC and MMC by 29.12%-48.54% and 21.81%-42.22%, respectively. Meanwhile, the decomposition rates of plant roots would decrease by 36.36%-55.17% and 14.10%-32.91%, and the 95% decomposition time would increase by 2.95-6.34 and 1.75-5.24 years, respectively. The changes in N content and N accumulation coefficients of TMC and MMC roots were relatively consistent, but the patterns of change in different sub-zones were variable. Under the hydrous condition, the N content in TMC and MMC roots in the six sub-zones displayed a consistent pattern of net release, although the pattern of release differed among the sub-zones. The C/N ratios played an important role in regulating the changes in N content during the root decomposition process. The N standing crops of TMC and MMC roots were estimated as 10.24 and 25.80 g/ m2.The annual returning rate for N was estimated to be greater than 3.90 and 4.96 g/m2 per year, respectively. This study indicated that temperature promoted while water condition inhibited the relative decomposition rates of roots system. Further analysis shows that the relative decomposition rate, to a great extent, depends on the substrate quality of roots if the nutrient status of decomposition environment does not change significantly. Conversely, if the nutrient status of decomposition environment changes significantly, the relative decomposition rate largely depends on the supply of nutrients in ambient environment.