【作者】 郭雪莲；

【导师】 吕宪国；

【作者基本信息】 东北师范大学 ， 湿地科学， 2008， 博士

【摘要】 湿地氮循环过程不仅影响湿地系统自身的调节机制,其在地球表层系统中所表现出的特殊动力学过程还与一系列全球环境问题息息相关。湿地水文过程控制着湿地的形成与演化,是形成和维持特殊湿地类型与湿地过程的决定性因子。湿地水文条件的变化影响着湿地植被的空间格局、植物的生长状况和植被的生存环境,并最终通过改变湿地植物群落特征而影响湿地氮循环过程。本文通过野外定位测定和室内分析,对比研究了三江平原不同水位梯度上3种典型湿地植物—土壤系统的氮循环特征,采用“空间代替时间”的方法,阐明湿地不同演替阶段氮循环的基本特征,揭示了淡水湿地不同水位梯度下植物—土壤系统氮循环模式,建立了淡水湿地不同水位梯度下植物—土壤系统氮循环模型,为深入研究湿地氮循环的生物地球化学机制和规律提供理论基础。主要得出以下结论:小叶章湿地、乌拉苔草湿地和毛苔草湿地土壤中,氮主要以有机氮的形态存在,有机氮在总氮中所占的比例高达99%以上,有利于氮的储存。3种湿地土壤中各形态氮的含量和分布特征均存在较大差异,这主要与由碟形洼地的中心向边缘倾斜的地形差异所导致的水分条件和土壤类型差异以及氮素物理运移的差异有关。3种湿地土壤中各形态氮的垂直分布和季节变化特征明显不同,这与不同土层和不同时期影响氮分布的主导因素不同有关。小叶章湿地、乌拉苔草湿地和毛苔草湿地植物地上部分各器官的总氮含量在生长季内均逐渐降低;地下根系中总氮含量在生长季内均波动较大;枯落物总氮含量在生长季内均逐渐降低,并表现为乌拉苔草湿地>小叶章湿地>毛苔草湿地。三者地上部分氮积累量表现为乌拉苔草湿地>小叶章湿地>毛苔草湿。毛苔草湿地地下根系氮积累量始终最高,乌拉苔草湿地和小叶章湿地则呈交替变化趋势。三者各器官的氮积累量在生长期表现为根>叶>茎,在成熟期表现为根>茎>叶,说明根是植物亚系统中主要的氮储库。三者枯落物中氮积累量均随时间的推移而逐渐增加。无论在地表还是在土壤剖面的不同深度,棉布在小叶章湿地、乌拉苔草湿地和毛苔草湿地分解小区内的分解速率均不同,说明环境条件对于物质分解有着重要影响。棉布的分解速率均与水温以及不同深度地温呈一定的正相关关系;与土壤含水量呈一定的负相关关系;与土壤容重正相关;与土壤pH值正相关。相同的环境条件下,小叶章、乌拉苔草和毛苔草湿地枯落物及根系的分解速率与棉布的分解速率明显不同,说明枯落物和根系的质量对物质分解有重要影响。枯落物的分解速率与其最初的N和P浓度均呈正相关关系,与最初的C、C/N、C/P和N/P均呈负相关关系。根系的分解速率与C/P和N/P均呈显著的正相关关系,而与P浓度呈极显著负相关关系。分解过程中,小叶章、乌拉苔草和毛苔草湿地枯落物和根系均发生氮的净释放,枯落物各时期的氮绝对量表现为毛苔草湿地枯落物<乌拉苔草湿地枯落物<小叶章湿地枯落物。根系各时期的氮绝对量均表现为小叶章湿地根系最低,乌拉苔草和毛苔草湿地根系则呈高低交替的变化趋势。小叶章湿地、乌拉苔草湿地和毛苔草湿地植物—土壤系统中,土壤是主要的氮储库;植物亚系统的氮储量所占比例较低,根和枯落物是植物亚系统中的主要氮储库。小叶章湿地、乌拉苔草湿地和毛苔草湿地植物—土壤系统的氮储量分别为714.93 g·m^-2、626.49 g·m^-2和552.59 g·m^-2。小叶章湿地、乌拉苔草湿地和毛苔草湿地植物—土壤系统中,每年地上部分吸收的氮量表现为乌拉苔草湿地>小叶章湿地>毛苔草湿地;每年地上部分向枯落物分室转移的氮量表现为毛苔草湿地<乌拉苔草湿地<小叶章湿地;每年从地上部分向根分室再转移的氮量表现为乌拉苔草湿地>毛苔草湿地>小叶章湿地,并且乌拉苔草湿地是毛苔草湿地的3倍,是小叶章湿地的5倍;每年根吸收的氮量和由根向土壤转移的氮量均表现为小叶章湿地<乌拉苔草湿地<毛苔草湿地;从枯落物分室向土壤分室转移的氮量则表现为小叶章湿地>乌拉苔草湿地>毛苔草湿地。小叶章湿地、乌拉苔草湿地和毛苔草湿地植物—土壤系统氮循环特征明显不同。虽然枯落物分解释放的氮量随水位降低而显著增加,但3种湿地土壤库的氮输出均超过氮输入,净释放量表现为乌拉苔草湿地<小叶章湿地<毛苔草湿地。植物从土壤中吸收的氮大部分存留在根系中,只有小部分用于内部循环。用于内部循环的氮量表现为乌拉苔草湿地>小叶章湿地>毛苔草湿地。植物地上部分每年吸收的氮大部分通过枯落物归还,小部分再转移到地下。氮的年吸收量和年存留量均表现为小叶章湿地<乌拉苔草湿地<毛苔草湿地。氮的年归还量则表现为小叶章湿地>乌拉苔草湿地>毛苔草湿地。可见,随着水位的升高,湿地氮的年吸收量和存留量均增加,而氮的年归还量减少。随着水位的升高,湿地植物的吸收系数和利用系数均增高,循环系数降低。可见,在氮的吸收和利用方面毛苔草湿地植物最强,乌拉苔草湿地植物次之,小叶章湿地植物最低;而在促进氮周转方面小叶章湿地植物最强,乌拉苔草湿地植物次之,毛苔草湿地植物最低。更多还原

【Abstract】 Nitrogen （N） cycling process of wetland not only affected its self-regulation mechanism, but also showed a special kinetics process in the Earch Surface System. Moreover, the special kinetics process was correlated with a series of global environmental problems. Hydrologic process was a decisive factor in the formation and maintenance of special type of wetlands, which constrained the succession of wetland system. Hydrological conditions controlled the spatial patterns of vegetation, the growth of plants and living environment of vegetation. Moreover, some aspects of plant community attributes controlled N cycling. In results, shifts in hydrological conditions may alter N cycling through changing community attributes. In order to provide an insight into the mechanism of hydrologic regime constraining the process of N circulation, patterns of N cycling in plant-soil systems were examined using compartments model in three freshwater wetlands along a water level gradient in the Sanjiang Plain, Northeast China. N storages, N distributions, N fluxes and cycle efficient were measured in Calamagrostis angustifolia wetland （XW）, Carex meyeriana wetland （WW） and Carex lasiocarpa wetland （MW）. The main results were drawn as following:Orgnic nitrogen was the main form in XW, WW and MW soils. More than 99% of total N storage was orgnic nitrogen in the three wetland soils. The N content and distribution pattern were different among the three wetland soils. Because the water condition and soil type which induced by morphological charictaristic and N physical transference were different in the three wetlands. The vertical distributions and seasonal change characteristics of all kinds of N were different significantly in XW, WW and MW soils. Because the main factors affected N distribution in various soil layers and times were different in the three wetland soils.Total N content in aboveground organs of plants in XW, WW and MW were declined gradually during the growing season. The total N content in roots was in greater fluctuation during the growing season. The total N content in litter was declined gradually with lapse of time and showed a significant decrease: WW>XW>MW. N accumulation amounts in the three wetlands showed a significant decrease: WW>XW>MW. The N accumulation amount in root was the highest in MW. In the three wetlands, the N accumulation amount in organs of plant in growth time showed a decrease: root>leaf>stem, and in autumn showed a different decrease: root>stem >leaf. It is indicted that root was the important N storage. The N accumulation amounts in litter among three wetlands were increased with lapse of time during the growing season.Calico decomposition rates were statistically different among the three wetlands in the upper soil profile and were also different in the lower depth range, which indicats environmental conditions influence on decomposition strongly. Calico decomposition rates were posively correlated with temperature and pH, but were negtively correlated with soil water contents. In this study, the strong influence of litter quality on decomposition was demonstrated by different decomposition rates between calico and litter/ roots in the same environment. Litter decomposition rates were positively correlated with initial N and P concentrations, but were not correlated with other parameters. Root decomposition rates were posively correlated with C/P ratio and N/P ratio, were negtively correlated with initial P concentration, but were not correlated with initial N and C/N ratio. The N contents in Calamagrostis angustifolia, Carex meyeriana and Carex lasiocarpa litter decreased gradually during the decomposition period and showed a significant increase all the time:Carex lasiocarpa litter <Carex meyeriana litter<Calamagrostis angustifolia litter. The N contents in Calamagrostis angustifolia, Carex meyeriana and Carex lasiocarpa roots decreased gradually during the decomposition period, and it was the lowest in Calamagrostis angustifolia litter all the time.In plant-soil system, soil was the main N storage, the N storage in plant subsystem was less, and root and litter were the main N storages in plant subsystem. The N storages in XW, WW and MW were 714.93 g·m^-2,626.49 g·m^-2 and 552.59 g·m^-2 respectively.In plant-soil systems, annual N uptake by aboveground biomass showed a significant decrease: WW>XW>MW. Annual N uptake by aboveground biomass was higher in WW, but the difference between XW and MW was not so significant. Annual N transferred from aboveground biomass to litter showed a significant increase: MW<WW<XW. N transferred from aboveground biomass to litter was lower in MW, but the difference betweenXW and WW was not so significant. Annual Re-translocation of N from aboveground biomass to root showed a significant increase: WW>MW>XW. Re-translocation of N from aboveground biomass to root in WW was three-fold higher than that in MW, but five-fold higher than that in XW. N uptake by root among the three wetlands showed a significant increase: XW<WW<MW. So did N translocations from root to soil. However, N translocations from litter to soil among the three wetlands showed a significant decrease: XW>WW>MW.Characteristics of N cycling in plant-soil system among the three wetlands along a water level gradient were different significantly. N outputs from the soil exceeded N inputs in plant-soil system of the three wetlands. Moreover, N release from litter decomposition increased significantly with water level decreasing. A large percent of N uptake from soil was detained in root, and just a small percent of N uptake was used in internal circulation. In addition, annual N used in internal circulation among the three wetlands showed a decrease: WW>XW>MW. A majority of annual N uptake by aboveground plant was returned through litterfall, and a small part was transferred from aboveground to belowground in the three wetlands. With water level increasing, annual N uptake and annual N retention increased, but annual N return, cycle coefficient decreased. These results suggest that the rate of biological cycling was decreased with water level increasing.更多还原