【作者】 傅民杰；

【导师】 王传宽；

【作者基本信息】 东北林业大学 ， 生态学， 2009， 博士

【摘要】 温带森林在全球森林生态系统中占有重要的地位,也是对全球暖化响应最为敏感的生态系统之一。研究该生态系统中氮素的转化过程和影响机制既可以加深对生态系统结构与功能的认识,也可为评估全球暖化的影响提供科学依据。本研究以4种典型温带森林生态系统:红松人工林（HS）、落叶松人工林（LYS）、蒙古栎林（MGL）和硬阔叶林（YK）为对象,研究了森林凋落物（叶片、细枝、未分解混合叶及半分解混合叶）氮素的固持与转化、土壤微生物量氮固持与释放、土壤有机氮硝化与矿化、生长季N₂O释放。以移栽自不同纬度的兴安落叶松林土壤为代表研究解冻期土壤N₂O的释放。结果表明:树种组成对凋落物分解影响显著,阔叶树种凋落物组分分解明显快于针叶树种。叶片或混合叶片的分解率高于细枝。凋落物分解率与初始C/N呈显著负相关。叶片、细枝以及地面未分解凋落物组分在分解早期阶段总氮含量均呈增加趋势,而半分解混合凋落物分解过程中总氮含量保持相对稳定。凋落物中氮释放与C/N显著负相关,初始C/N较低的水曲柳叶片和胡桃楸叶片在分解初期显示出明显的氮释放特征。4种森林土壤微生物量氮具有明显的时空特征:晚春和初夏期间微生物量氮固持明显,而秋季表现出明显的氮释放。森林土壤微生物量氮随土壤深度增加而减少。4种林型间微生物量氮差异显著,阔叶林微生物量氮高于针叶林。春季解冻期,0-10 cm（MGL:0-5 cm）土壤微生物量氮与土壤水分含量变化同步,在土壤水分最高的时期,微生物量氮达到固持高峰。生长季YK、MGL、HS和LYS 0-10 cm（MGL:0-5 cm）土壤中微生物量氮占其土壤总氮比例依次为:2.3%、2.4%、2.1%和1.1%。土壤微生物量氮与土壤水分呈显著正相关,而与温度无关。4种森林土壤无机氮（NH₄⁺-N和NO₃^--N）季节变化特征相似。土壤有机氮矿化和硝化具有明显的时空特征,5-7月矿（硝）化作用强烈。随土壤深度加深,净氮矿化率和净硝化率逐渐降低。4种林型间0-10 cm（MGL:0-5 cm）土壤净氮矿化率和净硝化率差异显著,净N矿化率依次为YK(0.60±0.01 mg.kg^-1.d^-1)＞HS(0.38±0.03 mg.kg^-1.d^-1)＞MGL(0.35±0.04mg.kg^-1.d^-1)＞LYS(0.24±0.03 mg.kg^-1.d^-1)。下层土壤净氮矿化率无显著差异。生态系统构成决定了土壤氮素的矿化能力,阔叶林和针阔混交林矿化率大于针叶林。春季解冻期4种温带森林土壤均存在明显的矿化过程。土壤氮矿化与土壤温度和微生物量氮显著正相关,而与土壤水分呈二次函数关系。4种温带森林生态系统均是N₂O释放源,生长季可释放0.07-0.93 kgN₂O-N.hm^-2。在生长季土壤干旱期,该森林可吸收环境中的N₂O,成为短期N₂O汇。4种林型间N₂O释放量差异不显著。土壤N₂O通量与土壤水分、NH₄⁺-N和微生物量氮显著正相关。土壤硝化过程是该森林生态系统生长季土壤N₂O释放的主导过程。该森林土壤在春季解冻过程中可释放出大量的N₂O(1.49-2.94 kgN₂O-N.hm^-2.29d^-1)。土壤温度和土壤微生物量碳是解冻过程中N₂O释放的主要影响因素。研究表明,温带森林凋落物氮释放受其初始C/N显著影响,初始C/N越高的凋落物组分其氮固持效应越显著。阔叶林微生物量氮的有效性显著高于针叶林。4种温带森林在生长季与非生长季均是N₂O源。4种纬度落叶松林土壤解冻过程中N₂O释放敏感性随纬度升高而下降。更多还原

【Abstract】 Temperate forest has been playing a key role in the global forest ecosystems,which is one of the most sensitive to the global climate warming.It is necessary to investigate nitrogen turnover and controlling factors for a better understanding of the structure and function of the temperate forest ecosystem.Additionally,these datas could be provided for evaluating the impacts by the climate warming.The research was based on 4 typical temperate forest ecosystems:Korean pine（Pinus koraiensis,HS） and Dahurian larch（Larix gmelinii,LYS） plantation,Mongolian oak forest（Dominated by Quercus Mongolica,MGL） and Hard-wood forest（Dominated by Fraxinus mandshurica,Juglans mandshurica and Phellodendron amurense,YK）,which represented secondary forest ecosystems in northeast China.N immobilization and release in different litter compositons（leaf litters,twigs,mixed undecomposition leaf litters and mixed semi-decompositon leaf litters）,N immobilization and release in soil microbial biomass,nitrification and N mineralization in soil and N₂O emissions were studied in the temperate forest ecosystems.We selected the Dahurian larch forest ecosystems transplanted from a latitudinal transect in northeast China and measured N₂O fluxes during spring thawing period.The decompositoin of litters was apparently affected by tree species.The decomposition of broad-leaved forest litters was faster than that of conifer forest litters.The decomposition rates of leaves were higher than that of twigs.The decomposition rate of litter was negatively correlated to C/N of litter.The total nitrogen content of leaves,twigs and mixed undecomposed leaves increased with the decomposition of these litters at primary stage of decomposition.The total N increased significantly in primary stage of decomposition.The release of litter N was negatively correlated to initial C/N of litter.And N release from the leaves of Fraxinus mandshurica and Juglans mandshurica with initial low C/N was increased in the primary decomposition stage.Temporal and spatial variability was found in soil microbial biomass nitrogen（N_M） in 4 forest ecosystems.Soil nitrogen was immobilized significantly by soil microbial in later-spring and pre-summer and was released in autumn.The soil N_M showed clearly spatial variability and decreased with soil depth.The soil microbial biomass nitrogens were significantly different among 4 forest soils and broad-leaved forests with microbial higher biomass nitrogen than conifer forests.The change of soil microbial biomass nitrogen at 0-10 cm depth（0-5 cm for MGL） was accord with soil water content and the peak of N_M appeared at the time of the highest soil water during soil thawing periods in spring.The percentages of N_M to total N in YK,MGL,HS and LYS during the growth season were 2.3%,2.4%,2.1%and 1.1%at 0-10 cm （0-5 cm for MGL） depth,respectively.The N_M was positively correlated to soil moisture content,but not to soil temperature.The inorganic nitrogen showed similar seasonal characteristics in four temperate forest ecosystems.Apparent temporal-spatial pattern was observed in nitrification and N mineralization,and the highest net N mineralization and net nitrification rates were found in May-July.Net nitrification and net N mineralization rates decreased with soil depth.Net nitrification and net N mineralization rates at 0-10 cm depth were significantly different among 4 forest ecosystems,and the rank of mean net N mineralization rate was YK(0.60±0.01 mg.kg^-1.d^-1)＞HS(0.38±0.03 mg.kg^-1.d^-1)＞MGL(0.35;±0.04 mg.kg^-1.d^-1)＞LYS(0.24±0.03 mg.kg^-1.d^-1). There were scarcely different in net nitrification and net N mineralization rates among 4 forest soils at 10-20 cm（5-15 cm for MGL）.The constitutes of forest ecosystem determined the level of N mineralization.The net N mineralization rates of the broad-leaved forest and pine mixed deciduous forest ecosystem were higher than that of conifer forest ecosystems.There existed clear N mineralizations during spring soil thawing period in 4 forest ecosystems.N mineralizations were positively correlated to soil temperature and N_M,and there was quadratic equation relationship between N mineralization and soil water.Four temperate forest soils were N₂O sources and released 0.07-0.93 kgN₂O-N.hm^-2 during the growth season.The temperate forest would absorb N₂O from the environment as a ephemeral sinks of N₂O during dry period in the growth season.The differences of N₂O flux in 4 forest ecosystems were not significant.The N₂O flux were significantly positively correlated to soil water content,NH₄⁺-N content and N_M.The nitrification is a leading process for N₂O emission during the growth season in the 4 forest ecosystems.A quantity of N₂O was released during soil thawing periods in spring in temperate forest ecosystems(1.49-2.94 kgN₂O-N.hm^-2.29d^-1). The soil temperature and microbial activity were the key factors in controlling N_O2 emissions during soil thawing periods.The results showed that N release of litters was affected significantly by initial C/N,and N immobilization increased with higher initial C/N in the temperate forest.Availibilities of microbial biomass N in broad-leaved forest soils were higher than that of the conifer forest soils.4 forest soils were N_O2 sources in growth and non-growth season obviously.The sensitivity of N₂O release for the four latitudinal Dahurian larch forest soils decreased with higher latitude during the thawing period in spring.更多还原