【作者】 谭波；

【导师】 杨万勤； 吴福忠；

【作者基本信息】 四川农业大学 ， 森林培育， 2013， 博士

【摘要】 凋落叶分解是陆地生态系统物质循环的重要组成部分,决定着全球碳收支和养分周转,受气候、基质质量和土壤生物等因子共同作用的影响。土壤动物群落可通过取食、破碎、混合等直接作用和通过影响土壤微生物数量、结构和活性以及改变土壤物理特性等间接作用控制凋落叶分解过程。它们对凋落叶分解的影响可能在很大程度上取决于凋落叶的分解环境、基质特性和土壤动物群落结构。长江上游森林生态系统是长江流域生态安全屏障的主体,其气候条件、植被组成和土壤动物群落结构沿流域海拔变化具有显著的时空分异。鉴于此,本研究以长江上游代表性森林植被群落为对象,基于“土壤动物对凋落叶分解的贡献是否集中体现了气候和树种(基质质量)对凋落叶分解的作用?土壤动物对凋落叶分解的贡献是否随海拔升高而降低?受季节性雪被影响的亚高山／高山森林土壤动物对凋落叶分解的贡献是否显著不同于常绿阔叶林区?”的科学假设,通过网袋法进行土壤动物群落控制试验,同步监测了不同海拔森林凋落叶分解的环境、土壤动物群落、质量(mass)损失、养分释放和质量(quality)变化动态。主要结果如下：(1)大气温度和降水量随海拔增加显著(P<0.05)降低,以海拔453m最高,3,582m最低,年平均温度相差12.89℃,年降水量相差479mm。凋落叶的平均温度随海拔增加显著(P<0.05)降低。整个研究期间,凋落叶温度在945m和453m始终高于0。C,在3,582m和3,023m的冬季则围绕0℃存在明显的冻融循环,且凋落叶分解湿度随降水量季节差异显著变化。这种截然不同的温湿度特征可能深刻影响土壤动物对凋落叶分解的贡献。(2)不同凋落叶的土壤动物优势类群和常见类群组成、个体密度和类群数量以及蜱螨目与弹尾目比值(A/C)差异显著。土壤动物群落优势类群和功能类群组成、个体和类群密度以及群落多样性和相似性随凋落叶分解过程表现出显著的动态变化,且受到海拔、基质质量和采样时间显著影响,与凋落叶的温湿度、化学性质和基质质量特征表现出显著的相关关系。这表明土壤动物群落结构随凋落叶分解过程不断变化,对海拔、基质质量和季节变化敏感响应,可能深刻作用于凋落叶的质量损失和养分矿化。(3)土壤动物参与显著(P<0.05)增加了凋落叶的质量损失和分解速率,缩短了分解所需时间,但土壤动物对凋落叶分解的贡献并未随随海拔升高而降低。整个研究期间,土壤动物对凋落叶质量损失和分解速率的贡献率分别为15.44%-42.56%和1].24%-36.35%,且对阔叶凋落叶的贡献率随海拔增加显著(P<0.05)降低,但对针叶凋落叶的贡献率随海拔增加降低不显著(P>0.05)。土壤动物对质量损失贡献效应的出现时间随海拔增加而延后,贡献率随分解时间增加而增加,在冬季受季节性冻融影响的高山和亚高山森林(海拔3,582m和3,023m)表现为针叶显著(P<0.05)高于阔叶,而在冬季分解温度较高的中山和低山森林(海拔945m和453m)表现为阔叶显著(P<0.05)高于针叶。此外,土壤动物对质量损失的贡献率受到海拔、基质质量和采样时间的显著影响,与凋落叶的温湿度、化学性质和土壤动物群落特征具有密切相关关系。这表明土壤动物群落显著影响了凋落叶的质量损失,其贡献率差异能有效体现气候和树种(基质质量)对凋落物分解的作用。(4)土壤动物对凋落叶元素释放的影响随元素类型变化而不同。总体而言,土壤动物参与促进了微生物对凋落叶氮和磷的固持,显著(P<0.05)增加了凋落叶氮和磷的含量,但对凋落叶碳含量的影响不显著(P>0.05)。土壤动物参与还显著(P<0.05)增加了木质素比例,降低了纤维素比例。并且,凋落叶元素释放受到海拔、基质质量和采样时间显著影响,与凋落叶的温湿度和土壤动物群落特征相关显著。这表明土壤动物群落显著影响了凋落叶的元素释放和养分周转,且土壤动物作用的元素释放特征对海拔、基质质量和季节变化敏感响应。(5)土壤动物显著改变了凋落叶分解过程中的基质质量特征。总体而言,土壤动物显著(P<0.05)降低了多数凋落叶分解初期的碳氮比、碳磷比、木质素氮比,特别是是针叶树种。土壤动物显著(P<0.05)增加了多数凋落叶分解初期的氮磷比以及整个分解期间的木质素纤维素比。凋落叶分解过程中的质量特征受到海拔、基质质量和采样时间显著影响,与凋落叶的温湿度和土壤动物群落特征表现出显著的相关关系。这进一步表明土壤动物促进了凋落叶分解,对分解过程的影响对海拔、基质质量和季节变化敏感响应。总之,长江上游典型森林凋落叶分解过程中维持着丰富多样的土壤动物群落,这些土壤动物对凋落叶的质量损失、养分释放和基质质量变化总体表现为正效应。它们能通过直接和间接作用增加凋落叶的可分解性,进而使整个系统的物质循环和能量流动稳定有序。并且,土壤动物贡献率的差异能有效体现气候和基质质量对凋落物分解的作用。更多还原

【Abstract】 Litter decomposition is one of the essential components of material cycles in terrestrial ecosystems, determining global carbon budget and nutrient turnover. The decomposition process is mainly regulated by climate, litter quality and soil organisms. Soil faunal community has been shown to accelerate the rates of litter decomposition and nutrient cycling in forest ecosystems. Their body sizes are large enough to disrupt physical structure of soil and litter, and then affect organic matter decomposition directly by fragmenting and comminuting of litter, further indirectly by altering soil moisture, soil structure and litter surface and regulating microbial activities during litter decomposition. Moreover, the influences of soil faunal community on litter decomposition could depend strongly on the conditions of microclimate, litter quality and soil faunal structure. The forests in the upper reaches of the Yangze River serve as fundamental ecological barriers to the Yangze River. The climate condition, plant composition and soil faunal structure in these forests significantly vary with the change in altitudes in the Yangze River valley. Hence, in order to assess the effects of soil faunal community on litter decomposition processes, we conducted an experiment using litterbag method in the representative forest ecosystems of the upper reaches of the Yangze River. Our objectives were to explore:(1) whether the contribution of soil fauna to litter decomposition could exhibit the influences of climate and litter quality on litter decomposition,(2) whether the contribution of soil fauna to litter decomposition would decrease with the increase in latitudes and altitudes,(3) what are the differences in the contributions of soil fauna to litter decomposition between subalpine and alpine forests and subtropical evergreen broad-leaved forests.(1) The air temperature and preciptation significantly (P<0.05) decreased with increasing altitude. The maximum and minimum of air temperature and preciptation were observed at the453m and3582m, respectively. The differences in temperature and preciptation between the453m and3582m were12.89℃and479mm, respectively. Moreover, the mean temperature in litterbags also significantly (P<0.05) decreased with increasing altitude. The temperature in litterbags at the945m and453m remained above0℃throughout the decomposition process, but those at the3582m and3023m experienced obvious freeze-thaw cycles with the air temperature fluctuates above and below0℃in the winter. Additionally, the moisture in litterbags significantly changed with the dynamics of preciptation during the whole decomposition process. These results suggest that the striking differences in temperature and moisture in litterbags can profoundly affect the contribution of soil fauna to litter decomposition in different forest ecosystems.(2) There were significantly differences in the composition of dominant groups and ordinary groups, density of individual and group as well as the rate of Acarina to Collembola of the soil faunal communities in the litterbags at different altitdues. Meanwhile, the composition of dominant groups and functional groups, density of individual and group, diversity index and similarity index of the soil faunal communities significantly changed as the decomposition processed, and showed obviously correlated with litter temperature and moisture, litter chemical properties and litter quality. Additionally, the altitude, litter quality and sampling date significantly influenced the soil faunal structure in the litterbags. These results suggest that the soil faunal structure changes during the litter decomposition process and shows sensitive response to the changes in altitude, litter quality and season, which can profoundly affect the litter mass loss and nutrients mineraliztion in different forest ecosystems.(3) As compared with soil fauna removal, soil fauna significantly (P<0.05) increased the litter mass loss and decay rat, and reduced the litter decomposition times. However, the contributions of soil fauna to litter mass loss did not decrease with the increase in altitudes. During the study period, the contributions of soil fauna to litter mass loss and decay rate were15.44%-42.56%and11.24%-36.35%, respectively. The contributions of soil fauna to litter mass loss and decay rate for the broadleaf species significantly (P<0.05) decreased with the increase in altitudes, but which for the coniferous species insignificantly (P>0.05) decreased with the increase in altitudes. The time of contribution effects delayed with increasing altitudes, and the contribution rate increased with increasing decomposition times. The contribution rates were higher (P<0.05) for the coniferous species than those for the broadleaf species at the3582m and3023m, but which were higher (P<0.05) for the broadleaf species than those for the coniferous species at the945m and453m. Additionally, the contribution rate showed obviously correlated with litter temperature and moisture, litter chemical properties and soil faunal structure and were significantly influenced by the altitude, litter quality and sampling date. These results suggest that the soil faunal community profoundly accelerates litter mass loss, and the differences in the contribution of soil fauna to litter can display the influences of climate and litter quality on litter decomposition.(4) The contribution of soil fauna to litter elements release varied with the change of element types. In general, as compared with soil fauna removal, soil fauna significantly (P<0.05) increased the content of N and P in litters by promoting the retention of N and P by microbes, but it showed little (P>0.05) effect on the C content. Moreover, soil fauna also significantly increased the content of lignin and reduced the content of cellulose. Additionally, litter elements release showed obviously correlated with litter temperature and moisture and soil faunal structure and were significantly influenced by the altitude, litter quality and sampling date. These results suggest that the soil faunal community profoundly influences litter elements release and nutrients turnover, and the contribution of soil fauna to litter elements release shows sensitive response to the changes in altitude, litter quality and season.(5) Soil fauna significantly (P>0.05) changed the litter quality throughout the decomposition process compared with soil fauna removal. In general, soil fauna significantly reduced the rates of C/N, C/P, and lignin/N during the early stage of litter decompotion, in particular for the coniferous species. However, soil fauna significantly increased the rate of N/P during the early stage of litter decompotion and the rate of lignin/cellulose during the whole decomposition process. Additionally, litter qualities showed obviously correlated with litter temperature and moisture and soil faunal structure and were significantly influenced by the altitude, litter quality and sampling date. These results suggest that the soil faunal community increases litter mass loss and nutrients turnover and has important contribution to litter decomposition process. Taken together, our results indicate that the forest ecosystems in the upper reaches of the Yangze River keep high diversity of soil faunal community during litter decomposition. Soil faunal community generally has positive effects on litter mass loss and nutrient release as decomposition processed by directly and indirectly improving litter decomposability. Furthermore, the positive effects show sensitive response to changes in climate and litter quality.更多还原