Role of dissolved organic nitrogen in the nitrogen cycle of a mountainous forest ecosytem in Taiwan

在低氮沉降条件下，溶解有机氮（DON）在森林土壤氮循环中起着突出作用，往往是溶液中氮的主要形式。对DON的来源、性质、成因和命运知之甚少，特别是在亚热带森林高降水条件下。在野外及室内研究中，我们计划在台湾山区的台湾樟树林中调查这些问题。在之前的研究中，我们发现该生态系统中溶解有机碳（DOC）和DON的通量非常高。DON、DOC和矿物元素的浓度和通量将以每两周的分辨率在穿透物、森林地面渗透物和渗漏物中进行测量。土壤中DOC和DON的释放和归宿与温度、降水和穿透化学有关。将在实验室提取中研究不同的森林地面层和分解根系作为DON和DOC来源的作用。利用碳氮比、氨基酸和氨基糖的组成来评价不同来源DON的质量。在实验室研究中，我们将使用含有不同质量的溶解有机物的溶液，研究DOC与亚硝酸盐反应形成DON的可能性。此外，微生物利用和土壤衍生DON和DOC的净矿化将在实验室培养中进行研究。在这里，我们使用了现场和实验室的样品，对亚硝酸盐反应生成DON进行了实验。这些结果有望大大提高我们对这些森林生态系统中氮循环的理解。

Dissolved organic nitrogen (DON) plays a prominent role in the N cycle of forest soils under conditions of low N deposition and often represents the dominant form of N in solution. Little is known about the sources, properties, genesis and fate of DON, especially in subtropical forests under high precipitation regime. In field and laboratory studies we plan to investigate these issues in a mountainous Chamaecyparis obtusa var. formosana forest in Taiwan. In previous studies we found the fluxes of dissolved organic carbon (DOC) and DON exceptionally high in this ecosystem. Concentrations and fluxes of DON, DOC and mineral elements will be measured in fortnightly resolution in throughfall, forest floor percolates and seepage. The release and fate of DOC and DON in the soil will be related empirically to temperature, precipitation and throughfall chemistry. Different forest floor layers and decomposing roots will be investigated in laboratory extractions for their role as sources of DON and DOC. The quality of DON from different sources will be evaluated using C/N ratios and the composition of amino acids and amino sugars. In laboratory studies we will investigate the potential formation of DON by reaction of DOC with nitrite, using solutions that contain different qualities of dissolved organic matter. Furthermore, the microbial use and net mineralization of soil derived DON and DOC will be studied in laboratory incubations. Here we use samples from the field and from the laboratory experiments on DON formation by reaction of nitrite. The results are expected to substantially improve our understanding of the N cycle in these forest ecosystems.