Effects of Taiwan voles (Microtus kikuchii) feces on soil nitrogen at the He-huan area

草食性動物取食植物，排出氮含量高且分解快的排遺，可以快速的將養分回歸到土壤，提供氮一個快速循環的途徑(fast cycle)，進而影響植物的生長與群聚的組成。大型草食性動物在生態系營養循環的作用已經有相當多的研究，但小型哺乳動物所扮演的角色相關研究較少。台灣高山田鼠(Microtus kikuchii)為草食性小型囓齒動物，在玉山箭竹草原中，族群數量多而穩定，並有排遺集中形成「公廁」的習性。本研究想了田鼠排遺對高山草原土壤氮含量的影響，探討以下問題：(1)高山田鼠的氮輸出量；(2)高山田鼠公廁的分佈及動態；(3)高山田鼠公廁對土壤氮含量的影響；(4)田鼠排遺對植物凋落物分解的影響。我於2007年起在合歡山的玉山箭竹草原中進行田鼠族群及野外公廁調查，透過飼養來計算田鼠排遺量，並在實驗室與野外進行田鼠公廁的孵育實驗。結果顯示，田鼠的氮輸出量範圍在0.33 ~ 0.41 kg N ha-1 year-1；高山田鼠族群及公廁分佈具空間異質性，公廁數目大抵隨田鼠族群數目波動，對土壤氮時空分佈影響很大；公廁會增加土壤中可萃取性氮，尤其是植物可利用的無機態氮；公廁易分解的養分主要在一個月內釋出，對土壤的有效供應期限約為1個月；田鼠排遺提供土壤微生物較易取得的食物資源而使其活性增加，加速土壤有機質的分解，微生物扮演的角色尚須進一步的研究以了解。綜合而言，在土壤有機質含量很高，但是分解緩慢的高山生態系，田鼠公廁不僅提供養分，並能加速原來土壤中的有機質分解，對高山生態系而言，扮演相當重要的角色。Herbivore returns nitrogen to soil by defecating high-nitrogen wastes. The fast decomposition rates of feces provide a “fast cycle” for returning plant nitrogen to soil. The temporal production and spatial distribution of feces can affect the dynamics of nutrient availability in soil, and change plant community structures. The effects of feces were well-documented for large herbivores, but not herbivorous small mammals. The Taiwan vole (Microtus kikuchii) is the dominant herbivorous rodent in alpine meadow in Taiwan. They deposit large amount of feces at latrine sites. I want to investigate the effects of latrines on soil nitrogen. This thesis is divided into four aspects: (1) Nitrogen output of vole; (2) The temporal dynamics of vole latrines; (3) The effects of latrines on soil nitrogen; (4) The effects of latrines on plant litter decomposition. I conducted vole and latrine survey starting in 2007 at an alpine meadow in He-huan Mountain. Nitrogen output was acquired by rearing voles in the laboratory. I also conducted two field and one laboratory incubation experiments with latrines. The results showed that, annual nitrogen output of voles was 0.33~0.41 kg N ha-1 year-1. Vole latrines increased the extractable nitrogen in soil, especially inorganic nitrogen. The release of nutrients from liable part of feces to soil occurred within one month. Latrines also provided liable carbon to microbes, increasing microbial activities and decomposition rates of soil organic matters. The spatial patterns of vole and latrine abundances were highly heterogeneous in alpine meadow. The temporal dynamics of voles and latrines further increased the spatial heterogeneity of soil nitrogen. Alpine meadows had high soil organic matters, yet decomposition rates were low. Vole latrines not only quickly return nutrients back to soil, but also enhance decomposition rates of soil organic matters, thus play a crucial role in alpine ecosystems