蚯蚓雨後漫遊地表與含氮廢物排泄之關連性探討

Abstract

在一陣子乾旱之後的連續大雨後，我們就有機會看見蚯蚓在夜晚至清晨間整隻爬出地表，在路面上漫遊，究竟是什麼原因讓蚯蚓有這樣的行為？蚯蚓的排泄多以氨及尿素為主。而氨與尿素具有一定的毒性，排泄時需要水分來稀釋。當環境乾旱時，蚯蚓體內水分短缺，排泄必定受到影響。針對雨後會爬出的Amynthas robustus以及無雨後爬出紀錄的Metaphire posthuma，利用模擬乾旱及乾旱後降大雨，測量蚯蚓體內和體外含氮廢物的變化，並藉由模擬環境含氮廢物濃度升高情形，觀察蚯蚓對含氮廢物的耐受力。實驗結果發現，兩種蚯蚓的排泄均會受乾旱影響，而在體內有累積增加的現象，並會藉由降雨的水分來恢復體內水分及滲透壓，並排除累積於體內的含氮廢物，加上土壤泡水後亦會釋出部份的含氮廢物，土壤中含氮廢物的濃度會升高。然而A. robustus對於環境中氨或尿素的忍受度皆不如M. posthuma，因此這可能就是造成A. robustus在乾旱後大雨會爬出地面漫遊，而M. posthuma不會爬出地表的重要因素。

After series heavy rainy days, it is possible to see earthworms coming out from soil, and wondering on the road from night to dawn. This biological mystery has never been experimentally unraveled because earthworm excreted predominantly urea or ammonia; they need sufficient water to excrete these nitrogenous wastes out. During desiccation, body water loss from earthworms must affect their excretion of urea or ammonia. In this study, two species of earthworms, Amynthas robustus and Metaphire posthum, with different behavior after series heavy rainy days was compared. (A. robustus has been observed wondering on soil surface after rains and M. posthuma does not show similar behavior.) The urea and ammonia concentration of earthworm's blood and of excretion solutions were measured when those earthworms were kept at a mimic situation from drought to a heavy rain after drought. In addition, urea or ammonia was added into the soil to test the endurances of earthworms in the nitrogenous condition. The result demonstrated that during drought, earthworm's internal concentrations of urea and ammonia increased. However, when water added into the drought soil to mimic heavy rain situation, the dehydrated earthworms can recover their blood nitrogenous concentration to normal state in couple hours. Actually, the urea and ammonia amounts were increased in the excretion solution at the first hour of rehydration in both species. Totally, the nitrogenous concentration of the rehydrated soil was significantly increased due to earthworm excretion. However, the endurance to nitrogenous wastes of M posthuma is better than A. robustus, this may be the main reason to explain that A. robustus come out of soil after a heavy rain but M. posthuma don't.