除草劑丁基拉草對稻田土壤微生物多樣性與固氮作用影響之研究

Abstract

丁基拉草 (N-butoxymethyl-2-chloro-2’,6’-diethylacetanilide)為水田中使用廣泛的除草劑，其快速降解及低毒性的特性使其成為具環境親和性的農藥選擇。本研究探討丁基拉草施用對非培養法（Culture-independent Method）及培養法（Culture-dependent Method）所得細菌族群組成及固氮活性的影響。結果顯示，水稻成活期時，於水田上層（0-3 cm）土壤中，兩種濃度（1.5 g are-1及15 g are-1）的丁基拉草施用皆能顯著的提高土壤的固氮活性。但在水稻成熟期時，只有高濃度的丁基拉草施用可以提升土壤的固氮活性。於水田下層（3-15 cm）土壤中，兩種濃度的丁基拉草施用皆能顯著的提高土壤的固氮活性，並且於水稻成熟期時，高濃度的丁基拉草施用較低濃度丁基拉草施用更能顯著地促進土壤固氮作用。由分析變性梯度凝膠電泳圖譜（Denaturing Gradient Gel Electrophoresis，簡稱DGGE）所得之不加權平均連結法（Un-paired Group Method Using Arithmetic Averages，簡稱UPGMA)圖譜結果得知，與對照組相比，微生物族群多樣性的變化在固氮菌族群中約為33-64 %，在細菌族群中約為28-52 %。為更進一步演繹集群分析結果，採用最小距離法（Minimum Distance，簡稱MD）決定UPGMA 圖譜的分群數目，所得結果顯示，丁基拉草的施用可影響游離固氮菌及真細菌菌族群之菌相組成，且經100天的水稻種植期後，未能恢復成原有的菌相狀態。高倍丁基拉草施用下，上層土壤中的可培養性優勢固氮菌種可能為Janthinobacterium sp.，而在下層土壤中，則為Arthrobacter sp.。在第39天時，固氮菌的族群種類多樣性增加，也因此造成土壤固氮作用的提升。

Butachlor (N-butoxymethyl-2-chloro-2’,6’-diethylacetanilide), one of the widely utilized herbicides in paddy fields, characterizes by its fast degradation rate and low toxicity and serves to be a herbicide that fulfills environmental friendliness purpose. The bacterial composition under butachlor application with rice plant cultivation was investigated by culture-independent and culture-dependent method and the change of nitrogenase activities under the same treatment were also investigated. The results showed that in the upper layer of paddy soils (0-3 cm), both concentrations of butachlor application (1.5 g are-1 and 15 g are-1) could significantly raise soil nitrogenase activities at rice survival stage. But at the rice ripening stage, only higer concentration of butachlor application could raise the soil nitrogenase activity significantly. In the lower layer of paddy soils (3-15 cm), both concentrations of butachlor could raise soil nitrogenase activities, while higher concentration of butachlor could raise the activity to a larger degree. From the results of un-paired group method using arithmetic averages (UPGMA) which interpreting the results of denaturing gradient gel electrophoresis (DGGE), the diazotrophic divergences upon butachlor application were ranged from 33-64% throughout rice growth stages; while that of eubacterial diversities were from 28-52%. For further interpretation and determination of the cluster numbers of each UPGMA dendrograms, minimum distance statistics (MD), was therefore applied. The results showed that the application of butachlor altered the composition of diazotrophic and eubacterial communities without recovery to the inceptive state after 100 days of rice cultivation. The predominant nitrogen fixation bacteria was Janthinobacterium sp. under higher dose of butachlor in upper layer soil, and was Arthrobacter sp. in lower layer soil. The diazothrophic biodiversity increased after 39 days and was the reason that boosted the soil nitrogenase activity.