人工林疏伐強度對土壤酵素活性及土壤功能多樣性之影響

Abstract

本研究目的為探究南投縣人倫林道人工林 (N 23˚ 44’ E120˚ 53’)不同疏伐強度對土壤酵素活性及土壤功能多樣性之影響，並分析土壤酵素活性及土壤功能多樣性之季節性變化以及人工林疏伐強度與土壤物理、化學與生物性質間之簡單相關分析。本研究試驗林為20~30年生的柳杉人工林 (Cryptomeria japonica D Don.)，其原始林木株數為每公頃943株至1525株。本研究採取三種疏伐強度 (0%、25%、50 %)處理 (疏伐三個月後)各四重複樣區 (1公頃/樣區)之表層 (0-15 cm)及底層 (15-30 cm)土壤，並分析其五種與碳、氮、磷、硫循環及微生物活性有關的土壤酵素 (纖維素酶、β-胺基葡萄糖苷酶、酸性磷酸酯酶、芳香基硫酸酯酶及去氫酶)活性及其十四種土壤物理、化學及其他生物性質 (質地、pH、EC、水分、有機質、全氮、銨態氮、硝酸態氮、無機態氮、有效性磷、水溶性磷、硫酸鹽、微生物生質碳及微生物生質氮等)，並依據分析所得之五種土壤酵素活性計算其土壤功能多樣性指數。結果顯示： (一)表層土壤纖維素酶活性在25%疏伐強度之處理顯著高於其他處理 (p<0.05)，β-胺基葡萄醣苷酶、酸性磷酸酯酶、芳香基硫酸酯酶及去氫酶活性在25%疏伐強度及50%之處理皆顯著高於控制組 (p<0.05)；底層土壤纖維素酶及去氫酶活性在不同疏伐強度間並無顯著差異 (p<0.05)，β-胺基葡萄醣苷酶及芳香基硫酸酯酶活性在25%疏伐強度及50%之處理皆顯著高於控制組 (p<0.05)，而酸性磷酸酯酶活性在50%疏伐強度之處理顯著高於控制組 (p<0.05)。依據以上之結果，25%疏伐強度及50%之處理顯著提高上述五種土壤酵素活性 (p<0.05)。 (二)表層土壤功能多樣性在50%疏伐強度及控制組之處理皆顯著高於25% (p<0.05)；底層土壤功能多樣性在50%疏伐強度之處理顯著高於25%及控制組 (p<0.05)。依據以上之結果，人工林50%疏伐強度處理之土壤功能多樣性顯著高於25%及控制組 (p<0.05)。 (三)人工林疏伐強度與土壤β-胺基葡萄糖苷酶、酸性磷酸酯酶、芳香基硫酸酯酶活性、有機質、全氮、有效性磷及土壤水分間皆呈顯著正相關 (p<0.05)。 (四)綜合以上之結果，並考量林業之生物多樣性保育及永續經營，本試驗林之人工林疏伐強度處理之優先次序建議為50%＞25%＞0%。

The aims of this study were to examine the effects of thinning intensities on soil enzyme activities and soil functional diversity of Renlun plantation forest, 20-30-year-old Cryptomeria japonica D Don. with initial density of 943-1525 trees ha-1, in Nantou, Taiwan (N 23˚ 44’ E120˚ 53’). Seasonal changes in soil enzyme activities and soil functional diversity, and the simple regression analysis between thinning intensity and soil properties were also investigated. Surface soil (0-15 cm) and subsurface soil (15-30 cm) samples were taken from three thinning treatments including control (0%), 25%, and 50% thinning intensities (3 months after thinning treatments), each with 4 replicates. Five soil enzyme activities (cellulase, β-glucosaminidase, acid phosphatase, arylsulfatase and dehydrogenase) were measured and from which soil functional diversity indexes were calculated. Soil moisture, organic matter, total nitrogen, inorganic nitrogen, available phosphate, water soluble phosphate, sulfate, microbial biomass carbon, and microbial biomass nitrogen were also determined. The results of this study can be summarized by the following: 1. The cellulase activity of surface soil was significantly higher in 25% thinning intensity than in other treatments (p<0.05), and the β-glucosaminidase, acid phosphatase, arylsulfatase and dehydrogenase activities of surface soil were significantly higher in 25% and 50% thinning intensities than in control (p<0.05); The cellulase and dehydrogenase activities of subsurface soil were no significant difference among treatments (p<0.05). The β-glucosaminidase and arylsulfatase activities of subsurface soil were significantly higher in 25% and 50% thinning intensities than in control (p<0.05), and the acid phosphatase activity of subsurface soil was significantly higher in 50% thinning intensity than in control (p<0.05). In short, the enzymes activities were significantly higher in 25% and 50% thinning intensities than in control (p<0.05). 2. The soil functional diversity index of surface soil was significantly higher in 50% and control than in 25% thinning intensity (p<0.05), and the soil functional diversity index of subsurface soil was significantly higher in 50% thinning intensity than in other treatments (p<0.05). In short, the soil functional diversity index was significantly higher in 50% thinning intensity than in other treatments (p<0.05). 3. The results of simple correlation analysis indicated that soil β-glucosaminidase, acid phosphatase, arylsulfatase, organic matter, total nitrogen, available phosphate and soil moisture were significantly positively correlated with thinning intensity (p<0.05). 4. In conclusion, considering the above results and the biodiversity and sustainability of forestry, we suggest that the priority of thinning intensity treatments in this study are: 50%＞25%＞0%.