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苗栗後龍海岸砂丘林土壤酵素活性的空間和季節性變化
Spatial and Seasonal Changes of Soil Enzymatic Activities in Coastal Sand-Dune Forests at Houlong, Miaoli
摘要
土壤酵素在生態系中扮演著分解凋落物及碳、氮等養分循環利用的重要角色。本研究以苗栗後龍海岸林為試驗對象，於2002年1月及7月採集地表之腐植層(FH)和0~10, 10~20cm土壤層試樣，藉以探討微地形、不同林相以及季節效應對於纖維素酵素(cellulose)、木質醣酵素(xylanase)及尿素酵素(urease)等3種酵素活性的差異。結果顯示，木麻黃高位砂丘腐植層的纖維素酵素及木質醣酵素活性均較低位砂丘高，各為6.08及14.61 mg g^(-1)d^(-1)，但僅纖維素酵素在腐植層有顯著性差異，木質醣酵素在表土層反而以低位砂丘較高；尿素酵素活性在低位砂丘腐植層及表土層之測值4.28及0.49mmol g^(-1)h^(-1)皆較高位砂丘高。本試驗腐植層的酵素活性明顯高於土壤層，且活性隨土壤深度增加而降低。木麻黃純林之纖維素酵素及木質醣酵素活性4.55及12.3 mg g^(-1)d^(-1)，較黃槿及混合林稍高，但各林相腐植層無顯著性差異，而表土層之纖維素酵素及木質醣酵素活性則顯著以木麻黃林最高，各為0.74及1.65 mg g^(-1)d^(-1)；尿素酵素活性明顯受到林相影響，黃槿純林腐植層及表土層的酵素活性28.45及0.79 mmol g^(-1)h^(-1)均其他林相高。在冬、夏兩季，木麻黃高位砂丘腐植層之纖維素酵素及木質醣酵素的活性皆較低位砂丘高，但黃槿林及混合林各層並沒有顯現出明顯的差異。可溶性有機氮含量以混合林腐植層在夏季時293.1 mg kg^(-1)最高，由於雨水供應較多的關係，尿素酵素的活性在夏季明顯較低，但土壤層的酵素活性並未隨季節而改變。
並列摘要
Soil enzymes play a key function in litter decomposition and the recycling of essential elements in ecosystems. The present study was conducted at a coastal sand-dune forest at Houlong, Miaoli, west-central Taiwan. Sampling plots were set up at different topographic locations and with different vegetation. Soil samples were collected from the humic layer (sieved from the FH horizon) and 2 mineral layers at depths of 0~10 and 10~20 cm in January and July 2002. The objectives of this study were to clarify the factors of topography, vegetation, and seasonal changes on the activities of such soil enzymes, as cellulase, xylanase, and urease. Results showed that the cellulase and xylenase activities in the humic layer were 6.08 and 14.61 mg g^(-1)d^(-1), and were higher at the upland site than that at the lowland site, while no significant differences were found in the mineral layers. Xylenase activity did not significantly differ between the upland and lowland sites in either the humic or mineral layers. Urease activities were 4.28 and 0.49 mmol g^(-1)h^(-1) in the humic and surface layers, and were higher at the lowland site for both samples. In general, these enzyme activities were higher in the humic layer than in the mineral layers, and activities declined with soil depth. Cellulase and xylanase activities in the humic layer were 4.55 and 12.3 mg g^(-1)d^(-1) and were higher for the pure Casuarina forest than for the other sites, while a significant difference was found for different vegetative cover. Cellulase and xylanase activities in the surface layer were 0.74 and 1.65 mg g^(-1)d^(-1) were the highest in the pure Casuarina forest. Urease activity significantly differed among the different vegetative types. Urease activities were 28.45 and 0.79 mmol g^(-1)h^(-1) and were the highest in the pure Hibiscus forest in both the humic and surface layers. Cellulase and xylanase activities in the humic layer were higher for the upland Casuarina forest than for the lowland site, while neither the cellulase nor xylanase activities in either the humic or mineral layers significantly differed between the Hibiscus and mixed forests. The dissolved organic nitrogen was 293.1 mg kg^(-1), which was highest in the humic layer of the mixed stands in July. Urease activity was lower in summer due to heavier rainfall. No seasonal changes in enzyme activities were found in the mineral layers.