溪頭三種林相之土壤性質、團粒穩定度和氮磷劃分研究

Abstract

森林生態系的永續經營須仰賴良好的土壤品質，而土壤的性質和養分循環在不同植生組成之林相間可能產生差異。本研究選擇溪頭地區環境條件相似之毗鄰林地，採集天然闊葉林、人工柳杉林和竹林土壤剖面，調查三種林相的土壤性質和團粒穩定度，並探討氮磷劃分在不同深度土層的有效性和分布，以瞭解不同植生對土壤性質之影響。研究結果顯示，三種林相之土壤 pH 值由低到高依序為天然林、柳杉林和竹林；有機質含量以竹林土壤最低，導電度值則在林相間沒有差異。Mehlich Ⅲ 可萃取性鈣、鎂、鐵、銅和鋅濃度在三種林相間沒有差異；Mehlich Ⅲ 可萃取性磷和鉀濃度由高到低則大致為天然林、柳杉林和竹林；Mehlich Ⅲ 可萃取性錳在竹林土壤中濃度最高。所有樣區的表層土壤 (0-10 cm) 有最低的 pH 值及最高的電導度，且有機質含量及 Mehlich Ⅲ 可萃取性磷、鉀、鎂、鐵、錳和鋅濃度最高。三種林相中，柳杉林和竹林的團粒穩定度高於天然林，不同深度的樣區間則無差異。不同劃分的氮中，除無機態氮與水解性銨態氮外，林相間各個氮劃分濃度大致以天然林最高、竹林最低，柳杉林則介於兩者之間；所有氮劃分濃度隨著土層深度增加而遞減，在 0-5 cm 土壤中濃度最高，10 cm以下則無差異。總磷、碳酸氫鈉萃取磷和氫氧化鈉萃取磷濃度大致以天然林最高、竹林最低，水萃取磷、鹽酸萃取磷和殘餘磷在林相間無差異；所有磷劃分在0-5公分土層中有最高濃度，並隨深度增加而遞減。綜上所述，天然林、柳杉林和竹林之土壤性質、團粒穩定度和氮磷形態及濃度分布具有一定之差異。

Sustainability of forest ecosystems relies on good soil qualities. The diversities of vegetation in forest stands may arise differences in soil properties and affect nutrient cycling. This study aimed to investigate the soil properties, aggregates stability, nitrogen (N) and phosphorus (P) fractions in soils collected from natural broad-leaf stand (Nat-F), Japanese cedar plantation (Cedar-F) and Moso bamboo plantation (Bamb-F) in Xitou, Taiwan. The results showed that soil pH value increased in the order of Nat-F, Cedar-F and Bamb-F; organic matter content was the lowest in Bamb-F soil and no significant difference in electrical conductivity among three forest stands. Concentrations of Mehlich Ⅲ extractable P and potassium (K) decreased in the order of Nat-F, Cedar-F and Bamb-F while manganese (Mn) was the highest in Bamb-F. There was no significant difference in concentrations of Mehlich Ⅲ extractable calcium (Ca), magnesium (Mg), iron (Fe), copper (Cu) and zinc (Zn) among three forest stands. The topsoil (0-10 cm) showed the lowest pH value and the highest electrical conductivities in all studied sites. The organic matter contents and Mehlich Ⅲ extractable P, K, Mg, Fe, Mn and Zn also showed the highest concentrations in 0-10 cm layers. Aggregate stability in Cedar-F and Bamb-F soil profiles was greater than in Nat-F, but there was no differences in aggregate stability in varied depths of the same forest stand. The concentrations of all N fractions studied were the highest in Nat-F and the lowest in Bamb-F soil with the exception of inorganic N and hydrolyzable ammonium N fractions. The concentrations of different fractions of N decreased with increase in depth and were the highest in 0-5 cm soil layer. The Nat-F soil had the highest concentrations of total P, NaHCO3-P and NaOH-P while there was no significant difference in H2O-P, HCl-P and residue-P in three forest stands. In conclusion, there were differences in soils of Nat-F, Cedar-F and bamboo-F in chosen properties, aggregate stability, different fractions of N and P.