桂北不同林龄桉树人工林土壤养分及生物学特性

采用时空互代法,以广西北部低山丘陵地区不同林龄(1、2、3、4、5 a)桉树人工林为研究对象,对土壤养分含量,微生物数量,微生物生物量和土壤酶活性等生物学特征进行研究,探讨土壤养分变化及其生物学特征的变化规律。结果表明:(1)土壤养分随土层的加深表现出降低的趋势。随林龄的增加,土壤有机碳和速效氮含量呈增加的趋势,全磷呈降低趋势,全钾和速效钾呈先减小后增加趋势,全氮和速效磷无明显规律。土壤pH随着林龄的增加呈降低趋势,随土层深度的增加呈升高趋势。(2)土壤微生物数量和微生物生物量随土层的加深逐渐减少。微生物数量中细菌比例最大,放线菌次之,真菌最小。随着林龄的增加,细菌,真菌,微生物量氮和微生物量磷呈先减小再增加的趋势,放线菌趋于减小,微生物量碳逐渐增大。(3)土壤酶活性随土层深度的增加而递减,且各土层之间差异显著。随着林龄的增加,土壤脲酶、蔗糖酶、酸性磷酸、过氧化氢酶活性均呈增大趋势。(4)土壤生物学特征(微生物数量,微生物生物量和酶活性)受林龄的影响显著,其最高值根据所在的林龄有所不同,与土壤有机碳、全氮、全磷、全钾、速效氮、速效磷、速效钾等因子密切相关,且呈显著相关,在一定程度上可以表征桉树人工林土壤肥力水平变化趋势。

Soil Nutrients and Biological Characteristics in Eucalyptus Plantations of Different Planting Ages at North Guangxi

By the methods of the spatial-temporal substitution method, we studied the change characteristics and correlations of soil nutrient, microbial biomass and enzyme activity at four soil depths (0-10, 10-20, 20-30 and 30-40 cm) of Eucalyptus plantations with different ages (1, 2, 3, 4 and 5 a) in the hilly areas of north Guangxi. The soil nutrient decreased with the increase of soil depth. Contents of soil organic carbon and available nitrogen increased with the increase of age of forest. In contrast, total phosphorus showed a decreasing trend, total potassium and available potassium increased after an initial decrease. There was no obvious rule of total nitrogen and available phosphorus. The soil pH values decreased with the increasing of stand ages, and increased with the increase of soil depth. The effects of stand ages on soil microbial quantity and microbial biomass were evident, which decreased with the increasing of soil depth. Bacteria accounted for most percentage parts in the sum of microbial population, followed by actinomycetes and fungi. Bacteria, fungi, microbial biomass nitrogen and microbial biomass phosphorus all appeared to have a ascent trend after an initial decline with the increase of stand ages, actinomycetes showed a tendency of decrease, microbial biomass carbon increased gradually, respectively. Soil enzyme activity all decreased with the increase of soil depth, increased with the increase of forest age. The effects of stand ages on soil biological characteristic were evident, and details about peaks differed. The microbial quantity, microbial biomass and soil enzyme had a significant relationship with soil nutrient, which could be used as the good biological indicators to evaluate soil quality and represent the change trend of soil fertility level to some extent.