华北落叶松人工林地土壤养分与土壤酶的季节变化及关系

以秦岭地区幼中龄林（5，10，20年生）华北落叶松Larix principis-rupprechtii人工林地土壤为研究对象，在林木生长季节（5-10月）每月中旬采集表层（0~20 cm）土壤样品，通过测定不同物候期的土壤速效养分质量分数与土壤酶活性，研究分析两者的物候季节动态特征及相互关系，旨在发现华北落叶松人工林地土壤肥力最低的时期并为人工林的合理施肥提供基础理论指导。结果表明:3种林龄人工林（5，10，20年生）土壤速效养分（速效氮、速效磷）质量分数在整个生长季节内变化规律趋于一致，在林木生长旺盛期土壤速效氮和速效磷质量分数最低，土壤速效氮质量分数最低值分别为29.49，19.96和47.32 mg·kg-1；土壤速效磷质量分数最低值分别为2.31，2.79和1.60 mg·kg-1。3种龄林人工林（5，10，20年生）土壤酶（脲酶、转化酶、磷酸酶、过氧化氢酶）活性在整个生长季节内变化规律基本相同，由萌芽展叶初期到落叶末期土壤脲酶活性和转化酶活性呈逐渐上升趋势，土壤脲酶活性最低值分别为0.33，0.25和0.15 mg·g-1；土壤转化酶活性最低值分别为40.82，41.91和22.25 mg·g-1。从生长旺盛初期到落叶期土壤磷酸酶活性呈缓慢下降趋势，土壤磷酸酶活性最低值分别为0.16，0.13和0.22 mg·g-1；在生长旺盛初期土壤过氧化氢酶活性最低，土壤过氧化氢酶活性最低值分别为1.39，1.44和2.68 mL·g-1。与幼龄林（5年生，10年生）相比，中龄林（20年生）土壤速效磷质量分数显著下降（P<0.05）。土壤速效养分与土壤酶相关性密切，说明土壤酶可以较好地反映土壤肥力状况。因此，土壤肥力由萌芽展叶期到生长旺盛期出现下降而到落叶期有上升趋势，且由幼龄林到中龄林土壤肥力有下降趋势，应在生长旺盛期对中龄林林地进行适当施肥。图2表3参38

Seasonal dynamics of soil nutrients and soil enzyme activities in Larix principis-rupprechtii plantations

This research was conducted to determine the stage when soil fertility was poorest within plantation growing seasons and to provide guidelines for rational application of fertilizer in an artificial forest. The mass fraction of soil available nutrients and soil enzyme activities characteristic of phenological and seasonal dynamics and their relationships in young-(5 a and 10 a) and middle-aged (20 a) stands of Larix principis-rupprechtii plantations of the Qinling Mountains were measured throughout the growing season. A fixed 20 m×20 m standard plot was randomly selected with three replications in each plantation stand. Surface soil samples (0-20 cm) were collected from the middle of May to October in 2012 and analyzed with a least significant difference (Duncan) test at 0.05 level and Pearson correlation analysis at 0.05 level. Results indicated that soil available nutrients (soil available N and soil available P) and soil enzyme activities (urease, invertase, phosphatase, and catalase) for three stand ages manifested the same rules throughout the growing season, and there was significant difference in the same indicator for each plantation stand among various stages (P<0.05). The mass fraction of soil available N and available P were lowest in the vigorous growth period with the lowest mass fraction of soil available N being 29.49 (5 a), 19.96 (10 a), and 47.32 (20 a) mg·kg-1 and the lowest mass fraction of soil available P being 2.31 (5 a), 2.79 (10 a), and 1.60 (20 a) mg·kg-1(P<0.05). Also, significant correlations was observed between soil available nutrient content and soil enzyme activity(P<0.05). Thus, soil enzymes could be used as positive biological indicators for weighing soil fertility.[Ch,2 fig. 3 tab. 38 ref.]