不同林龄樟子松叶片养分含量及其再吸收效率

Foliar Nutrients and Their Resorption Efficiencies in Four Pinus sylvestris var. mongolica Plantations of Different Ages on Sandy Soil

树木叶片的养分再吸收效率能够反映树木对养分保存、利用以及对养分贫瘠环境的适应能力。以科尔沁沙地东南缘章古台地区樟子松人工林为研究对象,分析了11、20、29、45年生树木叶片的基本特征、养分含量及其再吸收效率。结果表明:叶片衰老后其质量和面积明显减少;叶片凋落前的平均养分含量没有表现出随樟子松年龄增加而出现有规律的变化;凋落叶片中的N、P、K、Mg含量表现出随年龄增加而增加的趋势,而Ca的趋势与之相反;11年生和20年生的樟子松叶片N、P、K的再吸收效率相似,都显著高于29年生和45年生樟子松(P<0.05),而樟子松叶片对Mg的再吸收效率表现出随年龄增大而显著降低,Ca随叶片的衰老而不断累积,再吸收效率表现为负值,20年生的樟子松叶片Ca再吸收效率最大,11年生和45年生最低。樟子松叶片的N、P、K、Mg养分再吸收效率随年龄增加而降低的趋势表明,随年龄增加樟子松对贫瘠养分生境的适应能力逐渐降低,反映了樟子松养分保存方面的衰退特征。

Foliar nutrients, particularly nitrogen （N）, phosphorus （P）, and potassium （K） are transferred from the senescing leaves to other tissues of the plant for storage. The recovery of these nutrients, termed resorption, significantly affects plant growth in the following year, and is therefore important to plant adaptation to nutrient-poor habitats. Thus, foliar nutrient resorption efficiency can reflect the ability of nutrient conservation, nutrient use efficiency and adaptation to nutrient-poor habitat of trees. In this study, leaf characteristics and nutrient concentrations before and after leaf senescing, and foliar nutrient resorption efficiency in four Pinus sylvestris var. mongolica plantations of varying ages （11, 20, 29, 45 years old, respectively） were studied in Zhanggutai area, which is situated at southeastern Horqin Sandy Lands. The results showed that foliar leaf mass and area of P. sylvestris var. mongolica trees decreased obviously; the foliar nutrient concentrations of P. sylvestris var. mongolica trees before leaf senescing didn＇t show a tendency with tree ages. The concentrations of N, P, K and Mg in leaf litters of P. sylvestris var. mongolica trees showed an increased tendency with ages, but the Ca concentration tended to decrease with ages. The foliar N, P, K resorption efficiencies of 11-year-old P. sylvestris var. mongolica trees were similar to those of 20-year-old P. sylvestris var. mongolica trees, however, their resorption efficiencies were both significantly （ P 〈 0.05） higher than those of 29- and 45-year-old P. sylvestris var. mongolica trees. The foliar Mg resorption efficiency showed a decreased tendency with tree ages. The foliar Ca concentrations gradually increased during leaf senescing, thus the Ca resorption efficiencics were negative values. The foliar Ca resorption efficiency of 20-year-old P. sylvestris var. mongolica was the highest among the four aged trees, and the foliar Ca resorption efficiencies of 11- and 45-year-old trees were the lowest. On the whole, foliar N, P, K, Mg resorption efficiency of P. sylvestris var. mongolica trees decreased with tree ages, which indicated that the adaptation ability of P. sylvestris var. mongolica trees to nutrient-poor sandy habitat also decreased with ages, and reflected a decline characteristic on nutrient conservation of P. sylvestris var. mongolica trees.