森林生态系统作为陆地最大氮素储存库,在维系氮素生物地球化学循环方面发挥了重要作用。以我国人工林主产地广西马尾松(Pinus massoniana)、杉木(Cunninghamia lanceolate)、桉树(Eucalyptus robusta)3种主要人工林为研究对象,探讨了3种林型不同龄组、不同层次的氮储量组成与分配格局,结果表明:(1)随着林龄的变化,不同林龄马尾松、杉木、桉树林氮储量大小范围在6.64-15.15、8.44-14.90、3.22-11.29 Mg/hm2之间,其中马尾松、杉木、桉树分别在幼龄林、过熟林、成熟林达到最大,除幼龄阶段马尾松氮储量最高外,其他各林龄阶段均为杉木林最大。(2)各个林龄总体来看,3种人工林生态系统氮储量生态格局基本一致,绝大部分氮储存于土壤中(0-100 cm),乔木层氮储量仅次于土壤层,灌木层氮储量最小。0-100cm土层范围内,按10 cm每层进行划分,三种人工林各个林龄均是0-10 cm表层土壤氮储量最高。马尾松、杉木除幼龄林外土壤层氮储量均随着林龄增大而逐渐升高,在过熟林分别达到了10.71和16.63 Mg/hm2,桉树则幼龄林到成熟林逐渐升高,成熟林氮储量为11.26 Mg/hm2,过熟林则下降。同一林分各层次不同器官氮储量存在着差异,3种人工林乔木层中树干氮储量均占比最高,树干是乔木层的主要氮库;灌木层中叶片中含有更多的氮储量;草本层地上部分>地下部分,地上部分是氮储存的主要场所;细根氮储量0-20 cm>20-40 cm。不同造林树种生态系统氮固持能力有所差异,总体上,人工造林后期生态系统固氮能力逐渐增强,而速生桉树人工林收获期生态系统固氮有所下降。
Forest ecosystem, as the largest nitrogen storage pool on land, plays an important role in maintaining nitrogen biogeochemical cycle. In this study, three main plantation forests in China, namely Pinus Massoniana, Cunninghamia Lanceolate and Eucalyptus robusta, were selected as the research objects. The composition and distribution patterns of nitrogen reserves in different age groups and levels of three forest types were discussed. The results showed that:(1) With the change of stand age, the nitrogen storage of masson's pine, Cunninghamia lanceolata and Eucalyptus varied in 6.64-15.15 Mg/hm2, 8.44-14.90 Mg/hm2 and 3.22-11.29 Mg/hm2, in which the nitrogen storage of Masson's pine, Cunninghamia lanceolata and eucalyptus reached the maximum in young forest, overripe forest and mature forest, respectively. Except for the young stage, the nitrogen reserves of Masson pine were the highest in the other stages of Chinese fir forest. (2) The ecological pattern of nitrogen storage in the three plantations was basically the same at each stand age. Most of the nitrogen was stored in the soil (0-100 cm). The nitrogen storage in the tree layer was next to that in the soil layer, and the nitrogen storage in the shrub layer was the smallest. In the range of 0-100 cm soil layer, each layer was divided by 10 cm, and the soil nitrogen storage in the surface layer of the three artificial forests was the highest at 0-10 cm of each age. The soil nitrogen storage in the soil layer of Masson's pine and Chinese fir increased gradually with the increase of stand age except for the young forest, and reached 10.71 Mg/hm2 and 16.63 Mg/hm2 in the overripe forest, respectively. In eucalyptus, nitrogen storage increased gradually from young forest to mature forest. Nitrogen storage in mature forest was 11.26 Mg/hm2, but decreased in overmature forest. (3) There were differences in nitrogen storage of different organs at different levels in the same stand. The proportion of nitrogen storage in tree layer was the highest in the trunk of the three plantations, and the trunk was the main nitrogen pool in the tree layer. The middle layer of shrub layer had more nitrogen storage. Above ground part of herbaceous layer & GT; The underground part, the aboveground part is the main place of nitrogen storage; Fine root nitrogen storage 0-20 cm>20-40 cm. The nitrogen fixation capacity of different afforestation species was different. In general, the nitrogen fixation capacity of the ecosystem was gradually increased in the later stage of artificial afforestation, but decreased in the harvest stage of fast-growing eucalyptus plantation.