重庆酸雨区马尾松与木荷的叶凋落物分解特征

摘要

The Masson pine (Pinus massoniana) forests grow widely in south China, and are seriously damaged by the long-term acid rain. It is expected that an intercropping with broadleaved tree species, such as Schima superba which can grow well under the canopy of Masson pine forests, can improve the health condition of Masson pine trees damaged by acid rain by accelerating the nutrition cycling of forest ecosystems. In order to assess the possible improving effect of intercropping with Schima superba, a field study of litter decomposition was carried out at Tieshanping forest Farm of Chingqing, a region with severe acid rain and forest damage, to compare the decomposition rate of Masson pine needle litter with that of the broad-leaf litter of Schima superba, and to see if the decomposition rate of Pinus massoniana needle litter can be increased by mixing them with the broad-leaf litter of Schima superba. It was found that the decomposition rate of leaf litter of both tree species was very low because of the severe soil acidification, with the annual decomposition coefficient of 0.345 0 and 0.413 2 for Pinus massoninana and Schima superba respectively. The decomposition rates in Tieshanping amounted to only about half of that reported in the forests of Fuzhou City in Fujian Province (with the annul decomposition coefficient of 0.651 2 and 0.813 3). It needs 2.0 and 1.68 years for a 50%decomposition of the litter of Pinus massoninana and Schima superba, and 8.64 and 7.26 years for a 95%decomposition of them. It was also found that the decomposition rate of Pinus massoniana needles was not increased when it was mixed with the broad-leaf litter of Schima superba, probably because of the decomposer quantity reduction and the change of decomposer composition caused by severe soil acidification. It seems from this study that the intercropping of Schima superba can no more play the role of improving the health condition of Masson pine forests damaged by acid rain. Moreover, it was reported that the fast growth of Schima superba can lead to more soil acidification. Thus, Schima superba should not be suggested as a suitable tree species to be intercropped into the Masson pine forests for improving the health condition of Masson pines growing in the region with severe soil acidification.%　　为从林地养分循环角度评价林下生长良好的木荷(Schima superba)对受酸沉降严重危害的马尾松(Pinus massoniana)生长与健康的影响,在属于我国典型酸雨区和土壤酸化及森林受害严重的重庆市铁山坪林场,采用网袋法研究了马尾松与木荷的叶凋落物在不同混合比例时的分解特征.结果发现,由于土壤严重酸化,铁山坪的马尾松、木荷叶凋落物的年分解系数均很低,分别为0.3450和0.4132,与福州市国家森林公园(马尾松、木荷叶凋落物的年分解系数分别为0.6512、0.8133)相比降低了约一半；它们在铁山坪分解50%时所需时间分别为2.0、1.68 a,分解95%时所需时间分别为8.64、7.26 a；二者分解速率无显著差异,将二者以不同比例混合后也未发现阔叶凋落物促进针叶凋落物分解的作用.因而认为,在土壤已严重酸化的重庆铁山坪或类似地区,由于作为凋落物分解者的土壤动物、微生物的数量减少及种类变化,林下栽植木荷看来难以发挥促进马尾松针叶分解的作用,加之木荷生长过快有加重土壤酸化的不利作用,因此在改善酸沉降危害严重的马尾松林健康状况时,不宜推荐木荷作为林下栽植的阔叶树种.