四川盆地亚热带常绿阔叶林凋落叶多酚类物质在不同降雨期间的降解特征

植物多酚类物质是森林凋落物中的重要组分,其含量的多寡在一定程度上决定了凋落物的分解速率。然而,凋落物分解过程中多酚类物质的降解动态仍不十分清楚。因此,以四川盆地亚热带常绿阔叶林最具代表性的3个针叶树种马尾松(Pinus massoniana)、柳杉(Cryptomeria fortunei)、杉木(Cunninghamia lanceolata)和3个阔叶树种香樟(Cinnamomum camphora)、红椿(Toona ciliata)、麻栎(Quercus acutissima)凋落叶为对象,采用凋落物分解袋法,研究了6种凋落叶多酚类物质在第一年不同降雨期间的降解特征。结果表明:自微量降雨期起至雨季前期止,6种凋落叶多酚类物质具有一致的降解动态,降解率均表现为随着降水量的增加而增加;自雨季后期之后,多酚类物质含量均处于稳定状态。第一个分解年,6种凋落叶多酚类物质降解率大小顺序依次为:红椿(100%)柳杉(97.81%)杉木(94.45%)麻栎(93.67%)马尾松(93.06%)香樟(91.64%)。分解初期旱季两时期(微量降雨期和春季少雨期),6种凋落叶多酚类物质均有较大的降解量,其降解率占全年降解率的42.16%—71.20%。并且,除香樟以外的5种凋落叶多酚类物质大量降解释放发生在雨季前期,占全年降解率的44.46%—55.72%。此外,凋落叶多酚类物质初始含量与其降解率呈显著的二次函数关系。可见,降雨是湿润亚热带常绿阔叶林区凋落物多酚类物质降解的关键驱动因子之一,树种组成是影响凋落物多酚类物质降解的内部因素。

The polyphenol degradation characteristics of leaf litter at different rainy stages in a subtropical evergreen broad-leaved forest in the Sichuan Basin, China

Polyphenols are basic components in plant tissues and foliar litter, and play an important role in ecosystem functioning. In particular, the dynamics of polyphenol degradation in foliar litter determines the foliar litter decomposition to some extent. It is well-documented that litter decomposition and the degradation of basic components, such as cellulose and lignin, in litter are affected by precipitation, litter quality, soil organisms, and their interactive effects. Considerable attention has been given the effects of abiotic and biotic factors on mass loss, element releases, and the degradation of lignin and cellulose. However, there is little information available on the effects of seasonal precipitation patterns on the dynamics of polyphenol degradation in decomposing litter. To understand the characteristics of foliar litter decomposition as affected by seasonal rainfall pattern in the subtropical evergreen broad-leaved forest region, a litterbag decomposition experiment was conducted at the Chongzhou Modern Agricultural Research & Development Base at Sichuan Agricultural University, China. The dynamics of polyphenol degradation in the decomposing needle litter of Pinus massoniana, Cryptomeria fortunei, and Cunninghamia lanceolata, and in the decomposing broadleaved foliar litter of Cinnamomum camphora, Toona ciliata, and Quercus acutissima in the subtropical evergreen broad-leaved forest in the upper reaches of Yangtze River, China were therefore investigated at different critical periods. From the micro rainy stage to the early rainy stage, the polyphenol degradation rates in the decomposing litter of the six tree species increased continually as rainfall levels rose and thereafter, the concentrations of polyphenols in the remaining litter were stable. During the first decomposition year, the polyphenol degradation rates were in the order:T. ciliate (100%) > C. fortunei (97.81%) > C. lanceolata (94.45%) > Q. acutissima (93.67%) > P. massoniana (93.06%) > C. camphora (91.64%). The amounts of litter polyphenols degraded during the two dry stages accounted for 42.16%-71.20% in the early decomposition period, depending on tree species. Furthermore, except for C. camphora, 44.46%-55.72% of the polyphenols in the foliar litter of the other five tree species were degraded during the early rainy stage. The initial concentrations of polyphenols in foliar litter showed a significant quadratic function with the rate of litter polyphenol degradation, which implied that the initial concentration of polyphenols in foliar litter, as determined by tree species, is a key factor that affected litter quality and drove the litter polyphenol degradation process to a great extent. In conclusion, precipitation pattern is the crucial factor in driving the degradation of foliar litter polyphenols, while litter quality, as determined by tree species, is the internal factor regulating the polyphenol degradation dynamics of foliar litter in the humid subtropical evergreen broad-leaved forest regions.