高寒森林不同生境对凋落叶分解灰分动态的影响

Effects of environmental conditions on ash dynamics during foliar litter decomposition in an alpine forest

灰分是凋落叶的重要组成部分,其浓度直接关系到凋落叶的分解过程及有机组分的动态特征,且可能受生境和分解时期的影响,然而有关凋落叶分解过程中灰分动态的研究鲜有报道。采用凋落袋法,以岷江上游高寒森林4种代表性植物康定柳(Salix paraplesia)、高山杜鹃(Rhododendron lapponicum)、方枝柏(Sabina saltuaria)和四川红杉(Larix mastersiana)凋落叶为研究对象,研究了高寒森林凋落叶在3种不同环境条件下(林下、溪流、河岸带)分解过程中灰分的动态特征。结果表明,灰分量随凋落叶的分解整体呈现降低的趋势,且不同环境条件和不同物种之间存在明显的差异。与之相反,经过两年的分解,除溪流中康定柳凋落叶灰分浓度略有下降外(-0.99%),林下和河岸带中康定柳凋落叶及其它物种凋落叶中灰分浓度在所有环境条件下均表现出了增加的趋势(5.86%—72.15%)。凋落叶分解过程中灰分浓度变异量在不同分解时期存在明显或显著的差异,且受物种和环境因子的调控。这些结果表明,传统上认为凋落叶分解过程中灰分浓度比较稳定的观点是不准确的,且以凋落叶分解过程中灰分浓度不变的前提下采用无灰分质量损失(ash free mass loss)而计算凋落叶质量损失的方法存在一定的不准确性。研究为认识凋落叶分解过程中灰分的动态特征及凋落叶质量损失的测定方法提供了一定的参考。

Ash is an important component of foliar litter, the concentration of which is closely related to the process of litter decomposition and the concomitant organic matter dynamics. Ash dynamics in decomposing litter may be affected by environmental conditions and decomposition period. However, currently there is little information about the dynamics of ash concentration in decomposing litter. To fill this knowledge gap, we investigated the dynamics of ash mass and concentration in decomposing foliar litter （litterbag method） of four dominant species （Salix paraplesia, Rhododendron lapponicum, Sabina saltuaria, and Larix mastersiana） under different environmental conditions （forest floor, stream, and riparian zone） in an alpine forest in the upper reaches of the Minjiang River. The results indicated that ash mass in decomposing foliar litter generally decreased over the 2-year experiment, regardless of litter species and environmental conditions, but that there was variation in the magnitude of the decrease. In contrast, ash concentration in all litter species showed a general increasing trend （5.86%-72.15%）, except for S. paraplesia foliar litter in streams, which decreased approximately 0.99% over the two years. Changes in ash concentration varied significantly among different decomposition periods, and were significantly affected by initial litter quality and environmental factors. Overall, our results are inconsistent with the historical opinion that ash concentration is relatively stable during litter decomposition, which suggests that the method for calculating ash-free mass loss, using the initial ash concentration value based on the assumption that ash concentration is relatively stable during litter decomposition, is incorrect. The results of this study can provide the basis for a better understanding of ash dynamics during litter decomposition, and the correct method for calculating litter mass loss.