季节性冻融期间土壤动物对高山草甸两种凋落叶木质素降解的影响

Impact of soil fauna on lignin degradation of two foliar litters in an alpine meadow during freezing-thawing period

高山草甸冻融季节强烈的冻结作用和频繁的冻融循环可促进凋落叶木质素降解,进而影响凋落叶分解及其相关的物质循环过程,但严酷环境下仍然活跃的土壤动物是否具有明显的作用尚无定论.因此,以高山草甸代表性植物黄花亚菊(Ajania nubigena)和黑褐苔草(Carex atrofusca)凋落叶为研究对象,采用不同孔径凋落叶袋排除土壤动物的方法,探讨冬季不同冻融时期(冻结前期、冻结期和融化期)土壤动物对凋落叶木质素降解的贡献.结果显示,整个季节性冻融期间,土壤动物对凋落叶中木质素的降解具有明显的贡献.土壤动物作用的凋落叶木质素降解率(Cfau)为19.41%(黄花亚菊凋落叶)和2.02%(黑褐苔草凋落叶),总贡献率(Pfau)为32.47%(黄花亚菊凋落叶)和2.33%(黑褐苔草凋落叶).然而不同时期土壤动物具有不同程度的影响.相对于其他时期,冻结初期土壤动物作用于黑褐苔草凋落叶木质素降解率最大(13.59%),而融化期最小(-0.27%).与黑褐苔草不同,融化期土壤动物作用于黄花亚菊凋落叶木质素降解率最大(17.59%),而在冻结期最小(-5.12%).土壤动物作用于凋落叶木质素的降解率和贡献率均与负积温显著正相关(P<0.05),与凋落叶初始质量无显著相关性.可见,高寒草甸土壤动物在严酷的冬季环境下仍然对凋落叶木质素降解具有积极的作用,但相对于凋落叶质量,温度及其相关冻融环境的改变对土壤动物作用于木质素降解过程的影响更大.

Strong freezing and frequent freeze-thaw cycles could accelerate lignin degradation during litter decomposition in alpine meadow during the seasonal freezing-thawing period, which plays an important role in keeping circulation of materials and the balance of ecosystem nutrients. However, little information is currently available about whether soil fauna has obvious effects on lignin degradation under the crucial environment conditions during the freezing-thawing period in alpine meadow. Using litterbags with different mesh sizes, we conducted a field experiment to investigate the contribution of soil fauna to lignin degradation of two foliar litters in the freezing-thawing period in an alpine meadow on the eastern Tibetan Plateau. The predominant plants were Ajania nubigena and Carex atrofusca, and the litterbags were sampled in the pre-freezing period, the freezing period and the thawing period from November 2013 to April 2014. Soil fauna showed an obvious effect on the lignin degradation of foliar litter in the alpine meadow over the freezing-thawing period. The lignin degradation rate of A. nubigena and C. atrofusca foliar litter driven by soil fauna（Cfau） was 19.41% and 2.02%, respectively, with the corresponding contribution rate of soil fauna to litter lignin degradation rate（Pfau） as 32.47% for A. nubigena, and 2.33% for C. atrofusca. However, the effect of soil fauna to litter lignin degradation was different in different freezing-thawing stages. Among all, the thawing period showed the highest lignin degradation rate of A. nubigena foliar litter driven by soil fauna（17.59%）, and the freezing period（-5.12%） the lowest one. In contrast, lignin degradation rate of C. atrofusca foliar litter（13.59%） was the highest in the pre-freezing period, but the lowest in the thawing period（- 0.27%）. Additionally, Cfau and Pfau were significantly correlated with negative accumulated temperature（P〈0.05）, but insignificantly with the initial litter quality. These results suggested that soil fauna obviously affect lignin degradation during foliar litter decomposition in wint er; the temperature and freeze-thaw dynamics could have greater impact than the litter quality on the lignin degradation processes in the alpine meadow.