改变凋落物输入对川西亚高山天然次生林土壤呼吸的影响

2019年5月-10月，采用LI-8100A土壤碳通量自动测量分析仪对川西米亚罗林区20世纪60年代采伐后经自然更新恢复形成的岷江冷杉（Abies faxoniana）次生针叶林（针叶林）、红桦（Betula albo-sinensis）+青榨槭（Acer davidii）+岷江冷杉次生针阔混交林（针阔混交林）和青榨槭+红桦+陕甘花楸（Sorbus koehneana Schneid）次生阔叶林（阔叶林）的土壤呼吸及土壤温湿度因子（对照、去除凋落物和加倍凋落物）进行观测。结果显示：去除和加倍凋落物对土壤温湿度的影响不显著，且3种林型之间的土壤呼吸速率差异不显著。与对照相比，去除凋落物使针叶林、针阔混交林、阔叶林的土壤呼吸速率分别降低了17.65%、21.01%和19.83%（P<0.05）；加倍凋落物则分别增加6.76%、7.28%、8.16%（P>0.05）。3种林分土壤呼吸速率均与土壤温度极显著指数相关，与土壤湿度不相关。对照Q₁₀值变幅为2.01-3.29，去除凋落物降低了3种林型的Q₁₀值；加倍凋落物分别提高了针叶林和降低了针阔混交林和阔叶林的Q₁₀值。土壤呼吸速率仅表现在天然次生林对照处理中受到土壤pH、有机质、可溶性有机氮和草本Pielou均匀度指数的显著影响。研究结果表明，天然次生阔叶林和针阔混交林凋落物对土壤呼吸的贡献及Q₁₀值高于天然次生针叶林，说明在未来CO₂浓度及温度升高背景下，地表凋落物增加并未引起天然次生林土壤呼吸速率成倍增加，更有利于该区域天然次生林尤其是针叶林的土壤碳吸存。

Effects of litter manipulation on soil respiration in natural secondary forest in subalpine area of western Sichuan Province, China

Natural secondary forests play a crucial role in the subalpine forests of the upper reaches Minjiang River in the eastern margin of the Tibetan Plateau. However, the knowledge about influence of litter on soil respiration remain inadequately understood for the secondary forests. In order to evaluate the impact of litter on soil respiration under different natural secondary forests in subalpine area of western Sichuan Province, China. Aboveground litter manipulation experiment was carried out in three natural secondary forests including Abies faxoniana secondary coniferous forest, Betula albo-sinensis+Acer davidii+A. faxoniana secondary mixed broadleaf-conifer forest, and A.davidii+B.albo-sinensis+Sorbus koehneana Schneid broad-leaved forest by natural alternation after timber exploitation in 1960s in Jiabigou forest zone of Miyaluo town. Litter treatments consisted of control (CK, litter inputs un-allowed), no litter (aboveground litter excluded), and double litter (aboveground litter doubled by adding litter removed) in September 2018. Soil respiration rates were measured using automated CO₂ efflux systems (LI-COR 8100A) about every two weeks during the growing season in 2019 (May to October). During the experimental period, the litter addition and exclusion did not significantly affect soil temperature and moisture, respectively. Soil respiration rates among three forest types showed no significant difference. Soil respiration rate of the litter exclusion was 17.65%, 21.01%, 19.83% lower than that of control treatment (P<0.05) of the secondary coniferous forest, secondary mixed broadleaf-conifer forest and broad-leaved forest, respectively. While the soil respiration rate of litter addition was 6.76%, 7.28%, and 8.16% higher (P>0.05) in the three forest types, respectively. There was a significantly exponential correlation between soil respiration and soil temperature in all treatments (P<0.01), while no correlation was found with soil moisture. The Q₁₀ of control were 2.01-3.29. Compared with the control, the litter exclusion decreased all Q₁₀ in three forests, while the litter addition increased the Q₁₀ in the secondary coniferous forest, but decreased in secondary mixed broadleaf-conifer forest and secondary broad-leaved forest instead. The regression analysis indicates that soil pH, soil organic matter, dissolved organic nitrogen and Pielou index of herb layer had significant correlation with soil respiration rate in control plots of the natural secondary forests, respectively. It could be seen that the contribution of aboveground litter to soil respiration and Q₁₀ in broad-leaved forest and mixed broadleaf-conifer forest were higher than those in coniferous forest. Additionally, the magnitude of the increase did not match up with the doubling of litter inputs, indicating that under elevated atmospheric CO₂ concentration and temperature, the increased aboveground litter may be advantageous to the forest soil carbon sequestration in coniferous forest.