Abstract:

Extreme climate events such as ice storms and typhoons have severely disrupted the forest ecosystem, leading to the production of large amounts of abnormal litters like fallen leaves, broken branches and trunks, which will have a profound impact on the soil carbon pool. However, research on this phenomenon is still scarce. Three common tree species (Pinus massoniana, Castanopsis fissa, and Machilus chekiangensis) in southern subtropical forests were selected and labeled with ¹³C as our experimental materials. The fresh leaves were added to soil and incubated for 110 days. The CO₂ emissions, ¹³C abundance and changes in soil carbon pool before and after incubation were measured. The results showed that the carbon emission patterns of abnormal litter of different tree species were similar, which showed rapid increase in the early stage, then gradually decreased, and stabilized at a low level in the late stage. 91.39%-94.04% of the carbon efflux process occurred in the early and mid-term (0-45 d). During the 110-day incubation, 67.86-95.31% of the decomposed carbon in abnormal litter was released into the atmosphere in the form of C-CO₂.The priming effect of abnormal litter was mainly divided into three stages. In the early stage of incubation (0-7 d), the abnormal litter of all three plant species caused a strong negative priming effect. The intensity of negative priming effect gradually increased, with peaks of -50.05, -117.72 and -124.08, respectively. The intensity of the negative priming effect gradually decreased in the middle stage of incubation (7-35 d), showing a rapid decline followed by a slow decline. The priming effect of three plant species in the last stage of incubation (35-110 d) was stable, with differences between species. The priming effect of C. fissa and M. chekiangensis gradually turned to positive, while P. massoniana maintained a negative priming effect and gradually decreased to zero. After 110 days of incubation, the soil organic carbon content at 0-5 cm layer under the P. massoniana and C. fissa addition treatments were significantly higher than that of the control (P<0.05). The ¹³C isotope values of the soil at 0-5 cm and 5-10 cm layers under the C. fissa addition treatments were significantly higher than that of the control (P<0.05). There was no significant difference in total nitrogen and available nitrogen content between each treatment and the control (P>0.05). Abnormal litter input has a significant effect on the organic carbon of the surface soil but no effect on the deeper soil in a short-term incubation experiment. Most of the carbon produced by abnormal litter decomposition is emitted into the atmosphere in the form of C-CO₂.

Key words: south subtropical forest ecosystem, fresh plant leaves, ¹³C isotope, priming effect, decomposition process, soil carbon pool

摘要：

冰暴、台风等极端气候事件严重干扰了森林生态系统,导致大量落叶、断枝、断干等非正常凋落物产生,将对土壤碳库产生激发效应,然而目前对这种现象的研究仍十分匮乏。以马尾松（Pinus massoniana）、黧蒴锥（Castanopsis fissa）、浙江润楠（Machilus chekiangensis）3种南亚热带常见树种为研究对象,利用¹³C标记植株并采集其新鲜叶片添加至土壤表面,进行了为期110 d的室内培养实验,培养中分别测量了CO₂排放量、¹³C丰度值以及培养前后土壤碳库的变化。结果表明,不同树种的非正常凋落物的碳排放模式相似,均表现为前期快速升高,之后波动下降,后期稳定在较低水平。其中91.39%—94.04%的碳排放过程发生在前中期（0—45 d）。110 d的培养过程中,非正常凋落物分解产生的碳有67.86%—95.31%以C-CO₂的形式排放到大气当中。非正常凋落物输入对土壤有机碳的激发效应主要分为3个阶段。培养前期（0—7 d）3种非正常凋落物输入均引起了土壤碳强烈的负激发效应且在短期内达到峰值,峰值分别为-50.05、-117.72、-124.08;培养中期（7—35 d）负激发效应强度逐步下降,表现为先快速下降后速率转慢;培养后期（35—110 d）碳激发效应较为平稳,不同树种之间有所差异,黧蒴锥、浙江润楠的碳激发效应逐渐转为正向,而马尾松维持负激发效应并缓慢下降至消失。经过110 d的培养,马尾松、黧蒴锥的0—5 cm层土壤有机碳显著高于对照组（P<0.05）,黧蒴锥的0—5、5—10 cm层土壤的¹³C同位素值显著高于对照组（P<0.05）。各处理组与对照组之间全氮、有效氮差异均不显著（P>0.05）。非正常凋落物输入在短期内对表层土壤有机碳含量影响显著而对深层土壤没有影响,其分解产生的碳大部分以C-CO₂的形式排放到大气当中。

关键词: 南亚热带森林生态系统, 新鲜植物叶片, ¹³C同位素, 激发效应, 分解过程, 土壤碳库