Wei Xinyu, Yang Yulian, Shen Ya, Chen Zihao, Dong Yuliang, Wu Fuzhong, Zhang Li
Key Laboratory of Humid Subtropical Eco-geographical Process of Ministry of Education, Fujian Normal University, Fuzhou, China.
Long-Term Research Station of Alpine Forest Ecosystems, Key Laboratory of Ecological Forestry Engineering, Institute of Ecology and Forestry, Sichuan Agricultural University, Chengdu, China.
Front Plant Sci. 2020 Mar 5;11:254. doi: 10.3389/fpls.2020.00254. eCollection 2020.
Plant litter is one of the main sources of soil humus, but which can also promote primary humus degradation by increasing microbial activity due to the higher availability of energy released, resulting in a confusing relationship between litterfall and soil humus. Therefore, an incubation experiment was carried out in three subalpine forests (coniferous, mixed and broadleaved forests) on the eastern Qinghai-Tibetan Plateau. We set up two treatments. One that allowed litterfall to enter the soil normally and the other prevented litterfall to enter the soil. Soils were sampled in October (the end of the growing season), January (the onset of the freezing season), March (the end of the freezing season), and May (the start of the growing season) from May 2017 to May 2018. By assessing the litterfall production, the content of total extracted humus, humic acid (HA) and fulvic acid (FA) in the topsoil (0-20 cm) in each incubation period, we determined the impact of litterfall on the content of humus extracted from the soil during the freezing and the growing season. Over 1-year incubation, soil total extracted humus and HA showed considerable decreases in the treatment of retained litterfall in the mixed forest but not in the coniferous or broadleaved forests. Moreover, litterfall significantly reduced the contents of soil total extracted humus and HA during the growing season in all three forests, while only reduced soil HA content in the broadleaved forest in the freezing season. The relationship between litterfall and soil extracted humic substances was greatly regulated by the seasonal dynamics of litter types and litter production in all forest types. The larger the amount of litterfall was, the more litterfall could promote the reduction of soil extracted humic substances. Compared with a single type of broadleaf or needle litter, mixed litterfall could promote a higher degradation of soil humic substances. However, broadleaf litter might lead to much greater decreases in soil humic substance than needle litter because it is more decomposable. These results indicate that the effect of litterfall on soil humic substances are mainly regulated by litter types and litter production. Moreover, the effects of litterfall on soil humic substances are more significant during the growing season than winter. This suggests that the longer growing season and a shorter winter caused by ongoing global warming may alter the relationships between litterfall and extracted humic substances, further disrupting the carbon balance of forest ecosystems in the subalpine forests.
植物凋落物是土壤腐殖质的主要来源之一，但由于其释放的能量可用性更高，增加了微生物活性，从而也会促进初级腐殖质的降解，导致凋落物与土壤腐殖质之间的关系令人困惑。因此，在青藏高原东部的三种亚高山森林（针叶林、混交林和阔叶林）中进行了一项培养实验。我们设置了两种处理方式。一种允许凋落物正常进入土壤，另一种则阻止凋落物进入土壤。在2017年5月至2018年5月期间，于10月（生长季末）、1月（冰冻季开始）、3月（冰冻季末）和5月（生长季开始）采集土壤样本。通过评估每个培养期内凋落物产量、表层土壤（0 - 20厘米）中总提取腐殖质、腐殖酸（HA）和富里酸（FA）的含量，我们确定了凋落物对冰冻季和生长季期间从土壤中提取的腐殖质含量的影响。经过1年的培养，在混交林的保留凋落物处理中，土壤总提取腐殖质和HA显著减少，但在针叶林或阔叶林中没有这种情况。此外，在所有三种森林中，凋落物在生长季显著降低了土壤总提取腐殖质和HA的含量，而在冰冻季仅降低了阔叶林土壤中的HA含量。在所有森林类型中，凋落物类型和凋落物产量的季节动态极大地调节了凋落物与土壤提取腐殖质物质之间的关系。凋落物量越大，其促进土壤提取腐殖质物质减少的作用就越强。与单一类型的阔叶或针叶凋落物相比，混合凋落物能促进土壤腐殖质物质更高程度的降解。然而，阔叶凋落物可能导致土壤腐殖质物质的减少比针叶凋落物大得多，因为它更易分解。这些结果表明，凋落物对土壤腐殖质物质的影响主要受凋落物类型和凋落物产量的调节。此外，凋落物对土壤腐殖质物质的影响在生长季比冬季更显著。这表明，持续的全球变暖导致的生长季延长和冬季缩短，可能会改变凋落物与提取腐殖质物质之间的关系，进一步扰乱亚高山森林生态系统的碳平衡。
