三种不同类型亚高山森林凋落物输入对土壤腐殖化的影响

森林凋落物既是土壤腐殖质的主要来源，也可以通过新鲜凋落物中易降解组分的输入激发土壤原有腐殖质的降解，导致其相互关系并不明确。以王朗国家级自然保护区内的典型亚高山针叶林、针阔混交林以及阔叶林为研究对象，开展土壤原位培养试验，设置允许凋落物正常输入和去除凋落物两种处理，分析2017年-2019年期间不同凋落物处理下森林土壤可提取腐殖物质的光密度特征，研究土壤腐殖化程度与凋落物的关系。结果表明，在2年的试验过程中，3种森林土壤的腐殖化程度整体表现为针叶林>混交林>阔叶林，均展现出在冬季降低，生长季增加的动态规律；凋落物对3个森林的土壤腐殖化程度均无显著影响，但凋落物输入明显改变了土壤腐殖化程度的季节性变化趋势，且在冬季的阔叶林和混交林中表现更为突出。冬季凋落物的输入使得阔叶林和混交林土壤的腐殖化程度明显降低，而生长季凋落物输入对3种森林土壤腐殖化程度无显著影响。这些结果表明气候变暖情景下冬季温度的上升可能导致土壤的腐殖化程度增加，但凋落物的存在可以减缓增加的趋势。这些结果对于具有明显季节性冻融且对气候变化敏感的亚高山森林土壤肥力管理及可持续经营具有一定的科学意义。

Effects of litterfall on soil humification in three subalpine forests

Humus is the main component of soil organic matter, which is important for soil fertility and nutrient cycling. Forest litterfall as a carrier of nutrients and carbon plays an essential role in the formation of soil humus. The input of litterfall can provide raw materials for the synthesis of soil humus. However, the evidence shows that the incorporation of fresh organic matter into soil can increase microbial activity due to the higher availability of energy released, then stimulate the degradation of soil humus. These conflicted results can lead to a confusing relationship between litterfall and soil humus. Therefore, we carried out a field incubation experiment in three typical subalpine forests (coniferous, mixed and broadleaved forests) on the eastern Qinghai-Tibetan Plateau. There are two treatments in this experiment. One 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), March (the end of the winter season), and September (the middle of the growing season) from 2017 to 2019. Litterfall production, and the values of ΔlogK (the ratio of absorbance at 400 to that at 600 nm on a logarithmic scale), E4/E6 (the ratio of absorption at 465 to that at 665 nm), and A600/C ratios of soil extracted humic substances were analyzed in each period. The results showed that, during the two-year experiment, the overall performance of the soil humification degree in the three forests showed the order as coniferous forest>mixed forest>broadleaved forest, and exhibited an obvious dynamic pattern with decreasing in winter and increasing in the growing season. Statistical analysis indicated that litterfall had insignificant effects on the degree of soil humification in the three forests, but the input of litterfall significantly changed the seasonal tendency of soil humification, which was more prominent in broadleaf and mixed forests in winter. The input of litterfall significantly reduced the degree of soil humification in broadleaved and mixed forest in winter, while had no significant effect on the three forest soils in the growing season. These results suggested that the increase of temperature in winter under the condition of climate warming might lead to an increase in the degree of soil humification, and the presence of litterfall could slow the increase proceeding, which are scientifically significant for soil fertility management and sustainable management in subalpine forests due to seasonal frequent freeze-thaw cycles and the sensitivity to climate change.