摘要:凋落物和根系向土壤的碳输入是森林生态系统的关键过程，输入量及组分的变化直接影响森林土壤碳汇功能和生产力。在沂蒙山区栎类天然次生林中，开展添加/去除凋落物及去除根系的定位控制试验。于控制试验开展21个月后，采用Biolog Eco微平板培养法，研究凋落物和根系对土壤微生物碳源代谢功能的影响。结果表明，凋落物倍增处理增加了土壤微生物碳源代谢功能，增加了对糖类和胺类的代谢能力。去除凋落物处理、去除根系处理和无输入处理都降低了土壤微生物碳源代谢功能。去除凋落物处理降低土壤微生物碳源代谢功能的幅度大于去除根系处理，表明当前条件下凋落物对土壤微生物碳源代谢功能的影响大于根系，但如果抛除掉去除根系处理中残留根系的影响，凋落物和根系对土壤微生物碳源代谢功能的相对大小可能会发生变化。土壤有机碳含量、铵态氮含量显著影响微生物碳源代谢多样性（P<0.05），并与碳源代谢功能正相关。凋落物倍增处理通过增加土壤铵态氮和有机碳含量，增加微生物碳源代谢功能，去除凋落物处理和无输入处理通过降低土壤铵态氮和有机碳含量，降低微生物碳源代谢功能。结果深化了碳输入途径（地上凋落物与地下根系）和数量（凋落物倍增、凋落物去除与对照）对温带栎类天然次生林土壤碳代谢过程的认识。



Abstract:Carbon inputs from litter and roots to soil are key processes for nutrient cycling in forest ecosystem. Changes in carbon input pathways and quantities can directly affect the carbon sources to soil microorganisms and soil carbon sink function. However, there is debate regarding the effects of the carbon inputs on soil microbial carbon metabolism. In this study, a field experiment involving the control of litter input pathways (aboveground vs. underground) and quantities (doubled or removed vs. control), implemented through the addition or removal of litter and the removal of roots, was conducted in a natural secondary oak forest (35°10'-36°00' N, 117°35'-118°20' E) in the Yimeng mountainous area, Shandong Province, China. The experiment commenced in November 2014 and had a randomized block design with five different treatments (control, litter doubling, litter removal, root removal, and no detritus inputs by removing both litter and root) and five replicates for each treatment. On August 13^th, 2016, the soils were sampled at a depth of 0-10 cm to analyze soil microbial carbon metabolism. Soil microbial carbon metabolism was based on community-level physiological profiles (CLPPs) using Biolog Eco MicroPlate cultivation method. Each soil sample (10^-3 soil dilution) was inoculated 3 times, and cultivated at 25℃ for 240 h. The plates were scanned at 590 nm every 12 h. The litter doubling treatment increased the soil microbial carbon metabolism function, and increased the microbial utilization of sugars and amines. In contrast, the litter removal, root removal, and no input treatments reduced microbial metabolism of carbon sources, and decreased the microbial ability to utilize sugars, amino acids, carboxylic acids, amines, and polymers. Compared with root removal treatment, litter removal treatment resulted in a greater decrease in the microbial metabolism of carbon, indicating that litter exerted a greater influence on the carbon metabolism in this study. However, when considering the effects of trenched roots, the relative effects of litter and root might change. The redundancy analysis was used to analyze the relationship between soil microbial carbon metabolism and soil physiochemical characteristics including pH, contents of moisture, organic carbon, total nitrogen, ammonium, nitrate, and available phosphorus. The redundancy analysis revealed that the soil organic carbon and ammonium nitrogen contents significantly influenced the community-level physiological profiles of soil microbes (P<0.05). Spearman correlation analysis showed that soil organic carbon and ammonium nitrogen contents were positively correlated with carbon metabolism function. The ordination diagram for the redundancy analysis of the microbial community level physiological profiles and soil physicochemical properties indicated that the litter doubling treatment was distributed in the directions of increasing ammonium nitrogen and organic carbon contents, whereas the litter removal and no input treatments were located in the opposite direction. This indicated that litter doubling treatment increased the soil microbial carbon metabolism function by increasing the contents of ammonium nitrogen and organic carbon, whereas litter removal and no input treatments reduced the carbon metabolic function by decreasing the contents of ammonium nitrogen and organic carbon. The results of the study further deepen our understanding of the influences of carbon input pathways (aboveground litter vs. underground roots) and quantities (litter doubling or litter removal vs. control) on soil carbon metabolism processes in natural secondary forests in temperate zones.





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